Assessment of population management options for Styela clava

Assessment of population
management options for Styela
clava
MAF Biosecurity New Zealand Technical Paper No: 2009/04
Prepared for MAFBNZ Post-clearance Directorate
by Nick Gust, Graeme Inglis, Oliver Floerl, Lisa Peacock (NIWA); and
Chris Denny and Barrie Forrest (Cawthron)
ISBN No: 978-0-478-33871-3 (Online)
ISSN No: 1177-6412 (Online)
July 2008

Disclaimer
While every effort has been made to ensure the information in this publication is accurate, the
Ministry of Agriculture and Forestry does not accept any responsibility or liability for error or fact
omission, interpretation or opinion which may be present, nor for the consequences of any decisions
based on this information.
Any view or opinions expressed do not necessarily represent the official view of the Ministry of
Agriculture and Forestry.
The information in this report and any accompanying documentation is accurate to the best of the
knowledge and belief of the National Institute of Water and Atmospheric Research Limited (NIWA)
and Cawthron Institute (Cawthron) acting on behalf of the Ministry of Agriculture and Forestry.
While NIWA and Cawthron have exercised all reasonable skill and care in preparation of information
in this report, neither NIWA, Cawthron nor the Ministry of Agriculture and Forestry accept any
liability in contract, tort or otherwise for any loss, damage, injury, or expense, whether direct, indirect
or consequential, arising out of the provision of information in this report.
Requests for further copies should be directed to:
MAF Biosecurity New Zealand
Post Border Directorate
P O Box 2526
WELLINGTON
Telephone: 04-894 0100
Facsimile: 04-894 0736
This publication is also available on the MAF website at www.maf.govt.nz/publications
© Crown Copyright - Ministry of Agriculture and Forestry

Contents Page
1. Executive Summary 1
2. Introduction 8
2.1. Life history background 9
3. Objectives 10
Deliverable 1: Determine and map the extent of the distribution and density of Styela clava
in the Tutukaka Marina, Port of Lyttelton and Magazine Bay Marina 12
4. Methods 12
4.1. Field survey approach 12
4.2. Field identification of Styela clava 14
4.3. Above-water visual surveys 14
4.4. Survey design for diver searches 15
4.5. Phase 1 – Stratified, systematic diver sampling 15
4.6. Phase 2 – Validation of the diver survey technique 17
4.7. Styela collections 18
4.8. Mapping and kriging analysis 18
4.9. Estimating the sensitivity of the search methods 20
4.10. Water temperatures 20
5. Results 20
5.1. Search effort 20
5.2. Styela distribution in each location 28
5.3. Maximum Styela density estimates 31
5.4. Comparison of Styela density across locations and search techniques 36
5.5. Styela habitat associations 38
5.6. Styela size-distribution 38
6. Discussion 40
6.1. Tutukaka Marina 41
6.2. Lyttelton Port 42
6.3. Magazine Bay Marina 45
6.4. Review of survey methods 45
Deliverable 2: Identify human-mediated vectors with the potential to spread Styela to highvalue
areas. 48
7. Methods 49
7.1. Potential vectors and mechanisms for the human-mediated transport of Styela from Styela
fouled study locations 49
7.2. Description of facilities at three study locations and relevant vectors and mechanisms of
transport 50
i

7.2.1. Tutukaka Marina 50
7.2.2. Lyttelton Port 50
7.2.3. Magazine Bay Marina 51
7.3. Selection process for High Value Areas (HVAs) 51
7.3.1. HVA1: Poor Knights Islands Marine Reserve 53
7.3.2. HVA2: Marlborough Sounds aquaculture production area 53
7.3.3. HVA3: Banks Peninsula aquaculture production area 53
7.3.4. HVA4: Akaroa Harbour 53
7.4. Identification of the presence of high-risk vessels or mobile structures at the three Styela source
locations 53
7.4.1. Interviews with port and marina operations managers 53
7.4.2. Surface-based observations of fouling level of vessels and towed structures using fouling
ranks 56
7.5. Movement of potentially high-risk vessels and mobile structures from source locations to the
identified HVAs
7.5.1. Questionnaires / interviews of commercial vessel operators that operate from or frequently
57
visit the study locations 57
7.5.2. Recreational vessels: query of NIWA’s domestic boater survey and simulation model 58
7.5.3. Commercial shipping: Query of Lloyds Marine Intelligence Unit (LMIU) database 58
7.6. Movements of vessels associated with HVAs to the three source locations of Styela (Tutukaka
Marina, Lyttelton Port and Magazine Bay Marina) 59
7.6.1. Questionnaires / interviews 59
7.6.2. Banks Peninsula HVA 59
7.6.3. Marlborough Sounds HVA 59
7.6.4. Marine farms: harvesting vessel operators 59
7.6.5. Other agencies contacted 60
8. Results 60
8.1. Surveyed source location 1: Tutukaka Marina 60
8.1.1. Presence of vectors with the potential to facilitate the spread of Styela 60
8.1.2. Movements of vectors between Tutukaka Marina and the HVAs 62
8.1.3. Vectors that have a potential to transport Styela from Tutukaka Marina to HVAs 62
8.2. Surveyed source location 2: Lyttelton Port 63
8.2.1. Presence of vectors with the potential to facilitate the spread of Styela 63
8.2.2. Movements of vectors between Lyttelton Port and the HVAs 66
8.2.3. Vectors that have a potential to transport Styela from Lyttelton Port to HVAs 67
8.3. Surveyed source location 3: Magazine Bay Marina 71
8.3.1. Presence of vectors with the potential to facilitate the spread of Styela 71
8.3.2. Movements of vectors between Magazine Bay Marina and the HVAs 72
8.3.3. Vectors that have a potential to transport Styela from Magazine Bay Marina to HVAs 72
8.4. HVA 1: Poor Knights Islands 73
8.5. HVA 2: Marlborough Sounds 73
8.6. HVA 3: Banks Peninsula 75
8.7. HVA 4: Akaroa Harbour 75
ii

9. Discussion 75
9.1. Tutukaka Marina 76
9.2. Lyttelton Port 91
9.3. Magazine Bay Marina 93
9.4. Auckland region 93
9.5. Summary 93
Deliverable 3: Identify and determine the risk of Styela spreading to nominated high-value
areas. 95
10. Methods 95
10.1. Assessing the pathway risk of Styela spreading 95
10.2. Risk of Styela naturally dispersing to HVAs 96
10.3. Ranking the risk of Styela dispersing to HVAs using an IMEA approach 98
10.4. Assumptions 100
10.5. Interpretation of IMEA results 100
11. Results 101
11.1. Qualitative risk arising from human-mediated transport vectors 101
11.2. Qualitative risk values for natural dispersal 103
11.3. IMEA results 103
12. Discussion 110
12.1. Risk of introduction from Styela source locations 111
12.2. Vector risks 111
12.3. Risks to high value areas 115
12.4. Considerations and limitations to the risk assessment 117
Deliverable 4: Determine, categorize and prioritize key sites (risk areas) within each location,
based on the information obtained from deliverables 1-3, for efficacy trials
of control measures to mitigate the spread of Styela to high-value areas. 120
13. Methods 120
14. Results 120
14.1. Tutukaka Marina 120
14.2. Lyttelton Port 120
14.3. Magazine Bay Marina 121
14.4. Viaduct Basin, Auckland 122
15. Discussion 122
Deliverable 5: Design a population management programme for Tutukaka Marina, Lyttelton
Port and Magazine Bay Marina. 124
16. Methods 124
16.1. Development of management objectives 124
iii

16.2. Simulations of the influence of some management objectives on the spread of Styela 125
16.3. Simulation of management strategies 126
17. Management objectives and strategies: Tutukaka Marina 127
17.1. Status summary 127
17.2. Options for managing the risk of Styela spread from Tutukaka Marina 128
17.3. A: Population management options (Tutukaka Marina) 129
17.3.1. Option 1: No population management 129
17.3.2. Option 2: Local eradication 131
17.3.3. Option 3: Maintain population at or below current level 135
17.3.4. Option 4: Maintain population at or below a specified level (other than current level) 136
17.4. B: Vector management options (Tutukaka Marina) 138
17.4.1. Option 5: No vector management 138
17.4.2. Option 6: Minimise spread to HVAs 139
17.4.3. Option 7: Prevent spread to HVAs 142
17.4.4. Option 8: Minimise / prevent spread from Tutukaka Marina 144
17.5. C: Combined vector and population management options (Tutukaka Marina) 145
17.5.1. Option 9: Combination of population and vector management 145
17.6. Recommended approach for Tutukaka Marina 148
18. Management objectives and strategies: Lyttelton Port and Magazine Bay Marina 149
18.1. Status summary 149
18.2. Options for managing the risk of Styela spread from Lyttelton Port and Magazine Bay Marina 150
18.3. A. Population management options (Lyttelton Port and Magazine Bay Marina) 152
18.3.1. Option 1: No population management 152
18.3.2. Option 2: Local eradication 153
18.3.3. Option 3: Maintain population at or below current level 158
18.3.4. Option 4: Maintain population at or below a specified level (other than current level) 160
18.4. B. Vector management options (Lyttelton Port and Magazine Bay Marina) 162
18.4.1. Option 5: No vector management 162
18.4.2. Option 6: Minimise spread to HVAs 163
18.4.3. Option 7: Prevent spread to HVAs 167
18.4.4. Option 8: Minimise/prevent spread from Lyttelton Port and Magazine Bay Marina 169
18.5. C. Combined vector and population management options (Lyttelton Port and Magazine Bay
Marina) 170
18.5.1. Option 9: Combination of population and vector management 170
18.6. Recommended approach for Lyttelton Port and Magazine Bay Marina 172
18.7. Discussion of simulation model results 175
18.8. Conclusions 176
18.9. Available methods for population management of Styela 176
19. Acknowledgements 176
20. References 177
Appendices 185 – 228
iv

List of Appendices
Appendix 1: Major man made habitats present in Tutukaka Marina
Appendix 2: Beneath a representative wharf in Lyttelton Port
Appendix 3: Magazine Bay Marina
Appendix 4: Beaufort scale definitions
Appendix 5.1: Persons or companies contacted during collection of vector data for Tutkaka Marina
Appendix 5.2: Persons or companies contacted during collection of vector data for Lyttelton Port
Appendix 5.3: Persons or companies contacted during collection of vector data for Magazine Bay
Marina
Appendix 5.4: Persons or companies contacted during collection of vector data for Poor Knights
Islands HVA
Appendix 5.5: Persons or companies contacted during collection of vector data for Marlborough
Sounds HVA
Appendix 5.6: Persons or companies contacted during collection of vector data for Banks
Peninsula and Akaroa HVAs.
Appendix 5.7: Copies of the questionnaires used to survey vessel, aquaculture facility and
port/marine owners and operators.
Appendix 6.1 Hydrodynamic particle dispersal model simulation from release point in the Port of
Lyttelton under calm conditions.
Appendix 6.2. Hydrodynamic particle dispersal model simulation from release point in the Port of
Lyttelton under north-east winds.
Appendix 6.3. Hydrodynamic particle dispersal model simulation from release point in the Port of
Lyttelton under south-east winds.
Appendix 6.4. Hydrodynamic particle dispersal model simulation from release point in the Port of
Lyttelton under south-west winds.
Appendix 6.5. Hydrodynamic particle dispersal model simulation from release point in the Port of
Lyttelton under north-west winds.
Appendix 7.1: Concept and output summary of NIWA’s epidemiological model.
Appendix 7.2: Detailed discussion of population management tools for Styela.
v

1. Executive Summary
Executive Summary
This report describes research undertaken as part of a population management programme for the non-
indigenous clubbed tunicate Styela clava. Styela clava (hereafter referred to as Styela) was first
detected from New Zealand waters in August 2005, in the Viaduct Basin, Auckland. Concerns about
its potential impacts prompted MAF Biosecurity New Zealand (MAFBNZ) to initiate a number of
research projects to determine the distribution of the organism, limit its spread and evaluate options for
managing established populations.
Deliverable 1: Distribution and density of Styela clava in the Tutukaka Marina, Port of Lyttelton
and Magazine Bay Marina.
Field surveys were used to determine detailed patterns of Styela distribution, abundance and
demography in the Tutukaka Marina, Lyttelton Port and Magazine Bay Marina, Lyttelton Harbour.
Each location was surveyed between November and December 2006 using a combination of abovewater
visual searches and diver surveys. Since it was not possible to survey all possible habitats for
Styela within each location, we sampled a large number of representative habitats (e.g. pilings,
breakwalls, pontoons, ropes and vessels) distributed systematically throughout each location. Spatial
interpolation (kriging) was used to estimate the presence and abundance of Styela in unsampled areas.
To facilitate this, each location was divided into a linear grid of 50m long sites. In the largest location,
Lyttelton Port, the ≈7km perimeter was divided into 139 grid sites, whereas Magazine Bay Marina
contained only nine sites in total and Tutukaka Marina had 13.
In Tutukaka Marina, above-water searches covered 59% of the available artificial substrata around the
perimeter of the location. Dive searches representing over 23 hours of diver search time covered 91%
of the Marina perimeter. Only two Styela were found, both were adult-sized individuals (> 10cm total
length), discovered by divers approximately 100m apart. A previous rapid delimitation survey, in
November 2005, also found only two specimens, suggesting a very low density, widely dispersed
population and providing no evidence that the existing population successfully reproduced over the
year since it was first discovered in Tutukaka Marina.
Above-water searches covered 85 sites or 67% of the available substrata in Lyttelton Port. Forty sites
were also inspected by divers, accounting for an estimated 35% of the port perimeter. A total of 929
Styela were collected in Lyttelton Port, largely on piles, pontoons and ropes. No Styela were detected
on break-walls by either above-water or diver searches. Styela was widely dispersed and typically in
low densities (1-10 per m 2 ) at most (59%) of the sites searched in the inner harbour. Styela was also
present at low density at several sites along Cashin Quay, outside the inner harbour. The highest
observed densities of Styela in the Port of Lyttelton (between 11-100 per m 2 ), were detected on
pontoons comprising A and B jetties, and rafted pontoons located between Z berth and Gladstone pier.
The size of collected specimens varied from 1 to 18cm total length. The population included new
recruits as well as some of the largest specimens collected in New Zealand. There was evidence of a
strong cohort of small individuals (4 to 5cm total length), which suggested a widespread recruitment
event around Lyttelton Port had preceded the late 2006 survey.
Kriging of the distribution data from Lyttelton Port indicates Styela is widely present in low
abundance on man-made substrata around most of the perimeter of the inner harbour. Kriging analysis
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 1

Executive Summary
also indicated particularly high densities of Styela fouling at three locations: the western side of #2
Wharf, pontoons between the Z Wharf and Gladstone pier and the A and B pontoons. The only areas
that may currently be free of Styela are the cattle Wharf and dry dock facilities in the south-western
sector of the inner harbour and along the break-wall at the far eastern end of Cashin Quay. Kriging
predicts low Styela abundance (less than 10 individuals per 5*5m surface grid cell extending to a
depth of 10m) for 63% of cells around the perimeter of the Port.
In Lyttelton Port (the location with the deepest water) two phases of diver searches were undertaken to
test assumptions about the vertical distribution of Styela in the water column. Dives were initially
conducted at 40 sites in shallow water (

New Zealand wide vessel movements, MAFBNZ project ZBS2005-13 and an epidemiological
simulation model for yacht movements developed by NIWA.
Executive Summary
Potential vectors associated with the Tutukaka Marina included recreational yachts, diving and fishing
charter vessels and commercial fishing vessels. Fifty-four percent of recreational vessels, 15.4% of
diving vessels and 66.7% of fishing vessels resident at the marina were found to carry fouling
organisms on their hulls. All of these vessel types regularly or frequently travel between Tutukaka
Marina and the Poor Knight Islands HVA, but few movements occur to other HVAs.
Potential vectors associated with the Lyttelton Port included recreational yachts, scenic and fishing
charter vessels, merchant ships, commercial fishing vessels, operations and maintenance vessels,
towed barges and a towed pontoon. Of these, 69%, 34%, 72%, 25%, 100% and 100% were found to
carry fouling organisms on their hulls, respectively. Styela was observed on some of the barges and
the workshop pontoon. However, these vectors never leave the Port. All other vessels types
undertake regular to frequent visits to the Banks Peninsula, Akaroa Harbour and Marlborough Sounds
HVAs. Very occasionally, recreational craft travel from Lyttelton Port to the Poor Knights Islands
HVA.
Potential vectors associated with the Magazine Bay Marina included recreational yachts and a single
inactive commercial fishing vessel. Seventy-four percent of the recreational yachts encountered
carried fouling organisms on their hulls, in one case Styela. Occasional visits to all four HVAs occur
by recreational vessels from Magazine Bay Marina. Overall, this marina has by far the lowest vector
activity of the three surveyed source locations.
Movement patterns of vectors between New Zealand’s coastal ports and marinas are complex. The
four HVAs examined in this study are visited by vectors originating from all three source locations,
but at varying frequencies. In addition, they receive a considerable amount of vector traffic from the
Auckland region, where Styela is widely distributed. The Poor Knight Islands are very rarely visited
by vessels from Lyttelton, but receive frequent visits from marinas around Auckland where Styela is
known to be established. The Akaroa Harbour and Poor Knights Islands HVAs are unlikely to
become inoculated with Styela through aquaculture related vectors. Instead, recreational and
commercial (charter) vessel movements have a higher likelihood of transporting Styela to these HVAs.
Aquaculture operations, commercial and recreational vessel traffic all have the potential to transport
Styela to (and throughout) the Banks Peninsula and Marlborough Sounds HVAs.
Deliverable 3: Identify and determine the risk of Styela clava spreading from delimitation
locations to HVAs.
We calculated the risk of Styela being transported directly from known source populations to HVAs.
The source populations considered included the three delimitation locations and the wider Auckland
region (including Waitemata harbour and the Hauraki Gulf). The Auckland region was added since
we felt a nationwide assessment of the risks of Styela spreading to HVAs would be substantially
incomplete and potentially misleading without it. The HVAs considered were identified as being at
high risk in deliverable two. We considered four possible human-mediated vectors (recreational
boating, commercial shipping, aquaculture activities and the towing of barges and structures), as well
as natural dispersal as key vectors likely to spread Styela. As such there were 80 possible pathways
between source populations and HVAs considered.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 3

Executive Summary
Initially we conducted a qualitative risk assessment of each of the 80 possible pathways to provide a
broad summary of risks posed to HVAs by source populations and vectors. To estimate uncertainty
around pathway risks we then applied an Infestation Modes and Effects Analysis (IMEA). This
approach involved estimating the minimum and maximum likely risks for components of each
pathway using a log scale scoring system and compiling the range of risk scores, termed Risk Priority
Numbers (RPN scores). The minimum possible risk is termed RPNmin, the maximum RPNmax, and the
average of this range is RPNavg.
RPNavg values varied from 42 to 11,145 depending on the combination of source populations, HVAs
and vectors considered. The highest RPNavg values (> 10,000) were calculated for 13 of the 80
potential pathways between sources and HVAs, and indicated the highest risk individual pathways. Of
the 13 highest risk pathways identified, 10 involved either recreational or commercial shipping linked
to Lyttelton Port and the Auckland region. Since the risk of spread of Styela to HVAs is additive for
independent pathways, RPN scores were used to estimate cumulative risk from multiple source
populations and vectors. Importantly the range in values from RPNmin to RPNmax also provided an
estimate of the minimum and maximum likely threat posed by the various sources of risk.
IMEA analyses indicated that Lyttelton Port contributed the greatest overall risk of spreading Styela to
HVAs, followed closely by the Auckland region. In contrast Magazine Bay Marina represented a
reduced risk, and Tutukaka Marina represented the least risk. We conclude that the two vectors most
likely to spread Styela from source locations to the nominated HVAs in New Zealand are recreational
vessels and commercial shipping. Recreational boating and commercial shipping were both classified
as particularly high risk vectors (RPN >10,000) for introducing Styela to each of the four HVAs. In
particular they were implicated as key sources of risk to the Marlborough Sounds from both Lyttelton
Port and the Auckland region. RPNavg for recreational vessels and commercial shipping were similar,
with a very wide overlap of possible risk values from RPNmin to RPNmax. This range of potential risks
makes it impossible to unambiguously distinguish whether recreational or commercial vessels
represented greater threats of transporting Styela to HVAs.
Aquaculture activities associated with mussel farming was the third most likely vector to transport
Styela, followed closely by the towing of barges and structures. Both vectors pose a similar range of
risks and pose less threat than either recreational or commercial vessel movements. Much of the
aquaculture risk identified was associated with mussel harvester movements, particularly between
Lyttelton Port and both the Banks Peninsula and Marlborough Sounds aquaculture production areas.
The infrequent movement of towed barges or structures documented from source locations to HVAs is
balanced against the relatively high likelihood they would be fouled with Styela.
The four human-mediated vectors considered were far more likely to spread Styela to HVAs than
natural dispersal. Styela has a negligible risk of dispersing naturally to HVAs since their planktonic
propagules appear incapable of travelling large distances during their short (24 hour) competency
period. To assess the risk of natural dispersal in Lyttelton harbour we used a hydrodynamic and
particle dispersal model to determine likely patterns of dispersal under varying wind conditions. The
model predicted Styela propagules released in Lyttelton Port were extremely unlikely to exit the mouth
of Lyttelton harbour or reach the nearby Banks Peninsula aquaculture area. However Lyttelton Port
Styela propagules may reach Magazine Bay Marina, particularly if prevailing winds are from either
the north-east or north-west.
4 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

RPN estimates of the risk of Styela establishment were widely overlapping for the four HVAs,
Executive Summary
indicating a wide range of potential risk to each location. Nevertheless IMEA results suggest the
HVA at greatest risk is the Marlborough Sounds aquaculture area, followed by the Banks Peninsula
aquaculture area, Akaroa harbour and then the Poor Knights Islands. The key risks of Styela
establishment in the Marlborough Sounds aquaculture areas are posed by commercial shipping and
recreational boating visits to the ports of Nelson and Picton, as well as the Nelson, Havelock, Picton
and Waikawa Bay marina facilities. Vessels fouled with Styela have the potential to introduce Styela
to any of these six vessel movement hubs, or directly to farms. Considerable additional risk was posed
by activities of the aquaculture industry itself. The risk arises from the sharing of mussel harvesting
vessels such as the St George, and Tardis which are known to travel between Lyttelton Port and the
Marlborough Sounds on a seasonal basis.
The Banks Peninsula aquaculture area was at second highest risk of being colonised by Styela. Risk
arose principally from aquaculture activities, commercial and recreational vessels linked to Lyttelton
Port. Akaroa harbour was the HVA third most likely to be colonised by Styela. The major risks to
Akaroa harbour are posed by vessel movements from Lyttelton harbour and the Auckland region. The
Poor Knights Islands marine reserve was least likely to receive Styela. Existing records of vector
movement to the Poor Knights suggest the majority of risk arises from recreational and commercial
vessels associated with the Auckland region and commercial vessel movements from Tutukaka
Marina.
Deliverable 4: Determine, categorise and prioritise key sites within each location for efficacy
trials of control measures to mitigate the spread of Styela to HVAs.
We sought to identify key sites or “risk areas” within each of the three delimitation locations for
potential population management efficacy trials. We considered key sites as artificial habitats
containing high densities of Styela relative to the surrounding population. Key sites are likely to
provide major contributions to larval production within locations, and may indicate the sites at highest
risk of fouling adjacent vectors or other artificial structures within the location. We prioritize key
areas on the basis of adult Styela abundance, the strengths of likely links with human-mediated vectors
and the accessibility and feasibility of undertaking diving experimental treatments or monitoring at
each. Key sites were identified on the basis of Styela abundance from field surveys completed to
address Deliverable 1. Vector activity known in the vicinity of the key sites was derived from
personal observations in the field and from data collected during Deliverable 2. In ranking
accessibility we also consider the likely disruption to port or marina activities by conducting
management trials such as plastic wrapping of submerged structures at each key site.
Three key sites were clearly identified as nodes of high Styela abundance in Lyttelton Port. All key
sites were in the eastern half of the Port’s inner harbour. They included the western side of #2 Wharf
(constructed of wooden piles extending to a depth of approximately 10m), and pontoons between Z
Wharf and Gladstone pier, and the A and B pontoons. Both pontoon sites are constructed of foamfilled
concrete pontoons anchored to wooden piles. Access to the A and B pontoons is expected to be
problematic for efficacy trials since it is the busiest hub of small commercial vessel activity within
Lyttelton Port with frequent and unpredictable movements of some vessels. In contrast the pontoons
between Z Wharf and Gladstone pier, and the western side of # 2 Wharf are subject to less frequent
vessel movements and pose considerably less risk to divers.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 5

Executive Summary
Key sites of locally high Styela density were not evident in either Tutukaka Marina or Magazine Bay
Marina. In both marinas we identified a pair of sites that contained Styela, and were broadly
representative of the key artificial habitat types present in the location, but do not recommend them as
ideal sites for control measure trials. In Tutukaka Marina the current densities of Styela are so low
that selecting key sites is probably unwarranted, since we recommend monitoring of the entire marina,
and potentially hand picking individuals, rather than treatment trials on a site by site basis. In
Magazine Bay Marina we identified sites (sectors B and D) known to contain Styela and representing
typical construction techniques and materials for the location. Diver access to the sector B and D sites
is not problematic from a vessel movement point of view, but water clarity in the marina is typically
very poor. Water clarity measures of less than 0.7m Secchi depth are typical, and are likely to
compromise the efficiency of dive teams attempting plastic wrapping, hand picking or similar control
activities. The low priority rank for these two sites also reflects the derelict state of much of the
marina, and difficulty in accessing the piles from wharves suspended many meters above the
waterline. Rather than conducting trial control measures in either the Tutukaka or Magazine Bay
Marinas we recommend consideration of the Viaduct Basin in Auckland’s Waitemata harbour. This
location has an abundant, widespread Styela population and suitable replicate pontoon, wall and pile
structures for experimental treatments.
Deliverable 5: Design a population management programme for each delimitation location.
This section describes the design of a population management programme for Styela clava in each of
the three study locations (Tutukaka Marina, the Port of Lyttelton and Magazine Bay Marina). The
design of the programme draws upon information described in earlier sections of the report on the
status of Styela populations in each location (Deliverable 1), and the relative risks of spread of Styela
to nearby High Value Areas (HVAs) by a variety of potential vectors (Deliverables 2 and 3). The
overall aim of the management programme should be to control populations of Styela in these
locations to mitigate the risk of it spreading to HVAs.
We considered management of Styela populations and management of vectors as overall strategies for
the programme, and discussed and evaluated a total of nine management objectives associated with
these overall strategies. The management objectives included no management (do-nothing approach),
attempted eradication of Styela, maintenance of specified population densities, voluntary vector
management, mandatory vector management and combinations of population and vector management
options. All management objectives were evaluated against criteria listed in The Biosecurity Act 1993
for consideration in pest management: effectiveness, practicality, acceptability to stakeholders, likely
side-effects, legality, likelihood of success, cost of implementation and degree of uncertainty. A
scoring system was used to determine the most favourable management objectives for the prevention
of the spread of Styela to the high-value areas. We also used a stochastic epidemiological model to
simulate the nationwide spread of Styela under some of the optional management objectives (donothing,
vector management, population management) and incorporated the model outputs into our
evaluation of the various management options.
Based on our evaluations, we recommend a combination of population (attempted eradication) and
vector management (voluntary or mandatory) for preventing the spread of Styela to the Poor Knights
Islands HVA. It is important that any vector management should target vessels arriving at the Poor
Knights Islands, irrespective of their origin. Styela is widespread throughout the nearby Auckland and
6 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Executive Summary
Hauraki Gulf regions, and exclusive targeting of vectors departing Tutukaka will not prevent the
transport of Styela to the Poor Knights Islands from southern populations.
Our conclusions are similar for Styela populations in Lyttelton Harbour. We recommend a well-
designed, comprehensive vector management programme as the best immediate step to prevent the
establishment of Styela in the Marlborough Sounds, Banks Peninsula and Akaroa Harbour high-value
areas. We emphasise that it is important, particularly for the Marlborough Sounds HVA, that all
potentially high-risk vectors are targeted, including those arriving from other areas where Styela is
known to be present (e.g. Auckland and Hauraki Gulf). Negligence of these vectors by focusing
exclusively on vectors departing Lyttelton may lead to the introduction of Styela to the HVAs from
northern population and compromise the efficacy of all other management efforts.
We suggest that additional population management at Lyttelton port and marina may help to further
reduce the risk of spreading Styela to the HVAs. Eradication of Styela from the port (and therefore
also the marina) is probably unfeasible. Reducing or maintaining current population sizes may be a
feasible approach that can be achieved and that may reduce propagule pressure on resident vectors
travelling to the HVAs. However, we recommend that any population management is preceded by
experiments that determine the relationship between population size, distance from reproductive adults
and propagule pressure on susceptible nearby vectors. This knowledge does not currently exist but is
required to determine the feasibility and best format for population management for Styela in
Lyttelton.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 7

Introduction
2. Introduction
The clubbed tunicate, Styela clava is variously known as the Asian stalked sea squirt, Pacific rough
sea squirt or leathery sea squirt and is hereafter referred to as “Styela”. It is a solitary ascidian that is
native to the coastal waters of Japan, Korea, northern China and Siberia (Furlani 1996). Non-
indigenous populations of Styela are known to have established in both the northern and southern
hemisphere and include the south and west coasts of the British Isles, in Ireland, northern France,
Belgium, the Netherlands, Denmark and Germany (Minchin et al 2006). Styela has also spread to the
Baltic Sea and Nova Scotia (Minchin and Duggan 1988, Lützen 1999), Southern Australia and
California (Holmes 1976, Lambert and Lambert 1998), Washington State and British Columbia
(Cohen 2005). In some of these locations it has proliferated rapidly to reach very high densities
(thousands per m2). Styela is now also present at ports and marinas on the east coasts of the North and
South Islands of New Zealand (Gust et al 2006a).
Styela clava was first identified in New Zealand from the Viaduct Basin, Waitemata Harbour in
August 2005 by a visiting international marine scientist. Soon after, a second specimen was identified
from samples taken as part of a baseline survey of the Port of Lyttelton in 2004. Styela poses a
potential threat to valued New Zealand marine environments and resources, particularly mussel
farming. In its native range Styela is known to encumber the hanging culture of oysters, and foul fish
cages (references cited in Minchin et al 2006). In its introduced range in eastern Canada it has caused
declines in the production of the cultivated mussel Mytilus edulis (Bourque et al 2007). Concerns
about the potential impacts of Styela prompted MAF Biosecurity New Zealand (MAFBNZ) to initiate
a response to its discovery in Auckland.
MAFBNZ declared Styela clava an Unwanted Organism under the Biosecurity Act 1993 on the 14 th of
October 2005. A delimitation survey of Viaduct Basin and Freemans Bay, in October 2005, showed
that Styela was widely distributed in the area. It was also detected in nearby Westhaven Marina (Gust
et al 2005). Subsequent detection surveys were undertaken in 26 high-risk locations throughout New
Zealand to assess nationwide distribution, and determine whether Styela had become established in
any of the other high risk ports and marinas around the country. Twenty-six locations were surveyed
in November 2005, and Styela was detected at three of these locations: Tutukaka Marina, Lyttelton
Port and Magazine Bay Marina in Lyttelton harbour (Gust et al 2006a). A further five high risk
locations and a resurvey of Opua Marina were undertaken in June and July 2006, but no additional
incursions were detected (Gust et al 2006b). Specimens have also been detected on vessels moored in
Opua, Waikawa Marina (Picton), Nelson and Clyde Quay Marina, Wellington, but no established
populations have been found in these locations. In summary, established Styela populations have been
recorded in three locations: Waitemata Harbour and the Hauraki Gulf, Tutukaka Marina and Lyttelton
Harbour (Figure 1.1). In October 2006 MAFBNZ contracted NIWA and the Cawthron Institute to
assess population management options for Styela in Tutukaka Marina, Lyttelton Port and Magazine
Bay Marina. This contract (BSP21705) is the focus of the current report.
8 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Introduction
Figure 1.1 The high risk shipping locations searched nationwide for Styela clava in November 2005 and June-
July 2006. Styela was detected at Tutukaka Marina, Lyttelton Port and Magazine Bay Marina (Gust et
al 2006 a,b). These three locations are the focus of the current population management trial study.
Additional Styela populations in Waitemata harbour and the Hauraki Gulf are also considered.
2.1. Life history background
Styela clava is a large (up to 18 cm total length), stalked, solitary ascidian with a club-shaped body. It
is a fouling species common on artificial (man-made) substrata and is particularly abundant within 2m
of the water surface on structures such as pontoons, piles and ropes (Lützen 1999). Although it occurs
predominantly in shallow water in the low intertidal and shallow subtidal, it can occur as deep as 25 m
(Cohen 2005). It is largely confined to sheltered localities free from strong wave actions, such as
inlets, bays harbours or marinas (Lützen 1999). In New Zealand Styela has been found on a wide
range of artificial surfaces in ports and marinas. In the Viaduct Basin and Freeman’s Bay it was
detected on fixed surfaces including concrete break-walls and wooden pier piles. It was also regularly
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 9

Introduction
found on a variety of floating structures including; ropes, floating jetties, pontoons and vessel hulls
(Gust et al 2006a).
Styela is robust and capable of withstanding large fluctuations in salinity and temperature, grows
rapidly and can produce large numbers of recruits in suitable environmental conditions (Lambert and
Lambert 1998, 2003). Styela clava is hermaphroditic with a lecithotrophic (non-feeding) planktonic
larval phase (Minchin et al 2006), with propagules that can settle and subsequently grow to maturity
on a wide range of fixed or floating substrata. Larvae are known to be negatively buoyant and tend to
settle near the water surface (Davis 1997). Larvae hatch from released eggs after about 12 hours and
are active for a similar period of time before settlement (Minchin et al 2006). Consequently the short-
lived, non-feeding, swimming tadpole larvae disperse only over relatively short distances. The
appearance of a Styela population hundreds or thousands of kilometers from other known areas of
occurrence is an indication of transport via anthropogenic vectors such as ballast water or hull fouling
(Lambert 2007).
Individual Styela can grow rapidly and produce large numbers of recruits when environmental
conditions are suitable. A consequence is that populations can expand quite rapidly to large densities
(Lambert and Lambert 1998, 2003). Previous studies have reported densities of 500-1500 individuals
per m 2 (Lützen 1999, Osman and Whitlatch 1999). In some parts of its introduced range it has
achieved densities of thousands per m 2 (Minchin and Duggan 1988, Minchin et al 2006). Rapid
population growth has been previously observed in this species once it is introduced to novel
environments. For instance significant population growth was noted in Canada within three years of it
being discovered (Bourque et al 2005), and it spread from Maine to Connecticut within ten years of its
introduction to the eastern USA (Berman et al 1992). A large population expansion was also noted
over two years in the Netherlands (Christiansen and Thomsen 1981). However rapid population
expansions are not universal observations for Styela invasions, and there is some evidence that in
Hobsons’ Bay, Australia and San Diego Bay, USA prolonged periods of little or no population
expansion have occurred (Holmes 1976, Lambert and Lambert 1998).
3. Objectives
The broad aim of this study is to evaluate options for management trials of Styela populations in
Tutukaka Marina, Lyttelton Port and Magazine Bay Marina. The program aims to identify ways of
reducing the chances of Styela spreading from these three vessel movement hubs to nominated high
value coastal environments around New Zealand, and to provide information on control methods and
the feasibility of implementing them at various scales.
The five specific aims (deliverables) of the research were to:
1. Determine and map the extent of the distribution and density of Styela in Tutukaka Marina,
the Port of Lyttelton and Magazine Bay Marina.
2. Identify human-mediated vectors with the potential to spread Styela from areas identified in
deliverable 1 to high-value areas.
10 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

3. Identify and determine the risk of Styela spreading from the locations identified in
deliverable 1 to high value areas based on information obtained in deliverables 1 and 2.
4. Determine, categorise and prioritize key sites (risk areas) within each location, based on
Introduction
information obtained from deliverables 1-3, for efficacy trials of control measures to mitigate
the spread of Styela to high-value areas.
5. Design a population management programme for each location based on, but not limited to,
the information obtained in deliverables 1-4.
This report is divided into sections that detail the methods, results and discussion for each deliverable
separately. Deliverable 6, implementing the Styela management programme is not covered by the
current contract.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 11

Deliverable 1
Deliverable 1: Determine and map the extent of the distribution and density of
Styela clava in the Tutukaka Marina, Port of Lyttelton and Magazine Bay Marina
4. Methods
4.1. Field survey approach
We used a combination of above-water visual searches and diver inspections to determine detailed
patterns in the distribution and density of Styela from the three target locations. The survey was
designed to estimate the distribution and abundance of Styela in representative sites and artificial
habitats most likely to contain Styela in each location. The search methods were broadly based on
techniques developed for rapid Styela detection surveys (Gust et al 2005, 2006a, 2006b), that aimed to
determine probabilistic estimates of the presence or absence of Styela for an entire location. In
contrast the current delimitation surveys aimed to provide detailed assessment of the distribution and
density of Styela to facilitate the design of robust management trials.
Tutukaka Marina (Figure 1.2), Lyttelton Port and Magazine Bay Marina (Figure 1.3) each contain
large amounts of infrastructure as potential Styela habitat, including piles, pontoons, breakwalls, ropes,
fenders and vessel hulls (see Appendices 1, 2 and 3). Since it is not practical to survey all artificial
habitats at larger locations, the survey design in Lyttelton Port aimed to determine the density of
Styela in sample sites distributed throughout the location, and to interpolate to sites that could not be
examined. In the smaller marinas we attempted to systematically survey as much of the available
Figure 1.2: GIS map of Tutukaka Marina search area. Solid black lines indicate pontoon structures, points
indicate wooden piles. Jetties J, K, L and M are standard modern foam-filled concrete construction
(see Appendix 1). Jetties A-E consist of a series of small (approx 2 x 1m) foam-filled concrete
pontoon blocks supporting wooden walkways.
12 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

MBM
Figure 1.3: Map of northern Lyttelton Harbour, showing Lyttelton Port (LP) and Magazine Bay Marina (MBM)
approximately 1 km to the southwest. Source: MapToaster.
habitat as possible in the time available. In Lyttelton Port we adopted a regular spacing of sample
sites throughout, so that results could be interpolated to adjacent sites that could not be examined.
Deliverable 1
To ensure detailed descriptions of the distribution and density of Styela from each location we used;
1. Above-water visual searches to inspect a large proportion of the visible shallow habitat
within locations.
2. A systematic distribution of diver sampling effort in proportion to the availability of key
Styela habitats throughout locations wherever possible.
3. A structured sampling experiment to compare the abundance and depth distribution of Styela
in Lyttelton Port to validate the survey methods, and
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 13
LP
4. Spatial analysis (Kriging) to interpolate Styela distribution and relative abundance to
unsampled locations.
Initially, a thorough above-water visual survey of potential Styela habitats was conducted at each
location. The above-water searches endeavoured to cover the entire perimeter habitat accessible at
each location. This was followed by diver searches of shallow (

Deliverable 1
with the aim of ensuring a representative sample of each major habitat type (i.e. roughly in proportion
to its relative abundance within the location). A systematic sampling design was used in preference to
a random sampling design, in order to ensure all major habitat types were well represented, and that
large gaps did not exist between sampling sites so that interpolation would not be compromised by
long distances between data points.
4.2. Field identification of Styela clava
Styela clava is readily distinguished from the two congeneric species (S. plicata and S. gracilocarpa)
that already occur in New Zealand on the basis of its gross morphology (M. Page, NIWA, pers.
comm.). The main distinguishing features are its club-like shape and basal stalk. Styela plicata and S.
gracilocarpa do not have an obvious stalk. The external test of S. clava is leathery and on closer
inspection can be distinguished from S. plicata, which has a whitish, almost naked, tough test that is
not leathery (Kott 1985). All field staff involved in the current surveys had considerable previous
experience collecting and identifying S. clava during nationwide delimitation surveys. Field teams
also carried laminated hard copy photographs of the organism and species information guides during
each survey. These were often used to educate the public on characteristics of the target organism
when we were queried about the searches.
4.3. Above-water visual surveys
Above-water visual surveys were conducted from a vessel (where foot access was not possible), or
involved walking slowly around fixed and floating structures at each location and inspecting shallow,
submerged surfaces for the presence of Styela. We endeavoured to examine the entire accessible
perimeter of man-made structures within each location. The inspections covered fixed mooring lines
and ropes (particularly those that could be hauled up), the vertical sides of floating pontoons,
breakwalls, and wharf piles.
Fixed structures (predominantly breakwalls and wharf piles) were searched within 2 hours of low tide
to optimise the chances of observing Styela. Floating objects, such as pontoons, ropes or moorings,
were inspected regardless of tidal height. Because it was often difficult for surface observers to access
structures beneath wharves, visual surveys primarily concentrated on the outer row of pilings or
facings on these structures. Observers carried waterproof maps of the location and recorded the
numbers of Styela detected for each site searched. Above-water search maps were then compiled as
shape files within a GIS to indicate the sites searched and the distribution and density of Styela in
each. Additional data were recorded on environmental conditions at the time of the searches,
including water clarity using Secchi disc readings, sea state (using the Beaufort Scale, see
Appendix 4), and the duration of searches at each site.
Although most search effort in these three locations was devoted to inspections of the fixed and
floating structures that comprise these facilities, inspections were also made of heavily fouled vessels
when they were encountered. The vessel inspection approach was based on risk profiling techniques
developed by Floerl et al (2005), where surface-based observers assess the fouling intensity of visible
parts of vessel hulls using an ordinal rank scale. The scale ranges from zero (no fouling) to five (very
heavy fouling) and is based on the relative abundance of fouling visible to the observer and the
number of different identifiable taxa that can be seen (Table 2.3). Using this approach, we considered
vessels with a fouling rank of three or above had a “moderate to high likelihood” of Styela being
14 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

present. These heavily fouled vessels were targeted for inspection by above-water observers and
divers. We recorded the vessel’s name, where it was moored when inspected, and whether or not
Styela was found on its hull.
Deliverable 1
Where Styela was found, the position was recorded directly on laminated maps of the location carried
by observers. GPS coordinates of the observation, the substratum on which Styela was attached and
visual estimates of density were recorded on standardised data forms. Visual estimates of maximum
Styela density were made using a semi-quantitative log scale:
• 0 individuals per m 2 ,
• 1-10 individuals per m 2 ,
• 11-100 individuals per m 2 , or
• >100 individuals per m 2
If Styela was widely distributed, estimates of maximum density were recorded at least once every 50m
around the perimeter of the location.
4.4. Survey design for diver searches
Diver searches for Styela concentrated on floating pontoons, wharf piles, breakwalls and other mapped
hard substrata within each location. Additional diver inspections of floating buoys or heavily fouled
vessels were also conducted opportunistically. Water clarity at the searched locations was typically
poor (often < one meter). Past experimental results indicate that, unlike above-water searches, diver
searches retained relatively high sensitivity even in poor water clarity (Gust et al 2006b). Accordingly
we allocated a large proportion of the total survey effort in each location to diver searches. Diver
searches of floating structures such as pontoons and vessel hulls concentrated on the submerged areas
that could not be seen during above-water searches.
Searches of fixed structures (such as pier piles or breakwalls) were conducted from the surface to the
seabed in both Tutukaka and Magazine Bay Marinas where maximum depths were around five meters.
However water depths in Lyttelton Port often exceed 10m, and dive searches were implemented in two
phases. In the first phase, we inspected a sample of sites distributed systematically throughout the
location, using a standardized survey method. To ensure broad coverage, the survey method made
assumptions about the pattern of distribution of Styela based on existing literature and the results of
previous delimitation surveys in New Zealand. Notably we assumed that the majority of Styela would
be found in the upper five meters of the water column attached to artificial structures, and
concentrated our search efforts there accordingly. In the second phase, we tested these assumptions
using structured sampling to calibrate patterns of distribution for unsampled habitats.
4.5. Phase 1 – Stratified, systematic diver sampling
GIS was used to overlay a linear sampling grid 1 of sites over the survey locations. In the largest
location, Lyttelton Port, we also attached markers on fixed structures to facilitate the identification of
1 By “linear” we mean a one-dimensional sampling grid that traces the outline of the Port.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 15

Deliverable 1
each site around the ~seven km of perimeter (Figure 1.4). The grid cell length was the size of an
individual search unit or site (i.e. ~50 linear metres). Systematically-spaced sites were then chosen for
sampling. Not all selected sites could be sampled because of shipping movements at the time of
surveys, or health and safety considerations for divers operating in very low visibility where
entanglement issues exist. Care was taken to sample systematically selected representatives of each
major habitat type present (roughly in proportion to its relative abundance within the location). To
determine the distribution and abundance of Styela, a large proportion of available perimeter habitat at
each location was searched during the current program. In contrast the initial, rapid detection surveys
for Styela at these locations in November 2005 were concerned with determining the presence or
absence of Styela, and involved much less widespread search effort (Gust et al 2006a).
Although Styela is known to occur to depths of up to 25m overseas, it tends to be found most
commonly in relatively shallow water depths, in the low intertidal and shallow subtidal (Cohen 2005).
Surveys of Styela carried out under Project ZBS2005-32 recovered ~75% of all Styela specimens
within five meters of the water surface. In order to sample a large area of each location, maximise
chances of detection, and optimise the efficiency of searches, diver searches in phase one concentrated
on fouled artificial surfaces in the upper 5m of the water column. This was necessary since most
techniques for interpolation have greatest reliability when there are a comparatively large number of
well-dispersed sample points, rather than extremely detailed descriptions from just a few locations.
Our approach also allowed more areas to be searched by divers in the time available (because the
lower nitrogen debt accrued by the divers during shallow dives allows more dives to be completed in a
day). In Magazine Bay and Tutukaka Marinas, phase one searches covered the entire water depth,
since this was typically < 5m. Phase two diving was only possible in the deeper waters of Lyttelton
Port. At each sample site, a pair of divers conducted searches over a standard sampling unit of
Figure 1.4: GIS map of Lyttelton Port search area showing the grid of site markers used in the surveys.
Numbered points indicate ends to each site extending over ≈50m or Port perimeter.
16 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
perimeter ~50 m long. Inspections of floating pontoons concentrated this search effort along the
length of discreet floating finger wharves and inspected the underneath of these structures and any of
their surfaces not visible to above-water searchers. Wharf pile inspections concentrated search effort
within five meters of the surface and inspected a linear set of pilings (typically >10 pilings per site),
ropes and other structures on the outer face of the wharf. Inspections of breakwalls involved divers
searching ~50m of substratum from the surface down to a maximum depth of five meters. The sites
searched by divers were recorded in the field on laminated maps of survey locations. Additional data
were recorded on water clarity (Secchi disc depth in meters), sea state (using the Beaufort scale), the
substrata searched and the time taken to search each site. As with above-water searches, the position
of any Styela found was recorded on laminated maps, GPS coordinates of the location were taken, and
we recorded the substratum it was attached to. Maximum density estimates for Styela were recorded
from diver inspections at each site using the semi-quantitative log scale described in 3.2 above.
4.6. Phase 2 – Validation of the diver survey technique
The survey technique used in phase 1 of the diving assumes that:
• The density of Styela on structures in the surface waters (< five meters) is at least equal to, or
greater than the density present at greater depths at the same site, and
• The density of Styela on the outer piles of wharves is at least equal to, or greater than, that
present on piles underneath wharves at the same site.
Violation of these assumptions means that sites identified as being free of Styela from above-water
searches and/or phase one of the diving, may contain the target organism in unsampled, less accessible
habitats within the site. To test these assumptions, we chose six sample sites where Styela was found
in phase one diving. We distributed the replicate re-surveyed sites throughout the Lyttelton Port to get
representative coverage of predominant wooden and concrete pile habitats. At each site we sampled at
least 10 piles on the outer perimeter of the wharf. Over the course of two dives the divers surveyed
each piling from the surface to the seafloor. Separate estimates of density were made above and below
five meters depth on each piling, using the semi-quantitative log scale described above.
In Tutukaka Marina and Magazine Bay Marina the physical layout of Marina structures enabled us to
survey piles both on the perimeter and underneath jetties. However in Lyttelton Port health and safety
concerns arose for divers beneath wharves and piers because of poor water clarity, light attenuation at
depth and the chance of entanglement on discarded wiring, cables, steel rods and other unseen
obstacles that we encountered beneath the wharves. These risks prevented us from comparing the
distribution of Styela on piles searched along the relatively well-lit outer perimeter of wharves and
those in the gloom underneath. However above-water field observations and initial diver attempts at
searching beneath wharves provided no indication of a difference in Styela abundance between piles
along the perimeter and beneath wharves. We consider the probability of Styela occurrence to be
equivalent for piles irrespective of their location beneath a wharf for subsequent kriging analyses.
Generalised Linear Models (GLM) were used to determine relationships between the presence and
abundance of Styela in above-water searches and both shallow (5m) diver searches.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 17

Deliverable 1
4.7. Styela collections
Wherever possible, we collected each Styela individual detected by above-water and diver searches.
Styela from both search techniques and each site were bagged separately. Their total lengths (stalk
and body) were measured to the nearest 0.5cm either in the field or laboratory. We investigated
patterns of Styela body size across depths and substrata to determine whether there were patterns in
differences in the distribution of small and large individuals, since large individuals are likely to have
a higher reproductive output and thus represent a higher risk of fouling nearby vectors.
4.8. Mapping and kriging analysis
A number of separate layers were mapped in a Geographic Information System (GIS). We created
layers for both the above-water and diver survey effort and for the distribution and density of Styela
detected with each survey technique.
In Lyttelton Port observations of the presence and abundance of Styela at each site, at intervals of
50m, were used to predict its likely presence and relative abundance at unsampled sites using a spatial
analysis technique called “kriging”. Kriging is a method of interpolation used to generate a two
dimensional surface of predicted distribution from a set of variably-spaced data points. This approach
enables an investigator to use sampled data points to “fill in gaps” in a survey region which is
impractical to survey in its entirety. For instance it is not feasible to survey all the potential Styela
habitat in Lyttelton Port since counts indicate there are approximately 6,000 piles present, and GIS
estimates of the total perimeter occupied by all piles, pontoons and break-walls exceed 7 km.
The Kriging technique is based on the regionalised variable theory that describes spatial continuity or
“autocorrelation,” an inherent feature of many environmental datasets. The pattern of spatial variation
of sampled values is assumed to be similar throughout the sampling region (spatial homogeneity).
This spatial variation is quantified by a semi-variogram and is estimated from the sample data points;
the further the distance between two points the less likely that they will have similar values. This
distance between sample points is known as the lag distance and is used to construct the semivariogram.
Various models can be fitted to this semi-variogram and the “best-fit” model is then used
to estimate unknown values, usually at regular intervals in the sampling domain. A surface of
estimated values can then be created and mapped using a GIS. The robustness of this technique is
highly data-dependent, but is generally greater for large numbers of well-dispersed data points.
Kriging was applied in Lyttelton Port where the large size of the location meant it was not possible to
sample all potential Styela habitats. However kriging was inappropriate for Tutukaka Marina (due to
the very few Styela collected there), and was not applied in Magazine Bay Marina (since almost all the
available habitat was surveyed).
The kriging interpolation for Lyttelton Port was carried out with ArcGis 9.1, using the Geostatistical
Analyst extension. This is an interactive graphical program that assists the user with the choice of best
fit parameters for a given set of data points, for a selected model. To further enhance the kriging
procedure, a method was developed to exclude or “mask” off areas of landmass to prevent correlation
of data points that were close together but isolated to direct larval dispersal by impermeable barriers.
For instance kriging directly between submerged habitats on either side of a land barrier (such as a
peninsula) may lead to spurious patterns of predicted Styela distribution if direct larval transport
between those sites is not possible, or can only occur via an indirect, convoluted path. By masking we
18 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
avoid this potential source of error and in extrapolating to unsurveyed locations only consider Styela
abundance in nearby sites directly connected by water. Masking is achieved by programming a script
to run within ArcGis. The script invokes the Geostatistical engine and uses the previously determined
parameters and model.
Kriging routines were run to produce a variety of outputs using different attributes of the survey data.
Firstly we predicted the probability of Styela being present at all sites around the perimeter of the port
based on the presence or absence of Styela from surveyed sites. Then we estimated the relative
abundance of: (1) all Styela, (2) Styela < 5 cm long (“small” Styela) and (3) Styela > 5 cm long
(“large” Styela) around the perimeter of the port. The estimates were based on the numbers of Styela
of each size found at the sampled sites, corrected for variation in sampling effort. Since varying
combinations of above-water, shallow dive and deep dive searches were used to search individual
sites, the total number of Styela detected per site reflects both their true abundance and the sampling
effort. To allow for varying sampling effort, we generated a predicted number of individuals that
would be expected if all three search techniques had been used to search the full depth of the water
column at each site in Lyttelton Port.
This procedure initially involved checking that there were no significant correlations between the
numbers of Styela collected per site in each of the three search techniques. At the site level there was
no clear relationship between the number of Styela found in above-water searches and either shallow
or deep dive searches. However there was a relationship between the number of Styela found in the
shallow and deep dive searches at the six sites where both methods were used. The linear regression
equation (y = 0.31X -0.003, R 2 =0.70) suggests around 70% of the variability in the density of Styela
found in deeper dives can be predicted from the number found in shallower dives at the same site.
This relationship was used to predict the number of Styela likely to be found in deeper sites from
estimates of Styela numbers found in shallow dives.
We calculated the mean number of Styela collected per site in Lyttelton Port for each search
technique. These results suggest on average we would expect almost twice (1.8 times) as many Styela
to be found in shallow dives than in above-water searches. For example in sites where only an abovewater
search was conducted, we could then calculate the predicted number of Styela in the areas not
searched by shallow or deep dives. For instance if the number of Styela collected in an above-water
searches was 6, we would expect on average another 10.8 would be present in the shallow dive area.
We also know the number of Styela likely to be found in deeper water at a site is related to the number
in shallower water at the site according to the equation listed above. So we would expect on average
another 3.3 individuals in the deeper section of the site, giving a total of 20.1, rounded to 20
individuals.
Kriging analysis was then performed using the predicted total number of Styela for each sampled site.
After kriging computations a surface of probability or abundance was generated. The resulting two
dimensional surface was divided into a regular grid with a cell size of 5x5m, but actually represents a
three dimensional column of water with a 5x5m surface area that extends down to a depth of 10m
depth. The grid is then combined with other GIS layers to map the predicted patterns of Styela
presence/absence or relative abundance. Predicted Styela distribution at any unsampled point can then
be determined by interrogating the surface.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 19

Deliverable 1
4.9. Estimating the sensitivity of the search methods
During rapid searches of ports and marinas nationwide in 2005 and 2006 we conducted an experiment
to assess how well the survey method samples Styela (i.e. to determine the search sensitivity). The
experiment was conducted at multiple sites under varying water clarity conditions using Styela mimics
and standard NIWA above-water and diver search techniques. The experiment was designed to
determine the sensitivity of the search methods (called ‘effectiveness’ by Hayes et al 2005 and Inglis
et al 2005). Sensitivity refers to the proportion of Styela that would be observed using the above-
water or diver search methods when it is present in the observation unit. Sensitivity may be

Table 1.1: Survey dates and measures of search effort in each location. The number of sites 2 present and
searched for Styela clava using each technique is indicated, along with the time spent by divers
searching underwater in each location.
Location Survey dates Number
of sites
Number of sites
searched by
above-water
Number of sites
searched by
divers 5m
Deliverable 1
Diver search
time (hrs)
surveys
depth
depth
Tutukaka
Marina
13-15 Nov 2006 13 13 12 N/A 23.1
Lyttelton Port 27-28 Nov
2006,
1,5,6 and 14
Dec 2006
139 85 40 6 31.5
Magazine Bay
Marina
1,4,7 Dec 2006 9 9 7 N/A 10.5
Table 1.2: Geographic information system (GIS) estimates of man-made potential habitat for Styela, total
perimeter and the perimeter searched in each location. The proportion of total perimeter searched by
above-water and diver surveys is indicated (in brackets).
Location
Tutukaka
Marina
Potential
artificial
habitats3 (m2 )
Total
perimeter 4
(m)
Perimeter searched
by above-water
surveys (m)
Perimeter (m)
searched by
divers 5m deep
25,180 5,036 2973 (59%) 4605 (91%) N/A
Lyttelton Port 264,720 7,041 4697 (67%) 2484 (35%) 269 (5%)
Magazine Bay
Marina
9,685 1,937 1366 (71%) 1119 (58%) N/A 5
Above-water searches covered between 59% and 71% of the perimeter of man-made structures in each
of the three searched locations (Table 1.2). Diver searches in shallow water (

Deliverable 1
Lyttelton Port, where six sites were inspected and covered approximately 300 meters or 5% of the
perimeter of the location. Concerns for the health and safety of divers in extremely low water clarity
and entanglement issues on unseen obstructions prevented more extensive surveys of potential Styela
habitats in the shade beneath wharves, or in deep water at this location.
The specific areas searched by above-water techniques are indicated for Tutukaka Marina (Figure 1.5),
Lyttelton Port (Figure 1.6) and Magazine Bay Marina (Figure 1.7). The shallow dive sites (5m) were regularly
spaced around the perimeter of the Port (Figure 1.11).
Figure 1.5: Areas searched in Tutukaka Marina (in purple) using above-water surveys.
22 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Figure 1.6: Areas searched in Lyttelton Port (in purple) using above-water surveys.
Deliverable 1
Figure 1.7: Areas searched in Magazine Bay Marina using above-water surveys (in purple). Letters designate the
sites searched; in this location each discrete walkway and its associated pile and pontoon structures
represent sites.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 23

Deliverable 1
Figure 1.8: Shallow areas (

Figure 1.10: Shallow areas searched (

Deliverable 1
The perimeter lengths of artificial substrata that form suitable habitat for Styela are summarised for
each location (Table 1.3). The total perimeter distance comprised of piles, pontoons and breakwalls,
and the proportion of each inspected by the different above-water and diver search methods is
indicated (Table 1.3). Wharf piles dominate the perimeter of each location, however Tutukaka Marina
has a particularly large expanse (>1.6km) of pontoon perimeter. Above-water and shallow dives
searched between 18 and 100% of the perimeters of each major habitat type across the three locations,
although deep dives in Lyttelton Port covered only 5% of the perimeter.
Wind conditions experienced during searches were generally favourable for effective above-water
Styela searches at each location. Winds were typically calm to gentle (for definitions see Appendix 4)
with Beaufort sea states often less than 2 and small standard deviations in wind strength indicating
relatively consistent breezes rather than gusty conditions (Table 1.4). The effects of wind on search
sensitivity for Styela has not been experimentally determined, but there is likely to be a marked
decline in above-water search sensitivity as a function of increasing wind speed and the appearance of
ripples or waves on the surface.
Water clarity during Styela searches was generally very low, with mean Secchi disc measures less than
2m in all three locations (Table 1.4). The lowest water clarity was encountered in Magazine Bay
Marina where mean Secchi depth was 0.7 during above-water searches and 0.8m during diver searches
(Table 1.4). The highest water clarity was encountered in Tutukaka Marina where mean Secchi depth
was approximately twice that of Magazine Bay Marina (1.7m during above-water searches and 1.8m
during diver searches, Table 1.4). Water clarity in Lyttelton Port was generally better than in
Magazine Bay Marina but worse than Tutukaka. Within locations water clarity remained fairly
consistent throughout the search periods, as indicated by the small standard deviations for each
measure (Table 1.4).
The sensitivity of above-water searches varied widely between locations and substrata (Table 1.5).
The highest sensitivity (0.99) occurred for searches of shallow-sided pontoons in Tutukaka Marina and
Lyttelton Port where water clarity exceeded 1.4m Secchi depths. In contrast, above-water searches of
piles in Magazine Bay Marina, where the visibility was very poor, had very low sensitivity (0.02,
Table 1.5). Sensitivity of the dive searches on piles and break-walls (0.84) was slightly lower than for
dive searches on pontoons (0.90), (Table 1.5).
All heavily fouled vessels with fouling rank 3 or above were inspected by divers in each location
(Table 1.6). In Tutukaka Marina we inspected 54 vessels, in Lyttelton Port 9 vessels and Magazine
Bay 15 vessels (Table 1.6). The heavily fouled vessels present during surveys were typically
recreational yachts and motor launches under 10m in length. We did not encounter heavy fouling
(equivalent to fouling level 3 or above) on any large commercial vessels such as fishing boats,
container vessels or bulk carriers, although these vessel types are often present in the Port of Lyttelton.
Considerable additional detail on vessel types present in each location and their potential role as
vectors is covered in Deliverable 2. Here we consider heavily fouled vessels as potential Styela
habitat within each of the search locations.
26 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
Table 1.3: Construction details categorized by the major artificial substrates present around the perimeter of
each location. Perimeter distances searched by each technique are also indicated, along with the
percentage of that substrate searched (in brackets).
Location Substrate Total perimeter
Tutukaka Marina
Lyttelton Port
Magazine Bay
Marina
of substrate
present
Above-water
visual survey
Perimeter searched
Shallow dive
survey (5m)
Break-wall 692m 650m (94%) 324m (47%) n/a
Piles 2705m 684m (25%) 2642m (98%) n/a
Pontoon 1639m 1369m (100%) 1639m (100%) n/a
Break-wall 1024m 184m (18%) 371m (36%) n/a
Piles 5597m 6 4217m (75%) 1746m (31%) 269m (5%)
Pontoon 420m 296m (71%) 367m (87%) n/a
Break-wall n/a 7 n/a n/a n/a
Piles 1862m 1291m (69%) 1044m (56%) n/a
Pontoon 34m 34m (100%) 34m (100%) n/a
Table 1.4: Environmental conditions encountered during Styela surveys. Data are means ± one standard
deviation.
Secchi-disc depth Beaufort sea state Secchi-disc depth Beaufort sea state
Location
during above-water during above-water during diver
during diver
searches (m)
searches 8
searches (m)
searches
Tutukaka Marina 1.7 ± 0.3 1.1 ± 0.3 1.8 ± 0.3 1.4 ± 0.9
Lyttelton Port 1.4 ± 0.6 1.8 ± 0.7 1.1 ± 0.4 2.5 ± 1.3
Magazine Bay Marina 0.7 ± 0.1 2.1 ± 0.74 0.8 ± 0.05 1.9 ± 1.2
Table 1.5: Search sensitivities for Styela estimated using calculations described in Gust et al 2006b). Data
represent the proportion of Styela likely to be detected.
Location
Above- water
searches of piles
and break-walls
Above- water
searches of
pontoons
Diver searches of
piles and breakwalls
Diver searches of
pontoons
Tutukaka Marina 0.21 0.99 0.84 0.90
Lyttelton Port 0.17 0.99 0.84 0.90
Magazine Bay Marina 0.02 0.50 0.84 0.90
6 Calculation of perimeter here includes only the outermost row of piles, it does not include piles in rows beneath piers or
wharves.
7 Break-wall is not considered part of the Magazine Bay Marina as it does not enclose the Marina and is a continuous
structure spanning over a kilometre between the Port and Marina.
8 Sea state conditions were recorded using the Beaufort scale.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 27

Deliverable 1
Table 1.6: Fouled vessels inspected by divers for Styela clava at each location. Only vessels with a fouling rank
≥ 3 (using the risk profiling criteria developed by Floerl et al 2005), were inspected. Vessels where
Styela was not detected are indicated in plain font and those that had Styela detected on their hulls
are indicated in bold font.
Location Site Names (and berth locations) of searched vessels
Tutukaka Marina Piles Moorings
TKK098, TKK007, TKK023, TKK004, TKK146, TKK111, (no-
(main channel) name) x 2
Pile Moorings
(adjacent to jetty E)
TKK115, TKK030, TKK069
Jetty A TKK168 (A6), TKK151
Jetty B TKK032 (B9), TKK140 (B15), TKK128 (B16), TKK177 (B17),
TKK167 (B20), TKK112 (B25) , TKK024 (B26), TKK064
(B27)
Jetty C TKK157 (C1), TKK169 (C2), TKK106 (C5), TKK079 (C11),
TKK086 (C14), (no-name) (C15), TKK037 (C18), TKK105
(C26), TKK017 (C32)
Jetty D TKK068 (D1), TKK170 (D2), TKK171 (D3), TKK138 (D6),
TKK044 (D8), TKK040 (D14), TKK052 (D26), TKK137 (D29)
Jetty E TKK014 (E1), TKK094 (E5), G Force (E9), (no-name) (E10),
TKK002 (E14), TKK172 (E24), TKK173 (E26), TKK118 (E27)
Jetty K TKK059 (K13), Geneva May (K1)
Jetty L TKK072, TKK174
Jetty M TKK175, TKK176
Lyttelton Port Piles Moorings Stark Brothers Barge
(sectors 128 – 132)
9 , LYT039, (vessel names not
recorded) x 7
Magazine Bay Marina Sector B LYT008 10 , MAG015 11 , LYT016, Cat’O’Nine
Sector C MAG008, MAG003, MAG027, (vessel names not
recorded) x 8
5.2. Styela distribution in each location
Only two Styela individuals were found during the current survey of Tutukaka Marina. Both were
discovered by divers and were recovered approximately 100m apart on Jetties J and M in the north and
western sections of the Marina (Figure 1.12). Two specimens were also collected from Tutukaka
Marina during the earlier detection survey in November 2005. These were collected from Jetties A
and D on the eastern side of the Marina. Together these results indicate a widely dispersed, extremely
low density Styela population and provide no evidence of a shift in population size in Tutukaka
Marina through time.
9 Fifty-three Styela were collected from the hull of the “Stark brothers barge” in Lyttelton Port.
10 Twenty-six Styela were collected from the hull of the “LYT008” from sector B, Magazine Bay Marina.
11 Eight Styela were collected from the hull of “MAG015” from sector B, Magazine Bay Marina.
28 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Figure 1.12: Styela clava detection locations in Tutukaka Marina. The first two specimens found in November
2005 (in red), and two additional specimens detected in November 2006 (in orange).
Deliverable 1
A total of 929 Styela individuals were collected in Lyttelton Port, mostly from piles, pontoons and
ropes. Above-water searches collected 472 Styela and divers collected 457 individuals from shallow
and deep water searches. The distribution of Styela determined by above-water searches using rawdata
is shown in Figure 1.13. Above-water searches of the intertidal and upper subtidal zones found
Styela widely distributed through the inner Port, but did not find any individuals along Cashin Quay or
on the breakwalls outside the inner Port. Above-water searches detected a mean (± 1 se) of 5.5 ± 1.4
Styela per site, with 55% of the 85 searched sites containing the organism. In sites where Styela was
detected, the maximum density was typically in the range of 1-10 individuals per m 2 . However
pontoons between Z Wharf and Gladstone pier, and piles on the western side of # 2 Wharf (Figure
1.13), had noticeably higher abundances ranging from 41 to 89 individuals per site, and maximum
densities between 11 and 100 individuals per m 2 .
Shallow dive searches down to a depth of 5m in Lyttelton Port also found Styela widely distributed
throughout the inner harbour). The shallow dive searches detected a mean (± 1 s.e) of 11.0 ± 3.1
Styela per site, with the target organism found in 29 of the 40 searched sites (72%). Of the 27 sites
searched by both above-water and diver techniques, Styela was found by both techniques in 15 sites
(55%), and found only by shallow dives in 10 sites (37%). Notably shallow dives confirmed that
Styela was present in low numbers at multiple sites beneath Cashin Quay and along the south-eastern
tip of #7 Wharf (Figure 1.14). The highest numbers of Styela detected by shallow diver searches (in
the range of 41-89 per site) were beneath the A and B pontoons. Styela was also present, but less
abundant, at depths of between 5 and 13m. Deep dives detected a mean (± 1 s.e) of 2.8 ± 0.9 Styela
per site, with five of the six searched sites containing the target organism (Figure 1.15)
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 29

Deliverable 1
Figure 1.13: Distribution and abundance of Styela in Lyttelton Port determined by above-water searches of 85
sites. Scale indicates numbers of individuals collected in each site. For wharf labels see Figure 1.4,
Figure 1.9 and Figure 1.11
Figure 1.14: Distribution of Styela clava in Lyttelton Port as determined by shallow (

Deliverable 1
Figure 1.15: Distribution of Styela clava in Lyttelton Port as determined by deep (>5m) diver searches of six sites.
Scale indicates total number of individuals collected at each site.
Kriging analysis of presence/ absence data at each surveyed site from Lyttelton Port indicates that
Styela is likely to be present across virtually all artificial substrata around the perimeter of the inner
harbour (Figure 1.16). The two areas that may currently be free of Styela are in the south-western
sector of the inner harbour (near the cattle Wharf and dry dock facilities), and along the break-wall at
the far eastern end of Cashin quay (Figure 1.16).
In Magazine Bay Marina a total of 86 Styela individuals were collected. They were detected largely
from piles (n=38), vessel hulls (n=34) and ropes (n=13). Above-water searches accounted for 14
Styela and divers collected the remaining 72 individuals from shallow water searches. Above-water
searches found Styela widely distributed through the Marina in very low densities, with one to four
individuals found in each of the sectors. Diver searches of Magazine Bay Marina also detected
relatively uniform, low densities of Styela throughout the Marina. The vessels “LYT008” and
“MAG015” in sector B of the Marina, along the south-western Wharf of the Marina, contained the
largest number of individuals, with eight and 26 on their hulls respectively. The distribution of Styela
detected by both search methods in Magazine Bay Marina is indicated in Figure 1.17.
5.3. Maximum Styela density estimates
The maximum density estimates for Styela within each site in the three surveyed locations are
summarised in Table 1.7. In Tutukaka Marina maximum Styela densities only achieved 1 individual
per m 2 at two sites. The highest observed densities of Styela encountered during this program were in
the Port of Lyttelton, where maximum densities of between 11-100 individuals per m 2 were recorded
at one site inspected by above-water searches, and two sites inspected by divers. More than half of the
sites searched in Lyttelton Port contained Styela with maximum densities of between 1 and 10 per m 2
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 31

Deliverable 1
Figure 1.16: Estimated probability of Styela clava being present on artificial structures around the Port of
Lyttelton. The scale indicates the probability of at least one individual being present on suitable
habitats down to a depth of 10m. Points indicate pile moorings, and black lines indicate the outline
of wharves or pontoons.
Figure 1.17: Distribution of Styela clava in Magazine Bay Marina as determined from both above-water searches
and shallow (

Deliverable 1
Table 1.7: Maximum density estimates for Styela at the three surveyed locations. Data are the frequency of
sites in which each density class was recorded. The percentages of sites searched that fall into each
density category are also indicated in brackets.
Estimated maximum density (No. per m 2 )
Location Search method 0 1 – 10 11 – 100 >100
Tutukaka Marina
Lyttelton Port
Above-water 13 (100%) 0 0 0
Diver 10 (83%) 2 (17%) 0 0
Above-water 38 (45%) 46 (54%) 1 (1%) 0
Diver 13 (28%) 31 (68%) 2 (4%) 0
Magazine Bay Above-water 3 (33%) 6 (67%) 0 0
Marina Diver 0 7 (100%) 0 0
(Table 1.7). The maximum Styela density in Magazine Bay Marina was also in the range of 1- 10 per
m 2 .
Kriging analysis of weighted abundance data indicated low Styela abundance (less than 10 individuals
per 5x5m surface grid cell extending to a depth of 10m) for most of the western half of Lyttelton Port
and Cashin Quay (Figure 1.18). Higher Styela abundances (typically between 21 and 50 individuals
per grid cell) were predicted for much of the eastern side of the inner harbour (Figure 1.18). Kriging
results also indicate particularly high densities of Styela at three locations: 1) the western side of #2
Wharf; 2) pontoons between the Z Wharf and Gladstone pier; and 3) A and B pontoons. A breakdown
of the frequency of predicted grid cells in each abundance category (Figure 1.19) indicates that over
the entire port perimeter area the predicted Styela abundance remains low (100 individuals per grid cell) for 1.4% of grid cells.
Kriging analysis of weighted abundance data for both small (≤ 5cm), and large (>5cm) individuals
revealed the patterns of distribution and abundance of smaller, presumably recently recruited
individuals (Figure 1.21) clearly resembles those of larger adults (Figure 1.20). One exception is the
A and B pontoons in the northeast of the inner harbour which had high numbers of adult Styela (Figure
1.20), but medium numbers of small individuals (Figure 1.21).
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 33

Deliverable 1
Figure 1.18: Predicted abundance of Styela clava in Lyttelton Port determined by kriging weighted abundance
data at each sampled site. Scale indicates the predicted abundance of individuals found on suitable
habitat in each 5m by 5m surface grid cell extending to a depth of 10m. Locations (known as key
sites in deliverable 3) with the highest abundance are; 1. Western side of #2 Wharf, 2. Pontoons
between Z Wharf and Gladstone pier and 3. the A and B pontoons.
Percentage of predicted grid cells
60
50
40
30
20
10
0
0
1-10
11-20
21-50
51-75
76-100
34 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand
101-150
151-200
Styela abundance classes per grid cell
Figure 1.19: The percentage of predicted grid cells in Lyttelton Port in each Styela abundance category. Grid cells
mapped in Fig. 17 indicated 5m by 5m surface areas that extend to a depth of 10m.
201-250
251-299

Deliverable 1
Figure 1.20: Predicted abundance of large Styela clava in Lyttelton Port determined by kriging weighted
abundance data for individuals >5cm total length at each sampled site. Scale indicates the predicted
number of large individuals (High = 50, Medium = 25 and Low =

Deliverable 1
5.4. Comparison of Styela density across locations and search techniques
The overall mean density of Styela varied widely among locations and search techniques, with a
maximum (±1 standard error) of 0.354 ± 0.087 individuals per m 2 detected by above-water searches in
Lyttelton Port and a minimum of 0.002 ± 0.001 individuals per m 2 detected by shallow diver searches
in Tutukaka Marina (Figure 1.22). Within both Lyttelton Port and Magazine Bay Marina higher mean
Styela densities were obtained from above-water searches than shallow dive searches (Figure 1.22).
In Lyttelton Port the mean Styela density for above-water searches was approximately twice as high as
in shallow diver search areas, and around ten times as high as the mean density found in deep dives
(Figure 1.22). However analysis of variance found no significant differences in Styela densities
among search techniques within Lyttelton Port (ANOVA, F2,128 = 1.90, P = 0.15). Similarly there
were no significant differences in Styela densities among search techniques within Magazine Bay
Marina (ANOVA, F1,16 = 2.06, P = 0.17).
The available data allow coefficients from these statistical relationships to provide predictions of the
probability of Styela presence and abundance in habitats that were not sampled during the survey.
Within sites there wasn’t a strong linear relationship between the number of Styela found in above-
water searches and shallow diver searches (Figure 1.23). Similarly there was a weak linear
relationship between the number of Styela found in above-water searches and deeper diver searches (y
= 0.02x + 0.02, r 2 = 0.11). However there was a linear relationship between the numbers of Styela
found per site in shallow and deep dives. On average the number of Styela found in shallow dives
(5m) at the same
site, according to the relationship y = 0.31x - 0.003, r 2 = 0.70, (Figure 1.24)
Mean density of Styela per m 2 (± 1 s.e)
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
85
Lyttelton Port
Above water
search
40
Lyttelton Port
Shallow Dive
(

Deliverable 1
Figure 1.23: Number of Styela detected in above-water searches and shallow diver searches of the same sites in
Lyttelton Port. Each point indicates a site. Linear regression equation included.
Figure 1.24: Number of Styela detected in shallow and deep dive searches of the same piles at sites in Lyttelton
Port. Each point indicates a site. Linear regression equation included.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 37

Deliverable 1
5.5. Styela habitat associations
Across the three search locations Styela was recorded from a wide range of man-made substrata
including ropes, wooden, metal and concrete piles, concrete pontoons, yacht and barge hulls, ropes,
tyre-fenders, ladders and buoys. Styela was not found on rocky breakwalls at any of the searched
locations by either above-water or diver searches. It was found from the lower intertidal down to a
depth of 12m in Lyttelton Port, approximately 50cm above the flocculent sediment which comprises
the seabed in this location.
5.6. Styela size-distribution
Both of the Styela individuals found in Tutukaka Marina were > 10 cm long and, therefore, were
mature adults. No small Styela (< 5cm) were found in Tutukaka Marina despite extensive searches in
both intertidal and subtidal habitats. The large, widely distributed Styela population in Lyttelton Port
contained individuals ranging in size from 1cm to 18cm (Figure 1.25). The size-distribution was
negatively skewed with a large mode at 4 to 5cm total length, but an average size of 6.85cm
(SD = 3.38). The abundant small individuals probably represent a cohort of young individuals but
could potentially be explained by heterogeneity in growth rates. A time series of sampling is required
to confirm whether these individuals form a cohort.
Cumulative Frequency
150
125
100
75
50
25
0
0 2 4 6 8 10 12 14 16 18 20
50
25
0
Lyttelton Port
Magazine Bay Marina
0 2 4 6 8 10 12 14 16 18 20
Styela body size (total length in cm)
Figure 1.25: Styela population size structures in Lyttelton Port and Magazine Bay Marina.
38 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
In Magazine Bay Marina the population structure was normally distributed about a mean and median
body size of 7cm (Figure 1.25). Collected individuals ranged in size from 2 to 12cm total length and
no very large (>14cm) individuals were detected. The average size was 6.83cm (SD = 1.71).
There were a small number of individuals detected in the smallest size classes. However there was no
evidence of a strong mode of small individuals, as seen in the nearby Lyttelton Port population (Figure
1.25). In Lyttelton Harbour (where the largest number of Styela were collected), we could investigate
patterns in Styela body size among search methods and substrata. On average, Styela collected in
above-water searches were approximately 2cm smaller than those collected in shallow diver searches
(Figure 1.26). This difference in size was significant (ANOVA, F1,910= 69.8, P

Deliverable 1
Figure 1.27: Comparison of mean Styela body size (± 1 standard error) collected from key substrata by above-
water and diver searches in Lyttelton Port and Magazine Bay Marina. N indicates sample size.
Predictions of the potential duration of Styela spawning activity in Tutukaka Marina and Lyttelton
Harbour populations were also made by comparing mean monthly water temperatures with two
published estimates of the minimum threshold temperature at which Styela is capable of spawning
(10°C, Cohen 2005, and 15 o C, Paker et al 1999). In warmer waters near Tutukaka Styela appears
capable of spawning all year round since mean monthly water temperatures do not drop below 15°C
(Figure 1.28). In Lyttelton Harbour the duration of potential spawning depends on the estimate of the
minimum water temperature required for the species to spawn. If Styela can reproduce at water
temperatures as low as 10°C then spawning may be possible year round. However if Styela requires
temperatures of at least 15°C to spawn, then reproduction in Lyttelton Harbour may be limited to a
three month period between January and April each year (Figure 1.28).
6. Discussion
Despite very low abundance in the Tutukaka Marina, delimitation surveys for Styela clava in
November–December 2006 confirmed that Styela had persisted in Tutukaka Marina, the Port of
Lyttelton and Magazine Bay Marina for at least a year since surveys were undertaken in November
2005 (Gust et al 2005). In May 2002 a stalked ascidian specimen was collected from a tug boat in
Lyttelton Port by a Ph.D student and incorrectly identified. The specimen was re-examined in 2006
and identified as Styela clava, which confirms the species has been present in Lyttelton Port for at
least four years. Although available evidence suggests Styela may have been present in Lyttelton Port
for longer than the other two locations, it may never be possible to confirm the precise dates of
introduction to each. Recent population genetics studies of Styela collected nationwide suggest that
40 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
Figure 1.28: Mean monthly coastal sea surface temperatures near Tutukaka Marina and Lyttelton Harbour. Values
represent the 10 year average from 1992-2003 derived from satellite imaging maps (Uddstrom and
Oien 1999) and available at http://www.niwa.co.nz. The two contrasting published predictions on the
minimum water temperatures required for successful Styela spawning are included as hatched lines.
multiple independent inoculations of Styela may have occurred into New Zealand (S. Goldstein,
University of Canterbury, pers comm). Current survey results suggest populations in the three
searched locations reflect different stages of establishment, which may reflect the length of time Styela
has been present at each location. We discuss below current patterns in Styela distribution, relative
abundance and demography which differ widely between the three locations. We also discuss patterns
in the distribution and abundance of Styela determined by both search methods. The implications of
Styela delimitation results to potential population management initiatives in each location are
discussed in detail in subsequent sections of this report.
6.1. Tutukaka Marina
Only two large, adult Styela were found in Tutukaka Marina during the November 2006 delimitation
survey despite extensive above-water and diver searches, relatively high water clarity and
correspondingly high search sensitivities. Despite a considerable increase in search effort from
November 2005 to November 2006, there was no corresponding increase in the number of Styela
detected. Together these survey results indicate a widely dispersed, extremely low density adult Styela
population in Tutukaka Marina. No juveniles or small Styela individuals were collected from this
location during either survey. Accordingly there is no evidence of successful reproduction by this
population to date, and total Styela abundance does not seem to have changed markedly between
November 2005 and November 2006.
With a very small adult population, no evidence of successful recruitment or increase in population
size for this species over 12 months in Tutukaka Marina, it is currently unclear whether Styela has
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 41

Deliverable 1
become permanently established at this location. Tutukaka Marina contains the most northerly
population of Styela currently known from New Zealand waters. It is approximately 8 degrees of
latitude north of the Styela populations examined in Lyttelton Harbour. Mean monthly water
temperatures in Tutukaka (15-21 ° C) are within the known temperature tolerances of the species, from -
2°C to 23°C (Minchin et al 2006). Published estimates of the minimum water temperature required for
Styela spawning vary from 10°C (Parker et al 1999) to 15°C (NIMPIS 2002, Cohen 2005,). Parker et
al (1999) tentatively concluded that spawning is the only temperature-dependent process in the
reproductive cycle of Styela.
On the basis of water temperature Styela in Tutukaka Marina appear capable of reproducing year
round, though there is currently no evidence to indicate that they have done so successfully. The few,
scattered adults present at Tutukaka Marina suggest that Styela has only recently colonised this
location, is at a very early stage in the invasion process, and if additional individuals persist
undetected, the species may still be capable of achieving high abundance and distribution at this
location in the future. The individuals detected from piles and pontoons at Tutukaka Marina
potentially represent a single inoculation from one or more reproductive adults on the hull of a fouled
vessel visiting the Marina some time before November 2005.
Individual Styela can grow rapidly and produce large numbers of recruits when environmental
conditions are suitable, which allows for potentially rapid population growth (Lambert and Lambert
1998, 2003). It seems likely that if additional Styela individuals remain undetected in Tutukaka
Marina that spawning, recruitment and population expansion will occur. Although we found only two
individuals, it is impossible to conclude that no Styela are present in the estimated 25,180 m 2 of
artificial habitat present in Tutukaka Marina, and therefore we assume that Styela recruitment is likely
in the future.
6.2. Lyttelton Port
The Styela population in Lyttelton Port is now well-established, widespread, successfully reproducing
and increasing in abundance. A total of nearly 1000 individuals were collected in the November-
December 2006 delimitation survey, including a wide range of Styela body sizes, from 1cm long new
recruits to 18cm long adults. The largest adults are comparable to the maximum size reported for this
species overseas (Furlani 1996). A wide range of substrata were fouled by Styela in Lyttelton,
including piles, pontoons, ropes, floats, ladders, tyre fenders and a barge. Mean Styela body size was
relatively uniform across this range of substrata, although Styela detected by above-water searches of
intertidal and upper subtidal habitats were on average 2cm smaller than those collected by divers.
This result potentially reflects reduced growth in Styela individuals in the intertidal zone relative to the
deeper subtidal zone. Regular exposure to the air may reduce opportunities for filter-feeding and may
impart temperature or other physiological stresses. If Styela reproductive output is a function of body
size, overall there was little evidence to suggest major differences in the reproductive output of
individuals in Lyttelton Port that can be attributed to their depth or substrata attachments.
Styela were detected through a wide range of water depths, from intertidal heights where they are
regularly exposed to the air during low tide, down to a maximum recorded depth of 13m. Above-
water surveys detected Styela in 55% of the 85 sites searched (despite low mean search sensitivities of
0.17 due to low mean water clarities). In addition diver surveys detected Styela at 72% of the 40 sites
42 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
searched. Both search methods confirmed the Styela population is now widespread in Lyttelton Port’s
inner harbour. At the site level there was no relationship between the number of Styela detected in
above-water searches and the number detected by divers. Kriging analysis indicates Styela is likely to
be present on suitable man-made habitats around almost the entire inner Port area, with the possible
exception of the cattle Wharf and dry dock facilities on the western side of the inner Port. Outside the
inner harbour, Styela was also detected in low numbers along Cashin Quay, although kriging analysis
suggests it is likely to be absent from the far eastern end of the quay. Kriging analyses predicted that
during November-December 2006 only 7.5% of the total perimeter of Lyttelton Port was free of Styela
fouling.
The widespread Styela population in Lyttelton Port was typically present at mean densities < 0.35
individuals per m 2 . However three areas of locally high Styela density and total abundance were
discovered, all in Lyttelton Port’s inner harbour. These local nodes of high Styela abundance
(maximum densities of between 11 and 100 individuals per m 2 ) were associated with piles on the
western side of # two Wharf, pontoons located between Z Wharf and Gladstone Pier and the A and B
pontoons on the northern side of the inner harbour. Maximum Styela densities encountered in the Port
are however orders of magnitude lower than some extreme cases reported overseas. Styela has been
demonstrated to achieve densities of 500-1500 individuals per m 2 , although these situations are
exceptional and, in many areas where it has been introduced, Styela has persisted at much lower
densities (Leutzen 1999, Osman and Whitlatch 1999, Lambert and Lambert 2003).
The diver search strategy in Lyttelton Port concentrated effort on shallow waters within 5m of the
surface where Styela was predicted to be most abundant. This approach focused on the zone where the
organism appears most detectable, and also allowed more sites to be searched by divers in the time
available. Previous rapid detection surveys for Styela in New Zealand have detected the majority of
Styela specimens in these shallow depths, although the species can occur as deep as 25 m (Cohen
2005). To examine the distribution of the species in this deep water Port and determine the proportion
of populations likely to persist in deeper water, we compared Styela abundance from diver searches
above and below the 5m depth interval. Divers detected Styela on pile habitats down to approximately
13m. However diver estimates of Styela abundance in depths of between 5 and 13m were
approximately three fold lower then in the upper 5m of water column. Available evidence
incorporating above-water search results suggests that approximately 15% of the population exists
below 5m in Lyttelton Port. Concentrating diver search effort on substrata within 5m of the water
surface was therefore shown to maximise the chances of detecting Styela at each site. The strategy
provided the most reliable estimates of maximum Styela density and also protected divers from
potential injury by minimising the amount of bounce diving required during surveys.
The Styela population in Lyttelton Port has successfully reproduced and appears to have undergone a
considerable increase in abundance and distribution from November 2005 to November 2006. The
November 2005 rapid delimitation survey was conducted to establish whether Styela was present in
the Port. At that time above-water searches were conducted across areas that have subsequently been
gridded into 48 sites, and diver searches were conducted at 9 of these sites. A total of 15 Styela were
collected from 9 of the 48 inspected sites (19%) and maximum recorded densities at that time did not
exceed 1-10 per m 2 . All individuals detected were larger than 9cm total length (Gust et al 2006a). A
year later, the current survey detected nearly 1000 Styela, albeit with an approximate tripling of survey
effort. The percentage of sites where Styela was present grew from 19% to 60% overall, and the
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 43

Deliverable 1
population’s demography appeared to change markedly. Although the sample size in November 2005
was smaller, the Styela population at that time did not appear to include recruits or small individuals.
However in November 2006, over 300 individuals between 4 and 5cm long were collected from
widely spaced locations around the Port, which likely indicates a large cohort of small individuals
entering the population. Thus in the year between surveys, a significant recruitment of juveniles
probably occurred, the population became more widely established, and estimates of maximum
density increased by an order of magnitude at three sites. It appears that, within the space of 1 year,
Styela dispersed and established throughout the sheltered inner harbour of Lyttelton Port.
Conceptually nodes of high local adult Styela abundance on port or marina structures may represent an
increased risk of infecting vessels or other man-made structures located nearby. However it is
important to know whether patterns of adult distribution can predict patterns of local recruitment, and
the spatial scales at which this relationship may apply. A number of factors may strongly influence
these relationships, including the larval duration, swimming ability and behaviour of the larvae, as
well as the local hydrodynamics of the location which may transport larvae to, or from, particular
sites.
Kriging analysis of Styela abundance data in Lyttelton Port revealed a generally strong match between
local nodes of high large 12 and small Styela abundance. The relationship appeared generally robust at
the scale of meters to tens of meters around the Port. This match is consistent with largely selfseeding
local populations, and reflects the known larval biology of the species where most larvae do
not usually travel more than a few centimetres by active swimming (Minchin et al 2006). The pattern
is also consistent with the impression that most larvae settle within a short distance (≤ 10 m) of the
parent (Stoner 1990). Although Styela larvae tend to settle close to the parent population, some can be
passively dispersed over distances covered by 1-2 tidal excursions (equivalent to the duration of the
larval period), until they encounter potential settlement substrates.
While patterns of high adult abundance maximise the risk of colonisation of objects within a distance
of 10m, some larvae will spread more widely and any vessels within the entire inner harbour of
Lyttelton Port are now at risk of becoming colonised by Styela. Interestingly, one of the highest
density adult nodes (on the A and B pontoons) was associated with a widely distributed, moderate
density of juveniles. Larvae from this site in particular may have been advected and dispersed more
widely around the inner Port than at other sites. Potentially propeller-wash from regular movements
of active tugs, the Diamond Harbour ferry and other vessels in this very busy section of the Port
caused local disturbances to the water column in this location and could potentially have acted to
disperse larvae more widely from this site than others in Lyttelton Port.
12 Mean Styela body size at maturation is known to vary widely between localities. Reproductive maturity occurs at around
25 mm in Prince Edward Island, Canada; and between, 75–95 mm in Denmark (Kluza et al 2005). Information on the mean
size at maturation is not yet available for Styela populations in New Zealand, and for the purposes of this assessment we
consider individuals up to 50mm total length to be “small” and possibly juveniles, while those above 50mm are “large” and
probably mostly adults.
44 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

6.3. Magazine Bay Marina
Deliverable 1
The Styela population in Magazine Bay Marina currently appears to be small and widespread at low
densities. Comprehensive spatial coverage was achieved during the December 2006 delimitation
searches of this relatively small location. A total of 86 Styela individuals were detected, 14 by above-
water searches (a good result considering the very poor water clarity and estimated search sensitivity
of only 0.02), and 72 individuals were collected by divers. Styela was detected from each of the seven
searched sites, with most individuals recovered from piles (38), vessels (34) and ropes (13). The only
node of higher abundance encountered was associated with individuals on the hulls of two vessels, the
“LYT008” and “MAG015” moored in site B in the south-western section of the Marina. Maximum
Styela densities were consistently low throughout the Marina, with no more than 1-10 individuals
detected per m 2 on any substrata.
The Styela population described in Magazine Bay Marina includes a wide range of body sizes with
evidence of both recently recruited small individuals, and adults up to 12cm total length.
Approximately 18% of the population collected in Magazine Bay Marina were small (≤5cm long), as
compared to 43% of the population in the nearby Lyttelton Port. Thus although the Magazine Bay
Marina Styela population was apparently reproducing and probably largely self recruiting, there was
no evidence of a large, numerically dominant cohort of juveniles entering the population. Juveniles
were widely spaced through most sectors of the Marina and there was no evidence of local nodes of
high juvenile abundance. On the basis of water temperature Styela populations in both Lyttelton Port
and Magazine Bay Marina appear capable of spawning during a three month period between January
and April each year, though recruitment and larval studies are necessary to confirm patterns of
reproductive biology for this species in Lyttelton Harbour.
In Magazine Bay Marina above-water searches in November 2005 and December 2006 both covered
the entire perimeter of the location and experienced similar water clarities and search sensitivities.
However three fold higher numbers of Styela were found in the later survey. In November 2005
divers also inspected two sites and found no Styela. In December 2006 diver searches at seven sites
detected Styela in each, with an average of 10 individuals per site. Although differences in search
effort between surveys confound precise estimates of the magnitude of population increase, it seems
likely that Styela populations in Magazine Bay Marina expanded considerably in the year to December
2006. Detailed patterns in abundance, distribution and demography described in the three locations
surveyed suggest the Magazine Bay Marina Styela population is at an intermediate level of
development compared to the tiny, possibly non-reproducing population in Tutukaka Marina and the
well-established, rapidly expanding population in Lyttelton Port.
6.4. Review of survey methods
This study focused search effort on artificial (man-made) substrata and did not attempt to sample
Styela from natural habitats such as rocky reef communities or soft sediment habitats. As such it is
currently unclear whether Styela populations in Tutukaka Marina, Lyttelton Port and Magazine Bay
Marina have spread to nearby natural habitats. Other international experience provides some insight
into the likelihood of Styela spread from shipping locations to nearby communities on natural
substrata. For instance in Port Phillip Bay, Australia, Styela has successfully spread to soft sediment
communities and reached densities as high as 2 to 5 individuals per m 2 (Ross et al 2007). However in
California Styela occurs almost exclusively on artificial habitats and is virtually absent from nearby
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 45

Deliverable 1
natural reef assemblages, despite having been present in the region for more than 70 years (Lambert
and Lambert 2003). This may be due to fundamental differences that exist between natural and
artificial substrates where artificial substrates such as pontoons may constitute novel habitats for
epibiota (Connell 2000). On the northeast Atlantic coast of the USA, Styela does occur on natural
subtidal reefs over a broad geographic area, albeit in very patchy local distributions (Osman and
Whitlatch 1995). In these natural environments, young S. clava (< 2 weeks old) appear to be preyed
on by native snails and fishes, which limits recruitment to the adult population. However we currently
have no information on whether any New Zealand predators or parasites influence Styela distribution,
abundance or reproduction.
Significant logistical constraints influence surveillance programs for pests in marine environments
(Hayes et al 2005, Inglis et al 2005). The search effort required to achieve detailed mapping of marine
pest incursions must be reconciled with the expense of conducting rigorous delimitation programs
which are time and equipment dependent. This detailed delimitation program aimed to maximise
knowledge of the distribution and abundance of Styela across scales of meters to kilometers in three
locations that vary widely in size, construction and extent of potential Styela habitat. To achieve this
goal, we developed spatial analysis tools to map Styela distributions in Lyttelton Port where the
increased size and depth of the location meant it was not possible to survey all potential habitats.
Without detailed, accurate description of the patterns of Styela distribution and abundance in each
location any attempts to monitor the effects of control measures or changes through time will be
compromised. For this reason we spent considerable time and effort on deliverable 1. The
combination of survey techniques utilised in this study allowed us to rapidly and reliably determine
the distribution and abundance of Styela populations in each location. Initially we used above-water
visual surveys to cover large areas of potential substrate around the perimeter of each location.
Above-water searches were fast to implement and achieved wide spatial coverage, but were previously
shown to suffer losses in search sensitivity as water clarity declines (Gust et al 2006b). Above-water
searches are restricted to inter-tidal and upper subtidal habitats, and in each location achieved lower
mean Styela detection rates than diver searches. The lack of a relationship between the numbers of
Styela detected by above-water and diver searches of the same sites in Lyttelton Port also indicates
that above-water searches alone are inadequate to accurately predict the distribution and abundance of
a predominantly subtidal sessile pest such as Styela.
Diver searches complemented above-water searches by allowing detailed inspection of substrata
inaccessible to searchers on the shore or operating from boats. This two-pronged search approach
detected the species on a variety of submerged habitats and enabled rapid, systematic inspections of
the man-made substrates most likely to contain Styela in each location. The diver searches were
slower to conduct, require additional staff to search each site and are thus more expensive than abovewater
searches. Nevertheless they are more thorough, maintain high search sensitivity across a wide
range of water clarities (Gust et al 2006b), and represent the only currently feasible means of
inspecting deeper habitats or substrata hidden from surface observers in ports and marinas.
Lyttelton Port is much larger than both the surveyed marinas and required a variety of different search
and analysis techniques to ensure reliable delimitation of Styela. Lyttelton Port has a perimeter in
excess of seven kilometres, approximately 6000 piles and water depths typically in excess of 10m.
The key artificial substrata forming potential Styela habitats (piles, pontoons and breakwalls) are
46 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 1
approximately ten times more abundant in the Port than in Tutukaka Marina, and are 27 times more
abundant than in Magazine Bay Marina. As a consequence of the scale and depth of Lyttelton Port it
was not possible to search all potential Styela habitat in the time available. Nevertheless
comprehensive searches for Styela were achieved at this location by using a variety of complementary
survey techniques, prioritising the search effort to key Styela habitats, and then testing assumptions
about the areas of presumed highest Styela abundance. We adopted a number of approaches
previously developed to assist rapid delimitation searches for this pest in New Zealand.
Initially above-water searches ensured rapid coverage of a large proportion (67%) of the perimeter of
Lyttelton Port. Then an initial phase of shallow diving concentrated on the upper 5m of water column
where previous research (Gust et al 2005, 2006a) suggested the highest abundance of Styela were to
be found. A second phase of deeper diving was then required to determine the species’ abundance at
depths greater than 5m in Lyttelton Port. Mean Styela numbers encountered per site in these three
techniques suggest that the proportions of Styela population are distributed through the water column
as follows: 28% in the intertidal and upper subtidal zone, a further 57% in the subtidal zone down to
5m depth and 15% of the population in water greater than 5m deep. As such the search methodology
adopted correctly focused effort on those water depths where the majority of the population exits.
Difficulties in surveying this large area of artificial habitat indicate the magnitude of the problem in
any attempts to manage Styela numbers widely across this area.
Kriging procedures allow the three dimensional nature of the distribution and abundance of Styela
around Lyttelton Port to be portrayed visually and continuously in two dimensions. The short distance
dispersal patterns of juveniles suggested in Lyttelton Port, supports the underlying assumption of
autocorrelation in the data, and suggests that patterns of Styela distribution in unsurveyed sites are
likely to reflect the patterns of abundance determined in adjacent or nearby sites. Kriging was useful
for identifying local nodes of high Styela density and provided intuitive maps of distribution.
Nevertheless the procedure fills unsurveyed sites with best estimates of predicted Styela abundance,
and values generated for each of these sites are probably less reliable than those determined by direct
survey. Furthermore kriging based on the geographical proximity of sites will only produce sensible
predictions of Styela distribution if the sites are linked by water, and there is a feasible direct route for
larval dispersal between sites. We found it necessary to develop a masking procedure in the kriging
model, so that patterns of Styela abundance across impermeable barriers were not used to create
spurious patterns of predicted distribution.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 47

Deliverable 2
Deliverable 2: Identify human-mediated vectors with the potential to spread Styela
to high-value areas.
Human-mediated movements of organisms are the principal pathway for the introduction and spread
of non-indigenous species (NIS) worldwide (Mack et al 2000). The most common ways humans aid
the spread of marine NIS is through domestic and international shipping (via hull fouling, sea chest
fouling and ballast water transfer) and through the movement of aquaculture stock and equipment
(Minchin and Rosenthal 2002, Coutts et al 2003, Fofonoff et al 2003, Minchin and Gollasch 2003,
Ricciardi 2006). Styela may be moved between locations around the New Zealand coastline by any of
these vectors.
Management measures taken to limit or prevent the spread of Styela will be compromised if they do
not address all potential vectors for dispersal. Styela has a relatively short dispersal phase of
approximately 24 hours (Minchin et al 2006), and is likely to have arrived in New Zealand as fouling
on a vessel hull or sea chest. These mechanisms are also likely to be important in the domestic spread
of the organism. However, since travel times between New Zealand’s main shipping ports are
relatively short (hours to days) the domestic spread of Styela may also be facilitated by internal
transport in ships’ ballast water and other means, such as movement of aquaculture stock and
equipment.
The three source locations of Styela examined in this study comprise a large commercial shipping port
and two marinas. Vessels residing in these locations include large commercial ships that have ballast
water tanks, and smaller non-ballasted vessels such as recreational yachts and commercial fishing,
sailing and dive boats. In addition, there is a range of vessels engaged in port operations (e.g. tug
boats, pilot vessels), or maintenance (e.g. dredging vessels). The only dry dock in the South Island is
located within Lyttelton Port.
The principal aim of Deliverable 2 is to identify and quantify vectors associated with the three source
locations – Tutukaka Marina, Lyttelton Port and Magazine Bay Marina – that have the potential to
facilitate the spread of Styela to a range of high-value areas (HVAs). We define human-mediated
vectors as the physical processes that can translocate Styela from source locations to HVAs, while the
mechanisms of transport refer more specifically to hull fouling, sea chest fouling, ballast water or
fouled aquaculture stock or materials. A risk assessment of key vectors is presented in Deliverable 3.
We utilised two separate approaches to obtain a comprehensive understanding of vector movements
and the potential for spread to the HVAs.
Firstly, we identified vectors that move away from the three Styela fouled source locations, with
particular emphasis on the HVAs. Secondly, we identified vectors that arrive at the HVAs from all
known domestic sources of Styela. When this contract was envisioned and signed, the only additional
known area in which Styela was established was the Waitemata Harbour and Hauraki Gulf
(subsequently referred to as the Auckland region). Recently, three Styela were discovered on vessel
hulls at the Clyde Quay Marina in Wellington, as well as vessel hulls in Nelson and Opua (Gust et al
2007a). It is currently unclear whether Styela has become established at these three locations and they
are not included as potential source locations in this report.
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Deliverable 2
The principal human-mediated vectors for the transport of Styela from the three source locations to the
HVAs (and other locations) are movements of:
i Commercial and recreational vessels (transport via hull and sea chest fouling, and ballast
water),
ii Towed barges or other structures such as pontoons (transport via fouling),
iii Navigational or maritime equipment such as ropes, buoys, moorings (transport via fouling),
iv Maintenance vessels such as dredges that service a range of ports and/or marinas (transport
via fouling or in internal water/spoil tanks), and
v Vessels, equipment or stock associated with aquaculture facilities associated with the HVAs
(transport via fouling of vessels, equipment or stock).
7. Methods
7.1. Potential vectors and mechanisms for the human-mediated transport of Styela from Styela
fouled study locations
Table 2.1 lists our predicted primary vectors and the mechanisms for human-mediated transport of
Styela. They mostly involve transport of sessile adults or juveniles as fouling on submerged surfaces.
We considered recreational vessels, commercial vessels (self-propelled and towed) and aquaculture
activities to be the three highest risk human-mediated vectors for Styela transport.
Of the three source locations examined in this study, ballast water transport is only likely to be
relevant for Lyttelton Port since water ballasting is only employed by large ships. Similarly, sea
chests are only present on vessels with ballast water tanks; and this mechanism is only likely to apply
Table 2.1: Predicted vectors and mechanisms for human-mediated transport of Styela.
Vector Mechanism Life-stage transported
Shipping (international & domestic) Hull-fouling (including sea-chest fouling) Sessile adults or juveniles
Ballast water Larvae
Yachts & pleasure boats
(international and domestic)
Hull fouling Sessile adults or juveniles
Aquaculture
Fouled equipment (ropes, buoys, etc) Sessile adults or juveniles
Fouled stock Sessile adults or juveniles
Service vessels Sessile adults or juveniles
Towed barges Hull-fouling Sessile adults or juveniles
Movement of marine infrastructure (e.g.
pontoons, moorings, ropes, etc)
Fouled equipment Sessile adults or juveniles
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 49

Deliverable 2
to Lyttelton Port. However, the Auckland region is another major source for Styela and both ballast
water and sea chests are likely to act as transport mechanisms for the species from Auckland to other
commercial ports.
7.2. Description of facilities at three study locations and relevant vectors and mechanisms of
transport
7.2.1. Tutukaka Marina
Tutukaka Marina is a relatively small but busy marina that provides 218 pontoon berths and 24 pile
moorings for vessels ranging in size from 10 to 24m (Figure 1.2). It is the “gateway” to the Poor
Knights Islands Marine Reserve, with numerous commercial dive and sightseeing charter businesses
transporting passengers to the Poor Knights Islands for one- or multi-day trips. A range of game
fishing charter vessels that visit local coastal and offshore fishing grounds, are also based at the
marina. Tutukaka is a common port of call for recreational vessels, including domestic and
international yachts. Auxiliary facilities at the marina include a fuel pontoon, a boat ramp for trailer
boat launching and a wharf where commercial fishers offload catch. The marina also offers a
slip / haul-out facility, but many resident vessels go to Whangarei for maintenance work. The most
likely mechanism for the transport of marine NIS both to and from Tutukaka Marina is fouling of
vessels or mobile structures. There are no facilities for large ships employing water ballasting at the
Tutukaka Marina, and no aquaculture operations use the marina as a base for vessels or offloading
harvest.
7.2.2. Lyttelton Port
Lyttelton Port (Figure 1.3) is the main centre of import and export business for the South Island, with
over 1200 merchant ships visiting the port per year. Facilities are provided for loading and unloading
bulk products such as petroleum, fertiliser, gypsum, cement, logs, and conventional break-bulk and
imported vehicles. Cashin Quay provides facilities for container ship operations, berths for cruise
ships and a coal loading facility. Pacifica car freight vessels regularly use the roll on-roll off facility at
No. 7 Wharf. The Oil Wharf is used by tankers to unload liquid bulk cargoes and by commercial ships
to take on fuel. The Gladstone and No. 4 Wharves are condemned but provide berths for confiscated
vessels (e.g. the Malakhov Kurgen) and the tug Albatross. A and B pontoons provide a passenger
loading facility for the Black Cat vessels (including the Diamond Harbour ferry and wildlife cruise
vessels) and several tourism operators. The historical tug vessel Lyttelton is moored next to these
pontoons on No. 2 Wharf East.
The Port of Lyttelton tug and pilot vessels are moored at the Tug Wharf 20m to the east of A and B
pontoons. Lay-up berths and catch-offloading facilities are provided for commercial fishing vessels at
Wharves 2 and 3 and the Cattle Jetty. Smaller fishing vessels and marine farm harvester vessels
offload catch and berth at Z Wharf. The Fisherman’s Wharves provide approximately 20 berths for a
day fleet of small (11 – 16m) commercial fishing vessels and 3 – 4 fishing charter and tourism vessels.
The inner harbour pile moorings provide approximately 70 berths for recreational and charter vessels,
ranging in size from 7 – 15m. A small pontoon and walkway provides dinghy access to the pile
50 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
moorings. The Lyttelton Dry Dock opens into the Port basin and provides the only dry dock facility in
the South Island. A haul-out facility and small boat ramp are also located adjacent to the dry dock.
Lyttelton Port is frequented by merchant and recreational vessels, and used as an offloading facility for
a range of regional aquaculture facilities. Transport of Styela from Lyttelton Port could thus occur via
any of the mechanisms listed in Table 2.1.
7.2.3. Magazine Bay Marina
Magazine Bay Marina is approximately 1km southwest of the Lyttelton Port (Figure 1.3). It originally
consisted of a wooden pile jetty with five fingers and a range of floating pontoons that provided berths
for vessels up to 15m in length. The facility was severely damaged in a southerly storm in 2000; today
all that remains of the former marina is a series of large concrete piles to the south-east of the main
jetty. The damaged pontoons were shifted ashore and a range of intact ones were transferred to the
Port of Lyttelton, where they are now used as a passenger loading facility for ferries and tourism
vessels (A and B Pontoons), and as a work platform where they are rafted together between Z Wharf
and Gladstone Pier.
The marina company is in receivership and the jetty has fallen into disrepair in several sections. Plans
for reconstructing the marina and developing the facilities at this location are in place. A small
pontoon (approximately 25 x 4m) has been constructed by the Naval Point Yacht Club and is used to
rig and board small sailing dinghies. There is a private boat ramp located at the yacht club (adjacent to
the marina jetty) and a public ramp further to the south-east near the rocky break-wall. A small haulout
operation also occasionally utilises the public boat ramp.
7.3. Selection process for High Value Areas (HVAs)
The risk identification process requires that values or areas to be protected are explicitly and
defensibly identified (Forrest et al 2006). To define the scope of this project we sought to identify
which high value areas (HVAs) were to be considered before information was gathered on likely
human-mediated pathways. To do this we organised a workshop involving MAFBNZ, NIWA and
Cawthron staff on 30 January 2007 at NIWA’s Greta Point campus in Wellington. The main aims of
the workshop were to:
1. list HVAs potentially susceptible to Styela populations in the three study locations;
2. rank these HVAs according to perceived risk; and
3. select a short-list of the HVAs for investigation of potential human-mediated vectors.
Our criteria for ranking HVAs was based on workshop consensus and derived from consideration of a
number of issues. They included the perceived risk of Styela infection, likely public perception of the
value or importance of each HVA, and linkage to potential vectors that could spread Styela from any
of the source locations considered in this project. Locations considered as potential HVAs in this
program were those with high biodiversity, economic and/or amenity values. Each of the 19 proposed
potential HVAs were ranked on a scale of one (highest) to five (lowest), with a moderate level of
uncertainty in the measure (Table 2.2).
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 51

Deliverable 2
Table 2.2 High Value Areas potentially at risk from human-mediated transport of Styela from the three
delimitation locations. High Value Areas were selected for inclusion in this project if they were
ranked 1 or 2.
Potential source population High Value Areas Considered Rank
Lyttelton Port Marlborough Sounds Aquaculture
areas
Lyttelton Port Banks Peninsula Aquaculture areas 2
Lyttelton Port Akaroa Harbour 2
Lyttelton Port Kaikoura Peninsula 3
Lyttelton Port Lyttelton Harbour mataitai 3
Lyttelton Port Stewart Island 4
Lyttelton Port Fiordland 4
Lyttelton Port Chatham Islands 4
Lyttelton Port Pohatu Marine Reserve (Flea Bay) 5
Magazine Bay Marina Banks Peninsula Aquaculture areas 2
Magazine Bay Marina Marlborough Sounds Aquaculture
areas
3
Magazine Bay Marina Kaikoura Peninsula 4
Magazine Bay Marina Pohatu Marine Reserve (Flea Bay) 5
Tutukaka Marina Poor Knights Island Marine Reserve 1
Tutukaka Marina Bay of Islands 3
Tutukaka Marina Three Kings Islands 4
Tutukaka Marina Rainbow Warrior and Cavalli Islands 4
Tutukaka Marina Hen and Chicken Islands 5
Tutukaka Marina Great Barrier Island 5
Tutukaka Marina Goat Island Marine reserve (Leigh) 5
Tutukaka Marina Whangarei Harbour 5
Tutukaka Marina Mimiwhangata Marine Park 5
The four highest priority areas chosen as HVAs to be included in this project were the:
a Poor Knights Islands;
b Marlborough Sounds aquaculture production area;
c Banks Peninsula aquaculture production area; and
d Akaroa Harbour.
The Poor Knights Islands Marine Reserve was selected since it represents a location of high marine
biodiversity, and is at risk of receiving Styela via fouling of vessels travelling from nearby Tutukaka
Marina. The Marlborough Sounds and Banks Peninsula aquaculture areas were selected due to risk to
the large and economically important aquaculture industries (particularly mussel long-line farming)
undertaken in these areas. Akaroa Harbour was also selected on the basis that it is an important tourist
location close to Lyttelton Harbour and it includes aquaculture operations including a salmon farm,
blue pearl (paua) farming operation, mataitai areas and the nearby Pohatu Marine Reserve (Flea Bay).
52 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand
1

7.3.1. HVA1: Poor Knights Islands Marine Reserve
Deliverable 2
The Poor Knights Islands are located 22 km off the coast of Northland, with the Tutukaka Marina as
the closest shipping facility to the Reserve (Figure 2.1). The group consists of two main islands
(Tawhiti Rahi, 129ha; and Aorangi, 66ha) and numerous exposed rocks and reefs surrounding them.
The Poor Knights Islands are home to the Tuatara, the sole survivor of an ancient line of reptiles
known as Sphenodontia, and one of New Zealand’s most enigmatic and endangered reptiles. Visitors
to the Reserve are not allowed to access the islands.
7.3.2. HVA2: Marlborough Sounds aquaculture production area
The Marlborough Sounds are a network of intricate bays, inlets and islands at the top of New
Zealand’s South Island (Figure 2.2). The Marlborough Sounds are the country’s largest aquaculture
production area, with several hundred farms distributed throughout the system (Figure 2.3). For the
purposes of this project, we define the Marlborough Sounds HVA to range from the western side of
d’Urville Island to the eastern side of Port Underwood. Located within this HVA are a range of
commercial and recreational shipping facilities including the ports of Nelson, Picton and Havelock, as
well as the Nelson, Havelock, Picton and Waikawa Bay marina facilities.
7.3.3. HVA3: Banks Peninsula aquaculture production area
The Banks Peninsula (Figure 2.4) is located to the south of Christchurch and is of volcanic origin. It
features two large harbours – Lyttelton Harbour to its northern side and Akaroa Harbour to the south.
Currently, there are less than a dozen aquaculture operations around Banks Peninsula, but a number of
consent applications are pending and in preparation.
7.3.4. HVA4: Akaroa Harbour
Akaroa Harbour (Figure 2.5) is located in the South of Banks peninsula and a popular destination for
tourists. It features a range of maritime tourism operations and a small number of aquaculture
operations.
7.4. Identification of the presence of high-risk vessels or mobile structures at the three Styela source
locations
7.4.1. Interviews with port and marina operations managers
Port and marina operations managers at each of the three locations were interviewed in person or by
telephone to collect information about the number, type and lengths of vessels present, or frequently
visiting, the facilities (Appendices 5.1- 5.7). These contacts also provided information on the capital
or maintenance works at the three locations (e.g. dredging, constructions, etc), and the names and
contact details of a range of users.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 53

Deliverable 2
Figure 2.1: The Poor Knights Islands Marine Reserve HVA.
Figure 2.2: The wider Marlborough Sounds aquaculture areas. Footprints of existing aquaculture facilities are
shown in red.
54 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Figure 2.3: The Marlborough Sounds aquaculture areas, focusing on the Pelorus sound area. Footprints of
existing aquaculture facilities are shown in red.
Figure 2.4: Banks Peninsula aquaculture production areas. Footprints of existing aquaculture facilities are
shown in orange.
Deliverable 2
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 55

Deliverable 2
Figure 2.5: Akaroa Harbour. Footprints of existing aquaculture facilities are shown in orange.
7.4.2. Surface-based observations of fouling level of vessels and towed structures using fouling ranks
Fouling of vessels or towed structures is one of the most likely mechanisms for Styela to be spread to
HVAs. To estimate the probability that a vessel was fouled by solitary ascidians (and is therefore a
“high-risk vessel”), observers conducted surface-based visual inspections of all vessels ≤ 20m in
length present at each location at the time of the delimitation surveys (Deliverable 1). Using a risk
profiling technique developed by Floerl et al (2005), the visible section of each vessel hull was
assessed for fouling intensity and assigned a rank. The ordinal rank scale ranges from 0 (no fouling)
to 5 (very heavy fouling) and is based on the relative abundance of fouling visible to the observer and
the number of identifiable taxa that can be seen (Table 2.3). The rank scale was designed to enable
surface observers to distinguish among yachts that carry no fouling, sparse fouling, or extensive
fouling assemblages on their hulls. By calibrating fouling ranks against a relatively large sample of
yachts (n = 189), Floerl et al (2005) were able to estimate the probability that particular types of
fouling organisms (e.g. solitary ascidians) would occur on yacht hulls scored with different ranks. For
example, yachts with heavy fouling (rank 5) have between 10% and 75% chance of being fouled by
solitary ascidians.
Vessels with a fouling rank of 0 or 1 have a “very low likelihood” of solitary ascidians being present
(Table 2.3). Recent discussions (Biosecurity TAG meeting, 02 March 2007, MAFBNZ Wellington)
with MAFBNZ and research providers involved in the sampling of larger vessel types (Kingett
Mitchell and Associates; New Zealand Diving and Salvage) indicated the surface-based fouling rank
allocation is not a reliable estimator of fouling on large commercial vessels. Therefore, in this study
only vessels ≤ 20m in length were allocated fouling ranks.
56 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
Table 2.3: The ordinal fouling rank scale used by Floerl et al (2005) to estimate the intensity of hull fouling on
international yachts arriving to New Zealand. Shown are also the confidence intervals of the
probability of solitary ascidians occurring on vessel hulls with the various fouling ranks (results
obtained from logistic regression analysis; P = 0.009).
Rank Description
0 No visible fouling. Hull entirely clean, no
biofilm on visible submerged parts of the hull.
1 Slime fouling only. Submerged hull areas
partially or entirely covered in biofilm, but
absence of any macrofouling.
2 Light fouling. Hull covered in biofilm and 1-2
very small patches of macrofouling (only one
taxon).
3 Considerable fouling. Presence of biofilm, and
macrofouling still patchy but clearly visible and
comprised of either one single or several
different taxa.
4 Extensive fouling. Presence of biofilm and
abundant fouling assemblages consisting of
more than one taxon.
5 Very heavy fouling. Diverse assemblages
covering most of visible hull surfaces.
Visual estimate of fouling
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 57
cover
95% confidence intervals of
probability of solitary
ascidians on hull
Nil 0.001 – 0.025
Nil 0.001 – 0.025
1-5 % of visible submerged
surfaces
6-15 % of visible submerged
surfaces
16-40 % of visible submerged
surfaces
41-100 % of visible
submerged surfaces
0.001 – 0.050
0.005 – 0.100
0.025 – 0.250
0.100 – 0.750
We grouped vessels and towed structures into three risk categories depending on their fouling ranks.
Low Risk (fouling ranks 0 and 1), moderate Risk (fouling ranks 2 and 3) and high Risk (fouling ranks
4 and 5). The groups characterised their risk of becoming colonised by, or facilitating the transport of
Styela from the three source locations.
7.5. Movement of potentially high-risk vessels and mobile structures from source locations to the
identified HVAs
7.5.1. Questionnaires / interviews of commercial vessel operators that operate from or frequently visit
the study locations
Questionnaires were designed to standardise the collection of information about commercial vessels
present at, or known to frequent the three study locations (Appendices 5.1- 5.7). Vessel owners or
operators were interviewed regarding the type, length and antifouling paint maintenance of the vessel,
the berth and residence time within the study locations and any visits to the four HVAs. If the vessel
visited HVAs, the interviewee was further questioned to identify the frequency, duration and purpose
of visits to each HVA. The last port of call before visits to HVAs, and any visits to Auckland (another
known Styela source location) were also noted.
A list of operations contacted as part of Deliverable 2 is provided in Appendices 5.1-5.6.

Deliverable 2
7.5.2. Recreational vessels: query of NIWA’s domestic boater survey and simulation model
Summaries of information on known recreational vessel movements were created by querying
NIWA’s domestic boater survey database. This provided data on yacht arrivals to the HVAs of Banks
Peninsula (Akaroa), Marlborough Sounds (Nelson, Picton, Havelock and Waikawa marina) and the
Poor Knights Islands, from the source locations of Lyttelton, Tutukaka and Auckland.
The domestic boater survey was undertaken by NIWA in 2004, with the collaboration of Yachting
New Zealand. A mail-out questionnaire was sent to every domestic boat owner registered in the
Yachting NZ membership database (~5000 addresses). Responses were voluntary, but encouragement
was provided to respondents by (a) using a relatively short survey instrument (2-page questionnaire),
(b) supplying a pre-paid envelope to return the survey and, (c) providing an inducement in the form of
a random draw prize for all participants. Because contact information in the YNZ database contained
many old entries, many questionnaires were returned undelivered, but valid responses were obtained
for 923 vessels (~28% of delivered questionnaires) from throughout the country. This represents a
sample of ~4.6% of the estimated number of permanently moored recreational vessels present in New
Zealand (Busfield 2000).
The questionnaire contained a map of New Zealand and a list of 40 locations that included major
marinas, harbours, offshore islands and marine reserves. Respondents were asked to state the number
of overnight trips they had made away from their homeport in the last 12 months and to indicate on the
map and associated list of locations where these visits had been. Thus, the results provide a measure
of the relative strengths of movement between the homeports of the vessels and a range of locations,
but do not allow a direct estimate of the seasonality of these movements. An epidemiological model
developed by Floerl et al (in review) was used to provide modelled averages (means of 100 model
runs) of per annum yacht arrivals at the various locations.
7.5.3. Commercial shipping: Query of Lloyds Marine Intelligence Unit (LMIU) database
Information about the movements of commercial ships, with respect to fouled locations and HVAs,
was accessed via queries of the ‘SeaSearcher.com’ database, administered by Lloyds Marine
Intelligence Unit. MAFBNZ recently purchased access to this database for an analysis of domestic
shipping movements around the New Zealand coast (Research Project ZBS2005-13). The database
contains arrival and departure details of all ocean going merchant vessels larger than 99 gross tonnes
for all of New Zealand’s ports. It does not include movement records for domestic or international
ferries plying scheduled routes, small domestic fishing vessels or recreational vessels. Queries were
used to identify the frequency of visits, vessel type, and, where possible identify vessels that travel
between the Port of Lyttelton and ports close to the HVAs (Nelson, Picton, Whangarei and the Bay of
Islands). The database was also queried for data on vessel movements between the Port of Auckland
(an additional potential source location for Styela) and the ports close to HVAs.
58 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
7.6. Movements of vessels associated with HVAs to the three source locations of Styela (Tutukaka
Marina, Lyttelton Port and Magazine Bay Marina)
7.6.1. Questionnaires / interviews
A questionnaire was designed for interviews with marine farm operators (Appendix 5.7). The
questionnaire asked for general information about the farm size and construction, as well as for details
(length, type and antifouling paint maintenance history) of any vessels that belong to, service or visit
the farms. Contact with other marine farms, transfer of equipment or stock and the destination of
harvest were investigated. If any vessel belonging to, or frequenting, the farm was confirmed to visit
locations where Styela is established, interviewees were further questioned regarding the frequency,
duration and purpose of visits and the berth of the vessel within this location. Interviewees were also
asked about whether they have observed Styela at their facility and whether they employ any measures
to prevent the introduction of marine pests.
7.6.2. Banks Peninsula HVA
A list of marine farm licence holders in the Banks Peninsula region was obtained through
Environment Canterbury. Each operator was contacted by phone and asked to participate in an
interview. If initial attempts to make contact failed, several follow up phone calls were made and
phone messages left.
7.6.3. Marlborough Sounds HVA
Due to the large number of marine farm operations (300+) in the Marlborough Sounds Aquaculture
Production Area, operators could not be individually interviewed. We originally envisaged a survey
using mail-out questionnaires but this was not possible since marine farmers’ contact details were
considered confidential by Aquaculture New Zealand and were not provided to us. Instead, we used a
mailing list (email contacts) made available by the NZ Marine Farming Association to email a
questionnaire (Appendix 5.7) to a total of 16 marine aquaculture operators in the Marlborough Sounds
(Appendix 5.5). The recipients were also provided with a cover letter (sighted and approved by
MAFBNZ) explaining the nature of the study and asking for participation. In addition to this, we
approached port authorities at Nelson, Picton and Havelock for information about harvesting or other
aquaculture related vessels that frequent these locations.
7.6.4. Marine farms: harvesting vessel operators
Many marine farming operations use the service of commercial harvester vessels. The harvester
vessels often spend particular times of the year in a certain region, and then move to assist with
harvesting in other coastal regions. We attempted to contact all major operators of harvester vessels
used within the Banks Peninsula and Marlborough Sounds aquaculture production regions. Interviews
with Banks Peninsula marine farm operators identified two harvesting vessels that service farms in
both the Banks Peninsula and Marlborough Sounds aquaculture production areas, and that regularly
frequent the Port of Lyttelton whilst in the Banks Peninsula region. The operators of these vessels (St
George and Tardis) were further interviewed for details about vessel movements and which farms are
visited.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 59

Deliverable 2
The New Zealand Marine Farming Association provided contact details for registered harvester vessel
operators working in the Marlborough Sounds aquaculture production area. All operators were
emailed a questionnaire requesting information of harvester vessel movements between farming
operations and source locations for Styela (Appendix 5.7).
7.6.5. Other agencies contacted
We contacted a range of additional agencies to obtain information of vector movements between the
three surveyed source locations of Styela and the four HVAs. These included:
i Department of Conservation (Whangarei): provided list of Poor Knights Islands tourism
operators and information on moorings at the Islands
ii Department of Conservation (Canterbury): provided list of tourism operators / wildlife
licenses for Lyttelton and Akaroa Harbours
iii Environment Canterbury (ECan): provided a list of marine farming licence holders around
Banks Peninsula and Akaroa Harbour
iv “Sugarloaf” Tutukaka Tourism Centre: provided contact details for commercial vessels
operating from Tutukaka Marina and frequenting the Poor Knights Islands
v Aquaculture New Zealand: contacted to try and gain access to contacts for Marlborough
Sounds marine farm operators. No information was provided to us
vi Mussel Safety Quality Programme (MSQP): The MSQP was contacted regarding their
8. Results
Library Programme, since their records of landings of mussel harvest and harvester vessels
are useful tools to determine harvester vessel movements within the Marlborough Sounds.
We exclusively requested information on the movement patterns of vessels within and
outside the Marlborough Sounds. Our request was declined by the executive board on the
grounds that it did not have the authority to provide such information.
8.1. Surveyed source location 1: Tutukaka Marina
8.1.1. Presence of vectors with the potential to facilitate the spread of Styela
A total of 210 vessels ranging from 6.5 to 24m in length were present in the Tutukaka Marina at the
time of sampling. These included private yachts, commercial fishing and diving vessels (including
day boats and charter vessels) and a coastguard vessel (Table 2.4). Surface-based fouling ranks were
allocated to all vessels. According to (Floerl et al 2005), vessels with fouling ranks of 3 or higher
have >5% chance of having solitary ascidians on their hulls (Table 2.3).
60 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Table 2.4: Numbers and lengths (range) of vessels present in Tutukaka Marina at the time of the survey.
Vessel types Numbers
Private yachts 190
Diving vessels 13
Fishing vessels 6
Other vessel types 1
Pontoons # 0
Barges 0
Total 210
Deliverable 2
# Towed pontoons (e.g. workshop or crane pontoons) that are not part of a location’s infrastructure but likely to be moved around at times.
Diving vessels
We encountered a total of 13 dive boats at the Tutukaka Marina (Table 2.4). A number of vessels
were out on dive trips at that time, and through telephone interviews we were able to collect
information (but no fouling rank data) on an additional eight diving vessels. The 13 dive boats we
encountered had a length of 8 to 24m. Two of them (15 %) had visible fouling on their hulls
(Table 2.5). The age of the antifouling paint on dive vessels we surveyed ranged from 2 – 16 months.
Fishing vessels
Six charter fishing vessels were at the Tutukaka Marina at the time of our visit. Four vessels (67 %)
had visible fouling on their hulls. Two of these vessels had fouling ranks >3 (Tables 2.4 and 2.5).
Interviews were conducted with the operators of two of these vessels. Both of them had last renewed
the antifouling paint on their boat in December 2006.
Recreational yachts
The majority of vessels resident at the Tutukaka Marina were recreational yachts (91 % of total;
Table 2.4). They ranged from 6.5 to 20m in length and included sailing yachts as well as motor yachts
and launches. More than half of the yachts we inspected (54 %) had visible fouling on their hulls; in
Table 2.5: Distribution of fouling ranks for each category of vessel in Tutukaka Marina.
Fouling rank Private yachts Diving vessels Fishing vessels Other vessels
0 3 (1.6 %) 0 0 0
1 84 (44.2 %) 11 (84.6 %) 2 (33.3 %) 0
2 73 (38.4 %) 2 (15.4 %) 2 (33.3 %) 1 (100 %)
3 19 (10.0 %) 0 1 (16.7 %) 0
4 10 (5.3 %) 0 1 (16.7 %) 0
5 1 (0.5 %) 0 0 0
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 61

Deliverable 2
some cases the amount of visible growth was considerable (19 yachts with fouling rank 3, 10 yachts
with rank 4 and one yacht with rank 5; Table 2.5). A recent survey of New Zealand yacht owners
showed that 31 % of nearly 1,000 yachts have an antifouling paint of >12 months, and are likely to
carry fouling organisms as a consequence of ineffectual paint (Floerl, unpubl. data).
Other vessel types
The only vessel we encountered at Tutukaka Marina that was not a private yacht or a diving or fishing
vessel was an 8m motor vessel owned by the New Zealand Coastguard. It had a fouling rank of 2, and
small amounts of visible fouling along its hull (Table 2.5). There were no barges, non-permanent
pontoons or other mobile maritime equipment at the Tutukaka Marina. The absence of these
structures was confirmed by the Marina Manager.
8.1.2. Movements of vectors between Tutukaka Marina and the HVAs
Information on movements of potential vectors between Tutukaka Marina and HVAs was obtained
using a variety of methods. Data on commercial vessels was gathered through interviews with owners
or operators of 15 charter and fishing vessels. Not all vessels listed and described below were present
in the marina at the time of sampling, but they are all long-term customers that reside there frequently
and regularly. Information on movements of recreational yachts was derived from an epidemiological
model developed by NIWA to simulate the spread of fouling organisms by recreational yachts around
New Zealand.
8.1.3. Vectors that have a potential to transport Styela from Tutukaka Marina to HVAs
Diving vessels
We interviewed 10 commercial dive operators whose vessels are based at Tutukaka Marina. An
additional three companies were contacted but did not provide information to us (Appendix 5.1).
These 13 companies represent the major dive operators with vessels based at Tutukaka Marina. With
the exception of one vessel that takes divers to local coastal wrecks (the Tui and the Waikato), all of
those surveyed visit the Poor Knights Islands marine reserve on a regular basis. Trips range from day
trips to multi-day charters, with a typical multi-day charter lasting 1-3 nights. Eight of the 10 vessels
surveyed run 2 – 4 trips to the Poor Knights Islands per week, amounting to between 100 and >200
trips per year. When not at the Poor Knights Islands, the boats are moored within Tutukaka Marina.
The age of the antifouling paint on the vessels’ hulls ranged from 1 to 21 months. Occasionally, some
vessels have extended “down periods” due to change of ownership or maintenance. For example, at
the time of our survey, the Marlin Blue had been residing at Tutukaka Marina for a period of 3 weeks
without leaving. This vessel had the oldest antifouling paint (21 months) of those surveyed and is
likely to be susceptible to fouling by Styela. Also the Norseman, usually a busy vessel, is currently
only undertaking a single trip per week to the Poor Knights.
Fishing vessels
We were able to contact the operators of two of the six fishing vessels that commonly reside at the
Tutukaka Marina. Both fish offshore fishing sites and return to the marina without calling at other
locations. The Blue Striker generally spends 300 nights per year at Tutukaka Marina. The Cara Mia
62 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
is based at Tutukaka during the colder months and at Russell (Bay of Islands) during warmer months.
Conversation with the two operators and marina staff suggests that the remainder of Tutukaka’s
fishing fleet follows similar patterns, with the majority of nights per year spent at the marina, and only
rare visits to other coastal ports or marinas.
The response of the only Tutukaka based fishing vessel (Phoenix) surveyed as part of MAFBNZ
project ZBS2005-13 supports our findings described above. Also this vessel fishes offshore waters,
and the only other location the vessel had visited during the past 3 years was Leigh, approximately
85km south of Tutukaka.
Recreational yachts
NIWA’s simulation model does not include the Poor Knights Islands as a location since this area no
longer has any permanent mooring facilities (Department of Conservation, pers comm. 2007).
However, data from a previous study that collected travel information from 283 international yachts
and 906 domestic yachts show that 4.2 % of international visitors and 3.5 % of New Zealand-owned
yachts had visited the Poor Knights Islands marine reserve during the past 12 months (Floerl
unpublished data). Frequently, the yachts had resided (anchored) within the reserve overnight or for
several nights. The average annual number of yacht movements from Tutukaka to a range of locations
of interest was calculated by NIWA’s simulation model over a modelled period of 10 years. On
average only 1 yacht per year left Tutukaka for Lyttelton (potential source of Styela), 15 headed for
Nelson, Picton and Waikawa (Marlborough Sounds HVA), and 208 for Auckland (Table 2.6).
Other vessel types
We are not aware of any towed vessels or maritime structures such as pontoons or moorings that have
recently been removed from the Tutukaka Marina. According to marina staff, the pontoons that form
piers A to E have been in place for approximately 18 years, and those for piers J to M for about 13
years. The origin of these pontoons is unknown. No plans exist to expand the current marina, or
remove existing infrastructure for transport elsewhere. No dredging operations have been carried out
within the marina during the past 5 years.
Missing data
We were unable to contact four of the six fishing vessels we encountered in the Tutukaka Marina at
the time of sampling since they were out at sea. Messages were left with their operators or owners,
but no responses were received.
8.2. Surveyed source location 2: Lyttelton Port
8.2.1. Presence of vectors with the potential to facilitate the spread of Styela
At the time of our survey, a total of 123 vessels or towed structures ranging from 6 to 183m in length
were present in the Lyttelton Port. These included private yachts, charter vessels (sailing and motor
vessels), fishing vessels, merchant ships, pilot and tug vessels, towed barges and a workshop pontoon
(Table 2.7). Surface-based fouling ranks were only allocated to vessels and towed structures

Deliverable 2
Table 2.6: Annual movements of commercial (C) and recreational (R) vessels between source locations for
Styela and HVAs or locations within HVAs. Data for commercial vessels was obtained from the LMIU
database, is restricted to vessels ≥ 99 gross tonnes and represents the average of a 5-year dataset.
Data for recreational vessels was obtained from NIWA’s simulation model for domestic yacht
movements (presented are the averages of a 10-year dataset). Values have been rounded up or down
to the nearest integer.
To Akaroa Lyttelton Nelson Picton Havelock Waikawa Auckland
From :
Region
Akaroa R=40 R=24 R=11
Lyttelton C=124 C=5 C=26
Tutukaka
R=10 R=13 R=21 R=6 R=0 R=31 R=1
Nelson C=28 C=4 C=41
R=40 R=13 R=160 R=13 R=85 R=4
Picton C=3 C=2.25
R=24 R=21 R=2 R=6 R=58 R=183 R=4
Havelock R=6 R=12
Waikawa R=12 R=63
Auckland
Region
C=129 C=40 C=1
R=0 R=31 R=107 R=191 R=1 R=135 R=206
Tutukaka R=0 R=1 R=4 R=4 R=0 R=7 R=208
Table 2.7: Numbers and lengths (range) of vessels and towed structures present in Lyttelton Port at the time of
the survey.
Main port Inner harbour Fishing Wharf Dry-dock
Private yachts 2 73 (7 – 15 m) 2 (9 m) 0
Charter boats 1 (23m) 4 (10 – 15 m) 3 (11-14 m) 0
Merchant ships 8 (63-183m) 0 0 1 (length unknown)
Fishing vessels 3 (26-47 m) 1 (11 m) 15 (9-15 m) 0
Operations/maintenance vessels 4 (13 – 28m) 0 0 1 dredge (62m)
Pontoons # 1 (20 x 10m) 0 0 0
Barges 4 (6-9 m) 0 0 0
Total 23 78 20 2
# These include towed pontoons (such as those used as workshops or to accommodate cranes) that are not part of a location’s
infrastructure but likely to be moved around at times.
length. Since census of vessels and allocation of fouling ranks occurred on different days, not all
vessels counted within the Port were present when fouling ranks were allocated. Therefore, any
percentages presented in the sections below are calculated from the total number of vessels that had
fouling ranks allocated; they may not always correspond to the total vessel numbers presented in
Table 2.7.
64 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Commercial ships
Deliverable 2
At the time of our fieldwork, a total of 8 commercial merchant ships were present in Lyttelton Port
that ranged 63m to 183m length (Table 2.7). They included container ships, bulk carriers and an LPG
tanker. No fouling ranks were allocated to these vessels since the ranking system was designed for
yachts and vessels up to 20m in length. Since none of the vessels’ owners were available for
interviews at the time of our field visits, we were unable to collect information on the age of the ships’
antifouling paints.
Fishing vessels
We encountered 19 fishing vessels within the Port, including small vessels and larger factory ships,
ranging from 9 – 47m (Table 2.7). Smaller fishing vessels are generally moored at the Fishing Boat
Wharf, while larger vessels are given berths anywhere in the Port’s inner harbour depending on
availability (Figure 1.4). Twenty-nine per cent of fishing vessels ≤ 20m were free of fouling. None
had a fouling rank of 0; slime fouling was observed on all of these vessels. Light to heavy fouling
(ranks 2 – 5) was observed on the remaining 71% of fishing vessels. Eight vessels had a fouling rank
of 3 or higher (Table 2.7). Three fishing boats had a fouling rank of 5, which is associated with a 10 –
75% chance that they harbour solitary ascidians on their hulls (Tables 2.3 and 2.8). The age of the
antifouling paint on vessels we were able to contact ranged from 2 months to 2.5 years.
One vessel of particular interest is the Malakhov Kurgen, an Asian vessel that was impounded by
authorities in 2006 and has since been laid up at Gladstone Pier, adjacent to an area of high Styela
densities (see Deliverable 1). The operator of this ship was not contactable. During numerous
occasions when NIWA field staff visited the Lyttelton Port, abundant marine growth was noted along
the hull of this vessel. This vessel was not inspected by divers but is likely to be fouled with Styela.
Recreational yachts
A total of 77 private recreational yachts were encountered within Lyttelton Port. They ranged from
7 – 15m in length and the majority (73 yachts) are moored to piles at the Inner Harbour (Figure 1.4).
Table 2.8: Percentage of vessels in each vessel category with fouling ranks 0 - 5. Note that only vessels ≤ 20m
were allocated fouling ranks. Since the allocation of fouling ranks and mapping of vessels at the
various sites occurred on different days, fouling ranks could not be allocated to all vessels presented
in Table 2.7.
Fouling
rank
Private
yachts (%)
Charter
boats (%)
Commercial
(%)
Fishing
vessels (%)
Operational
(%)
Pontoons
(%)
Barges (%)
0 0 0 3 (100 %) 0 0 0 0
1 20 (32 %) 4 (67 %) 0 5 (29 %) 3 (75 %) 0 0
2 27 (43 %) 1 (17 %) 0 4 (24 %) 1 (25 %) 0 2 (50 %)
3 5 (8 %) 0 0 4 (24 %) 0 0 1 (25 %)
4 8 (13 %) 0 0 1 (6 %) 0 0 0
5 3 (5 %) 1 (17 %) 0 3 (18 %) 0 1 (100 %) 1 (25 %)
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 65

Deliverable 2
The Lyttelton Port Company has recently introduced plans to develop this area into a floating marina.
The majority (68%) of private yachts had visible fouling on their hulls (ranks 2-5). Three yachts had
large amounts of visible fouling and a fouling rank of 5. Overall, 16 yachts had a ≥ 5% chance of
having solitary ascidians on their hulls (Table 2.3). Since none of the yachts’ owners were available
for interviews at the time of our field visits, we were unable to collect information on the age of the
vessels’ antifouling paints.
Charter vessels
We identified a total of eight charter vessels (10 – 23m) within Lyttelton Port, including sailing,
fishing and nature/sightseeing charters (Table 2.7). The majority (67%) of charter vessels had no
visible fouling on their hulls. One charter vessel, the Lyttelton (23m) was allocated a fouling rank of
5, associated with a 10 – 75% chance of having solitary ascidians on her hull. The charter vessels we
encountered had last received new antifouling paint between June 2006 and February 2007.
Operational and maintenance vessels
Five operational and maintenance vessels were present during our visit to the Port (Table 2.7). These
included two tugs (the Purau and the Blackadder), one pilot boat (Canterbury) and one lifeboat that
acts as a back-up pilot vessel (Sumner Lifeboat). A dredging vessel, the Pelican, was being serviced
within the Lyttelton drydock at the time of sampling. The two tugs and pilot/lifeboats last received
new antifouling paint between April and November 2006.
Barges and other floating structures
We identified four towed barges and one non-permanently attached pontoon (Table 2.7). All barges
had visible fouling on their hulls. Two of them (6 and 8m) are owned by the Stark Brothers company
and are moored outside the slipway and dry-dock. Both are used to transport equipment between
locations within the Port basin; trips to Cashin Quay being the only exception. One of these barges
(8m) had a fouling rank of 5 and was slipped for cleaning and antifouling maintenance during our visit
to Lyttelton Port (Figure 2.6). NIWA field staff inspected its hull and found 20 mature Styela
individuals on it. Two additional barges of 6 and 9m length are owned by Lyttelton Engineering and
had fouling ranks of 2 and 3.
A floating pontoon (approx 20 x 10m) is permanently moored between Gladstone Pier and Z Wharf.
The entire underside of the pontoon is covered in fouling organisms. During this study and an earlier
rapid assessment (Gust et al 2006a) this pontoon had some of the highest densities of Styela reported
from the Port. Several vessels, including the Diamond Harbour ferry and the mussel harvester St
George, are frequently moored in the vicinity of this pontoon.
8.2.2. Movements of vectors between Lyttelton Port and the HVAs
Information on movements of potential vectors between Lyttelton Port and HVAs was obtained from
interviews with Lyttelton Port Company staff and owners or operators of charter and fishing vessels.
Not all vessels listed and described below were present in the Port at the time of sampling; however,
our aim was to gather information also on potential vectors that occasionally frequent the Port or have
resided there in the recent past.
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Deliverable 2
Figure 2.6: Barge slipped for cleaning from Lyttelton Port. Twenty adult Styela were removed from the hull of
this vessel by observers.
8.2.3. Vectors that have a potential to transport Styela from Lyttelton Port to HVAs
Below we summarise information gathered on movements of potential vectors for Styela to areas
outside the Port of Lyttelton, with particular reference to the HVAs. Detailed information is provided
if available from interviews with Port staff or vessel owners (e.g. charter vessels, some commercial
vessels). In other cases, information obtained from the LMIU database (merchant ships) or an
epidemiological simulation model developed by NIWA (private yachts), is presented as a summary.
Commercial ships
The Lloyds Marine Intelligence Unit (LMIU) database contains movement records for 2,923 vessel
departures from the Port of Lyttelton between 2002-2005 to 19 New Zealand ports in both the North
and South Islands (Table 2.6). Most commonly domestic movements involved vessels departing the
Port of Lyttelton for Wellington (613 movements), Nelson (494), Dunedin (464), Lyttelton (i.e.
closed-loop trips; 313 departures) and New Plymouth (270). Container ships and roll-on / roll-off
(Ro/ro’s) vessels dominated the vessel types leaving the Port of Lyttelton on domestic voyages (1,142
departures), followed by general cargo vessels (515), passenger / vehicle / livestock carriers (346) and
bulk / cement carriers (249 movements). All of these vessels have ballast water tanks that are being
used to increase stability when the vessels move without cargo. Empty or lightly loaded vessels
leaving Lyttelton Port take on ballast water from the Port basin and may export it to other locations.
Between 2002 and 2005, commercial ships travelled from Lyttelton Port to the ports of Nelson and
Picton 494 and 20 times, respectively. Both Nelson and Picton are located within the Marlborough
Sounds HVA.
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Deliverable 2
A number of vessels move between Lyttelton Port and other New Zealand ports on a regular basis.
The Spirit of Resolution, for example, undertakes weekly trips to Onehunga Port. On her way to the
North Island, this vessel calls in at Nelson Port. In addition the Spirit of Competition, undertakes
between one and three trips per month to Nelson Port, 2-monthly trips to Auckland and 4-monthly
trips to Timaru Port. In addition to the larger vessels captured by the LMIU, a large number of
movements between Lyttelton Port and other locations is undertaken by smaller commercial vessels.
We provide a number of examples below.
The St. George is a 23-m long mussel harvester that operates in the Lyttelton and Banks Peninsula
area for approximately 4 months per year. During this period, the barge visits Lyttelton Port three
times a week to offload mussels harvested from Banks Peninsula aquaculture farms located in Scrubby
Bay, Pigeon Bay, Big Bay and Port Levy (Figure 2.4). When in Lyttelton Port, the barge is berthed at
Z Wharf, in close proximity to a large pontoon identified as one of the key nodes of high Styela
density in the Port (Figure 1.18). The St. George also services mussel farms located within the
Marlborough Sounds HVA but we were not provided with the names of these farms. However,
shortly after our survey was conducted, the St. George was scheduled to travel to Port Underwood
(Marlborough Sounds HVA) and operate there until the end of May 2007. The barge generally
receives new antifouling paint every 12-15 months and was scheduled for maintenance at the Lyttelton
slipway following its work at Port Underwood.
The Tardis is a 24-m long mussel harvesting vessel that services a wide range of South Island farms
located around the Banks Peninsula and Marlborough Sounds HVAs. Over a 3 - 4 week period each
year, the Tardis spends most nights within Lyttelton Port. Its berthing location varies depending on
availability, but frequently the harvester resides at Z Wharf, an area associated with high densities of
Styela. Around Banks Peninsula, the Tardis services mussel farms located at Menzies Bay and Big
Bay (Figure 2.4). In the Marlborough Sounds region, the harvester operates at 11 mussel farms
located in Port Underwood, four farms within Pelorus Sound, three farms within East Bay (near
Picton) and two farms located in the inner Marlborough Sounds area (more detailed information was
unavailable; Figures 2.3, 2.4).
Fishing vessels
During fieldwork and follow-up interviews with port and vessel operators, we gathered information on
a total of 41 fishing vessels (12 – 52m) that regularly visit the Lyttelton Port (Table 2.12). Smaller
vessels are generally moored at the Fishing Boat Wharf, while vessels over 20m in length are allocated
berths at Z Wharf, No. 6 Wharf or the Dry Dock Wharf. For 19 of these vessels, no information on
maintenance or travel history could be obtained despite repeated attempts to make contact with their
owners or operators. Most of the fishing vessels surveyed spend the majority of time at sea, and make
between 12 and 60 visits to Lyttelton Port per year that generally last 2-4 days. Some larger vessels,
such as the Argos Georgia and the Argos Helena, visit Lyttelton biannually and reside at the Port for
2-8 weeks on each visit. There is considerable variation in the destinations of fishing vessels leaving
Lyttelton Port. Some fish local inshore areas and generally do not call at other ports, while others
head to Antarctic waters or follow schools of tuna and may visit other ports while away from
Lyttelton. A number of fishing vessels also occasionally call at the ports of Picton and Nelson (within
Marlborough Sounds HVA) and Auckland when not in Lyttelton. Of the smaller vessels surveyed, 11
visit Akaroa on a regular basis. The LMIU database contains records for 10 trips from Lyttelton to
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Deliverable 2
Nelson Port made by fishing vessels ≥ 99 tonnes between 2002 and 2005. None of the fishing vessels
surveyed had antifouling paint older than 2 years.
Information obtained from a nationwide questionnaire survey of 262 commercial fishing vessel
owners or operators (MAFBNZ project ZBS2005-13) supports the findings described above and
indicates that fishing vessels based at Lyttelton Port use a range of other ports and marinas between
trips to their fishing grounds. Of ten Lyttelton-based vessels surveyed for this project, nine had visited
the Port of Nelson during the past year, two had been to Akaroa and one had resided at Havelock Port.
All of these locations are within the HVAs identified for this project. Nelson, located within the
Marlborough Sounds HVA, had the longest average residency times for fishing vessels: 21 days.
Recreational yachts
NIWA’s simulation model does not contain Lyttelton Port and Magazine Bay Marina as separate
locations; instead, Lyttelton is treated as a single homeport or destination for recreational yachts. The
average annual number of yacht movements from Lyttelton (Port and Magazine Bay Marina) to HVA
locations, obtained over a modelled period of 10 years, was 10 for Akaroa, 13 for Nelson, 21 for
Picton, six for Havelock and one to Tutukaka (Table 2.6). Two owners of domestic yachts surveyed
for a different project had also visited the Poor Knights Islands.
Charter vessels and ferries
A number of vessels offer fishing and sightseeing charters around Lyttelton Harbour and Banks
Peninsula. The Black Diamond is a 12-m long motor catamaran owned by the Black Cat Company
that operates as a passenger ferry between Lyttelton and Diamond Harbour on Banks Peninsula. On
weekdays, this service operates up to 23 times per day, on weekends up to 21 times per day. During
operating hours, the Black Diamond leaves and arrives from B-pontoon (Figure 1.18). Outside
operating hours (approximately between 23:00 and 06:00) this vessel is moored to a pontoon at the
intersection of Z Wharf and Gladstone Pier, an area identified as a “key site” for Styela during
Deliverable 3. The Black Diamond last received new antifouling in July 2006. Black Cat own an
additional two vessels, the Canterbury Cat (15m) used for tourism harbour cruises, and the Onawi
(12m) used as a back-up ferry for passenger movements to and from Diamond Harbour. The
Canterbury Cat spends 1 month each year (usually during winter) moored at Akaroa. At Lyttelton
Port, both vessels are moored to B-pontoon, an area with a particularly high density of Styela (Figure
1.18).
The Lyttelton is a former tug boat (23m length) that now operates as a historic charter vessel for
parties and scenic cruises. It is based at the inner No. 2 East Wharf inside the Port and, during
summer months, leaves the port approximately 3-5 times per month for charter cruises lasting from 1.5
to 3 hours. Fewer trips occur during the winter. The Lyttelton generally remains within Lyttelton
Harbour, but occasionally travels as far as Port Levy, within the Banks Peninsula HVA (Figure 2.4).
The Angitu, Crusader, Pegasus II and Strathallan (13.0 - 16.7m) are privately-owned motor-powered
charter vessels that take customers for fishing or sightseeing tours around Banks Peninsula and nearby
Motunau Island (Crusader only). Trips of varying lengths (several hours to several days) are
undertaken on demand (usually several trips per month and vessel). During some of these trips, brief
stops at or near marine farms around Banks Peninsula do occur, in particular around Port Levy. The
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 69

Deliverable 2
Pegasus II usually travels 30 nautical miles offshore for fishing trips and on an irregular basis stops at
Akaroa. All of these vessels receive antifouling paint renewals at approximately 12-month intervals;
most recently the paint was renewed in August 2006 (Angitu) February (Strathallan; Pegasus II) and
March 2007 (Crusader). During the majority of visits to Lyttelton Port, these vessels reside inside the
Port at the Fishing Boat Wharf and Inner Harbour pile moorings.
Three sailing vessels – the Emma Lady Hamilton, Fox II and Oyster (9 – 15m) - offer tourist charters
out of the Lyttelton Port. When in port, they reside at the Inner Harbour pile moorings and the Fishing
Boat Wharf. Each of these boats goes on 1-3 day trips per week during which no other mooring
facilities are visited. However, the Fox II is based and moored at Akaroa for 9 months each year.
Each of these boats had its antifouling paint renewed in October or November 2006.
Operational and maintenance vessels
Lyttelton Port owns, or regularly uses, a range of vessels for operation and maintenance purposes.
The Canterbury is a 13-m long pilot vessel owned by the Lyttelton Port Company and has a
permanent berth at the Tug Wharf (Figure 1.6). The Canterbury leaves the Port to greet and direct
visiting merchant ships at the pilot station two nautical miles outside the harbour mouth. During these
trips, the vessel does not moor at any locations. The Canterbury was last antifouled in November
2006.
Three tug vessels are associated with the Lyttelton Port. The Albatross (21m) is owned by a private
company and usually resides at No. 5 Wharf. Approximately 50% of its work takes place within the
Port, while the remaining 50% consist of salvage and maintenance work on offshore pipelines.
Occasionally (but infrequently) the Albatross travels to Akaroa Harbour. At the time of our interview,
the vessel had just towed another vessel around Banks Peninsula into Akaroa. The operator of the
Albatross is currently trying to secure contract work with Banks Peninsula aquaculture facilities. The
vessel received new antifouling paint in March 2007. The Lyttelton Port Company owns an additional
two tug vessels of 24 and 28m length (the Purau and Blackadder). Both are permanently moored at
the Tug Berth, and only operate within 1 km of the Port’s boundaries. The larger tug vessel has a
ballast tank that on demand is flooded with treated freshwater. Both of the Port’s tug vessels received
new antifouling paint in April 2006.
The Pelican is a 62-m long dredging vessel that spends approximately 4-5 weeks per year at Lyttelton
Port for maintenance operations. While in the port, it usually resides at No. 2 Wharf East (Figure 1.6).
The Pelican dredge services a range of New Zealand ports, including the Port of Nelson within the
Marlborough Sounds HVA. At the time of sampling, the Pelican was in the Lyttelton dry-dock for
survey and antifouling paint renewal. The paint had last been renewed 5 years earlier, so the dredge
was likely to be heavily fouled when dry-docked (Floerl and Inglis 2005). The vessel conducted
dredging operations in the Port of Nelson for a period of 4 weeks in 2006. The Pelican also operates
in the ports of Timaru, Tauranga and Taranaki. Transfer of Styela could occur as juveniles or adults
via hull fouling or residual dredged material, or potentially as larvae in residual seawater contained in
the dredging tanks (although this is considered unlikely).
The Genesis (12m) is owned by Canterbury Sea Tours and Marine Logistics and on demand is hired
out by Lyttelton Port and Environment Canterbury to service buoys and moorings, or collect water
70 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

samples around Lyttelton Harbour. The vessel undertakes infrequent visits to Akaroa, where
overnight stays occur. The last antifouling paint treatment occurred in November 2006.
Barges and other towed structures
Deliverable 2
We are not aware of any towed structures that have recently left Lyttelton Port or are scheduled to
leave in the near future. The Hood Williams is a pile-driving barge (15m in length) that is
permanently moored within Lyttelton Port and does not leave for other locations. It had its antifouling
paint renewed once during the past 5 years and is likely to be highly susceptible to fouling by Styela.
Missing data
Despite numerous attempts, we were not able to obtain travel and maintenance information for 16
fishing vessels and one charter vessel (Appendix 5.2). The owners or operators were either not
contactable, did not return our calls or questionnaires, or refused to take part in the survey.
8.3. Surveyed source location 3: Magazine Bay Marina
8.3.1. Presence of vectors with the potential to facilitate the spread of Styela
A total of 34 vessels ranging from 7 to 15m in length were present in the Magazine Bay Marina at the
time of sampling. These included 33 private sailing and motor yachts and one inactive commercial
charter vessel (Table 2.9). Surface-based fouling ranks were allocated to 32 of the vessels; two yachts
could not be accessed.
Commercial vessels
The Cat ‘o’ Nine is a 12-m long sailing charter that, according to the marina management, is entirely
inactive and has been laid up at the marina for several years. The vessel was allocated a fouling rank
of 3 (surface observation). This yacht was the only commercial vessel encountered within the
Magazine Bay Marina.
Table 2.9: Types and numbers of vessels present in Magazine Bay Marina during the survey.
Vector Number
Private yachts 33
Commercial vessels 1
Fishing vessels 0
Pontoons # 0
Barges 0
Total 34
# Towed pontoons (e.g. workshop or crane pontoons) that are not part of a location’s infrastructure but likely to be moved around at times.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 71

Deliverable 2
Recreational yachts
We allocated fouling ranks to 31 recreational vessels (sailing boats and motor yachts) at Magazine
Bay Marina. Of these, 23 (74%) had visible fouling on their hulls, and in 26% of vessels fouling was
high to very high (ranks 4 and 5; Table 2.10). One of the five yachts with a fouling rank of 5,
MAG015, was inspected by divers during Deliverable 1, and was found to have Styela on her hull.
Other vessel types
We did not encounter any barges, non-permanent pontoons or other mobile maritime equipment at the
Magazine Bay Marina. The absence of these structures was confirmed by the marina manager.
8.3.2. Movements of vectors between Magazine Bay Marina and the HVAs
Information on movements of commercial vessels between Magazine Bay Marina and HVAs was
obtained from an interview with the operator of a commercial fishing vessel that arrived after we had
conducted our field and fouling rank surveys. Information on movements of recreational yachts was
derived from an epidemiological model developed by NIWA to simulate the spread of fouling
organisms by recreational yachts around New Zealand (see Methods section for details).
8.3.3. Vectors that have a potential to transport Styela from Magazine Bay Marina to HVAs
Commercial vessels
The Magazine Bay Marina is used infrequently by commercial vessels. Most customers are private
yacht owners and long-term residents at the marina. During talks with the marina manager, we were
informed that a commercial fishing vessel (a catamaran clam dredge of 13m length) had arrived at the
Marina in January 2007. It had received new antifouling paint in December 2006 and was most likely
to have a clean hull. The vessel (Storm Cat) had arrived from Picton. It had previously worked from
both Picton and Havelock. The vessel currently fishes in northern Pegasus Bay, and spends
approximately 1 hour at Lyttelton Port 2-4 times per week to offload the catch. The owner has plans
to relocate to Akaroa in the near future, but no detailed information is currently available.
Recreational yachts
NIWA’s simulation model contains Lyttelton Port and Magazine Bay Marina as a single location. The
Table 2.10: Percentage of vessels in Magazine Bay Marina in each vessel category with fouling ranks 0 - 5.
Fouling rank Private yachts Commercial vessels
0 0 0
1 8 (25.8 %) 0
2 10 (32.3 %) 1 (100 %)
3 5 (16.1 %) 0
4 3 (9.7 %) 0
5 5 (16.1 %) 0
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Deliverable 2
average annual number of yacht movements from Lyttelton (Port and Magazine Bay Marina) to HVA
locations, obtained over a modelled period of 10 years, was 10 for Akaroa, 13 for Nelson, 21 for
Picton, 6 for Havelock and 1 to Tutukaka (Table 2.6). Two owners of domestic yachts surveyed for a
different NIWA project had also visited the Poor Knights Islands HVA.
8.4. HVA 1: Poor Knights Islands
The Poor Knights Islands have no existing marine infrastructure. The permanent moorings that were
in place have been removed by the Department of Conservation (DOC, pers. comm. 2007). Vectors
that do come into contact with the Poor Knights Islands originate from coastal locations, most
frequently from the nearby Tutukaka Marina, as described above in Section 3.1. We obtained
information on an additional three commercial vessels that offer diving and fishing charters in the
region and operate out of locations other than Tutukaka. From a list of regional charter boat operators
provided by the Northland Regional Council, we identified two dive charter vessels and one scenic
cruise operator that are based and operate out of Whangarei (two vessels) and Whangaruru Harbour
(one vessel) and that undertake cruises to the Poor Knights Islands on a regular basis. Operators of
these vessels were not available for information on their hull maintenance history.
Data collected in 2002-2004 during a previous NIWA research project showed that, of a sample of 923
New Zealand owned yachts, 34 had visited the Poor Knights Islands in the previous 12 months.
Similarly, of 283 international yachts surveyed upon their departure from New Zealand, 12 had visited
the Poor Knights Islands during their stay. All of the international and 17 of the domestic yachts had
also resided at marinas around Auckland during this time.
8.5. HVA 2: Marlborough Sounds
Of the 105 aquaculture facility operators contacted via email (facilitated through the New Zealand
Marine Farming Association Ltd), only two replied and completed our survey. This figure did not
change after a second approach to the 105 operators was made. Of eight companies operating mussel
harvesting vessels that we contacted, four provided information (Appendix 5.5). Attempts to gather
information on movements of marine farming vessels and equipment to and from the ports of Nelson,
Picton and Havelock yielded no usable information; our staff were informed that records on farming
vessel movements were not kept by the respective port authorities.
ASL Contracting was the only farming company that supplied information on their operations. The
company farms mussels on an area of approximately 250 hectares, but did not provide information on
the location of the farm. Spat for this facility is flown in from Kaitaia, or transported from other farms
in the Marlborough Sounds and Golden Bay area via vessel. Farming gear (ropes, buoys, etc) is
transported 5-6 times per year via road transport between the ASL farm and other facilities located in
Golden Bay. The operators stated that “care is taken to prevent the spread of fouling organisms during
these transfers” but were no more specific than that. The company operates a total of six vessels (10 –
25m in length) including three work boats, a harvester, a dumb barge and a barge towing vessel
(Appendix 5.5). All vessels are in frequent contact with Picton and Havelock ports and the Waikawa
Bay Marina. All of these locations are connected to Lyttelton Port and Magazine Bay Marina via
commercial and recreational vessel movements. Five of ASL’s vessels are cleaned annually by waterblasting,
while the dumb barge Keri Moana is cleaned every two years.
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Deliverable 2
While no other farming operations responded to our queries, there is evidence that the information
supplied by ASL Contracting is likely to be similar for a range of other operations. Forrest and
Blakemore (2002) report:
“Inter-regional spat transfer on ropes or frames appears to have been relatively common within
the mussel industry historically, and still occurs between some regions (e.g. between Golden
Bay and the Marlborough Sounds). Recently, however, the New Zealand Mussel Industry
Council (NZMIC) developed a voluntary code of practice identifying three geographic marine
farming zones and requiring that mussel spat moved between these zones be declumped,
thoroughly washed, transferred as single seed (typically referring to mussels > 20 mm length),
and visually free of blue mussels, Ciona intestinalis (a sea squirt), and Undaria. Blue mussels
and Ciona are particularly problematic bio-foulers in some marine farming regions.
Inter-regional movements of service vessels are relatively infrequent and intermittent and, where
they do occur, follow the same pathways for spat and seed mussels. The greatest inter-regional
vessel activity appears to occur between the Marlborough Sounds and Golden/Tasman Bays,
otherwise movements are mainly within regions. Post-harvest processing and waste disposal
practices appear to occur primarily within areas already colonised by Undaria or involve
treatment processes that would minimise any risk. In Bluff, some mussels from the
Marlborough Sounds are processed, but hot water and infra-red sterilisation are part of the
production system. Furthermore, processed wastewater is discharged to the local sewerage
system, solid wastes are land-filled, and the bulk bags in which the mussels are transported are
autoclaved (a high-temperature sterilisation process).”
Five operators of harvesting vessels supplied information on movement and maintenance patterns.
The St George is owned by the Nelson Ranger Fishing Company and services farms in the
Marlborough Sounds (Pelorus Sound and Port Underwood) and Banks Peninsula aquaculture
production areas for a duration of 2-4 months per area. Mooring for offloading of stock occurs at
Lyttelton Port, Oyster Bay (near Port Underwood) and Havelock. The vessel’s operator is aware of
Styela but has never observed it on the St George or any of the farms he services.
None of the seven vessels operated by the remaining four companies leave the Marlborough Sounds
HVA at any time. The vessels range from 16 to 26m in length and include self-propelled harvesting
vessels and towed dumb barges (Appendix 5.5). The vessels service a range of farms located in
Golden Bay, Croisilles Harbour, Pelorus Sound, Queen Charlotte Sound and a range of additional
locations “within the Marlborough Sounds” (no detailed information was provided). The frequency of
visits to facilities varies between vessels and seasons. During harvesting season, individual facilities
may be serviced on a daily basis, with harvest drop-off locations for Marlborough Sounds farms
located at Tarakohe (Golden Bay farms), Havelock, Elaine Bay, Okiwi Bay, Picton. Port Underwood
farms drop off product at Oyster Bay. At other times of the year, visits associated with maintenance of
the facilities may occur on a monthly or bi-monthly basis. None of the seven vessels undertake trips
to areas outside the Marlborough Sounds.
The Marlborough Sounds HVA includes three ports (Nelson, Picton, Havelock) and several
recreational yacht marinas (Nelson, Havelock, Waikawa Bay, Picton) that receive ship and boat traffic
from the majority of New Zealand’s coastal locations. According to NIWA’s simulation model for
74 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

yacht movements, each year the Marlborough Sounds HVA receives 40 yachts from Lyttelton, 15
from Tutukaka and 434 from Auckland. In addition, larger commercial ships and fishing vessels
Deliverable 2
arrive within the HVA from Auckland throughout the year (Table 2.6). Equipment and stock used on
mussel farms in the Marlborough Sounds HVA is regularly sourced from aquaculture operations in the
vicinity of Auckland (Firth of Thames and Coromandel region) (Dodgshun et al 2007).
8.6. HVA 3: Banks Peninsula
We were able to conduct telephone interviews with six aquaculture facilities (6 to 100 ha in size per
facility) located around Banks Peninsula (Appendix 5.6). As detailed in Section 8.2 above, two
harvesting vessels (St. George and Tardis) that service Banks Peninsula aquaculture facilities are in
regular contact with Lyttelton Port. The Banks Peninsula aquaculture facilities have additional service
and maintenance vessels; in most cases these are trailer boats or small runabouts that do not leave the
farms. All farming equipment was purchased new and is not transferred or sold between facilities.
8.7. HVA 4: Akaroa Harbour
We interviewed operators of three tourism vessels based at the Akaroa swing moorings
(Appendix 5.6). The Black Cat (20m), Cat II (12.5m) and Clipper (8m) are all owned by the Black
Cat Company and used for scenic and dolphin cruises on Akaroa Harbour. All three vessels visit
Lyttelton Port once a year for maintenance and antifouling paint renewal, and return to Akaroa free of
any fouling. Akaroa does receive regular visits from fishing vessels and recreational yachts based in
Lyttelton (see Section 8.2). According to results from NIWA’s epidemiological simulation model, an
additional 12 yachts arrive each year from marinas based in the Auckland region, most likely New
Zealand’s largest current source of Styela (Table 2.6).
We conducted interviews with two operators of salmon and paua aquaculture farms in Akaroa Harbour
(Appendix 5.6). The farms are 5 and 6 ha in size. Paua stock is obtained from Kaikoura or the
Marlborough region (no resident populations of Styela reported from either location), or from a range
of hatcheries. The salmon farm is stocked with smolt from NIWA’s Silverstream facility. Paua
equipment (culture barrels) and stock are transferred between the 2 farms located in Akaroa Harbour
as well as facilities in the Marlborough Sounds. However, the operator ensured that any structures or
equipment are “thoroughly cleaned” prior to transfer.
9. Discussion
The aim of Deliverable 2 was to identify human-mediated vectors with the potential to spread Styela
from the three surveyed source locations (Tutukaka Marina, Lyttelton Port, Magazine Bay Marina) to
four high-value areas (Poor Knights Islands Marine Reserve, Marlborough Sounds aquaculture
production area, Banks Peninsula aquaculture production area, Akaroa Harbour). In the three
surveyed locations we identified private and commercial vessels or towed structures that:
1. have a moderate or high likelihood of becoming colonized by Styela while they are in the
survey location, but for which there is no information available on their likely movement
from the study area;
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 75

Deliverable 2
2. have a moderate or high likelihood of becoming colonized by Styela and subsequently
transporting the species to one or several of the HVAs (information on the movement
patterns of these vectors is available);
3. are already colonized by Styela and will transport the species elsewhere if they depart the
survey location;
4. have an unknown likelihood of becoming colonized by Styela (no fouling information
available), but have a potentially significant risk of transporting the species to a HVA
(information on the movement patterns of these vectors is available); and
5. may become colonized by Styela but have zero likelihood of transporting it elsewhere since
no movements occur away from the survey location.
In Tables 2.11, 2.12 and 2.13 we have provided a list of all vessels and towed structures encountered
by our field teams during the survey of the Tutukaka Marina, Lyttelton Port and Magazine Bay
Marina, and an assessment of the risk associated with each vector of transporting Styela outside the
survey location. For many vessels, in particular recreational yachts, the assessment is based solely on
the fouling rank, since we were unable to obtain specific information on current or planned patterns of
movement. Where this additional information was available, we have included it in the Table. Styela
was encountered on two recreational vessels (MAG015 and LYT008) sampled at the Magazine Bay
Marina during Deliverable 1. The LYT008 was subsequently cleaned and moved to the inner harbour
pile moorings within Lyttelton Port.
Many of the private and commercial vessels we examined regularly travel to a range of destinations
outside the three surveyed source locations (see Results section). However, in many cases they do not
moor for extended periods at their destinations. We have assumed that the risk of inoculating a new
location with propagules of Styela increases with the time a fouled vessel or towed structure spends in
the location (Minchin and Gollasch 2002). However, ascidians can release eggs and sperm
spontaneously in response to stress or shock (M. Page, NIWA, pers. comm.). For this reason, any
vessel or structure that leaves Tutukaka Marina, Lyttelton Port or Magazine Bay Marina poses a risk if
it carries Styela with it. Spread may occur via release of sexual propagules from adult ascidians
fouling the hulls or by release of bilge or ballast water from large commercial vessels. Styela’s short
planktonic phase of 12-24 h may be sufficient for propagules to encounter suitable substrata in the
vicinity of their point of release.
9.1. Tutukaka Marina
At the Tutukaka Marina, diving charter vessels were on average less likely than fishing or recreational
vessels to become colonised by Styela and/or transport the species to locations outside the Marina.
Only 10 % of diving vessels were found to have a moderate or high likelihood of transporting Styela,
compared to 67% of fishing and 54% of recreational vessels (Table 2.11). However, fouling
information could not be obtained for seven dive vessels that are known to travel to the Poor Knights
Islands HVA on a regular basis. These vessels were considered “potentially significant’ in
transporting Styela to the Poor Knights.
76 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Since fishing is not allowed within the Poor Knights Islands marine protected area, fishing vessels
Deliverable 2
generally pass through this area and have a negligible likelihood of infecting the Islands. However,
some of them may occasionally anchor in the shelter of the islands. The Tutukaka Marina is not being
used by any vessels engaged in aquaculture activities. Our surveys of marina and vessel operators
suggest that diving and recreational vessel movements are the most likely human-mediated vectors for
transport of Styela propagules to the Poor Knights Islands HVA. Data collected during past projects
shows that a larger number of yachts with homeports around the Auckland region visit the Poor
Knights Islands each year than yachts resident at the Tutukaka Marina. This fact and the higher
density of Styela observed in the Auckland region may translate into a higher overall risk being posed
by boat movements from Auckland (also see Section 4.4).
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 77

Deliverable 2
Table 2.11: Assessment of vector risk # for Styela associated with vessels and towed structures inspected during
the survey at TUTUKAKA MARINA. For most vessels or structures the assessment is based only on
the level of fouling rank, and represents the risk of the vessel being colonized by Styela. The bold
type denotes vessels or towed structures for which we were able to obtain additional information on
current or planned movement patterns. For these vessels and structures, the estimate of risk
represents their likely potential to transport Styela to locations outside Tutukaka, with particular
reference to HVAs. Vessels with unknown fouling information that are known to travel to the Poor
Knights Islands were allocated the risk “potentially significant”.
Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
TKK142 Recreational 5 High Refer to Table 2.3
Geneva May Fishing 4 High Refer to Table 2.3
TKK088 Recreational 4 High Refer to Table 2.3
(unknown) Recreational 4 High Refer to Table 2.3
TKK098 Recreational 4 High Refer to Table 2.3
TKK007 Recreational 4 High Refer to Table 2.3
(unknown) Recreational 4 High Refer to Table 2.3
(unknown) Recreational 4 High Refer to Table 2.3
TKK023 Recreational 4 High Refer to Table 2.3
TKK004 Recreational 4 High Refer to Table 2.3
TKK146 Recreational 4 High Refer to Table 2.3
TKK111 Recreational 4 High Refer to Table 2.3
Lady Jude Fishing 3 Moderate Refer to Table 2.3
TKK069 Recreational 3 Moderate Refer to Table 2.3
(unknown) Recreational 3 Moderate Refer to Table 2.3
TKK052 Recreational 3 Moderate Refer to Table 2.3
(unknown) Recreational 3 Moderate Refer to Table 2.3
TKK112 Recreational 3 Moderate Refer to Table 2.3
TKK106 Recreational 3 Moderate Refer to Table 2.3
TKK164 Recreational 3 Moderate Refer to Table 2.3
TKK105 Recreational 3 Moderate Refer to Table 2.3
TKK017 Recreational 3 Moderate Refer to Table 2.3
(unknown) Recreational 3 Moderate Refer to Table 2.3
TKK140 Recreational 3 Moderate Refer to Table 2.3
TKK121 Recreational 3 Moderate Refer to Table 2.3
TKK056 Recreational 3 Moderate Refer to Table 2.3
TKK133 Recreational 3 Moderate Refer to Table 2.3
TKK130 Recreational 3 Moderate Refer to Table 2.3
TKK100 Recreational 3 Moderate Refer to Table 2.3
(unknown) Recreational 3 Moderate Refer to Table 2.3
TKK158 Recreational 3 Moderate Refer to Table 2.3
TKK057 Recreational 3 Moderate Refer to Table 2.3
Blue Striker Fishing 2 Moderate Some fouling, does pass through Poor
Knight Islands on fishing trips
El Tigre Diving 2 Moderate Some fouling, does visit Poor Knight
Islands
78 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
Cave Rider Diving 2 Moderate Some fouling, does visit Poor Knight
Islands
G Force Fishing 2 Moderate Refer to Table 2.3
TKK124 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK144 Recreational 2 Moderate Refer to Table 2.3
TKK087 Recreational 2 Moderate Refer to Table 2.3
TKK014 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK094 Recreational 2 Moderate Refer to Table 2.3
TKK110 Recreational 2 Moderate Refer to Table 2.3
TKK037 Recreational 2 Moderate Refer to Table 2.3
TKK002 Recreational 2 Moderate Refer to Table 2.3
TKK084 Recreational 2 Moderate Refer to Table 2.3
TKK163 Recreational 2 Moderate Refer to Table 2.3
TKK085 Recreational 2 Moderate Refer to Table 2.3
TKK033 Recreational 2 Moderate Refer to Table 2.3
TKK118 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK138 Recreational 2 Moderate Refer to Table 2.3
TKK044 Recreational 2 Moderate Refer to Table 2.3
TKK078 Recreational 2 Moderate Refer to Table 2.3
TKK156 Recreational 2 Moderate Refer to Table 2.3
TKK068 Recreational 2 Moderate Refer to Table 2.3
TKK139 Recreational 2 Moderate Refer to Table 2.3
TKK074 Recreational 2 Moderate Refer to Table 2.3
TKK006 Recreational 2 Moderate Refer to Table 2.3
TKK015 Recreational 2 Moderate Refer to Table 2.3
TKK016 Recreational 2 Moderate Refer to Table 2.3
TKK054 Recreational 2 Moderate Refer to Table 2.3
TKK071 Recreational 2 Moderate Refer to Table 2.3
TKK051 Recreational 2 Moderate Refer to Table 2.3
TKK029 Recreational 2 Moderate Refer to Table 2.3
Protector Coastguard 2 Moderate Refer to Table 2.3
TKK132 Recreational 2 Moderate Refer to Table 2.3
TKK041 Recreational 2 Moderate Refer to Table 2.3
TKK079 Recreational 2 Moderate Refer to Table 2.3
TKK096 Recreational 2 Moderate Refer to Table 2.3
TKK086 Recreational 2 Moderate Refer to Table 2.3
TKK024 Recreational 2 Moderate Refer to Table 2.3
TKK117 Recreational 2 Moderate Refer to Table 2.3
TKK107 Recreational 2 Moderate Refer to Table 2.3
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 79

Deliverable 2
Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
TKK077 Recreational 2 Moderate Refer to Table 2.3
TKK009 Recreational 2 Moderate Refer to Table 2.3
TKK095 Recreational 2 Moderate Refer to Table 2.3
TKK064 Recreational 2 Moderate Refer to Table 2.3
TKK022 Recreational 2 Moderate Refer to Table 2.3
TKK019 Recreational 2 Moderate Refer to Table 2.3
TKK062 Recreational 2 Moderate Refer to Table 2.3
TKK141 Recreational 2 Moderate Refer to Table 2.3
TKK020 Recreational 2 Moderate Refer to Table 2.3
TKK070 Recreational 2 Moderate Refer to Table 2.3
TKK151 Recreational 2 Moderate Refer to Table 2.3
TKK065 Recreational 2 Moderate Refer to Table 2.3
TKK109 Recreational 2 Moderate Refer to Table 2.3
TKK134 Recreational 2 Moderate Refer to Table 2.3
TKK143 Recreational 2 Moderate Refer to Table 2.3
TKK080 Recreational 2 Moderate Refer to Table 2.3
TKK026 Recreational 2 Moderate Refer to Table 2.3
TKK160 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK101 Recreational 2 Moderate Refer to Table 2.3
TKK049 Recreational 2 Moderate Refer to Table 2.3
TKK027 Recreational 2 Moderate Refer to Table 2.3
TKK126 Recreational 2 Moderate Refer to Table 2.3
TKK031 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK123 Recreational 2 Moderate Refer to Table 2.3
TKK032 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK093 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
TKK025 Recreational 2 Moderate Refer to Table 2.3
TKK060 Recreational 2 Moderate Refer to Table 2.3
TKK103 Recreational 2 Moderate Refer to Table 2.3
TKK150 Recreational 2 Moderate Refer to Table 2.3
Marlin Blue Diving (unknown) Potentially significant Fouling status unknown but antifouling
paint 20 months old and travels to
Poor Knight Islands
Cara Mia Diving (unknown) Potentially significant Fouling status unknown, but travels to
Poor Knight Islands
Cdiver Diving (unknown) Potentially significant Fouling status unknown, but travels to
Poor Knight Islands
PK Charters Diving (unknown) Potentially significant Fouling status unknown, but travels to
Poor Knight Islands
80 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
Bright Arrow Diving (unknown) Potentially significant Fouling status unknown, travels to
Poor Knight Islands, antifouling paint
12 months old
Pacific Hideaway Diving (unknown) Potentially significant Fouling status unknown, travels to
Poor Knight Islands, but antifouling
paint new
Rumblefish Diving (unknown) Potentially significant Fouling status unknown, travels to
Poor Knight Islands, but antifouling
paint new
Knight Diver Diving 1 Low Currently no fouling but does visit Poor
Knight Islands
Norseman Diving 1 Low Currently no fouling but does visit Poor
Knight Islands
Perfect Day Diving 1 Low Currently no fouling but does visit Poor
Knight Islands
Calypso Diving 1 Low Currently no fouling but does visit Poor
Knight Islands
Crazee Diver Diving 1 Low Refer to Table 2.3
Yukon Diving 1 Low Refer to Table 2.3
Mazuka Diving 1 Low Refer to Table 2.3
Blue Zone Diving 1 Low Refer to Table 2.3
Adrenaline Diving 1 Low Refer to Table 2.3
Shadowfax Diving 1 Low Refer to Table 2.3
Lady Jess Fishing 1 Low Refer to Table 2.3
Riko Riko Fishing 1 Low Refer to Table 2.3
TKK115 Recreational 1 Low Refer to Table 2.3
TKK030 Recreational 1 Low Refer to Table 2.3
TKK055 Recreational 1 Low Refer to Table 2.3
TKK166 Recreational 1 Low Refer to Table 2.3
TKK053 Recreational 1 Low Refer to Table 2.3
TKK136 Recreational 1 Low Refer to Table 2.3
TKK152 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK036 Recreational 1 Low Refer to Table 2.3
TKK082 Recreational 1 Low Refer to Table 2.3
TKK092 Recreational 1 Low Refer to Table 2.3
TKK046 Recreational 1 Low Refer to Table 2.3
TKK147 Recreational 1 Low Refer to Table 2.3
TKK104 Recreational 1 Low Refer to Table 2.3
TKK067 Recreational 1 Low Refer to Table 2.3
TKK131 Recreational 1 Low Refer to Table 2.3
TKK075 Recreational 1 Low Refer to Table 2.3
TKK120 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK050 Recreational 1 Low Refer to Table 2.3
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 81

Deliverable 2
Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
TKK119 Recreational 1 Low Refer to Table 2.3
TKK114 Recreational 1 Low Refer to Table 2.3
TKK102 Recreational 1 Low Refer to Table 2.3
TKK040 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK137 Recreational 1 Low Refer to Table 2.3
TKK034 Recreational 1 Low Refer to Table 2.3
TKK162 Recreational 1 Low Refer to Table 2.3
TKK157 Recreational 1 Low Refer to Table 2.3
TKK083 Recreational 1 Low Refer to Table 2.3
TKK035 Recreational 1 Low Refer to Table 2.3
TKK043 Recreational 1 Low Refer to Table 2.3
TKK028 Recreational 1 Low Refer to Table 2.3
TKK113 Recreational 1 Low Refer to Table 2.3
TKK001 Recreational 1 Low Refer to Table 2.3
TKK155 Recreational 1 Low Refer to Table 2.3
TKK011 Recreational 1 Low Refer to Table 2.3
TKK135 Recreational 1 Low Refer to Table 2.3
TKK008 Recreational 1 Low Refer to Table 2.3
TKK090 Recreational 1 Low Refer to Table 2.3
TKK013 Recreational 1 Low Refer to Table 2.3
TKK148 Recreational 1 Low Refer to Table 2.3
TKK159 Recreational 1 Low Refer to Table 2.3
TKK047 Recreational 1 Low Refer to Table 2.3
TKK010 Recreational 1 Low Refer to Table 2.3
TKK097 Recreational 1 Low Refer to Table 2.3
TKK058 Recreational 1 Low Refer to Table 2.3
TKK045 Recreational 1 Low Refer to Table 2.3
TKK021 Recreational 1 Low Refer to Table 2.3
TKK149 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK153 Recreational 1 Low Refer to Table 2.3
TKK128 Recreational 1 Low Refer to Table 2.3
TKK161 Recreational 1 Low Refer to Table 2.3
TKK127 Recreational 1 Low Refer to Table 2.3
TKK039 Recreational 1 Low Refer to Table 2.3
TKK076 Recreational 1 Low Refer to Table 2.3
TKK042 Recreational 1 Low Refer to Table 2.3
TKK012 Recreational 1 Low Refer to Table 2.3
TKK048 Recreational 1 Low Refer to Table 2.3
TKK081 Recreational 1 Low Refer to Table 2.3
TKK091 Recreational 1 Low Refer to Table 2.3
82 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
TKK129 Recreational 1 Low Refer to Table 2.3
TKK116 Recreational 1 Low Refer to Table 2.3
TKK145 Recreational 1 Low Refer to Table 2.3
TKK165 Recreational 1 Low Refer to Table 2.3
TKK089 Recreational 1 Low Refer to Table 2.3
TKK059 Recreational 1 Low Refer to Table 2.3
TKK038 Recreational 1 Low Refer to Table 2.3
TKK072 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK066 Recreational 1 Low Refer to Table 2.3
TKK073 Recreational 1 Low Refer to Table 2.3
TKK005 Recreational 1 Low Refer to Table 2.3
TKK125 Recreational 1 Low Refer to Table 2.3
TKK154 Recreational 1 Low Refer to Table 2.3
TKK122 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK061 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK099 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
TKK018 Recreational 0 Low Refer to Table 2.3
TKK003 Recreational 0 Low Refer to Table 2.3
TKK063 Recreational 0 Low Refer to Table 2.3
Hendrick J Diving 1 None No fouling, does not visit Poor Knight
Islands
# “Vector risk” is here used to describe the likelihood that a given vessel or towed structure can become colonised and/or facilitate the
transport of Styela away from a source location. It does not relate to the likelihood or consequences of Styela establishing at a new
location.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 83

Deliverable 2
Table 2.12: Assessment of vector risk # for Styela associated with vessels and towed structures inspected during the survey at LYTTELTON PORT. For most vessels or structures the
assessment is based only on the level of fouling rank, and represents the risk of the vessel being colonized by Styela. The bold type denotes vessels or towed structures
for which we were able to obtain additional information on current or planned movement patterns. For these vessels and structures, the estimate of risk represents their
likely potential to transport Styela to locations outside Lyttelton Port. The risk estimate is within brackets “(…)” when the vector is known to travel to other locations not
associated with the four HVAs of interest. For vessels with unknown fouling information that are known to travel to locations outside the Port, the risk level “potentially
significant” was allocated. The risk estimate of vectors known to be associated with any of the three identified Styela hotspots was raised by a category over that predicted
by fouling rank alone. Site codes: GP (general port); FW (fishing boat wharf); IH (inner harbour moorings).
Site Hotspot? Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
GP Yes Lyttelton Charter 5 Very high Heavily fouled, resides at Styela hotspot, travels to Banks Peninsula
HVA
GP Yes Malakhov Kurgen Fishing 5 (Very high) Heavily fouled, resides at Styela hotspot, may move.
GP Yes Purau Operational 2 High Some fouling, and does travel into vicinity of Banks Peninsula HVA
GP Yes Canterbury Cat Charter (unknown) Potentially high Vessel not present at time of sampling. Based at Port 11 months per
year, berth close to Styela hotspot. Spends 1 month per year at Akaroa
HVA.
GP Yes Tardis Harvester (unknown) Potentially high Vessel not present at time of sampling but frequents Lyttelton Port and
Banks Peninsula / Marlborough Sounds HVAs on a regular basis
GP Albatross Operational (unknown) Potentially significant Vessel not present at time of sampling. Based at Port most of year,
occasionally travels to Akaroa HVA.
GP Yes Argos Georgia Fishing (unknown) (Potentially significant) Vessel not present at time of sampling. Stays at Port 4-8 weeks per
year, berth close to Styela hotspot. Visits other NZ ports.
GP Yes Argos Helena Fishing (unknown) (Potentially significant) Vessel not present at time of sampling. Stays at Port 4-8 weeks per
year, berth close to Styela hotspot. Visits other NZ ports.
GP Yes Southern Progress Fishing (unknown) (Potentially significant) Vessel not present at time of sampling. Stays at Port 6 days per month,
berth close to Styela hotspot. Visits other NZ ports.
GP Yes Sharp Shooter II Fishing (unknown) (Potentially significant) Vessel not present at time of sampling. Stays at Port 6 days per month,
berth close to Styela hotspot. Visits other NZ ports.
GP LYT048 Recreational 2 Moderate Refer to Table 2.3
GP Yes Black Diamond Ferry 1 Moderate Currently no fouling, but travels to Banks peninsula HVA every day
GP Yes Onawi Ferry 1 Moderate Currently no fouling, but travels to Banks Peninsula HVA occasionally
GP Yes Blackadder Operational 1 Moderate Currently no fouling, but does travel into vicinity of Banks Peninsula HVA
84 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Site Hotspot? Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
Deliverable 2
GP Yes Canterbury Operational 1 Moderate Currently no fouling, but does travel into vicinity of Banks Peninsula HVA
GP Yes Sumner Lifeboat Operational 1 Moderate Currently no fouling, but does travel into vicinity of Banks Peninsula HVA
GP Yes Pelican Dredge 0 Moderate Recently cleaned in dry-dock but berth close to Styela hotspot.
Regularly moves between Lyttelton Port and Marlborough Sounds HVAs
GP Yes St George Harvester 1 Moderate Currently no fouling, but high potential risk since frequently resides in
area of high S. clava density and travels to several HVAs each year
GP Shemara Fishing 1 Low Refer to Table 2.3
GP LYT070 Recreational 1 Low Refer to Table 2.3
GP Lyttelton
Engineering barge 1
Barge 5 None Barge never leaves the Port
GP Starks barge 1 Barge 3 None Barge never leaves the Port
GP Lyttelton
Engineering barge 2
Barge 2 None Barge never leaves the Port
GP Starks barge 2 Barge 2 None Barge never leaves the Port
FW Govenor Fishing 5 High Refer to Table 2.3
FW Navora Fishing 5 High Refer to Table 2.3
FW (no name) Fishing 5 High Refer to Table 2.3
FW LYT073 Recreational 4 High Refer to Table 2.3
FW Harold Hardy Fishing 3 Moderate Refer to Table 2.3
FW Aotea Fishing 3 Moderate Refer to Table 2.3
FW Canopus Fishing 3 Moderate Refer to Table 2.3
FW Silver Foam Fishing 3 Moderate Refer to Table 2.3
FW Angitu Charter 2 Moderate Some fouling, does travel to Banks Peninsula HVA
FW Lady Waiana Fishing 2 Moderate Refer to Table 2.3
FW Phoenix Fishing 2 Moderate Refer to Table 2.3
FW Triton Fishing 2 Moderate Refer to Table 2.3
FW Kia Ora Fishing 2 Moderate Refer to Table 2.3
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 85

Deliverable 2
Site Hotspot? Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
FW Strathallan Charter 1 Low Currently no fouling, but does travel to Banks Peninsula HVA
FW Crusader Charter 1 Low Currently no fouling, but does travel to Banks Peninsula HVA
FW Emma Lady
Hamilton
Charter 1 Low Currently no fouling, does not moor anywhere outside Port
FW Manurere Fishing 1 Low Refer to Table 2.3
FW Marie Anne Fishing 1 Low Refer to Table 2.3
FW Caroline Fishing 1 Low Refer to Table 2.3
FW LYT008 Recreational 1 Low Recently cleaned but had Styela on hull when inspected in Dec 2006.
Vessel has been active since then.
IH Mistress Fishing 4 High Refer to Table 2.3
IH LYT046 Recreational 4 High Refer to Table 2.3
IH LYT039 Recreational 4 High Refer to Table 2.3
IH LYT015 Recreational 4 High Refer to Table 2.3
IH LYT052 Recreational 4 High Refer to Table 2.3
IH LYT001 Recreational 4 High Refer to Table 2.3
IH LYT022 Recreational 4 High Refer to Table 2.3
IH (no name) Recreational 4 High Refer to Table 2.3
IH LYT018 Recreational 5 High Refer to Table 2.3
IH LYT019 Recreational 5 High Refer to Table 2.3
IH LYT024 Recreational 5 High Refer to Table 2.3
IH LYT071 Recreational 2 Moderate Refer to Table 2.3
IH LYT057 Recreational 2 Moderate Refer to Table 2.3
IH LYT009 Recreational 2 Moderate Refer to Table 2.3
IH LYT013 Recreational 2 Moderate Refer to Table 2.3
IH LYT032 Recreational 2 Moderate Refer to Table 2.3
IH LYT037 Recreational 2 Moderate Refer to Table 2.3
IH LYT012 Recreational 2 Moderate Refer to Table 2.3
86 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Site Hotspot? Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
IH LYT051 Recreational 2 Moderate Refer to Table 2.3
Deliverable 2
IH LYT035 Recreational 2 Moderate Refer to Table 2.3
IH LYT064 Recreational 2 Moderate Refer to Table 2.3
IH LYT058 Recreational 2 Moderate Refer to Table 2.3
IH LYT060 Recreational 2 Moderate Refer to Table 2.3
IH LYT031 Recreational 2 Moderate Refer to Table 2.3
IH LYT055 Recreational 2 Moderate Refer to Table 2.3
IH LYT045 Recreational 2 Moderate Refer to Table 2.3
IH LYT066 Recreational 2 Moderate Refer to Table 2.3
IH LYT068 Recreational 2 Moderate Refer to Table 2.3
IH LYT061 Recreational 2 Moderate Refer to Table 2.3
IH LYT007 Recreational 2 Moderate Refer to Table 2.3
IH LYT026 Recreational 2 Moderate Refer to Table 2.3
IH LYT033 Recreational 2 Moderate Refer to Table 2.3
IH LYT076 Recreational 2 Moderate Refer to Table 2.3
IH LYT027 Recreational 2 Moderate Refer to Table 2.3
IH LYT041 Recreational 2 Moderate Refer to Table 2.3
IH LYT050 Recreational 2 Moderate Refer to Table 2.3
IH LYT063 Recreational 2 Moderate Refer to Table 2.3
IH LYT016 Recreational 3 Moderate Refer to Table 2.3
IH LYT028 Recreational 3 Moderate Refer to Table 2.3
IH LYT010 Recreational 3 Moderate Refer to Table 2.3
IH LYT044 Recreational 3 Moderate Refer to Table 2.3
IH LYT059 Recreational 3 Moderate Refer to Table 2.3
IH Fox II Charter (unknown) Potentially significant Mooring location alternates between Lyttelton Port and Akaroa moorings
IH Genesis Charter (unknown) Potentially significant Fouling rank unknown, but does frequently travel to Banks Peninsula
and Akaroa HVAs
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 87

Deliverable 2
Site Hotspot? Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
IH Pegasus II Charter 1 Low Currently no fouling, but does travel to Banks Peninsula HVA
IH Oyster II Charter 1 Low Currently no fouling, does not moor anywhere outside Port
IH LYT011 Recreational 1 Low Refer to Table 2.3
IH LYT017 Recreational 1 Low Refer to Table 2.3
IH LYT029 Recreational 1 Low Refer to Table 2.3
IH LYT006 Recreational 1 Low Refer to Table 2.3
IH LYT002 Recreational 1 Low Refer to Table 2.3
IH LYT023 Recreational 1 Low Refer to Table 2.3
IH LYT014 Recreational 1 Low Refer to Table 2.3
IH LYT074 Recreational 1 Low Refer to Table 2.3
IH LYT069 Recreational 1 Low Refer to Table 2.3
IH LYT003 Recreational 1 Low Refer to Table 2.3
IH LYT042 Recreational 1 Low Refer to Table 2.3
IH LYT047 Recreational 1 Low Refer to Table 2.3
IH LYT021 Recreational 1 Low Refer to Table 2.3
IH LYT072 Recreational 1 Low Refer to Table 2.3
IH LYT067 Recreational 1 Low Refer to Table 2.3
IH LYT025 Recreational 1 Low Refer to Table 2.3
IH LYT040 Recreational 1 Low Refer to Table 2.3
IH LYT004 Recreational 1 Low Refer to Table 2.3
IH LYT056 Recreational 1 Low Refer to Table 2.3
IH LYT075 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT038 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT062 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT005 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT049 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
88 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Site Hotspot? Vessel name Vessel type Fouling rank Vector Risk Justification of risk estimate
IH LYT034 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT020 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT054 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT043 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT030 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT053 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT065 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
IH LYT036 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
# “Vector risk” is here used to describe the likelihood that a given vessel or towed structure can become colonised and/or facilitate the transport of Styela away from a source location. It does not relate to the likelihood or
consequences of Styela establishing at a new location.
Deliverable 2
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 89

Deliverable 2
Table 2.13: Assessment of vector risk # for Styela associated with vessels and towed structures inspected during
the survey at MAGAZINE BAY MARINA. For most vessels or structures the assessment is based only
on the level of fouling rank, and represents the risk of the vessel being colonized by Styela. The bold
type denotes vessels or towed structures for which we were able to obtain additional information on
current or planned movement patterns. For these vessels and structures, the estimate of risk
represents their likely potential to transport Styela to locations outside Magazine Bay Marina, with
particular reference to HVAs.
Vessel Name Vessel type Fouling Rank Risk Justification of Risk Estimate
MAG015 Recreational 5 Very high
Heavily fouled, hull colonised by Styela, active
vessel
MAG007 Recreational 5 High Refer to Table 2.3
(unknown) Recreational 5 High Refer to Table 2.3
MAG008 Recreational 5 High Refer to Table 2.3
MAG020 Recreational 5 High Refer to Table 2.3
MAG004 Recreational 4 High Refer to Table 2.3
(unknown) Recreational 4 High Refer to Table 2.3
MAG013 Recreational 4 High Refer to Table 2.3
MAG024 Recreational 3 Moderate Refer to Table 2.3
MAG022 Recreational 3 Moderate Refer to Table 2.3
(unknown) Recreational 3 Moderate Refer to Table 2.3
MAG019 Recreational 3 Moderate Refer to Table 2.3
(unknown) Recreational 3 Moderate Refer to Table 2.3
Cat'o'nine Fishing 2 Moderate Inactive since > 1 year
MAG017 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
MAG014 Recreational 2 Moderate Refer to Table 2.3
(unknown) Recreational 2 Moderate Refer to Table 2.3
MAG016 Recreational 2 Moderate Refer to Table 2.3
MAG002 Recreational 2 Moderate Refer to Table 2.3
MAG005 Recreational 2 Moderate Refer to Table 2.3
MAG012 Recreational 2 Moderate Refer to Table 2.3
MAG011 Recreational 2 Moderate Refer to Table 2.3
MAG001 Recreational 2 Moderate Refer to Table 2.3
MAG009 Recreational 1 Low Refer to Table 2.3
MAG010 Recreational 1 Low Refer to Table 2.3
MAG006 Recreational 1 Low Refer to Table 2.3
(unknown) Recreational 1 Low Refer to Table 2.3
MAG023 Recreational 1 Low Refer to Table 2.3
MAG003 Recreational 1 Low Refer to Table 2.3
MAG021 Recreational 1 Low Refer to Table 2.3
MAG025 Recreational 1 Low Refer to Table 2.3
MAG026 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
MAG018 Recreational (unknown) (unknown) Fouling status and travel patterns unknown
# “Vector risk” is here used to describe the likelihood that a given vessel or towed structure can become colonised and/or facilitate the
transport of Styela away from a source location. It does not relate to the likelihood or consequences of Styela establishing at a new
location.
90 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

9.2. Lyttelton Port
Deliverable 2
Our estimation of the likelihood that vectors may become colonised by and/or transport Styela from
Lyttelton Port is more complex since a range of factors need to be considered. One of them is whether
a given vector commonly resides within or nearby one of the three ‘Styela hotspots’ identified within
the Port (Figure 1.18, also see Delivery 3). Based on the short larval phase of Styela and the spatial
correlation between the distribution of adult and juvenile individuals identified in Deliverable 1
(Figures 1.19 and 1.20) we have attributed a higher risk for colonisation/transport of Styela to vectors
that frequently reside within such hotspots than to otherwise similar vectors that reside outside the
hotspots (Table 2.12). There is currently no scientific evidence for spatial variation in colonisation
likelihood related to adult density. However, until this has been investigated such variation must be
considered a possibility and represents a conservative and precautionary approach.
A second factor applies to vectors that are known to travel to locations outside Lyttelton Port. The
focus of this study was to identify vectors with the potential to transport Styela to HVAs. A number of
potential vectors identified for Lyttelton Port regularly travel to other locations that are outside the
HVAs but that are currently not known to be colonised by Styela. Rather than ignoring such vectors,
we have also ascribed an estimate of likelihood for colonisation/transport to them, but present this
likelihood within brackets “(…)” in Table 2.12 to distinguish them from vectors at risk of infecting
HVAs.
Of the 123 vessels and structures encountered in Lyttelton Port, 16 were moored, or are usually
moored, within the three Styela hotspots (Figure 1.18; Table 2.12). Two of these vessels, the Lyttelton
(charter vessel) and the Purau (tug vessel) had a high or very high likelihood of transporting Styela to
the Banks Peninsula HVA since both vessels had visible fouling on their hulls, spend most of the time
moored adjacent to a Styela hotspot and visit Banks Peninsula or locations in its vicinity on a frequent
basis. A further nine vessels had a moderate or potentially significant (fouling rank unknown, but
known to travel to HVAs) likelihood of transporting Styela to the Banks Peninsula region.
With the exception of towed barges (none of which leaves the Port at any time), we encountered
diverse vessels (commercial, charter, operational and recreational) that had a moderate, high or very
high risk of becoming colonised by Styela and/or facilitating its transport to HVAs. Although
recreational and fishing vessels had the highest proportions (56% and 57%, respectively) of hulls with
visible fouling, the data collected during this study are not comprehensive enough to suggest that they
pose a proportionally greater risk for transporting Styela to any of the HVAs than other vessel types –
a consequence of the low numbers of fishing and recreational vessels who supplied details of their
travel patterns. Essentially, any vessel that is susceptible to fouling and that resides within the Port
has the potential to carry Styela to other destinations. Data from this study, NIWA’s domestic
yachting model and MAFBNZ project ZBS2005-13 suggest that each year charter vessels,
maintenance vessels, ferries, fishing vessels, merchant vessels, aquaculture vessels and recreational
yachts all travel from Lyttelton Port to the Akaroa HVA and/or the Banks Peninsula HVA.
Some vessel types vary distinctly in the frequency with which they travel to the HVAs, and in the
duration of their residence within the HVAs. For example, fishing vessels travelling from Lyttelton
Port to Akaroa are likely to pass through the Banks Peninsula HVA without stopping, but will moor
inside Akaroa Harbour and reside there for one or several days. If some of them carry Styela on their
hulls, the likelihood of inoculating Akaroa Harbour while residing there for several days may be
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 91

Deliverable 2
greater than that of inoculating the Banks Peninsula region while passing through. However, each
stage of the invasion process is characterised by stochastic elements (Sakai et al 2001) and while this
assumption appears reasonable there is no guarantee that it will hold at all times.
Based on our estimates of movement frequency and duration of stays at HVAs of vessels leaving
Lyttelton Port, we consider it more likely that Styela will be transported to the Banks Peninsula HVA
than to Akaroa Harbour HVA. This is for the following reasons:
1. The majority of operational vessels at Lyttelton Port (e.g. tugs, pilot vessel) have a
permanent berth within a Styela hotspot (high likelihood of infection), leave the Port on a
frequent basis (several times each day) and travel into the vicinity of Banks Peninsula.
2. Charter vessels and ferry services travel between Lyttelton Port and the Banks Peninsula
HVA far more frequently than between the Port and Akaroa Harbour. Some charter vessels,
e.g. the Lyttelton, are heavily fouled, spend the majority of time moored within a Styela
hotspot and frequently travel to locations within the Banks Peninsula HVA. The Black
Diamond ferry spends days and night in two different Styela hotspots and travels to Diamond
Harbour > 20 times each day.
3. Harvester vessels such as the Tardis and St. George reside at Lyttelton Port for weeks to
months each year, with frequent intermittent trips to a range of Banks Peninsula aquaculture
operations where they spend considerable amounts of time harvesting mussels that are then
offloaded at Lyttelton Port. None of these vessels comes into contact with Akaroa Harbour,
where aquaculture operations engage in salmon and paua farming.
4. Commercial vessels based in Akaroa (e.g. scenic charter vessels) are taken to Lyttelton for
maintenance and antifouling paint renewal, following which they may be assumed to return
clean to Akaroa.
Overall, of 30 vessels surveyed at Lyttelton Port whose operators supplied movement and maintenance
information to us, four occasionally or regularly travel to Akaroa Harbour, while 13 vessels regularly
or frequently travel to or into the vicinity of Banks Peninsula HVA (Table 2.12). Based on our data,
commercial shipping, recreational boating and aquaculture activities are the principal, possibly only,
human-mediated vectors for Styela between Lyttelton Port and the Banks Peninsula and Akaroa
Harbour HVAs. Since no large ships move between these locations, ballast water can most likely be
ignored as a transportation vector.
Movements of vessels between Lyttelton and the Marlborough Sounds HVA may also facilitate the
transport of Styela. The ports of Nelson and Picton receive more than 500 commercial vessels (>99
gross tonnes) from Lyttelton each year. Many of these are large merchant ships that are able to
transport Styela on their hulls, in their sea chests or within their ballast water. As described in Section
8.2, the Banks Peninsula and Marlborough Sounds HVAs are both serviced by a number of
aquaculture harvesting vessels that reside at Lyttelton Port for much of the year, and a considerable
number of recreational yachts travel from Lyttelton to the Marlborough Sounds every year.
With 1,200 annual vessel arrivals Lyttelton is the busiest port in the South Island. Since it harbours a
large population of Styela and caters for most regular vessel types and sizes, our conclusion is that
92 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 2
vector movements from Lyttelton Port could facilitate the transport of Styela to most coastal locations
New Zealand wide.
9.3. Magazine Bay Marina
Magazine Bay Marina is located approximately 1 km from Lyttelton Port and currently caters mainly
for recreational yachts. A large proportion of vessels there are long-term residents that are
infrequently used and poorly maintained. Overall, 75% of the vessels surveyed at Magazine Bay
Marina had visible fouling on their hulls (Table 2.13). Two of 15 recreational yachts our divers
inspected had been colonised by Styela. The profile of vessel types residing at Magazine Bay Marina,
and interviews with the marina manager, suggest that recreational boating is likely to be the key
human-mediated pathway by which Styela may become transported to HVA locations.
9.4. Auckland region
The Auckland region was not part of the Styela source locations investigated in this study. However,
our approach included an assessment of the arrival of potential vectors (e.g. vessels, equipment) at
HVAs from all known sources of Styela. Our data show that Styela may be transported from the
Auckland region to two nominated HVAs – the Poor Knights and Marlborough Sounds - via a range
of vectors, including recreational boating, commercial shipping, towed structures and aquaculture
operations. Auckland has New Zealand’s largest population of recreational yachts and the country’s
largest and busiest port. Significant numbers of recreational and commercial vessels travel between
Auckland and locations within and close to the Poor Knights Island and Marlborough Sounds HVAs
each year, and our data contain several examples that illustrate a high movement frequency or a long
residency period for a range of vectors.
9.5. Summary
The data presented in the sections above were derived using a range of methods. Some, such as the
enumeration of vectors in the three source locations and allocation of fouling ranks, represent one-off
snapshots in time, while other data, such as those gathered through interviews with port and vessel
operators or from the LMIU database, provide a relatively accurate estimate of temporal patterns in
vector activity. To provide an overview of the extensive and complex data gathered for Deliverable 2,
we present a simple summary in Table 2.14, where the relative strength of pathways (see Table 2.1)
between all links among source locations and HVAs is summarised. All indications of relative
pathway strength are qualitative and intended to represent broad patterns discernable from the data.
They do not take into consideration vector susceptibility, residence periods or abundance of Styela in
the source locations (this is addressed in Deliverable 3). For example, Table 2.14 illustrates the
relatively higher pathway strength of commercial shipping and aquaculture activities between
Lyttelton Port and the Banks Peninsula HVA than between Lyttelton Port and the Akaroa Harbour
HVA.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 93

Deliverable 2
Table 2.14: Broad summary of pathway strengths between the three Styela source locations and the four HVAs. Auckland has been included as an additional source location since it is
an important hub for shipping activities in New Zealand. Pathway types: CS = commercial shipping; RB = recreational boating; AQ = aquaculture movements; TB = towed
barges; IN = marine infrastructure. For the purposes of summarizing the information presented in Deliverable 2, we present a relative and qualitative comparison of
pathway strengths between the various Styela source locations and HVAs. These are based on the estimates of movement frequencies different vessel types between
source locations and HVAs. Pathway strength: - = none, + = low; ++ = moderate; +++ = high. Entries with high uncertainty are marked by a ‘?’.
From ↓ / To → Tutukaka Marina Lyttelton Port Magazine Bay
Marina
Tutukaka Marina CS: -
RB: +
AQ: -
TB: -
IN: -
Lyttelton Port CS: -
RB: +
AQ: -
TB: -
IN: -
Magazine Bay
Marina
CS: -
RB: +
AQ: -
TB: -
IN: -
Auckland region CS: ++
RB: +++
AQ: -
TB: ?
IN: ?
CS: +
RB: ++
AQ: -
TB: -
IN: -
CS: +++
RB: ++
AQ: +
TB: ?
IN: ?
CS: -
RB: +
AQ: -
TB: -
IN: -
CS: +
RB:++
AQ: +
TB: -
IN: -
CS: -
RB: +
AQ: -
TB: -
IN: -
Auckland region Poor Knights Is.
HVA
CS: -
RB: +++
AQ: -
TB: -
IN: -
CS: +++
RB: ++
AQ: +
TB: + ?
IN: -
CS: -
RB: +
AQ: -
TB: -
IN: -
CS: +++
RB: +++
AQ: -
TB: -
IN: -
CS: -
RB: +
AQ: -
TB: -
IN: -
CS: -
RB: +
AQ: -
TB: -
IN: -
CS: +
RB: +++
AQ: -
TB: -
IN: -
94 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand
Marlborough
Sounds HVA
CS: -
RB: +
AQ: -
TB: -
IN: -
CS: +++
RB: +++
AQ: ++
TB: -
IN: -
CS: +
RB: ++
AQ: -
TB: -
IN: -
CS: +++
RB: +++
AQ: +?
TB: ?
IN: ?
Banks Peninsula
HVA
CS: -
RB: +
AQ: -
TB: -
IN: -
CS: ++
RB: ++
AQ: ++
TB: -
IN: -
CS: +
RB: +
AQ: -
TB: -
IN: -
CS: +
RB: +
AQ: -
TB: -
IN: -
Akaroa Harbour
HVA
CS: -
RB: +
AQ: -
TB: -|
IN: -
CS: +
RB: ++
AQ: +
TB: -
IN: -
CS: +
RB: +
AQ: -
TB: -
IN: -
CS: +
RB: +
AQ: -
TB: -
IN: -

Deliverable 3: Identify and determine the risk of Styela spreading to nominated
high-value areas.
10. Methods
10.1. Assessing the pathway risk of Styela spreading
Deliverable 3
Our approach to calculating pathway risk is based on the direct transport of Styela adults or propagules
from known source populations to HVAs. The source populations considered were Tutukaka Marina,
Lyttelton Port and Magazine Bay Marina. We also considered additional risk arising from the wider
Auckland area (including Waitemata Harbour and the Hauraki Gulf), since this region includes key
hubs for vessel movement within New Zealand (Inglis 2001) and has known established populations
of Styela. The HVAs considered (Poor Knights Islands, Marlborough Sounds aquaculture area, Banks
Peninsula aquaculture area, and Akaroa Harbour) are the four highest priority areas identified in
Deliverable 2. Since risk of a Styela incursion is likely to increase over time, we consider for the
purposes of this analysis that the pathway risk refers to a period of approximately the next five years.
Initially we compiled qualitative rankings of likely risk arising from each vector type potentially
moving from source populations to HVAs. We considered the human-mediated pathway risk to arise
from four key potential vectors; recreational vessels, commercial vessels, aquaculture activities, and
towed barges and structures. The risk of natural dispersal by Styela eggs and larvae is also
characterised as a fifth potential vector. The risk of Styela being spread from the three delimitation
survey locations and wider Auckland region to individual HVAs is considered additive. We have
separated the likelihood of Styela introduction into the key pathways because management
interventions would typically address specific pathways in order to reduce the risk of introduction
(Forrest et al 2006).
For clarity we define terms and each of the human-mediated vectors considered in the pathway risk
analysis. We consider that hull-fouling, sea chest fouling, fouled aquaculture stock or ballast water are
the “mechanisms” of transport. We consider each vector moving between a source population and an
HVA as a “pathway”, and the 16 possible connections between the four source populations and four
HVAs as “links”. Recreational vessels include yachts and motor launches not operated for
commercial gain, and are most likely to transport Styela via hull fouling rather than ballast water
(which is rarely carried). Commercial vessels include merchant ships, commercial fishing and charter
vessels, and have the potential to transport Styela via hull fouling, ballast water or in sea-chests. The
short Styela dispersal period suggests eggs and larvae could potentially be spread by ballast water
transfer if they can survive short voyages among ports in New Zealand, or if adults can become
established within ballast tanks. For both recreational vessels and commercial shipping we consider
only the risk associated with these vessels transporting Styela from already colonised locations around
New Zealand. We do not evaluate the possibility that vectors could introduce additional stocks of
Styela from international source locations. Such an investigation requires detailed information on
patterns of Styela occurrence in international shipping hubs, and interrogation of databases on
international shipping and recreational vessel movements among countries, and is beyond the scope of
the current program.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 95

Deliverable 3
We consider aquaculture activities to include movement of vessels, spat, stock, lines or other
equipment directly associated with the marine aquaculture industry in New Zealand. Aquaculture
activities may transport Styela via either hull fouling or fouled stock or equipment. Towed barges and
structures (such as pontoons, drilling or maintenance platforms) are often slow moving and heavily
fouled, and may transport Styela amongst fouling communities. Our approach to pathway risk
assessment aims to identify the relative risk of Styela spreading from known sources to HVAs via five
key vectors. It does not consider the probability that once transported; Styela will reach pest densities
if it becomes established at each HVA, although we speculate on this potential.
The overall qualitative pathway risk assessment involved 80 pathways, 64 arising from human-
mediated vectors and 16 from natural dispersal. These pathways arise since there are four potential
Styela sources for each of the four HVAs, and for each of these 16 links we consider four human-
mediated vectors and natural dispersal vectors. We classified each of the 80 pathways into one of five
broad qualitative categories of risk; “very likely”, “likely”, “possible”, “very unlikely” or “negligible”.
The risk categories identified represent the general impressions of NIWA and Cawthron marine
biosecurity scientists. To derive these risk categories we considered patterns of Styela distribution,
abundance and demography derived in Deliverable 1 and patterns of vector movement determined in
Deliverable 2. The five qualitative levels chosen to characterise risk provide a broad initial indication
of pathway risks among locations and vectors.
10.2. Risk of Styela naturally dispersing to HVAs
We include consideration of natural Styela spread potential here to illustrate the relative risk posed by
natural planktonic dispersal and human-mediated dispersal mechanisms. A variety of information is
available to validate our estimates of the risk of natural dispersal. For instance Styela produce eggs
that persist for about 12 hours and then develop into larvae which can spend another 12 hours in the
water column (Minchin et al 2006). The eggs can be considered passive particles and then larvae
typically disperse over very small distances, often only centimetres to meters (Stoner 1990, also see
results of Deliverable 1). Styela larvae are not strong swimmers, and do not usually travel more than a
few centimetres by active swimming (Minchin et al 2006). Consequently they tend to congregate
close to the parent population, although they can be passively dispersed over distances covered by 1-2
tidal excursions (equivalent to the duration of the planktonic period).
The maximum possible dispersal distances for a single cohort of Styela propagules will thus be
determined by prevailing currents during the short dispersive phase. For this reason we consider
hydrodynamic models of the source locations where they exist (section 10.3 below). We calculated
the risk of Styela larvae spreading naturally to HVAs using the methodology outlined in 10.1 for
human-mediated transport risks. Values for model parameters were derived by considering the risk
that Styela larvae produced by existing source populations travel directly to HVAs. We do not
consider the potential risk associated with possible stepping stone dispersal of Styela. That is we do
not estimate the risk of larvae produced by existing source populations creating intermediate
populations that enable subsequent generations of larvae to disperse to HVAs. We also do not
consider the remote possibility of adults dispersing from source populations to HVAs by natural drift
if attached to flotsam. This has been observed in Denmark where fronds of Sargassum muticum (a
macroalga introduced to Europe from Asia in the early 1970s) with Styela clava attached are often
washed up on shores in the Limfjord (Lützen, 1999). Fronds were thought to have become detached
96 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

from their holdfasts towards the end of the growth cycle and can float for “considerable distances”
(Lützen, 1999).
Deliverable 3
Hydrodynamic models can be useful tools for simulating the likely natural dispersal of marine pests
from their points of introduction. When used in conjunction with particle dispersion models they can
be used to simulate the likely movement and concentration of particles through time at different
locations away from a potential source location. Areas at greatest risk from initial establishment are
identified by tracing the movement and density of particles released from the likely site of
introduction. This assumes that the likelihood of recruitment to benthic populations by an invasive
species is related to the density of its dispersive propagules; a reasonable assumption for most marine
species with passive planktonic dispersal stages (Underwood and Fairweather 1989, Ruiz et al 2000).
NIWA previously developed hydrodynamic and particle dispersion models for Lyttelton Harbour as
part of MAFBNZ project ZBS2001-01. The model simulates likely patterns of ballast water or larval
dispersal away from the inner harbour of Lyttelton Port. Equivalent hydrodynamic models have not
yet been developed for Tutukaka Marina or Magazine Bay Marina. Detailed description of the method
used to develop the hydrodynamic models for Lyttelton Port is available in Inglis et al 2005. We
describe key components of the model below.
Hydrodynamic and particle analysis models were established to simulate dispersion of larvae from
likely points of introduction using 100 m by 100 m grids derived from the most recent hydrographic
chart. Tidal boundary conditions were extracted from a tidal model covering the New Zealand EEZ
(Goring 2001). Five separate simulations were carried out for Lyttelton Harbour. These simulated
conditions of no wind, and constant steady-state winds of 12 m/s, from the northeast, northwest,
southeast and southwest. For each simulation, a particle analysis model was run whereby particles
were released from cells chosen within the berthing areas in the major ports within the harbour.
Particles were continuously released into the surface layer (1m) of the water column and tracked for a
period of four days. The resultant map of particle concentrations estimated under each of these
simulations is presented in Appendix 6.1 – 6.5. A four day simulation for a hypothetical propagule
was chosen because a wind of 12 m/s from a fixed direction is unlikely to occur for more than this
time. It is important to note that this simulation period is approximately four times longer than Styela
propagules are likely to remain viable (Minchin et al 2006), and the model outputs therefore represent
worst case predictions of maximum potential natural dispersal in this species.
The particles were considered passive and did not have any capacity for active vertical transport other
than vertical diffusion. Dispersion coefficients in both the horizontal and vertical directions were
proportional to the predicted currents. From the particle tracks, a map of the relative maximum
concentration of particles within each surface layer cell was made for each simulation. Particle
concentrations were calculated relative to a maximum value of one, set at the source of release. The
five mapped simulations defined areas in each harbour where larvae released from the berthing area
would accumulate under particular wind conditions. To obtain a map of average particle dispersion,
we calculated a weighted mean concentration for each grid cell, where concentrations predicted by the
individual simulations were weighted by the proportion of time wind blew from that direction. The
weights were calculated from wind roses obtained from the nearest meteorological station and
summarised at least ten years of wind recordings.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 97

Deliverable 3
10.3. Ranking the risk of Styela dispersing to HVAs using an IMEA approach
The qualitative approach to pathway risk assessment described initially provides a broad initial
assessment of relative risk posed to HVAs from each of the source locations and key vectors.
However each of the 80 qualitative assessments of pathway risk summarise many sources of potential
variability and uncertainty. For instance in assigning a qualitative category for each human-mediated
vector moving from a source location to an HVA we are simultaneously considering the following
issues:
• The distribution and abundance of Styela in each source location.
• The period of time vectors are present in source locations.
• The susceptibility of the vector to being fouled.
• The frequency of direct vector movements from source locations to HVAs.
• The period of time vectors are present in HVAs.
We believe it is important to provide estimates of the magnitude of uncertainty around the risk of
Styela spreading. To estimate uncertainty we applied a hazard identification approach to ranking risks,
using an Infestation Modes and Effects Analysis (IMEA) developed for marine invasions by Hayes
(2002). This methodology is a rigorous and systematic hazard analysis, developed from its industrial
counterpart Failure Modes and Effect Analysis (FMEA) in the aeronautical industry. IMEA has
previously been used to investigate the potential spread of marine organisms by human vectors (Hayes
2002), and to rank marine species posing varying invasion risks (Nyberg and Wallentinus 2005). It
can be considered a hierarchical approach to estimating risk, since the movement of each vector
between potential source populations and HVAs is considered in increasingly detailed parts where we
have sufficient information to assess their likelihood.
The IMEA approach allows calculation of uncertainty around risks by considering BOTH the
minimum and maximum likelihood of events occurring along the vector pathway that contribute to
risk. IMEA provides simple comparison of risks through a risk priority number (RPN) with an
average risk estimate and an interval from minimum to maximum possible risk calculated around the
mean. IMEA involves the use of interval arithmetic, a method for evaluating calculations over sets of
numbers contained in intervals. In this case the interval we are interested in exists between the
maximum and minimum estimates of pathway vector risk. Three NIWA biosecurity scientists
reviewed available data on Styela distribution and abundance and vector movements and provided
their opinions on the likely minimum and maximum values for key components of each pathway. The
resulting estimates were reviewed and discussed with collaborating staff from the Cawthron Institute.
For a human-mediated vector to transport Styela from a source population to an HVA, the vector must
undergo three broad processes. It must become fouled, transport Styela to the HVA and then provide
an opportunity for Styela to release propagules into the HVA. We identified five parameters of
human-mediated vector pathways that reflect the risks of the vector becoming fouled and releasing
propagules. We assume 100% survivorship of Styela during transport in each human-mediated vector.
To systematically estimate the possible range of risk values we score the likelihood of particular
outcomes during each vector pathway using a log ranking system according to the IMEA approach.
For each component we allocated a Risk Priority Number (RPN) from 1 to 10 (1 being the least risk
98 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

and 10 the highest). Where information was not available, assessors make an ‘educated guess’ to
Deliverable 3
select the most appropriate score. The five components of human-mediated vector pathways scored
are indicated in Table 3.1 below. The rationale for the use of the log scale and time units is discussed
in detail in Hayes 2002 and not reproduced here.
Then minimum and maximum RPN scores (designated RPNmin and RPNmax) were calculated as the
averages of the product of the minimum or maximum scores allocated by each assessor to the
components of risk within each vector pathway using the following equation.
RPN
1 ⎡
⎢
⎣
Min Popln. Density .
Min Time in source
⎤
Min Time in HVA
⎥
⎦
n
i
i
min = ∑ n i=
1 Min Susceptibilityi
. Min Movement Freq i .
i
Where n indicates the number of experts used to score components in the analysis. The five variables
scored are indicated in Table 3.1. In this case three NIWA marine biosecurity scientists (NG, GI and
OF) considered the available data and independently provided both minimum and maximum RPN
scores for each component of the IMEA risk model. These individual scores are available to MAF
Biosecurity New Zealand if required. To graphically display uncertainty around risk for each pathway
or vector of interest we plotted confidence intervals linking estimates of RPNmin and RPNmax. RPNavg
is the mean of the RPNmin and RPNmax scores.
Table 3.1: The log category risk guide used to score components of pathway risk for each of the humanmediated
vector pathways considered. Note that for each human-mediated vector pathways moving
between a source population and an HVA, the minimum possible Risk Priority Number (RPN) in this
example would be five, and the maximum 50.
RPN Source population Styela
mean density per m 2
Time in source
population
Susceptibility to
being fouled
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 99
.
Frequency of
movement to HVA
Time spent
in HVA
1 .000001 1 sec 1.00E-09 ≈ 30 years 1 sec
2 .00001 10 sec 1.00E-08 ≈ 3 years 10 sec
3 .0001 100 sec 1.00E-07 ≈ 3 months 100 sec
4 .001 ≈ 15 min 1.00E-06 ≈ 2 weeks ≈ 15 min
5 .01 ≈ 3 hours 1.00E-05 ≈ 1 day ≈ 3 hours
6 .1 ≈ 1 day 0.0001 ≈ 3 hours ≈ 1 day
7 1 ≈ 2 weeks 0.001 ≈ 15 min ≈ 2 weeks
8 10 ≈ 3 months 0.01 100 sec ≈ 3 months
9 100 ≈ 3 years 0.1 10 sec ≈ 3 years
10 1000 ≈ 30 years 1 1 sec ≈ 30 years

Deliverable 3
The IMEA approach to Deliverable 3 is formalised in the following steps:
1. Identify key vectors with the ability to transfer Styela from source populations to HVAs.
(These were identified in the qualitative risk assessment as: recreational vessels, commercial
vessels, aquaculture activities, towed barges and structures and natural dispersal).
2. Within each vector pathway identify key components likely to influence the risk of Styela
being spread. For human-mediated vectors we considered 5 components of the pathway we
felt were likely predictors of risk and for which we had data (see Table 3.1). For natural
dispersal we considered 2 components; the source population density and likelihood of
dispersal to HVAs.
3. Experts then individually score components contributing to each of the pathway risks. They
select BOTH a minimum and maximum risk priority number RPN (from 1 lowest to 10
highest) for each component using a table of log component values. (see Table 3.1).
4. Calculate the minimum and maximum risk priority number (called RPN, designated RPNmin
and RPNmax), and the average RPN (designated RPNavg) for each vector pathway between
source populations and HVAs.
5. To compare risk we can then sum RPN scores for each vector, HVA or source population.
The range of RPNmin to RPNmax indicates the possible values RPN could take.
10.4. Assumptions
Since we have little data to reliably estimate differences in survivorship of Styela during transport we
conservatively estimate that once a human-mediated vector is fouled, Styela survive transport to the
HVA in 100% of cases. We also assume that vector pathway risks are independent of each other but
not mutually exclusive. So, for example, the total risk to an HVA is equal to the sum of the vector
risks from each potential source population.
10.5. Interpretation of IMEA results
The interpretation of IMEA results is straight-forward. The higher the RPN number the higher the
relative risk between source populations and HVAs. The range of possible values the RPN could take
are given between RPN min and RPN max. This range is plotted as a bar and is a measure of
uncertainty, not comparable to normal statistical standard deviation (Nyberg and Wallentinus 2005).
Since different vectors and sources provided additive risk of Styela transport to HVAs, by summing
RPN numbers from vectors and sources we can assess their contributions to relative risk. It is
important to note that the RPN score is not a direct measure of probability. It is a relative risk measure
derived from log categories and allows comparison of vectors with differing numbers of component
pathway risk scores. We use the interval between minimum and maximum RPN to indicate the
uncertainty interval around the true risk.
100 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

11. Results
Deliverable 3
We present the risk of Styela spreading to HVAs from a variety of perspectives to indicate the risks
attributed to source populations, vectors and HVAs. Firstly we consider qualitative impressions of
risk posed to individual HVAs by four human-mediated vectors and natural dispersal from each source
population. Then to characterise the considerable uncertainty associated with these estimates, we
present results of the IMEA hazard assessment.
11.1. Qualitative risk arising from human-mediated transport vectors
The qualitative categories determined for each of the 64 pathways of human-mediated transport risk
are summarised in Table 3.2. Of the 64 pathways, seven (11%) were considered to represent a “very
likely” risk of transporting Styela, five (8%) were considered a “likely” risk, nine (14%) were
considered “possible” and the remaining 43 (67%) were considered to pose either “very unlikely” or
“negligible” risk of spreading Styela to HVAs. We discuss in turn below our justification for the
seven model pathways considered to pose the highest likelihood of transporting Styela.
Table 3.2: Qualitative risk categories assigned to the likelihood of Styela dispersing from source populations to
HVAs via the vectors indicated. We consider Styela source populations from the three detailed
delimitation locations, and the wider Auckland region (including Waitemata Harbour and the Hauraki
Gulf). High Value Area (HVA) codes: AH = Akaroa Harbour, BP = Banks Peninsula aquaculture areas,
MS = Marlborough Sounds aquaculture areas and PK = Poor Knights Islands Marine Reserve.
Potential Styela Recreational Commercial Aquaculture Towed barges/ Natural HVA
sources
boating shipping activities structures dispersal
Auckland region possible very unlikely very unlikely negligible negligible AH
Auckland region very unlikely negligible very unlikely negligible negligible BP
Auckland region very likely very likely possible possible negligible MS
Auckland region very likely possible negligible negligible negligible PK
Lyttelton Port possible possible very unlikely negligible negligible AH
Lyttelton Port likely likely very likely negligible negligible BP
Lyttelton Port likely very likely likely possible negligible MS
Lyttelton Port possible very unlikely negligible negligible negligible PK
Magazine Bay
Marina
possible very unlikely very unlikely negligible negligible AH
Magazine Bay
Marina
possible very unlikely very unlikely negligible negligible BP
Magazine Bay
Marina
likely very unlikely very unlikely negligible negligible MS
Magazine Bay
Marina
possible very unlikely negligible negligible negligible PK
Tutukaka Marina very unlikely very unlikely negligible negligible negligible AH
Tutukaka Marina very unlikely negligible negligible negligible negligible BP
Tutukaka Marina possible very unlikely very unlikely negligible negligible MS
Tutukaka Marina very likely very likely negligible negligible negligible PK
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 101

Deliverable 3
The highest pathway risk identified for Styela being transported to the Banks Peninsula aquaculture
areas was associated with aquaculture activities linked to the Port of Lyttelton (Table 3.2). Banks
Peninsula aquaculture operations employed the services of the harvester vessels St George and Tardis.
These vessels spend several months each year harvesting mussels on Banks Peninsula farms.
Harvested mussels are transported to Lyttelton Port for off-loading. Both the St George and Tardis
can spend periods of days to weeks at Lyttelton Port. Should Styela larvae be in the water column
during these times, they may colonise susceptible parts of harvester hulls and be transported directly to
the Banks Peninsula HVA. For further details of vector risks see Deliverable 2.
The highest risks of infesting the Marlborough Sounds Aquaculture area was ascribed to three sources;
recreational boating and commercial shipping associated with the Auckland region, and commercial
shipping movements from Lyttelton Port (Table 3.2). Based on our data, 51 commercial and 434
recreational vessels arrive at ports and marinas within the Marlborough Sounds HVA each year
(Table 2.6). The figure for commercial vessels only includes ships ≥ 99 gross tonnes; the overall
figure including smaller commercial merchant and fishing vessels is likely to be substantially higher.
Styela may be transferred from Auckland via sea-chest or hull fouling, or in the ballast water of larger
vessels.
Approximately 130 commercial vessels (≥ 99 gross tonnes) travel from Lyttelton to the Ports of Picton
and Nelson each year, as well as an unknown number of smaller commercial ships. Some of these
vessels undertake regular round-trips. An example provided in Section 8.2 is the Spirit of Resolution
that travels between Lyttelton, Nelson and Auckland (Onehunga) on a weekly basis. Styela may be
transferred from Lyttelton to the Marlborough Sounds via sea-chest or hull fouling, or in the ballast
water of larger commercial vessels.
In the Marlborough Sounds region, Styela has so far been encountered on the hulls of three vessels,
and Auckland has been implicated as a possible source. In the first instance, the fishing vessel
Physalie was found to have Styela present when it was hauled out for maintenance at the commercial
slipway in Nelson Port in July 2006 (Morrisey et al 2006). Subsequent delimitation searches found no
other individuals on port wharf structures but detected Styela on a nearby ex-French navy vessel the
Marara which had not left its berth in Nelson port for at least 2 years (Morrisey et al 2006). Marara
was berthed in Auckland for several years before moving to Nelson, and Styela may have settled on its
hull during that period (Morrisey et al 2006). Surveys of recreational vessels in Auckland’s Viaduct
Harbour Basin in 2005 detected Styela on the hulls of a range of yachts (Gust et al 2005), which
demonstrates the clear potential for this location to spread Styela.
The three vectors considered to pose the highest risk of infesting the Poor Knights Islands marine
reserve with Styela were associated with recreational and commercial vessels from Tutukaka Marina,
and recreational vessel movements from the Auckland region (Table 3.2). As outlined in Deliverable
2, the vast majority of diving and scenic charter vessels that visit the Poor Knights Islands are
permanent residents at the Tutukaka Marina. These vessels can spend days to months there between
voyages to the Poor Knights Islands. Diving charter vessels may then reside at the Poor Knights for
periods of several days. If dive charters become fouled in the marina, spawning of Styela individuals
on their hulls may occur during their regular visits to the Poor Knights Islands and propagules may
come into contact with the coastal rocky reefs in the marine reserve. More than 200 recreational
vessels travel from Auckland to Tutukaka Marina each year, and a large proportion of them visit the
102 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 3
Poor Knights Islands. In addition, an unknown number of Auckland yachts undertake return trips to
the Poor Knights Islands without calling at Tutukaka Marina.
11.2. Qualitative risk values for natural dispersal
Natural dispersal of Styela eggs and larvae is thought to currently pose a “negligible” risk of infesting
HVA’s (Table 3.2). This conclusion reflects the short natural dispersal distances (cm to m) of Styela
propagules, relative to the large distances (km to hundreds of km) between source locations and
HVAs. Even for potential source locations situated relatively closet to HVAs (e.g. Lyttelton Port and
the Banks Peninsula aquaculture area) the risk of natural dispersal was considered negligible. The
Lyttelton Port hydrodynamic model indicated Styela larvae released from the port were likely to be
concentrated on the northern side of Lyttelton Harbour, and were unlikely to exit the harbour’s eastern
entrance even after a four day simulation period (Figure 3.1). As such it seems there is a negligible
risk of Styela propagules dispersing naturally directly to Banks Peninsula aquaculture areas (the
closest HVA). The hydrodynamic model suggests it is possible however that Styela larvae could be
transported from Lyttelton Port to Magazine Bay Marina (Figure 3.2). This transport may take place
over a range of wind directions including calm conditions (Appendix 6.1), and particularly during
north-easterly (Appendix 6.2), and north-westerly winds (Appendix 6.5).
11.3. IMEA results
Risk priority number (RPN) scores determined for pathway transport risks are summarised in Table
3.3. RPNavg values varied from 42 to 11,145 depending on the combination of source populations,
HVAs and vectors considered. The highest RPNavg values (> 10,000) were calculated for 13 of the 80
Figure 3.1: Weighted dispersion model simulation for particles dispersing from Lyttelton Port into Lyttelton
Harbour over a 4 day period. This average particle dispersion map was calculated from individual
wind direction simulations weighted by the proportion of time wind blew from each direction.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 103

Deliverable 3
potential pathways between sources and HVAs, and are indicated in bold in Table 3.3. These highest
individual risks included eight pathways originating from Lyttelton Port, four pathways from
theAuckland region and one from Tutukaka Marina (Table 3.3). Of the 13 highest risk pathways
identified, six involved commercial shipping, five involved recreational boating and two involved
aquaculture activities (Table 3.3).
There was general agreement between initial qualitative estimates of pathway risks (Table 3.2) and
IMEA scores (Table 3.3). For instance of the 12 pathways initially considered to represent either
“very likely” or “likely” risks of spreading Styela (Table 3.2), and the thirteen pathways calculated as
highest risk categories in Table 3.3, ten were identified by both approaches (75% agreement). Since
IMEA scores are calculated in a more systematic reductionist approach, and provide confidence
intervals around risk estimates we consider them more reliable and informative than initial qualitative
estimates of risk.
The risk of Styela transport for each of the 16 links among source populations and HVAs is shown
separately for each human-mediated vector (Figure 3.2). Recreational and commercial vessels showed
similar general patterns of risk over the 16 links, with higher risks for links 3,4,5,6 and 7 and reduced
risk for links 12, 13, 14 and 15 in both cases. Aquaculture activities and the movement of towed
barges and structures pose generally higher risks when connected to Auckland and Lyttelton Ports
(links 1-8), than when connected to either of the marinas (links 9-16).
The cumulative risks of Styela being transported from four source populations to four HVAs varied
widely (Figure 3.3). In most cases there was considerable overlap in the range of possible values RPN
could take, indicating considerable uncertainty in relative risk. The highest average and maximum
risks were associated with vector pathways from Auckland to the Marlborough Sounds (link 3 in
Figure 3.3), and vector pathways from Lyttelton Port to Akaroa Harbour, Banks Peninsula aquaculture
area and the Marlborough Sounds aquaculture area, (links 5, 6 and 7 in Figure 3.3). There were
broadly two levels of risk apparent, with generally higher risk associated with links 1-8 (those that
connect Auckland and Lyttelton Port to HVAs), and reduced risk associated with links 9-16 (those that
connect Magazine Bay and Tutukaka Marina to HVAs (Figure 3.3). This trend is explained by the
lower RPN scores for aquaculture activities and towed barges and structures evident in Figure 3.2.
There was a negative relationship between the risks of Styela being transported, and the distance
between source populations and HVAs (Figure 3.4). The slope of the regression line was significantly
different from zero (Table 3.4).
The four potential source populations all contributed to the risk of spreading Styela to HVAs, with a
wide overlap in the range of potential risk posed by the sources (Figure 3.5). Lyttelton Port and the
Auckland region contributed the highest risk of infecting HVAs with Styela. Magazine Bay Marina
represented an intermediate source of risk, and Tutukaka Marina represented the least risk of
spreading Styela to HVAs (Figure 3.5). RPNavg for Lyttelton Port and the Auckland region exceeded
RPNmax for Tutukaka Marina (Figure 3.5).
Although there were wide and overlapping ranges of potential risk for each vector, the average risk of
spreading Styela (RPNavg) differed over three levels (Figure 3.6). Recreational vessel movements and
commercial shipping contributed the highest risks of spreading Styela from source populations to
104 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 3
Table 3.3: Risk Priority Numbers (RPN 13 ) for the dispersal of Styela from potential sources to HVAs. RPNavg is
indicated in each case, with the range of RPNmin and RPNmax included in brackets below. RPN scores
>10,000 are shown in bold to highlight these highest risk links. High Value Area codes; AH = Akaroa
Harbour, BP = Banks Peninsula aquaculture areas, MS = Marlborough Sounds aquaculture areas, and
PK = Poor Knights Islands Marine Reserve. Link indicates the possible pathways between Styela
source populations and HVAs.
Potential
Styela
sources
Auckland
region
Auckland
region
Auckland
region
Auckland
region
Lyttelton Port
Lyttelton Port
Lyttelton Port
Lyttelton Port
Magazine
Bay Marina
Magazine
Bay Marina
Magazine
Bay Marina
Magazine
Bay Marina
Tutukaka
Marina
Tutukaka
Marina
Tutukaka
Marina
Tutukaka
Marina
Recreational
boating
9569
(6048-13090)
9155
(5616-12693)
10523
(6767-14280)
11145
(6750-15540)
10733
(6767-14700)
10617
(6533-14700)
10733
(6767-14700)
9263
(5832-12693)
9767
(6048-13487)
9659
(5832-13487)
9767
(6048-13487)
8388
(5183-11594)
7304
(4400-10208)
6945
(4033-9856)
8193
(4792-11594)
9137
5581-12693)
Commercial
shipping
8575
(5183-11968)
7374
(4585-10164)
10824
(6552-15096)
10137
(6067-14208)
10372
(6067-14677)
10156
(6067-14245)
10703
(6309-15096)
6395
(3879-8910)
9027
(5382-12672)
8829
(5382-12276)
9225
(5382-13068)
5999
(3703-8294)
5687
(3373-8000)
5153
3373-6933)
6426
(3987-8866)
10255
(6264-14245)
Aquaculture
activities
8065
(5250-10880)
8225
(5250-11200)
8400
(5250-11550)
4811
(3381-6240)
9621
(6525-12716)
10563
(7254-13872)
10136
(6786-13487)
4040
(3080-5000)
6473
(4333-8613)
6473
(4333-8613)
6473
(4333-8613)
2704
(2027-3381)
1453
(1031-1875)
1423
(971-1875)
1491
(1031-1950)
1069
(789-1350)
Towed
barges/
structures
7738
(4784-10692)
7322
(4600-10044)
8312
(4968-11655)
5373
(3456-7290)
8361
(5400-11322)
7728
(4800-10656)
8420
(5184-11655)
5036
(3024-7047)
4574
(2369-6760)
4039
(1995-6084)
4564
(2369-6760)
3927
(1995-5859)
3757
(1680-5833)
3444
(1680-5208)
3861
(1680-6042)
3757
(1680-5833)
Natural
dispersal
114
(114-114)
114
(114-114)
114
(114-114)
189
(114-264)
173
(131-216)
290
(180-400)
131
(114-147)
114
(114-114)
116
(84-147)
192
(120-264)
84
(72-96)
72
(72-72)
42
(42-42)
42
(42-42)
42
(42-42)
104
(58-149)
HVA Link
AH 1
BP 2
MS 3
PK 4
AH 5
BP 6
MS 7
PK 8
AH 9
BP 10
MS 11
PK 12
AH 13
BP 14
MS 15
PK 16
13
The RPN score is an indication of the relative likelihood that an HVA will receive Styela from the source locations via the
vector considered. The score allows comparison of relative risk among high value areas and potential source locations. It is
not a direct measure of the probability that a location will become fouled with Styela, or that pest densities of Styela will
develop.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 105

Deliverable 3
Figure 3.2: Human-mediated vector risks. The risks of Styela being transported by the human-mediated vectors
is shown for each of the 16 possible links among source Styela populations and HVAs (link numbers
indicated in Table 3.2)
Figure 3.3: The cumulative risks of Styela being transported from source populations to HVAs by four human-
mediated vectors and natural dispersal. The 16 possible links among source Styela populations and
HVAs are indicated in Table 3.2.
106 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Figure 3.4: Linear regression of the risks of Styela being transported versus the distance between source
populations and HVAs. The risk intervals plotted for the 16 possible links among source Styela
populations and HVAs consider cumulative risk arising from both human- mediated vectors and
natural dispersal (numbers beside each data point indicate the link number listed in Table 3.3).
Deliverable 3
Table 3.4: Regression model for the risk of Styela spread versus the distance between source populations and
HVAs.
Source df MS F p
Regression model 1 281260524 6.308 0.025
Residual 14 624183356
HVAs. Aquaculture activities and the towing of barges and structures contributed lower risks of
spreading Styela, and natural dispersal contributed minimal risk (Figure 3.6). RPNavg for recreational
vessels and commercial shipping both exceeded RPNmax for aquaculture activities, towed barges and
structures, and natural dispersal (Figure 3.6). Thus the overall risks of spreading Styela to HVAs are
higher for recreational vessels and commercial shipping than they are for aquaculture activities, towed
barges or structures, while natural dispersal represents a minimal risk.
The four high value areas were exposed to a range of pathways for receiving Styela (Figure 3.7). If we
consider risks arising from each vector potentially linking HVAs to source populations there is a large
amount of cumulative uncertainty around risk, as indicated by confidence intervals linking the
maximum and minimum risks posed to each HVA (Figure 3.7). The wide overlap in the range of
potential risk among the four HVAs, indicates the considerable uncertainty in ranking relative risk
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 107

Deliverable 3
Figure 3.5: This figure sums RPN scores arising from all vectors and pathways originating from each Styela
source population. It provides an overview of the relative risk posed by the source populations to all
four HVAs.
Figure 3.6: Vectors contributing to the risk of transporting Styela to HVAs. This figure sums the risks each
vector type poses to all four HVAs. It provides an overview of the cumulative risk posed by vectors.
108 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 3
Figure 3.7: Risks of Styela being transported to high value areas by human-mediated vectors and natural
dispersal. This figure sums the vector risks arising from the four potential source populations. It
provides an overview of the relative risk posed to HVAs.
among locations. Nevertheless existing results (as measured by both RPNavg and RPNmax risk scores)
suggest that the HVA at highest risk is the Marlborough Sounds aquaculture area, followed by Banks
Peninsula aquaculture area, Akaroa Harbour and the Poor Knights Islands Marine Reserve. RPNavg for
the Marlborough Sounds is approximately 7000 higher than Banks Peninsula, 10,700 higher than
Akaroa Harbour and 26,500 higher than the Poor Knights. The risk of Styela introduction to the
Marlborough Sounds HVA is approximately 0.7, 1 and 2.5 times greater than the risk of Styela being
introduced to the Banks Peninsula, Akaroa Harbour and Poor Knight Islands HVAs, respectively.
We ranked the priority of HVAs for potential management actions in Table 3.5 to assist efforts to
reduce the risk of introductions of Styela. Identifying priorities and worst case scenarios at each HVA
may assist management actions if limited budgets prevent population control measures being widely
implemented. Given that the Marlborough Sounds are both at the highest risk of an incursion, and the
mussel farming industry there is likely to face the greatest impact and potential economic losses if
Styela becomes well established, it seems a clear candidate for management priority. Furthermore, it
is considered suitable for developing high pest densities because of the high abundance of floating
artificial substrates preferred by Styela. Priority around the remaining three HVAs is less clear and
opinions are likely to vary among interest groups. However for the reasons listed in Table 3.5 we
conclude that management priorities to prevent Styela spreading should then consider, in order, the
Banks Peninsula aquaculture area, Akaroa Harbour and then the Poor Knights Islands Marine Reserve.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 109

Deliverable 3
Table 3.5: Summary of risks posed by Styela to HVAs. Infestation risk is measured as RPN values from all
vectors and source populations considered in the IMEA assessment. The likelihood of establishing
pest densities is a speculative qualitative estimate derived from consideration of the species’
invasion history and the physical and environmental characteristics of the recipient environments.
Potential consequences of pest densities are worst case scenarios in the event of pest densities
establishing.
Priority High Value Areas
1 Marlborough Sounds
aquaculture areas
2 Banks Peninsula
aquaculture areas
Infestation Risk
RPNavg
(RPNmin- RPN max)
128,422
(78,547 - 178,297)
121,511
(75,010 - 168,012)
3 Akaroa Harbour 117,743
(72,760 - 162,727)
4 Poor Knights Islands
Marine Reserve
12. Discussion
101,913
(63,049 - 140,777)
Likelihood of
pest
densities
Worst case consequences to the HVA
Likely Significant economic costs to the major
centre of the mussel industry. Reduced
mussel growth, stock densities and
Likely
reduction in harvest are possible along with
increased costs to major multi-million dollar
operations.
Significant economic costs to a regional
centre of the mussel industry. Reduced
mussel growth, stock densities and
Possible
reduction in harvest. Increased costs to
individual operators.
Moderate economic costs to individual paua
and salmon farms due to fouling of
Possible
structures. Possible infestations on natural
habitats.
Infestations on natural habitats. Unknown
effects on native biodiversity in an area of
international conservation value. Potential
adverse impacts on diving tourism.
In this Deliverable we considered the likelihood of Styela spreading by four human-mediated transport
vectors and natural dispersal from the three detailed delimitation locations to nominated high value
areas. We also considered the additional risk of Styela introductions HVAs arising from the wider
Auckland region (including Waitemata Harbour and the Hauraki Gulf). The Auckland region was
included because of its potential to act as a source for its spread to HVAs. We felt a nationwide
assessment of the risks of Styela spreading to HVAs would be substantially incomplete and potentially
misleading without it.
Conclusions were drawn on the likelihood of HVAs becoming colonised, and the importance of source
locations and vectors with the potential to spread Styela to HVAs. In each case these conclusions
should be considered relative rather than absolute since they summarise the cumulative influences of
16 potential links among source locations and HVAs, via five potential vectors, and for each vector
multiple components of risk were estimated with varying degrees of uncertainty. It is therefore
important to consider the outcomes of the risk assessment as identifying trends and ranking relative
risk, rather than taking RPN scores as deterministic predictors of the future probability of an incursion.
We discuss in turn below; 1. Key source populations contributing to the risk of Styela being spread to
HVAs. 2. Key pathways that may transport Styela to HVAs, and 3. The risk that each HVA will
110 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

ecome colonised over approximately the next five years. We then discuss considerations and
limitations of the current risk assessment.
12.1. Risk of introduction from Styela source locations
Deliverable 3
The four potential source locations contributed varying risks of spreading Styela to the nominated high
value areas. Differences in contribution to risk roughly reflected the source’s relative proximity to
HVAs, with increasing distances often reducing the frequency of vector visits and thus the risk of
introducing Styela. However distance among source locations and HVAs was only a loose proxy for
relative likelihood of Styela transport, since many other factors were involved. For instance the risk of
spread was also affected by the existing Styela population density in the source location, the vector
types linking source populations with HVAs, the time vectors spend in both the source population and
HVAs, and the frequency of movements between them. Our analyses indicated that Lyttelton Port
contributed the greatest overall risk of spreading Styela to HVAs, followed closely by the Auckland
region. In contrast Magazine Bay Marina represented a drop in relative risk, and Tutukaka Marina
represented the least risk of being the source of Styela because of its currently small Styela population
and limited links to HVAs other than the Poor Knights Islands.
These findings are intuitive on two levels. Firstly, the highest risk source locations (Auckland and
Lyttelton) are physically large and contain well established, abundant Styela populations. Secondly
they are busy hubs of both commercial shipping and recreational boating and are widely connected to
other coastal regions of New Zealand (see Deliverable 2 for details). These factors suggest higher
numbers of vector inoculations, and regular movement of human-mediated vectors to HVAs may
spread Styela depending on the stochastic nature of events along invasion pathways. In comparison,
both the Tutukaka and Magazine Bay Marinas possess relatively small, widely dispersed Styela
populations that lack nodes of high abundance and pose reduced risk of colonising resident vectors.
The marinas primarily cater for recreational vessels and small commercial dive and charter vessels.
The absence of large commercial carriers or ships carrying ballast water largely excludes the
possibility of sea-chest or ballast water transport of Styela from these marinas. Furthermore both
marinas are small and are linked to fewer potential commercial vessels, towed barges or structures and
are less involved with aquaculture activities as vectors than either Lyttelton Port or the Auckland
region.
12.2. Vector risks
We conclude that the two vectors most likely to spread Styela from source locations to the nominated
HVAs in New Zealand are recreational vessels and commercial shipping. With recreational vessel
movements the risk of Styela transport almost solely represents the risk of hull-fouling transport. In
contrast, commercial shipping could transport Styela in three ways; adults via either hull fouling or
sea-chests, or propagules in ballast water. Despite the differences in the potential transport
mechanisms between recreational vessels and commercial shipping, the overall risks calculated for
these two vectors were similar, with a very wide overlap of possible risk from RPNmin to RPNmax. The
extent of this overlap in potential risk makes it impossible to unambiguously attribute differences in
risk to recreational or commercial vessels. Clearly they are both very important vectors to the overall
risk of spreading Styela to HVAs.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 111

Deliverable 3
Aquaculture activities and the towing of barges or structures are potentially important mechanisms for
spreading Styela via individual links between sources and HVAs, particularly when they are linked to
either Lyttelton Port or the Auckland region. However overall they both posed less risk of
transporting Styela to HVAs than either recreational or commercial vessel movements. Barges and
towed structures are highly susceptible to fouling by Styela, but the frequency at which they travel
between source locations and HVAs translates into a reduced relative risk. All four human-mediated
vectors considered were far more likely than natural dispersal to spread Styela to HVAs. Below we
briefly discuss characteristics of each of the five vectors in order of decreasing likelihood of spreading
Styela to HVAs.
Recreational boating
Recreational boating was classified as a particularly high risk vector (RPN >10,000) for introducing
Styela to all four HVAs. In particular it was implicated as a key source of pathway risk to the
Marlborough Sounds from both Lyttelton Port and the Auckland region. Hull fouling of recreational
vessels has been demonstrated to have the capacity to transport Styela in many parts of New Zealand.
Styela has been encountered on yachts moored in Wellington and Opua. Recreational vessels fouled
with Styela have now been observed in both Waitemata Harbour (Gust et al 2005) and Magazine Bay
Marina (see Deliverable 1). One of the most difficult components of estimating the risk posed by the
movement of recreational vessels is that, while vessels that are neglected are often heavily fouled and
thus have the highest likelihood of being fouled by Styela (Floerl et al 2005), they are also probably
the least likely to travel widely, or if they do are likely to be cleaned in preparation for the journey.
We suggest that in order to better understand the potential risk posed by the movement of recreational
vessels, a better quantitative understanding of the relationships among vessel fouling levels and
frequency of domestic voyages would be informative.
Commercial shipping
Commercial shipping was identified as the second vector most likely to transport Styela to HVAs.
Like recreational boating, commercial shipping was classified as a particularly high risk vector (RPN
>10,000) for introducing Styela to all four HVAs. Commercial shipping has long been regarded as a
major vector for the transport of marine non-indigenous species (e.g. Carlton and Geller 1993,
Wonham et al 2000). In this study we consider commercial shipping to encompass both large
merchant ships and smaller commercial enterprises such as fishing, diving and charter vessels. Large
ships have the potential to carry Styela in three ways: through hull fouling, ballast water or sea-chests,
while the smaller vessels would likely only include Styela amongst hull fouling communities.
Together these commercial vessel types and mechanisms are considered a high risk to transporting
Styela from both Lyttelton Port and the Auckland region to the Marlborough Sounds. Commercial
shipping was also implicated as a key source of pathway risk to the Poor Knight Islands from both
Tutukaka Marina and the Auckland region.
It is unclear whether commercial or recreational vessels will play the greater role in spreading Styela
within New Zealand. Although our model suggests recreational vessels pose slightly greater threat,
other studies have often implicated commercial shipping as the key vector for the introduction and
spread of non-indigenous marine organisms. For instance commercial shipping and fisheries are
considered the dominant vectors for marine invasions in North America, where they account for 89%
of all initial invasions and 74% of the known secondary invasions, i.e. domestic spread after it is
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Deliverable 3
initially established (Ruiz et al 2000). Considerable fruitless debate is possible on the relative risks
posed by these two key vectors, but ultimately to reduce the future potential spread of Styela vector
management is required for both.
Aquaculture pathways
The movement of aquaculture species and equipment has long been acknowledged as an important
international pathway for the inadvertent introduction of non-indigenous marine species (Elton 1958).
For instance in San Francisco Bay, thirty species, representing about 15% of the introduced biota, are
attributed to activities of the Atlantic oyster industry in the late 19th and early 20th centuries (Cohen
and Carlton 1995). Aquaculture activities also clearly have the capacity to move introduced species
around at smaller scales within countries.
Aquaculture activities associated with mussel farming are the third most likely vector to transport
Styela from source regions to HVAs. Risks posed by aquaculture activities are comparable to those
posed by the towing of barges and other floating structures, but lower than risks posed by recreational
and commercial vessel movements because of their lower frequency of occurrence. Much of the
aquaculture risk identified was associated with the activity of mussel harvester vessel movements,
particularly between Lyttelton Port and both the Banks Peninsula and Marlborough Sounds
aquaculture production areas.
In New Zealand, the marine aquaculture industry has burgeoned over recent years, with long-line
mussel farming being the most dominant activity in terms of total area, national coverage, and export
earnings. Standard operational practices such as moving stock and equipment between locations could
potentially assist the transfer of Styela from one locality to another. However, despite these potentials,
difficulty in discussing these issues directly with the Marlborough Sounds aquaculture industry made
it hard to assess this potential component of pathway risk. The tendency of many exotic marine
organisms (e.g. Styela, Undaria pinnatifida, or Sabella spallanzanii) to colonise floating or suspended
artificial structures is now well known (e.g. Forrest et al 2000, Gust et al 2005, Glasby et al 2007).
This means firstly that marine farms are potentially important reservoirs for the secondary spread of
non-indigenous marine organisms, and secondly that inter-regional activities within the marine
farming industry can be significant pathways for their national spread (Forrest et al 1997). Our
analyses may underestimate the risk posed by the aquaculture industry if stock transfers occur from
aquaculture facilities already colonised by Styela. Our risk estimates are based on the assumption that
Styela is not yet present in such facilities. Potentially, the movement of aquaculture vessels among
farms could lead to the rapid spread this pest if it initially becomes established in a port or marina in
the region.
Towed barges and structures
The infrequent movement of towed barges or structures documented from source locations to HVAs is
balanced against the high likelihood that these vectors may be fouled with Styela. Overall we believe
this vector currently represents a moderate relative risk of transferring Styela to HVAs. Its risk of
spreading Styela is considered greater from Lyttelton Port and the Auckland region than from either of
the two marinas. Barges and towed structures are generally more likely to be found in busy
commercial ports than marinas, and the established Styela population are also larger there.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 113

Deliverable 3
If barges and towed structures continue to be moved rarely among source locations and HVAs, we do
not anticipate this vector will contributing significantly to the future likelihood of spreading Styela to
HVAs. However even irregular, infrequent events of towed barges or structures may be highly
significant in transferring marine pests such as Styela to HVAs or other intermediate locations
nationwide. Individual barges and towed structures can pose high marine biosecurity risks. They
often have large surface areas, can be heavily fouled, are typically towed slowly (and thus are unlikely
to damage assemblages in transit or self-clean), and then often spend long periods in ports or marinas
where they are capable of introducing and receiving fouling organisms. Precedents exist for the
movement of pest organisms on towed barges or structures within New Zealand. The introduction of
Didemnum vexillum to the Marlborough Sounds has been attributed to the movement of a single
fouled barge, from Tauranga to Shakespeare Bay, Picton (Coutts and Forrest 2007).
Natural dispersal
Currently we consider that Styela has a negligible risk of dispersing naturally to the high value areas
considered in this report. Styela eggs and larvae appear incapable of travelling large distances during
their short (24 hour) competency period (Minchin et al 2006). Styela larvae do not usually travel more
than a few centimetres by active swimming (Minchin et al 2006). Their poor swimming ability and
short planktonic period is consistent with the impression that most larvae settle within a short distance
(≤ 10 m) of the parent (Stoner 1990). In contrast, distances from source locations to the HVAs
considered here are tens to hundreds of kilometers, and thus are orders of magnitude higher than
known larval dispersal capabilities. Detailed hydrodynamic investigations would likely support this
prediction in each location. Arguably, the risk of Styela dispersing naturally from Tutukaka Marina to
the Poor Knights, or from Lyttelton Port to the Banks Peninsula aquaculture areas is higher, since in
both cases the distance required for dispersal is only around 10 - 25km. Nevertheless, the risk of
natural dispersal is very small in both cases, and unimportant in comparison to the risks associated
with human-mediated transport.
It is possible, however, that the risk of Styela spreading by natural dispersal to HVAs may increase
over time. If Styela gradually infests hubs of human vector activity outside the regions identified in
Deliverable 1, or if additional locations with natural substrates become colonised in the future, Styela
populations may form closer to HVAs. In this worst case scenario the potential exists for Styela to
eventually disperse to high value areas over many years by a stepping stone model of dispersion where
intermediate populations are established between the currently fouled locations and HVAs. Planktonic
dispersal distances may eventually become short enough for larvae to reach HVAs with the assistance
of strong currents. This currently seems an unlikely proposition, given the apparent tendency of Styela
to preferentially colonise artificial rather than natural substrates. In summary, natural dispersal of
Styela is not considered an important or likely means of this invasive ascidian reaching any of the high
value areas addressed in this report in the foreseeable future.
The relative importance of natural dispersal and human mediated vectors is likely to depend, at least in
part, on the pest’s larval behaviour and the duration of the viable planktonic period. Natural dispersal
in other non-indigenous marine species in New Zealand may play a much more significant role in their
dispersal than is likely for Styela. Patterns of initial spread by marine invaders with dispersive
planktonic propagules are often correlated with the strength and predominant direction of water
movement within the bays in which they were initially found. For example, soon after its discovery in
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Deliverable 3
Port Phillip Bay, Australia, populations of the exotic seastar, Asterias amurensis expanded along the
eastern shoreline, away from the Port of Melbourne, in accordance with known patterns of water
circulation (Parry and Cohen 2001, Parry et al 2001). Natural patterns of spread by invading
fragments of Caulerpa taxifolia (Ceccherelli and Piazzi 2001), the sporophytes of Undaria pinnatifida
(Hay 1990), and the planktonic larvae of Carcinus maenas (Grosholz and Ruiz 1996) have also been
associated with known movements of water currents at different scales of observation.
12.3. Risks to high value areas
RPN estimates of the potential risk of Styela incursions were widely overlapping for the four HVAs,
indicating a wide range of potential risk to each location. All four HVAs are at risk of Styela
incursions. Over approximately the next five years IMEA results indicate the HVAs at greatest risk
are the Marlborough Sounds aquaculture area, followed by the Banks Peninsula aquaculture area,
Akaroa Harbour and then the Poor Knights Islands. The Marlborough Sounds aquaculture area is at
the highest risk of a Styela incursion because of the numerous vectors (particularly commercial and
recreational vessels and aquaculture activities) demonstrably linking it directly to source locations of
Styela in both the North and South islands. The key risks of an incursion to the Marlborough Sounds
are posed by commercial shipping and recreational boating visiting the wider Marlborough Sounds
aquaculture areas and the ports of Nelson and Picton, as well as the Nelson, Havelock, Picton and
Waikawa Bay marina facilities. Fouled vessels have the potential to introduce Styela to any of these
six shipping facilities, or directly to farms. For instance the ports of Nelson and Picton alone receive
more than 500 commercial vessels (>99 gross tonnes) from Lyttelton Port each year. Once a port is
fouled within the Marlborough Sounds it will be difficult to prevent further spread to the mussel
farms.
Considerable additional risk is posed by activities of the Aquaculture industry itself. We initially
considered aquaculture activities “likely” to transport Styela from Lyttelton Port to the Marlborough
Sounds, and subsequent IMEA analysis also identified this pathway as high risk. The risk arises from
the sharing of mussel harvesting vessels such as the St George, and Tardis which are known to travel
between Lyttelton Port and the Marlborough Sounds on a seasonal basis. In the absence of effective
vector management this highly valuable mussel farming industry centre is highly vulnerable to being
colonised by Styela in the short to medium term future (e.g. at some time during the next 5 years).
Initially, an incursion is most likely to occur in a port or marina within the Marlborough Sounds,
followed by secondary spread to farms. Surprisingly, the aquaculture industry does not appear to be
overly concerned with this possibility, perhaps due to their current preoccupation with biosecurity
issues arising from Didemnum vexillum incursions.
The Banks Peninsula aquaculture area was considered the HVA at second highest risk of being
colonised by Styela. Risk to this HVA arose principally from aquaculture activities linked to the
Lyttelton Port and commercial and recreational vessels also associated with Lyttelton Port. The
harvesting vessels Tardis and St George reside at Lyttelton Port for weeks to months each year. They
undertake frequent intermittent trips to a range of Banks Peninsula aquaculture operations where they
spend considerable amounts of time harvesting mussels that are then offloaded at Lyttelton Port. The
St George in particular is known to moor on, or within 20m of a node of high Styela abundance in
Lyttelton Port and is thus at high risk of becoming fouled if hull cleaning and regular antifouling is not
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 115

Deliverable 3
maintained. If colonised, this vessel has the potential to spread Styela directly to both Banks Peninsula
and Marlborough Sounds mussel farms.
Additional risk to the Banks Peninsula aquaculture area arises through the movements of both
commercial and recreational vessels from Lyttelton Port. Commercial vessels such as the tugs and
pilot vessel have a permanent berth adjacent to a node of high Styela abundance and thus have a high
likelihood of becoming colonised. Furthermore, they leave the port on a frequent basis (several times
each day) and travel towards the opening of the harbour (near Port Levy and the closest of the Banks
Peninsula marine farms). Additional charter vessels such as the Lyttelton, are heavily fouled, spend
the majority of time moored adjacent to a Styela hotspot in Lyttelton Port and frequently travel to
locations within the Banks Peninsula HVA.
Akaroa Harbour was identified as the HVA third most likely to become colonised by Styela. The
major risks to Akaroa Harbour are posed by vessel movements from Lyttelton Harbour and the
Auckland region. Akaroa Harbour was considered to be at less risk than Banks Peninsula aquaculture
areas from the nearby Lyttelton Port (see section 9.2 for details), but was calculated to be exposed to
marginally higher risk from commercial and recreational vessels and towed barges arising from
Auckland and Magazine Bay Marina. Although the mussel harvester vessels Tardis and St George are
potentially susceptible to being fouled by Styela while they reside at Lyttelton Port, they do not come
into contact with Akaroa Harbour, where aquaculture operations currently consist of salmon and paua
farming. Commercial vessels based in Akaroa (e.g. scenic charter vessels) are taken to Lyttelton for
maintenance and antifouling paint renewal, after which they return clean to Akaroa Harbour. Based
on our Deliverable 2 data, no large ships move between Lyttelton Port and either the Banks Peninsula
or Akaroa Harbour and ballast water is likely of negligible importance as a transportation vector to
both HVAs.
The Poor Knights Islands Marine Reserve was identified as the HVA least likely to receive Styela.
Nevertheless, a real and ongoing risk of Styela incursion exists for this area. Existing records of
vector movement to the Poor Knights suggest the majority of risk arises from recreational and
commercial vessels associated with the Auckland region and commercial vessel movements from
Tutukaka Marina. The Poor Knights receive frequent recreational and commercial vessel traffic
departing from the wider Auckland region. This is likely to have two affects: (1) direct opportunities
for fouling of natural habitats in the Poor Knights Islands as indicated in the risk assessment, and (2)
increased risk of further introductions to Tutukaka Marina. The Poor Knights Islands are visited
regularly by commercial and recreational vessels resident in Tutukaka Marina. Most of these visits are
1–3 day trips with ecotourism and diving operations predominating. Although Tutukaka Marina
currently contains a very small Styela population (see Deliverable 1), the high residence time of
vessels in the marina and high frequency of vessel visits to the Poor Knights suggests a significant risk
of spreading Styela in the future, particularly if the Styela population of Tutukaka Marina increases in
size. Surveys from Lyttelton Port in November 2005 and 2006 suggest that once Styela is established,
its abundance can increase by at least an order of magnitude within a year. The currently low density
population in Tutukaka Marina therefore does not warrant complacency because of the risk posed to
the Poor Knight Islands.
Some evidence exists to support the relative estimates of risk to the HVAs determined in this
deliverable. The Marlborough Sounds region was calculated to be at highest risk of receiving Styela,
116 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

and to date is the only one of the four HVAs where Styela has been detected. In July 2006 a single
specimen of Styela was found on the hull of a fishing vessel (the “Physalie”) in the Slipway Basin,
Deliverable 3
Nelson. Subsequent rapid delimitation searches also found two individuals on the hull of the vessel
“Marara”, moored on the Calwell Slipway in Nelson Port, both were adults (ca 15 cm long), but only
one was still alive (Morrisey et al 2006). Speculation exists as to how these specimens arrived in the
Marlborough Sounds, but “Marara” was berthed in Auckland for several years before moving to
Nelson, and Styela could potentially have settled on its hull during that period and been transported to
Nelson. Although individuals may have spawned in Nelson (resulting, perhaps, in the presence of the
single individual found on “Physalie”), the July 2006 survey did not find any other Styela individuals
in the surrounding port area, which suggests that population growth and spread has either not occurred
or been limited (Morrisey et al 2006).
12.4. Considerations and limitations to the risk assessment
Our initial qualitative estimates of pathway risk are generally intuitive and can be determined
relatively quickly, but did not include estimation of uncertainty around risk measures. The use of
interval arithmetic for quantifying risks using the IMEA approach provided a simple approach to
obtain values for comparing risks posed by source populations, vectors and the various links between
sources and HVAs. Furthermore, they allow the relative risk of Styela incursions in HVAs to be
explicitly examined from the sum of all component risks. Importantly, the IMEA approach allowed us
to incorporate different levels of uncertainty in the assessment (Hayes 2002), and as such we feel it
provides a more informative and rigorous approach to the risk assessment. The IMEA risk analysis
could be expanded and improved by circulating the relevant data set to additional marine biosecurity
experts who could independently classify each of the components of the risk model. This would
provide an additional measure of the relative confidence around each of the risk estimates presented
here.
Our assessment of risk was focused on key high value areas at risk of colonisation from areas of New
Zealand’s coastline where Styela has established populations. The risk assessment is based on
tangible elements of known vector movement patterns. It attempts to predict the relative risk of Styela
arriving from known potential source locations rather than providing probabilities of when or where
novel populations may become established. Given the stochastic nature of many aspects of each step
in the invasion process, our pathway risk analysis (and the risk scores) should be viewed as a guide to
relative risk. Predicting the statistical probability of invasions remains elusive due to the lack of data
on the probability of pest species surviving various phases of the invasion pathway. For instance in
order to reliably predict the probability that a particular vessel successfully introduces Styela from a
fouled location to a high value area by hull fouling the probability of each of the following sequential
events must be estimated.
1. The vector’s hull must become fouled by larval propagules of Styela.
2. Styela must grow to reproductive size and survive the passage to recipient location.
3. Viable larvae must be released at the recipient location.
4. The larvae must then settle, survive, grow and reproduce in the novel environment.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 117

Deliverable 3
In this deliverable we characterised the risk of Styela being spread from four potential sources to high
value areas via four key human-mediated vectors and natural dispersal. We focused on the most likely
vectors and pathways of domestic spread, however additional sources of unquantified risk may also
exist. For instance, unquantified risk may arise from additional source populations around New
Zealand that potentially have become established since the nationwide surveys were completed in
November 2005 (Gust et al 2006a). Additional shipping facilities could have become colonised either
from the movement of domestic vectors or potentially additional inoculations of Styela from visiting
international vessels. Genetic evidence suggests that separate origins of the Styela populations in
Auckland and Lyttelton (Sharyn Goldstien, University of Canterbury pers comm), and additional
inoculations are feasible. We also do not consider stepping stone models of possible Styela spread,
where intermediate locations may become fouled from the source locations if vectors travel indirectly
to HVAs. As such we may underestimate the total risk to HVAs via human-mediated vectors
(particularly recreational vessels) that move from source populations to HVAs via intermediate Ports
or Marinas that may now be fouled.
Natural dispersal via planktonic propagules is considered to pose a negligible risk of spreading Styela
from source locations to HVAs. However it is possible that juveniles or adults could also be spread by
natural dispersal if they recruit to floating objects that are then dispersed by wind or waves. Another
potential mechanism for the spread of Styela not considered in our vector pathway analysis is the
possibility of deliberate spread. It currently seems very unlikely that people would deliberately spread
this pest in New Zealand waters, and if they did it is not obvious which areas would be at greater
threat of introduction. We mention these two mechanisms as additional possibilities and unmanaged
risks, though we feel they are very unlikely to occur.
The pathway risk model adopted in this deliverable considers the likelihood of transport vectors but
does not explicitly consider the risk of Styela becoming established once it arrives, or the risk of pest
densities arising. It is likely for instance that Styela would establish higher densities in areas with
extensive artificial surfaces rather than natural habitats. As such the risk of Styela becoming
established on artificial structures associated with the Port of Nelson, or mussel farms in the
Marlborough Sounds aquaculture area may be considerably higher than in native communities on
rocky reefs at the Poor Knights Islands. The current risk assessment also does not explicitly consider
the possible lag time between establishment and potential population increase, which may vary
between locations. For instance it appears that the Styela population in Lyttelton Port did not increase
rapidly in abundance for at least 4 years after it was first detected. International experience also shows
that Styela has taken widely varying periods to establish high densities (and in some cases pest
densities have not yet eventuated) so the lag time between arriving in an HVA and having an
appreciable impact is likely to take years.
Pathway risk assessments provide reliable information on the relative risks of Styela becoming
established in particular locations but prediction of population dynamics and hence potential impacts
are more difficult (Williamson 1999). An adequate knowledge of underlying invasion processes,
likely population growth and density-dependent effects is seldom available, with a general consensus
that even with detailed study the prospect of making reliable predictions of invasion success is remote
(Kareiva et al 1996, Forrest et al 2006). Determination of the likelihood that an invader will reach
pest density will often rely on expert judgement and consideration of likely success based on factors
118 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

such as the invader’s life history characteristics, and the physical and biological attributes of the
recipient environment (Forrest et al 2006).
This deliverable was concerned with assessing the pathway risks, and relative risks of Styela being
Deliverable 3
transported from potential source regions to HVAs. We suggest that to provide clear justification for
management priorities of this species the next step in a full risk assessment is to explicitly assess the
risk associated with reaching pest densities if Styela is introduced to each HVA, followed by an
avaluation of potential impacts Styela may have at a range of densities. Although a formal risk
assessment process has not been undertaken to assess these two components of post-establishment risk
to HVAs, we made some preliminary predictions from existing information. For instance it seems
likely that Styela will proliferate and achieve highest densities in areas of artificial rather than natural
substrata. As such, HVAs associated with mussel aquaculture activities that involve extensive
networks of backbone lines, rope droppers, buoys and moorings and are more likely to develop high
density Styela populations than HVAs with extensive natural habitats and high native biodiversity
values. However there is even uncertainty in inferring Styela’s impact on native assemblages on the
basis of its density and a limited knowledge of its ecology, as highlighted by Ross et al (2007). These
authors suggest that to prioritise management efforts, quantitative assessment of real impacts is
imperative to assess the risk of ecological damage from species such as Styela clava.
Reconciling the relative financial, biodiversity, aesthetic and cultural values of these distinctly
different types of highly valued marine areas is not simple. There is as yet no universally accepted
way to measure or estimate the potential impact of an introduced species. Indeed this is often the least
objective part of any bio-invasion debate because stakeholders and interest groups have different
values and opinions about what is ‘harmful’ and what therefore constitutes a negative impact (Hayes
et al 2004). Fundamentally financial, biodiversity, aesthetic and cultural values are measured in
different units, with economic values generally being protected before biodiversity values.
The worst case scenario of extensive pest densities of Styela in the Marlborough Sounds aquaculture
area potentially threatens profits and the sustainability of a growing industry aiming to be worth
approximately one billion dollars by 2025 (http://www.nzmic.co.nz/ accessed May 2007). In the face
of unknown biodiversity impacts, Styela currently represents more compelling immediate risks to the
financial interests and economic development of the aquaculture industry than it does to the tourism
industry and visitation rates of the unique high biodiversity area of the Poor Knights Islands.
Economic rationalism and the protection of aquaculture industries in the short term seems likely to
take priority over the need to protect biodiversity values which are probably less at risk, and more
difficult to place a financial value on.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 119

Deliverable 4
Deliverable 4: Determine, categorize and prioritize key sites (risk areas) within
each location, based on the information obtained from deliverables 1-3, for
efficacy trials of control measures to mitigate the spread of Styela to high-value
areas.
13. Methods
We sought to identify key sites or “risk areas” within each of the three delimitation locations for
potential population management efficacy trials. We consider key sites as artificial habitats containing
particularly high densities of Styela relative to the surrounding population. These key sites are likely
to provide major contributions to larval production within locations, and may indicate the sites where
moored vectors may be at highest risk of becoming colonised by Styela. We prioritize key areas on
the basis of: (1) adult Styela abundance, (2) the strengths of likely links with human-mediated vectors,
and (3) the accessibility and feasibility of undertaking diving experimental treatments or monitoring at
each site. In ranking accessibility we also consider the likely disruption to port or marina activities by
conducting management trials such as plastic wrapping at each key site. Patterns of Styela abundance
were identified from the detailed information on distribution and abundance determined by field
surveys in Deliverable 1. Vector activity known in the vicinity of the key sites is derived from data
collected during Deliverable 2 and personal observations in the field.
14. Results
Three key sites were clearly identified in Lyttelton Port. However, sites of locally high Styela density
were not clearly evident in either Tutukaka Marina or Magazine Bay Marina. In both marinas we
selected sites that contained Styela and are broadly representative of the key artificial habitat types
present in the location, but do not recommend them as suitable for management control trials. The
seven key sites identified across the three locations and their attributes are summarised in Table 4.1.
14.1. Tutukaka Marina
No key sites of high Styela abundance were evident at Tutukaka Marina from either the November
2005 or November 2006 delimitation surveys (Figure 1.12). Very low densities of Styela were
detected during both surveys, with a total of only 4 individuals detected over both surveys.
14.2. Lyttelton Port
Three key sites of high Styela abundance were identified from Lyttelton Port; The western side of #2
Wharf, pontoons between Z Wharf and Gladstone Pier, and the A and B pontoons. All key sites are in
eastern half of the Port’s inner harbour (see Figure 1.18). The three key sites are characterised by the
highest adult Styela densities encountered during the delimitation survey (see Figure 1.20).
Furthermore, each site is associated with areas of high juvenile Styela abundance (Figure 1.20). Two
of the key sites are constructed of foam-filled concrete pontoons anchored to wooden piles. The
western side of # 2 Wharf is constructed of wooden piles extending to a depth of approximately 10m.
120 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 4
Table 4.1: Key sites identified for potential efficacy trials of control measures. Rank indicates the suitability of
each site for possible trials, 1-3 indicate highest priority, while those marked 4-7 are low priority.
Styela source
populations
Tutukaka
Marina
Lyttelton Port Western side
of #2 wharf
Pontoons
between Z
Wharf and
Gladstone
Pier
The A and B
pontoons
Magazine Bay
Marina
Key Sites Construction details Estimated
maximum Styela
density
(No. per m 2 )
Jetty M Modern foam filled
concrete pontoons
Jetty D Wooden piles and
wharf
Wooden piles and
wharf
Modern foam filled
concrete pontoons
Modern foam filled
concrete pontoons
Sector B Derelict wooden piles
and wharf
Sector D Wooden piles and
wharf
Key links to nearby
vectors
1 Commercial and
recreational
vessels
1 Commercial and
recreational
vessels
11-100 Commercial
vessels
11-100 Aquaculture
activities
1-100 Commercial and
recreational
vessels
1-10 Recreational
vessels
1-10 Recreational
vessels
Diver
Access
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 121
Rank
High 6
High 7
Med. 2
High 1
Low 3
Med. 4
Med. 5
Access to the A and B pontoons is expected to be problematic for efficacy trials of control measures
since it is the busiest hub of small commercial vessel activity within Lyttelton Port. Hourly
movements include the Black Diamond ferries moving passengers to and from Diamond Harbour.
Ecotour vessels such as the Fox 2 and other wildlife viewing vessels use the A and B jetties, often for
daily excursions. In addition pilot boats and tug vessels are moored within 20m of A and B pontoons
on the Tug jetty and these vessels frequently come and go to assist large ships entering and exiting the
port. Diving activities in the vicinity of the A and B jetties are problematic due to the frequent and
unpredictable activities of some of these vessels. In contrast the pontoons between Z Wharf and
Gladstone pier, and the western side of # 2 Wharf are subject to less frequent vessel movements and
pose considerably less risk to divers.
14.3. Magazine Bay Marina
No key sites of high Styela abundance are apparent in Magazine Bay Marina. Instead we selected two
sites known to previously contain Styela (see Figure 1.17), that represented typical construction
techniques and materials for the location. Diver access to the sector B and D sites is not problematic
from a vessel movement point of view, but water clarity in the marina is typically very poor. Water
clarity measures

Deliverable 4
14.4. Viaduct Basin, Auckland
We suggest that the Viaduct Basin in Auckland’s Waitemata Harbour also be considered as a potential
location for management control trials. It is known to contain a widespread and abundant Styela
population (Gust et al 2005), has numerous Styela fouled pontoons, wooden piles and concrete walls
suitable as experimental units, and is also relatively protected from the weather. Water clarity values
are fairly standard for New Zealand port and marina environments, though polluted water and run-off
from Auckland city poses a risk to divers, particularly after rain. The abundance of Styela, and
replicated array of structures in the location represent potential advantages over either of the marinas
considered here.
15. Discussion
Key sites identified in Lyttelton Port are those currently most heavily fouled by Styela and with the
potential to produce the highest numbers of larvae. These three key sites presumably represent the
greatest threat of inoculating nearby vectors given the short distance dispersal of larvae indicated in
Deliverable 1. Furthermore these key sites are likely to contribute a large proportion of the total
reproductive output of the Lyttelton Port population. Control measures that either remove or reduce
the density of Styela from these sites may both slow the growth of the population in this location, and
reduce the risk of vectors becoming fouled. The coarse spatial resolution of the Lyttelton Harbour
hydrodynamic model (presented in Deliverable 3) currently precludes its use for investigating the fine
scale study of particle movements within the inner port area. As such it is unclear whether the key
sites selected are likely to widely export larvae to other sites within the port.
The pontoons between Z Wharf and Gladstone Pier were selected as the highest priority site for
possible control measure efficacy trials for a number of reasons. They are extensively covered in adult
Styela, offer ready access for divers and above-water operations, are not exposed to regular boating
movements, and are closely linked to a potential vector with the Aquaculture industry. When in
Lyttelton Port, the mussel harvester barge St George is frequently moored within 20m of this location.
It was previously identified as a key vector with the potential to spread Styela to Banks Peninsula and
Marlborough Sounds Aquaculture areas. Treatment of the pontoons between Z Wharf and Gladstone
Pier may reduce (but probably not eliminate) the probability that this and other vessels mooring
nearby will become fouled with Styela.
The risk analysis in Deliverable 3 identified Lyttelton Port and the Auckland regions as being the
source populations at highest risk of exporting Styela to HVAs. Conversely Magazine Bay Marina
and Tutukaka Marinas with currently relatively small Styela populations were considered to pose less
of a threat. Within both marinas there are no clear candidate sites meeting the criteria of “key sites”.
The widely dispersed adult Styela populations at Tutukaka Marina and Magazine Bay Marina have
mean densities of approximately 0.001 and 0.01 individuals per m 2 respectively. As such we
recommend control measures be implemented at either Lyttelton Port or in the Auckland region first.
Representative sites within Magazine Bay Marina were selected as possible sites for trial control
measures. However there are a number of practical limitations to conducting experimental treatments
in Magazine Bay Marina that suggest it is not well suited to trials of management control options.
122 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Water clarity is typically very low in Magazine Bay Marina (typically

Deliverable 5
Deliverable 5: Design a population management programme for Tutukaka Marina,
Lyttelton Port and Magazine Bay Marina.
This section describes the design of a population management programme for Styela clava in each of
the three locations that were the focus of this study; namely Tutukaka Marina, the Port of Lyttelton
and Magazine Bay Marina in Lyttelton Harbour. The design of the programme draws upon
information described in earlier sections of the report on the status of Styela populations in each
location (Deliverable 1), and the relative risks of spread of Styela to nearby High Value Areas (HVAs)
by a variety of potential vectors (Deliverables 2 and 3).
As stated in the MAFBNZ Request for Proposal, the overall aim of the management programmes
should be to control populations of Styela in these locations to mitigate the risk of it spreading to
HVAs. Four HVAs have been considered in the context of this report: the Marlborough Sounds
aquaculture production area, Banks Peninsula aquaculture production area, Akaroa Harbour and the
Poor Knights Islands Marine Reserve.
Each management plan consists of a set of objectives for the Styela population concerned and
management strategies that could be implemented to achieve each objective. The final section
provides an evaluation of the proposed strategies.
16. Methods
16.1. Development of management objectives
Draft objectives for management of Styela at each location and strategies for achieving these
objectives were developed during a workshop held between the NIWA and MAF Biosecurity NZ
Project teams on 12 October 2007.
For each of the three Styela populations (Tutukaka Marina, Lyttelton Port and Marina), management
strategies were grouped into two, complementary approaches. Each approach was associated with
several independent management objectives:
i Direct management of the Styela population
Management Objectives:
• No population management
• Local eradication
• Maintenance of population at or below current levels
• Maintenance of population at or below specified level
124 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

ii Management of potential vectors entering and leaving the infested location
Management Objectives:
• No vector management
• Minimise spread to HVAs
• Prevent spread to HVAs
• Minimise/prevent spread from source population
Deliverable 5
Strategies and tools for achieving each management objective, along with recommended combinations
of options, are described and evaluated in sections A (population management), B (vector
management) and C (combination of population and vector management). Each management
objective is evaluated and prioritised using the following criteria adapted from The Biosecurity Act
1993 (discussed in (Forrest et al. 2006)):
• Effectiveness
• Practicality
• Acceptability to stakeholders
• Likely side-effects
• Legality
• Likelihood of success
• Cost of implementation, and
• Degree of uncertainty
To derive an estimate of the relative feasibility, or merit, of the nine management objectives we
allocated scores of 0–5 to each evaluation criterion for each management objective. We perceived that
some criteria may carry more importance in the decision making process and therefore gave higher
weighting to the following criteria: effectiveness (score x 3), acceptability to stakeholders (x 2), sideeffects
(x 2), likelihood of success (x 3), cost (x 3) and degree of uncertainty (x 2).
16.2. Simulations of the influence of some management objectives on the spread of Styela
We used an epidemiological model developed by NIWA to simulate the spread of Styela around New
Zealand and to the identified HVAs in the presence or absence of population and vector management.
Our model simulates the dispersal of a hypothetical invader via hull fouling on recreational vessels
and is parameterised using empirical field observations and responses from a survey of yacht owners
in New Zealand. It is important to note that this model was not specifically developed or
parameterised to simulate the spread of Styela. Any conclusions derived from our simulations concern
the relative differences in spreading rate under no management, population management or vector
management, but not the specific rate at which model locations became or may become colonised over
time.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 125

Deliverable 5
The starting conditions of all simulations specified a geographically restricted distribution of Styela
consisting of self-sustaining and continually growing populations located in Lyttelton and Auckland
(Waitemata Harbour). During the NIWA-MAFBNZ workshop held in December 2007 it had been
agreed to include the Auckland population because: (i) it is very likely to largest nationwide
population of Styela, and (ii) this region represents a central node in New Zealand’s network of yacht
movements and yachts frequently travel between Auckland and the Poor Knights Islands marine
reserve. It was agreed to exclude the Tutukaka population from the model because only four
individuals of Styela had ever been encountered at the Tutukaka Marina and it is unknown whether
there actually is a viable population.
The model incorporated parameters for the following events: (i) colonization of yachts in ports and
marinas by Styela if populations are present, (ii) transport of Styela on yachts hulls to their
destinations, (iii) successful or unsuccessful establishment at new locations, (iv) gradual increase in
population size in locations successfully colonised by Styela, and (v) colonisation of further yachts and
spread of Styela to further locations. The model was parameterised using empirical data on the
susceptibility of yacht hulls of different antifouling paint ages to colonisation by fouling organisms,
and the travel and maintenance history of approximately 1,300 domestic and international yachts
surveyed around New Zealand. For details on the model parameterisation refer to Appendix 7.
16.3. Simulation of management strategies
Our objective was to examine the spread of Styela to the four HVAs (Banks Peninsula, Akaroa
Harbour, Marlborough Sounds and the Poor Knight Islands) under a range of possible management
scenarios. The 36 locations included in the model did not cover the HVAs in their entirety and
representative locations had to be used instead:
i The only model location that fell within the Banks Peninsula and Akaroa Harbour HVAs
was Akaroa (township with mooring facilities). The spread of Styela to Akaroa was used as
a representation of the spread to both HVAs.
ii The model locations that fell within the Marlborough Sounds HVA were Nelson, Havelock,
Picton and Waikawa Bay. The spread of Styela to these locations was used as a
representation of the spread to the Marlborough Sounds HVA.
iii Our model did not include the Poor Knight Islands as a location. The risk of spread of Styela
to this HVA can thus not be adequately addressed by using the model. To examine whether
Styela population management at the Tutukaka Marina had any influence on the spread of
the species from this location we examined infection rates of locations to the north of
Tutukaka (Opua, Russell, Kerikeri). However, this approach needs to be treated with caution
because it assumes that yachting traffic to these locations predominantly passes through
Tutukaka.
We ran 100 iterations of the model for each of four management options, over a simulated period of
10 years:
i No management. Lyttelton and Auckland were seeded with a Styela population covering
0.11 % of available habitat.
126 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

ii Vector management. Lyttelton and Auckland were each seeded with a Styela population
Deliverable 5
covering 0.11 % of available habitat. Increased vector (yacht) maintenance was simulated
by decreasing the proportion of susceptible yacht hulls. Ninety percent of yachts that
normally receive new antifouling paint after a period of ≥ 18 months (when susceptibility to
fouling is very high) instead received new paint after 12 months (susceptibility to fouling
low to moderate).
iii Population management A. Lyttelton and Auckland were each seeded with a Styela
population covering 0.11 % of available habitat. Population size in Lyttelton was then
reduced to 50 % of the “existing” population (i.e. 0.055 % of habitat).
iv Population management B. Lyttelton and Auckland were each seeded with a Styela
population covering 0.11 % of available habitat. Each time the Tutukaka Marina became
colonised by Styela, a successful eradication campaign was simulated resulting in the
removal of Styela from this location.
Modelling of these strategies had been decided on in consultation with MAFBNZ during the
December 2007 workshop. For each simulated strategy, we determined: (a) the number of model
locations (nationwide) that became colonised by Styela over the 10-year period, (b) the time at which
Styela colonised locations within the HVAs, (c) the probability of infection of locations within the
HVAs (proportion of 100 model runs that resulted in infection), and (d) the number of infected yacht
arrivals at the model locations within the HVAs.
We did not use statistical tests to compare outcomes of modelled management options because the
replicate model runs for each scenario are not strictly independent. Instead, we calculated 95 %
confidence intervals for each response variable and management scenario and interpret the results
based on these. General model results are incorporated in the discussion of management objectives
below. A detailed account of the results of the simulations is provided in Appendix 7.
17. Management objectives and strategies: Tutukaka Marina
17.1. Status summary
Surveys of Tutukaka Marina in November 2006 detected only two adult Styela clava, at widely
separated sites within the marina. The surveys covered a large proportion of the potential habitat for
Styela within the marina area and the water clarity and sea state during the survey provided relatively
good search conditions. Detection of the two individuals in 2006 suggests that the population has
persisted at a very low density since the initial survey of Tutukaka in November 2005 when, again,
only two specimens were detected. It is also possible that the specimens represent a secondary
incursion from another source population.
Because of the distance of the Poor Knights Islands marine reserve from known populations of Styela,
the short larval phase of this species, and the deep waters surrounding the reserve, it is more likely that
Styela would reach the Poor Knights Islands associated with a human transport pathway than by
natural dispersal. Tutukaka Marina is the base for many of the commercial tourism, diving and scenic
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 127

Deliverable 5
tour operators that frequent the Poor Knights Islands (refer to Deliverable 2). These vessels, along
with some recreational vessel traffic, comprise the majority of potential pathways by which Styela
may be transported from Tutukaka Marina to the Poor Knights Islands. There is no known
aquaculture vector activity at this location. Commercial fishing pathways are limited to infrequent and
short-term visits by Tutukaka-based vessels to the Poor Knights Islands to shelter or over-night. A
large increase in the size of the Styela population in Tutukaka Marina could significantly increase the
risk of its successful establishment at the Poor Knights Islands. Vessel traffic originating from the
Hauraki Gulf also represents a potentially significant of suite of vectors by which Styela may be
introduced to this HVA or re-introduced to the Tutukaka Marina (refer to Deliverable 2).
17.2. Options for managing the risk of Styela spread from Tutukaka Marina
Nine possible management objectives were identified for Tutukaka Marina. These are described in
Table 5.1 and are summarised in the sections below.
Table 5.1: Styela clava management objectives for Tutukaka Marina. PKI: Poor Knights Islands.
Management objectives Focus Strategy
1 No population management (Population) Do nothing to manage the population
2 Local eradication:
“Non-detection over a
specified time by surveys of a
specified level of detection
probability”
3 Maintain population at or
below current levels (of
abundance or distribution)
4 Maintain population at or
below specified levels (of
abundance or distribution)
Population Survey and remove entire population, followed by surveillance and
maintenance.
(Vectors) (Should be coupled with management of incoming vectors to
prevent re-introduction of Styela.)
Population Monitor the population with a survey of sufficient power to
determine when the current level of abundance or distribution (in
this case the level detected in the Nov. 2006 survey) has been
reached or exceeded. Control action is implemented if this level is
exceeded by a specified amount (e.g. doubling of distribution).
Population Monitor the population with a survey of sufficient power to
determine when a pre-specified level of abundance or distribution
has been reached or exceeded. Control action is implemented if
this level is reached or exceeded by a specified amount.
5 No vector management (Vectors) Do nothing to control the movements or hygiene of potential
6 Minimise spread to HVAs
vectors coming into, mooring in or leaving the marina and travelling
to HVAs
Vectors: Voluntary management of infested and potentially infested vectors
- outgoing and
bound for HVAs
departing for the PKI.
• Use of social marketing to elicit change in vessel hygiene.
• Communication strategy specific to key risk groups
(recreational vessel owners and commercial tourism
operators).
128 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Management objectives Focus Strategy
6 Minimise spread to HVAs
(continued)
7 Prevent spread to HVAs
8 Minimise/prevent spread from
marina
9 Combinations of management
options
- outgoing and
bound for HVAs
(cont.)
- incoming
vessels
Vectors:
- outgoing and
bound for HVAs
Vectors:
- all outgoing
vectors
Population +
vectors
Deliverable 5
• Encourage an industry code of practice and accreditation that
includes monitoring hull cleaning and antifouling.
Risk profiling
Encourage marina operators to implement their own risk profiling
and management of incoming vessels to enforce hygiene
requirements.
Regulatory management:
17.3. A: Population management options (Tutukaka Marina)
17.3.1. Option 1: No population management
Monitor compliance and outcomes.
• Incorporate conditions for vessel hygiene monitoring and
compliance in resource consent for operation of Tutukaka
Marina.
• Incorporate conditions for vessel hygiene and compliance in
permits for commercial operators visiting the PKI.
• Implement a controlled or restricted area around the PKI where
there are strict requirements for vessel hygiene.
Monitor compliance and outcomes.
As Objective 6 above but includes all vessels and vectors which
depart the marina, regardless of their destination
It is recommended that all population management objectives be
coupled with some level of vector management to reduce likelihood
of re-introduction of Styela and/or to minimise the possibility of
Styela being introduced to the PKI.
This option involves no specific management of the Styela population in Tutukaka Marina or of
vectors entering or leaving the marina (Table 5.1).
Effectiveness
Without any management, it is likely that there will be an increase in the size, density and distribution
of the Styela population within Tutukaka Marina over time, and a concomitant risk that it may be
spread to other locations, including the Poor Knights Islands. The time frame and magnitude of any
changes in the population size are uncertain.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 129

Deliverable 5
Practicality
This option requires no additional resources or changes to current management of the marina and its
operations.
Acceptability to stakeholders
There are no direct effects of this option on stakeholders, unless Styela populations became large
enough to impact on vessel maintenance and operation. However, because there is increased risk of
Styela spreading to nearby natural habitats and HVAs, particularly the Poor Knights Islands, there is
strong potential for adverse environmental outcomes. In this context, doing nothing is likely to be
unacceptable to stakeholders, particularly those who have strong financial, social or cultural
connections to potentially affected environments, such as the Poor Knights Islands.
Likely side-effects
The most immediate side-effect of this option is a potential increase in risk of spread of Styela to more
valued environments, including the Poor Knights Islands. MAF Biosecurity NZ prepared a summary
of possible effects of Styela on subcomponents of core New Zealand values as part of its Organism
Impact Statement (OIA) for Styela (Kluza et al. 2005). This summary is reproduced in Table 5.2.
The values encompassed by the Poor Knights Islands include a number of these subcomponents:
biodiversity, habitat, protected areas, trophic interactions, and aesthetics/diving. Although there is
uncertainty over the actual effects Styela may have on these values, they are generally considered to
have ‘moderate’ consequences.
Legality
This option involves no change to the current management regime.
Likelihood of success
Not applicable.
Cost of implementation
There are no direct costs involved with implementation of the ‘do nothing’ option.
Degree of uncertainty
The outcome of this strategy is associated with a moderate degree of uncertainty. Styela was
discovered at the Tutukaka Marina 3 years ago (in 2005) and, in the absence of management action,
has neither noticeably increased in local abundance nor been reported from the Poor Knights Islands.
However, no thorough target surveys have been conducted for Styela in the Poor Knights Islands that
would allow us to state with confidence that the species is not yet established in this HVA. Occasional
inoculation of this HVA by vectors originating from the Tutukaka Marina may take place. The
unmanaged population at Lyttelton Port has increased in density since 2005, and this may also occur
for the unmanaged Tutukaka Marina population in the future.
130 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Table 5.2. Consequences of Styela effects on core value subcomponents.
Subcomponent Consequence
Biodiversity Minor to Moderate—May reduce local biodiversity, but tends to have a patchy distribution.
Habitat Minor to Moderate—Can overgrow biotic and abiotic structures, but tends to have a patchy
distribution.
Deliverable 5
Protected areas Moderate—A function of biodiversity and habitat consequences; by virtue of competing with native
species for space and food, could alter the conservation value of an area.
Trophic interactions Moderate—Large aggregations may alter local resource availability. Cumulative effects of introduced
ascidians and other filter-feeders may cause a shift in trophic structure towards an ecosystem
dominated by epibenthic/benthic biomass rather than pelagic biomass.
Aquaculture Major to Significant—Extensive macrofouling of gear and stock increase operational costs
(handling, maintenance and control efforts), and can cause diminished returns due to poorer
condition and increased discards of fouled stock. Infestations not known to be reversible.
Vessels/moorings Moderate to Major—Potential mitigation measures or best management practices may call for
greater investment in maintenance/cleaning efforts for owners and operators of vessels and marinas.
Morbidity Moderate—This is an arbitrary assignment of a median value, given a lack of information on the
severity and duration of asthmatic condition.
Aesthetics/diving Moderate—A function of potential effects on biodiversity and habitat structure/composition. Styela
aggregations may reduce aesthetic value, in turn altering patterns of use/tourism.
Vessels/access Moderate to Major— Potential mitigation measures or best management practices may call for
greater investment in maintenance/cleaning efforts; potential for movement restrictions into or out of
affected areas, or into high-value areas (e.g. aquaculture sites, marine reserves), which could affect
patterns of commercial and recreational use.
Recreational harvest Moderate—A function of potential effects on biodiversity and habitat structure/composition.
17.3.2. Option 2: Local eradication
Eradication occurs when every potentially reproducing individual has been removed from the affected
area (Myers et al. 1998). However, like extinction of a species, eradication is impossible to verify
directly. For this reason, it is usually defined operationally through the outcomes of surveillance, with
reference to specified levels of confidence in the detection of individuals by the survey and to a time
period over which no detections have occurred (Regan et al. 2006). In this context, we define local
eradication of Styela to mean:
“removal of all detectable individuals from Tutukaka Marina and continued non-detection of Styela
within the marina for a period equivalent to at least the length of two generations, when a survey
equivalent in power to that used in this study is implemented.”
Overseas research suggests that Styela has a lifespan of up to 3 years (Kluza et al. 2005), meaning that
any programme to declare eradication using this definition would need to continue for at least 6 years.
Because of the very low abundance of individuals recorded in the 2006 surveys of Tutukaka Marina
the recommended tool for removal of Styela marina is hand-picking by divers. This is the most
efficient technique for targeting low densities of Styela. Removal of individuals would be
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 131

Deliverable 5
accompanied by regular surveillance of the marina that must meet detection standards at least as great
as that achieved in the survey described in Deliverable 1.
Effectiveness
Removal of Styela to levels of abundance below that detected in the November 2006 will ensure that
risk of infestation of vectors and spread to other areas, including the Poor Knights Islands, will remain
low. Hand removal is only effective and practical for very small, low density infestations (Thresher
and Kuris 2004), as is currently the case in Tutukaka. However, it relies on visual detection of
individuals and, as a consequence, small and cryptic individuals may be missed (Hewitt et al. 2005).
Stress induced in reproductive Styela individuals by physical removal can cause the release of larvae
(M. Page, NIWA, pers. comm.). Risk of spawning (which may lead to renewed settlement) will be
minimised by conducting removal operations outside the local population’s reproductive season and
by removing individuals in a, as far as possible, non-destructive manner (e.g. severing the stalk instead
of holding on to, and compressing the test). Provided these measures are taken and all material is
disposed of on land, manual removal by divers will most likely be very effective.
The relatively small size and semi-enclosed layout of Tutukaka Marina make the use of more intrusive
techniques, such as bunding and draining, de-oxygenation and/or flushing of the waterway with
freshwater, or application of chemical biocides to poison the marina waters possible options. At the
correct level of application, chemical treatments are likely to be more effective than hand removal at
killing all Styela within the marina. However, they are also likely to be considerably more
expensive 14 , less acceptable (Thresher and Kuris 2004) and will require consents from a range of
statutory authorities (e.g. Northland Regional Council, Maritime Safety Authority, and Environmental
Risk Management Authority).
Re-introduction of Styela on vessels entering Tutukaka is possible under this option, as it contains no
measures to manage vectors. Tutukaka is a common port of call for Hauraki Gulf-based recreational
vessels travelling along the Northland coast, particularly during summer months. Our model
simulations indicate that approximately 180 yachts travel from the Hauraki Gulf region to the
Tutukaka Marina every year. Population genetics work undertaken in the Hauraki Gulf indicates a
high degree of vectoring throughout the Gulf with multiple incursions of Styela at a range of sites
(S. Goldstien, pers. comm.). This indicates that, in the absence of vector management, re-introduction
is a very strong possibility. Eradication may only be achieved if this source of immigration to the
Tutukaka population is managed
Practicality
Eradication is only feasible when the following criteria can be met (Bomford and O'Brien 1995):
• all reproductive animals are at risk of removal and can be detected at low densities
• the rate of removal from the population exceeds the rate of increase
14 Eradication of the Black Striped Mussel in Darwin from a marina of similar size cost in excess of A$2 million, not
including personnel costs
132 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

• immigration to the population is zero, and
• there is general public acceptance of the control programme.
The most significant challenge for this strategy involves detection of all individuals before they
become reproductive. Styela are hermaphroditic so that a single individual can produce viable
Deliverable 5
offspring. Juvenile Styela and new recruits are very difficult to detect visually, particularly when the
water clarity is poor. This means that all adults may be removed from the population, but a supply of
new recruits remains undetected. Visual surveys by divers and shore searches may be complemented
by the use of larval monitoring techniques in the surveillance plan. Plankton trawls which use a gene
probe to screen the samples for the target species can be a cost-efficient way of monitoring for
freedom from infestation (Hayes et al. 2005), particularly as sensitive, robust genetic markers have
been developed for Styela clava (Goldstien unpubl. data). Alternatively, passive larval collectors
such as ropes or settlement plates may be useful for detecting juvenile Styela. An integrated
surveillance programme would include both visual surveys by divers for adult Styela and larval
monitoring techniques.
Acceptability to stakeholders
Physical removal by divers is generally viewed as among the most acceptable of options available for
eradication or control of marine pests (Kuris and Thresher 2004).
Likely side-effects
An eradication campaign may affect the operation of the Tutukaka Marina for the period of the
operation. The eradication and follow-on monitoring activities are likely to impose minor restrictions
on vessel movements in the marina. Manual removal of Styela will have no ecological effects,
whereas the application of chemicals may be associated with ecological impacts on non-target biota
inside and outside the marina. However, the magnitude of such impacts is dependent on the size of the
Styela population at the time of the eradication campaign.
Legality
As Styela clava is an Unwanted Organism, removal and disposal of Styela would require approval
from MAF Biosecurity NZ under the Biosecurity Act 1993. Given the small quantities of individuals
anticipated for disposal, consent from local authorities for disposal on land is unlikely to be required.
Likelihood of success
Eradication campaigns have been successful on a number of occasions, and exclusively when the
target species had been discovered shortly following its establishment at the location when its
abundance and density were restricted (Anderson 2005, Culver and Kuris 2000, Ferguson 2000). Use
of effective and appropriate removal techniques, and rigorous monitoring for survivors or reintroduced
individuals of Styela, should afford this management objective a relatively high likelihood
of success.
Cost of implementation
The major costs involved in this option are for regular monitoring of adult and larval Styela. To
achieve the same level of visual search effort achieved in the November 2006 survey would require a
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Deliverable 5
field team of six people (four divers and two support crew) for three days. Using the cost estimates
published by Hayes et al. (2005 15 ), this equates to around $9,500 for a single survey, not including the
costs of transport, accommodation, reporting and project management. In addition, use of larval
monitoring techniques would cost around $2,300 per survey if a gene probe was used to screen
plankton samples, or ~$2,500 per survey if larval collectors were deployed and monitored.
Styela become reproductively mature at between 2 and 7 months of age (Kluza et al. 2005). To
ensure that any new recruits are detected early, visual surveys should initially be carried out at least
quarterly, so that new individuals can be removed before they reach reproductive maturity. Once
sequential surveys begin to return no individuals it may be possible to reduce the frequency of survey
to 6-monthly.
The optimal time to stand-down monitoring and eradication operations is a trade-off between the costs
of maintaining emergency operations, including on-going surveys (Cs), and the cost of escape
(including likely impacts) if eradication is declared too soon (Ce). A rule-of-thumb can be used to
calculate the optimal number of surveys. This is given as:
n* =
⎧ − Cs
⎫
ln⎨
⎬
⎩Ce
ln( r)
⎭
,
ln( r)
where r = p(1-q) is the probability that the pest is not detected, but is still present in the survey area.
Guidance for calculating this decision-point is provided in (Regan et al. 2006).
Some of the costs of monitoring may be defrayed through involvement of local stakeholders in, for
example, monitoring larval collectors or undertaking above-water searches for adult Styela. There is
strong local interest in the issue from dive-tourism operators, Northland Regional Council and
Department of Conservation staff and a willingness to be engaged in regular monitoring. However,
strong Quality Assurance / Quality Control procedures would need to be implemented to ensure that
the work was done reliably at a standard needed to achieve detection of low densities.
Degree of uncertainty
The degree of uncertainty associated with this management objective is dependent on the rigorousness
of eradication attempts and post-eradication monitoring. Sensitivity and associated variation of
monitoring surveys for particular population sizes can be calculated for a given methodology and
sampling effort. Uncertainty can therefore be quantified a priori (Hayes et al. 2005). We expect
moderate to low uncertainty for a well-designed eradication and monitoring campaign.
15 Each diver was costed at $500 per day, each Field technician was $500 per day and a support dive vessel was $500 per day.
These estimates are four years old and likely to be understimates for operations in 2008/09.
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17.3.3. Option 3: Maintain population at or below current level
This management objective is very similar to Option 2, except that the objective is not to remove
Styela completely, but to ensure that it becomes no more abundant than it is currently (Table 5.1).
Deliverable 5
Again, because the current density of Styela is so low, the emphasis is also on monitoring to detect the
current level of abundance. If the population approaches or exceeds this threshold, control action is
implemented. Since recent surveys have detected a very low density and widely dispersed current
population, it is appropriate to specify population size as the measure of abundance and the
recommended management tool is manual removal by divers. Given the low population size of Styela
in Tutukaka Marina, we recommend that the threshold be set at an abundance value which is an order
of magnitude greater than the reported population sizes to account for variation in detection success.
Alternatively or additionally, a spatial population distribution pattern may be specified as the threshold
unit, allowing particular areas of the marina to be targeted (e.g. the commercial tourism and dive
charter vessel mooring area). However, because current knowledge about the relationship between
Styela density and inoculation risk is limited and there is uncertainty regarding the influence of the
proximity of vessels to Styela populations, this approach is not recommended for Tutukaka Marina. A
specified catch-per-unit-effort (CPUE) may also be considered as a threshold measurement in place of
a population size. This threshold should be set by MAFBNZ, in consultation with a Technical
Advisory Group. The frequency of survey will be determined by the proximity of the population level
to the threshold. At population levels well below the threshold, sampling may be conducted at a lower
frequency, with an increase in frequency as the threshold is approached to improve precision of
population estimates.
Effectiveness
As for Option 2.
Practicality
As for Option 2.
Acceptability to stakeholders
As for Option 2.
Likely side-effects
As for Option 2
Legality
As for Option 2
Likelihood of success
The success of the control action will be evaluated by the sequential surveys. If hand removal by
divers is unable to maintain the population below the threshold level, then the strategy will need to be
re-evaluated, potentially with implementation of alternate control methods (e.g. application of
chemical biocides, encapsulation or removal of structures). Given a robust survey and monitoring
regime, this management objective is likely to be associated with a high likelihood of success.
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Cost of implementation
The initial costs for this option will be similar to Option 2, but two key differences will affect the longterm
cost of implementation. First, the frequency of surveys may be lower than that recommended for
eradication, depending on the level at which the threshold for control is set. Second, unlike an
eradication action, where there is an anticipated stand-down of operations once successful eradication
has been declared, the costs of monitoring for this option are ongoing. As a control option, it requires
ongoing financial support and, therefore, would need long-term budgetary support to be effective.
Long-term, we expect this option to be more expensive than eradication (Option 2).
Degree of uncertainty
The degree of uncertainty associated with the effectiveness this management objective in preventing
the spread of Styela to the Poor Knights Islands is likely to be higher than that for Option 2. This
management objective assumes that a reduced population size will reduce the risk of spreading Styela
to the Poor Knights Islands. However, there is a lack of information on the relationship between local
population size and inoculation risk of susceptible vectors residing at the marina.
17.3.4. Option 4: Maintain population at or below a specified level (other than current level)
This management objective is similar to Objective 3 (above), except that the threshold is set at a level
other than the current level (Table 5.1). The population is monitored using surveys with a specified
probability of detection and active management is implemented if a specified threshold is approached
or exceeded.
The task of setting the threshold value and unit is complex and careful consideration should be given
to ensure that it is acceptable and manageable. For example: the threshold may be set at a level higher
than current which will allow the population to increase beyond the existing abundance and/or
distribution before being controlled. Once this option is implemented it is unlikely that a change to a
more conservative strategy (e.g. local eradication) would be possible. The choice of threshold value
should be associated with some knowledge of how it relates to the inoculation risk of locally moored
vectors by Styela or the likelihood of its dispersal into adjacent natural coastal environments.
Effectiveness
The choice of threshold unit (population size vs. density) and threshold size (or density) will affect the
outcome and the tools required to control the population should it exceed the threshold. For example:
if the threshold is set at a density of one individual per m 2 throughout 10 % of the marina habitat, both
the population abundance will increase and the distribution will become more widespread before
population control is actioned. The control tools that are currently available, other than manual
removal, don’t allow populations to be easily managed at a specific density (e.g. pile encapsulation
and/or chemical treatment). Therefore we suggest that population size is selected as the threshold unit
at Tutukaka Marina. If the threshold is approached or exceeded, active management is implemented
to reduce the population to a lower level. Suitable active management tools for Tutukaka (depending
on the threshold population size) include: manual removal, encapsulation, and temporary removal
from water for treatment (e.g., water-blasting or chemical) (Coutts and Forrest 2005).
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Re-introduction of Styela on vessels entering Tutukaka, and/or persistence of Styela within the marina
on infected resident vessels is possible under this option, as it contains no measures to manage vectors.
The effectiveness of this management objective to prevent the spread of Styela to HVAs may be
further compromised if Styela is “transmitted” from infected visiting vessels (e.g. from the Hauraki
Gulf, see Option 2) to susceptible local vessels.
Practicality
As for Option 2.
Acceptability to stakeholders
As for Option 2.
Likely side-effects
As for option 2.
Legality
As for Option 2
Likelihood of success
As for Option 2
Cost of implementation
This option may be more expensive than Objective 3 (maintaining the population at the current level),
due to the cost of active management of a potentially larger population.
Degree of uncertainty
As for Option 3.
As described in Objective 3 there is the option to manage some areas of the marina in a different way
to other areas. For example, control could be targeted at areas where potential vectors to the Poor
Knights Islands berth or depart from. However, propagule pressure to suitable settlement substrates
can be high throughout yachting marinas (Floerl and Inglis 2003), and current knowledge about the
relationship between Styela density and inoculation risk is inadequate to support this strategy.
The advantage of setting the threshold at a level other than current is that at locations where Styela is
currently abundant the threshold can be set at a lower level to reduce and maintain the population at
the threshold. However, because the current population level at Tutukaka is very low, we consider
this strategy not useful. Conversely, if there was evidence that the risk of spread of Styela to HVAs
would not significantly increase if the current population increased to a certain degree then the
threshold could be set a level higher than current to delay or avoid management costs. However,
again, this information is currently not available and in its absence we do not recommend the use of an
arbitrarily chosen population threshold size as a management strategy.
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17.4. B: Vector management options (Tutukaka Marina)
The options evaluated in this section are treated as exclusive and assume an absence of population
management. Combinations of vector and population management options are evaluated in a separate
section below.
17.4.1. Option 5: No vector management
This option involves no management of vectors entering or leaving the Tutukaka Marina (Table 5.1).
Effectiveness
Without vector management, vessels carrying Styela will be able to enter and leave the Tutukaka
Marina unnoticed. In the absence of population management at Tutukaka Marina (Options 2–4) it is
likely that, eventually, Styela will become transported to the Poor Knights Islands via fouling of local
vessel hulls by propagules originating from the resident population. This likelihood would be nullified
(Option 2) or reduced (Options 3 and 4) if population management is adopted and successful.
However, irrespective of population management at Tutukaka Marina, a lack of vector management
will enable Styela to reach the Poor Knights Islands from Tutukaka via: (i) vessels that carry Styela
originating from the Hauraki Gulf (or other) populations and that are stopping over at Tutukaka
Marina, or (ii) Tutukaka vessels that become colonised by Styela following release of propagules from
adjacently moored vessels containing Styela originating from the Hauraki Gulf or other populations.
Practicality
This option requires no additional resources or changes to current management of the marina and its
operations.
Acceptability to stakeholders
As in Option 1.
Likely side-effects
As in Option 1.
Legality
This option involves no change to the current management regime. However, clarification would be
needed on the obligations (if any, under the do-nothing approach) of vessel owners and operators who
observe Styela on their vessels, and the implications for knowingly translocating an Unwanted
Organism.
Likelihood of success
Not applicable.
Cost of implementation
There are no direct costs involved with implementation of the ‘do nothing’ option.
138 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Degree of uncertainty
As in Option 1.
17.4.2. Option 6: Minimise spread to HVAs
Deliverable 5
Minimising the risk of spreading Styela from Tutukaka Marina to the Poor Knights Islands can involve
two dimensions of voluntary management. Firstly, management of infected or potentially infected
vessels departing from Tutukaka Marina to the Poor Knights Islands. Secondly, risk profiling of
incoming vectors to prevent inoculation of resident vessels with Styela (Table 5.1).
Minimising the potential of spread of Styela to the Poor Knights Islands by departures from the
Tutukaka Marina can be achieved by eliciting changes in vessel maintenance practices among owners
and operators of recreational and commercial marina users that visit the Poor Knights Islands. Such
changes could include: (i) evaluation of appropriateness of current antifouling paints used (possibly
change to a more appropriate product), (ii) (where appropriate) increased frequency of antifouling
paint renewal to lower risk of colonisation by Styela, and/or (iii) regular inspection and (if required)
manual cleaning of vessel hulls involving appropriate containment of fouling material. Pro-active
behaviour of owners and operators can be elicited through the use of social marketing aimed at
increasing awareness of the risks posed to the Poor Knights Islands and surrounding natural habitats
by Styela. This option would require the development of a detailed communication strategy that is
specific to key risk groups (e.g. recreational boaters, tourism operators, resident fishermen).
Additional options include the development of industry codes of practice for “responsible hull
maintenance” and certified accreditation of operators who comply with these standards.
Vector management measures may also be initiated by the marina operators. The development of risk
profiling and management procedures for incoming vectors would further help reduce the risk of
spreading Styela to the Poor Knights Islands. The arrival of Styela on the hulls of visiting vessels
could, in the right circumstances, result in the inoculation of adjacently moored vessels that may
subsequently visit the Poor Knights Islands. Such importation of Styela may compromise the efficacy
of population management efforts if carried out in conjunction with vector management. Styela is
widespread throughout the Auckland and Hauraki Gulf regions and may arrive at Tutukaka Marina via
transport on recreational boats or charter and tourism vessels (see Deliverable 2).
There are numerous options for how the Tutukaka Marina could engage in vector management,
including surveying of resident and visiting vessels with regard to hull maintenance, offering special
rates for compliant customers, and offering integrated berthage and maintenance packages (e.g. fees
for longer-term residents include berthing charges and regular hull maintenance). Such measures
could be rewarded, or made attractive, by implementing accreditation systems that certify
environmental awareness and commitment of the facility. Such accreditation systems are already in
place (e.g. the Blue Flag system for marinas worldwide; www.blueflag.org) and membership is sought
after by New Zealand marinas (K. Hogan, pers. comm.).
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Effectiveness
Reducing the frequency at which Styela is transported to the Poor Knights Islands is likely to reduce
the species’ likelihood of becoming established in this HVA. Studies of plant and animal invaders
have demonstrated that transport of species by human vectors can dramatically accelerate spreading
rates. A reduction in transport frequency will thus bring about a decreased probability of
establishment of the species in new locations (Buchan and Padilla 1999). The effectiveness of this
management objective will be determined by the level of participation among vessel and marina
owners and operators. Species invasions are highly stochastic processes (Sakai et al 1998) and even
rare transportation events can result in the establishment of new populations (Buchan and Padilla
1998). We suggest that vector management can be a very powerful tool to minimise the potential for
Styela to reach the Poor Knights Islands and other HVAs, provided it is practised by all or the majority
of vessel owners and operators and includes management of both incoming and Poor Knights Islandsbound
traffic. Because natural dispersal of Styela to the Poor Knights Islands is unlikely (see above)
the use of vector management is likely to be more important for preventing the species’ introduction to
this HVA than population management at Tutukaka Marina. Maximum effectiveness will be achieved
if the management campaign includes vectors travelling to the Poor Knights Islands from other source
locations of Styela.
Practicality
The development of an effective voluntary vector management programme will require the approval
and commitment of all major marina users (recreational and commercial vessel owners) and the
marina operators. The main objectives of such a programme can be identified through workshops
between MAFBNZ, marina users and operators and, possibly, the antifouling paint industry.
Acceptability to stakeholders
A voluntary vector management programme is likely to have a very high acceptability to stakeholders.
Likely side-effects
We expect small direct adverse effects to be associated with this management objective. More
frequent application of antifouling paints, and a higher incidence of in-water hull cleaning by
scrubbing or brushing may result in higher concentrations of antifouling toxins in marina water and
sediments, which can have adverse effects on resident non-target biota (Comber et al. 2002,
Katranitsas et al. 2003, Thomas et al. 2002). Any potential effects on water and sediment chemistry,
and local biota, can be minimised by promoting the use of non-toxic antifouling paints (Johnson and
Gonzalez 2007, Johnson and Miller 2002). Increased in-water removal of biofouling resulting from
improved hull maintenance must be accompanied by appropriate containment and disposal of the
material on land.
Legality
As in Option 2.
Likelihood of success
We predict a high likelihood of success of this management objective provided attention is given to
the sensitivity of recreational and commercial vessel owners and marina operators during the
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Deliverable 5
development of a code of practice and/or accreditation system. To be attractive to these stakeholder
groups, any vector management measures must have tangible benefits also for the target groups. One
example of such benefits may be their contribution to the prevention of Styela establishment in the
Poor Knights Islands or, in a broader context, preservation of the perceived pristine state of New
Zealand’s coastal environments. A benefit for marina operators may be that their adaptation of the
accreditation system may result in increased popularity of their facility because of their certified
concern for the environment.
One important factor contributing to the success of this strategy is continual monitoring of compliance
with voluntary measures and the outcomes of these measures. This could be done by before-and-aftermanagement
hull surveys of resident and visiting vessels, and by boat and marina owner and operator
surveys with regard to their awareness of Styela (and marine biosecurity in general) and level of
commitment to the voluntary guidelines.
Cost of implementation
The initial costs associated with this management objective are for the development of effective social
marketing and communications strategies targeting marina users and operators. Initially, the specific
objectives of the vector management strategy should be identified by MAFBNZ in consultation with
scientific experts. Additional costs will arise through periodic monitoring of compliance and the
outcomes of the strategy. Resources should be available for a periodic review process, the results of
which can be used for refining elements of the campaign (e.g. poor compliance of private yacht
owners) or developing new information material to update participating stakeholders (e.g. via
dissemination of statistics of “success stories” such as Styela finds on vessel hulls, incidence of hull
negligence etc.). We anticipate the cost to MAFBNZ associated with the implementation of a
voluntary vector management programme to be considerably less than the costs required for
population control. The majority of foreseeable costs will be associated with staff time and possibly
the outsourcing of the development of social marketing and communications strategies and associated
information materials.
Degree of uncertainty
NIWA’s past research on the spread of marine organisms via vessel movements has involved close
collaboration with New Zealand’s main yachting bodies, marina operators, antifouling paint
companies and owners of private and commercial small craft. It is evident from this work that all of
these groups have a considerable level of interest in the conservation of marine environments.
However, at the same time there is a high level of sensitivity toward being over-managed and a strong
desire – in particular for the case of recreational boaters - to see all potential vectors of marine pests
managed. Based on our experience with these groups we believe that the degree of uncertainty
associated with this management objective can be reduced provided the way in which voluntary vector
management is initiated and communicated is non-threatening and respectful of these group’s
concerns and needs.
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17.4.3. Option 7: Prevent spread to HVAs
Preventing the spread of Styela to the Poor Knights Islands would require the implementation of
mandatory measures that result in the exclusion of infected or potentially infected vectors from the
Poor Knights Islands (Table 5.1). The specific methods involved in preventing fouling and transport
of Styela on vessel hulls are similar to those described in Option 6 above. However, this management
objective requires legislation to be developed and put in place.
A large proportion of the Tutukaka Marina’s clientele are operators of tourism vessels used for diving
and sight-seeing in the Poor Knights Islands. Prevention of transport of Styela to this HVA could be
achieved by making the resource consent for the operation of the marina contingent on the
development (or adaptation) and operation of a monitoring and compliance programme for vessel
hygiene of resident commercial vessels that travel to the Poor Knights Islands. Many New Zealand
Marinas have loose guidelines in place already that require resident vessels to be in a reasonable state
of repair. These programmes are not well enforced at present but could be made more rigorous to
increase the overall state of vessel maintenance at the facility. The marina can conduct such a
programme in several ways, for example by monitoring hull maintenance intervals (antifouling
renewal and/or manual hull cleaning) of vessels frequenting the Poor Knights Islands, notifying vessel
operators when maintenance is overdue and reporting of non-compliance with regulations. This
programme could be extended also to resident recreational vessels aiming to visit the Poor Knights
Islands. One option would also be the inclusion of regular hull surveys in the marina’s monitoring
programme that result in mandatory hull maintenance for vessels that fail the inspection requirements.
Mandatory hull inspections have been used by the Northern Territory Fisheries Authority in Australia
following the black-striped mussel incursion at Darwin marinas. From a managerial perspective, this
exercise was considered very useful as several dozen cases of non-indigenous species introduction
were intercepted through mandatory hull cleaning (A. Marshall, pers. comm.).
Alternatively (or in addition), similar regulations may be imposed on the operators of commercial or
recreational vessels visiting the Poor Knights Islands. For example, commercial permits for visits to
the Poor Knights Islands, issued by the regional council and/or the Department of Conservation, could
be made to expire after a period that is equal to or slightly shorter than the recommended renewal
interval for antifouling paints used by the vessels. Renewal of access permits would be made
contingent on demonstrated compliance with vessel hygiene regulations.
One additional option is the implementation of a controlled and/or restricted area around the Poor
Knights Islands that is only accessible to vessels that are compliant with certain requirements for
vessel hygiene (as above).
Any regulations relating to hull husbandry should be meaningful, reasonable and defensible, and be
developed by MAFBNZ in consultation and collaboration with experts on biofouling, the antifouling
paint industry and representatives of commercial and recreational users of the Tutukaka Marina (e.g.
tour operators, fishermen, recreational yachters).
Effectiveness
The criteria determining the effectiveness of this management objective are the same as those
described for Option 6. In this case, effectiveness in preventing the spread of Styela to the Poor
Knights Islands can be assumed to be very high as mandatory exclusion of infected and potentially
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Deliverable 5
infected vectors from the Poor Knights Islands will prevent any introduction of Styela to this HVA.
Maximum effectiveness will be achieved when guidelines are imposed on all vectors, including those
travelling to the Poor Knights Islands from other locations where Styela is established (e.g Auckland).
The likely incidence of non-compliance and illegal visits to the Poor Knights Islands by potentially
infected vessels can not be easily determined.
The effectiveness of a mandatory vector management programme can be determined – and increased –
by regular compliance monitoring and the development of disincentives for non-compliance (e.g.
fines, suspension of licences, etc.).
Practicality
The practicality of this management objective is lower than that of Option 6 because of the large
number of stakeholder groups and management authorities that need to be involved in the policymaking
process.
Acceptability to stakeholders
The acceptability to stakeholders of this management objective is likely to be lower than for Option 6.
Key risk groups, such as diving operators and recreational boaters, will consider mandatory guidelines
an imposition on the operation of their business (commercial vessels) or pursuit of their lifestyle
(recreational vessels). However, a well-designed communications strategy that includes awareness
workshops and effectively demonstrates the benefits of keeping Styela and other invaders out of the
Poor Knights Islands in a manner that affected risk groups can relate to, is likely to overcome a
considerable part of this resistance and increase the level of acceptability of this objective.
Likely side-effects
As for Option 6.
Legality
Adoption of this management objective would require the development of legislation that facilitates
the development, implementation and monitoring of the vector management programmes discussed
above. This is likely to be a complex task requiring input and cooperation of several agencies. For
example, resource consents are the responsibility of regional councils (Northland Regional Council in
this case), while the Poor Knight Islands Marine Reserve is managed by the Department of
Conversation. The powers and responsibilities of both agencies and MAFBNZ in a management
programme as described above need to be established, including a penalty system for non-compliance.
Likelihood of success
We expect this option to be associated with a very high likelihood of success in particular if access to
the Poor Knights Islands is restricted to vessels with demonstrably low or no potential to transport
Styela. This option would have the advantage of also targeting vectors arriving from areas other than
Tutukaka Marina, such as the Hauraki Gulf region where Styela is abundant and widespread.
Cost of implementation
The costs associated with this management objective will be higher than those associated with Option
6 because of the addition of policy making. All cost items discussed for Option 6 will incur, with the
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addition of the costs involved in translating a voluntary management programme into a mandatory one
that potentially involves several government authorities (regional council, DoC, MAFBNZ).
Because this management objective requires the development of communication strategies, awareness
campaigns, etc., in the same manner as described for Option 6, it may be feasible to commence with a
voluntary vector management programme and decide on the adaptation of mandatory guidelines when
levels of compliance, effectiveness and potential problems of the voluntary programme have been
quantified and reviewed. One possible shortcoming of this approach is, however, that the accidental
introduction of Styela to the Poor Knights Islands during the trial period of the programme may not be
reversible.
Degree of uncertainty
If vector management is mandatory and vessel owners and operators visiting the Poor Knights Islands
have no choice, the degree of uncertainty associated with this management objective is likely to be
low.
17.4.4. Option 8: Minimise / prevent spread from Tutukaka Marina
This management objective aims to prevent or minimise the spread of Styela from the Tutukaka
Marina by targeting all outgoing vectors (tourism, fishing and recreational vessels), regardless of their
destination. Minimising spread from the Tutukaka Marina would require the implementation of the
voluntary vector management programme described for Option 6, but extended to all outgoing vectors.
Preventing spread of Styela from the Tutukaka Marina would require the implementation of
mandatory vector maintenance guidelines described in Option 7, for all outgoing vectors.
Effectiveness
As for Options 6 and 7.
Practicality
As for Options 6 and 7.
Acceptability to stakeholders
As for Options 6 and 7. However, owners or operators of vessels or other vectors travelling from
Tutukaka to other areas with known populations of Styela (e.g. Whangarei Harbour, Hauraki Gulf,
Waitemata Harbour) will likely oppose such measures.
Likely side-effects
As for Options 6 and 7.
Legality
As for Options 6 and 7.
Likelihood of success
As for Options 6 and 7.
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Cost of implementation
As for Options 6 and 7.
Degree of uncertainty
Deliverable 5
The degree of uncertainty for the spread of Styela to the Poor Knights Islands associated with this
objective is higher than the uncertainty associated with management objectives outlined in Options 6
and 7. Management objectives that aim to minimise or prevent the spread of Styela to the Poor
Knights Islands target potentially high-risk vessels from all locations, not just the Tutukaka Marina.
Measures that prevent the spread from the Tutukaka Marina may be successful, but can not control the
fact that Styela may become transported to the Poor Knights Islands by vessels from the Hauraki Gulf.
17.5. C: Combined vector and population management options (Tutukaka Marina)
17.5.1. Option 9: Combination of population and vector management
This management objective would combine population management (eradication or maintenance of
population at/below current or other levels; Options 2–5) with vector management
(minimisation/prevention of spread to the Poor Knights Islands, or prevention of spread from the
Tutukaka Marina; Options 6-8) at the Tutukaka Marina.
A combination of population and vector management could for example consist of an eradication
attempt at the Tutukaka Marina (feasible because of low current population size and because the
majority of visits to the Poor Knights Islands originate from Tutukaka; see Option 2) followed by
regular target surveillance and a well-designed voluntary vector management (Option 6) programme.
Effectiveness
The effectiveness of this combined approach is likely to be higher than for the exclusive use of a
single measure, which can leave ‘loopholes’ for Styela. A combination of population and vector
management as the management objective has distinct advantages because: (i) both population
(particularly eradication) and vector management minimise or prevent transport of Styela by vessels
travelling from Tutukaka (or other sources of Styela) to the Poor Knights Islands, and (ii)
management of vectors arriving at the Tutukaka Marina will reduce the likelihood of re-infection of
the marina with Styela from southern populations after considerable resources have been spent on
population management at Tutukaka Marina. Particularly favourable approaches are those that
minimise or prevent the arrival of high-risk vectors at the Poor Knights Islands, as this would also
target vectors arriving from other known sources of Styela (e.g. Auckland and Hauraki Gulf regions).
Population management at Tutukaka Marina without vector management can not prevent the transport
of Styela to the Poor Knights Islands from other sources.
Practicality
The level of practicality associated with this management objective depends on the combination of
population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above).
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Acceptability to stakeholders
The level of acceptability associated with this management objective depends on the combination of
population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above). A voluntary vector management
programme will have a higher level of acceptability than mandatory guidelines.
Likely side-effects
The magnitude of side effects associated with this management objective depends on the combination
of population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above).
Legality
The legality of this management objective depends on the combination of population and vector
management measures used: refer to the appropriate combination of management objectives among
Options 2–4 and 6–8 above).
Likelihood of success
The likelihood of success of this management objective depends on the combination of population and
vector management measures used: refer to the appropriate combination of management objectives
among Options 2–4 and 6–8 above).
Cost of implementation
The costs associated with this management objective depend on the combination of population and
vector management measures used: refer to the appropriate combination of management objectives
among Options 2–4 and 6–8 above). They will be higher than the cost of only population or only
vector management.
Degree of uncertainty
The degree of uncertainty associated with this management objective depends on the combination of
population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above). We suggest uncertainty will be lower for
a combined approach than for only population or only vector management.
146 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Table 5.3: Evaluation of management objectives for Styela at Tutukaka Marina based on pest management criteria listed in The Biosecurity Act 1993 (Forrest et al 2006). Values in
brackets indicate relative weighting of criteria (e.g. ‘2’ = rank score multiplied by 2). Relative ranking system: 0 = unfavourable; 5 = favourable.
Option 1: No population
management
Effectiveness
(weighted x 3)
Practicality
Acceptability to
stakeholders
(weighted x 2)
Likely side-effects
(weighted x 2)
Deliverable 5
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 147
Legality
Likelihood of
success
(weighted x 3)
Cost of
Implementation
(weighted x 3)
1 5 1 1 5 0 b 5 3 38
Option 2: Local eradication 2 3 5 4 a 5 4 3 3 59
Option 3: Maintain population
at/below current levels
Option 4: Maintain population at or
below specified level
3 3 5 4 5 4 4 2 63
3 3 5 4 5 4 4 2 63
Option 5: No vector management 1 5 1 1 5 0 b 5 3 38
Option 6: Minimise spread to HVAs 4 c 3 5 4 5 4 4 3 68
Option 7: Prevent spread to HVAs 5 c 2 1 4 2 5 3 5 63
Option 8a: Minimise spread from
marina (voluntary)
Option 8b: Prevent spread from
marina (mandatory)
Option 9a: Combination of
population and voluntary
vector management
Option 9b: Combination of
population and mandatory
vector management
a Assuming manual removal of Styela by divers, without use of chemicals.
3 3 5 4 5 4 4 2 63
4 2 1 4 2 5 3 3 56
5 c 3 5 4 5 4 2 3 65
5 c 2 1 4 2 5 2 5 60
b We evaluated the likelihood of success to prevent the transport of Styela to the HVAs via the do-nothing approach.
c Maximum effectiveness if guidelines apply to high-risk vectors arriving from anywhere, not just Tutukaka Marina.
Degree of uncertainty
(weighted x 2)
Final score

Deliverable 5
17.6. Recommended approach for Tutukaka Marina
Evaluation of the nine optional management objectives against criteria relevant for the development of
pest management strategies under The Biosecurity Act 1993 identified a voluntary vector management
programme targeting vectors arriving at the Poor Knights Islands, or a combination of population and
voluntary vector management as the best strategy to prevent the spread of Styela to the Poor Knights
Islands (rating of 68 and 65, respectively; Table 5.3). Population management without vector
management (eradication or maintenance of population), as well as mandatory vector management
yielded lower ratings (59–63; Table 5.3)). The least favourable approach was the do-nothing option
(38 points).
The high overall scores associated with a combination of population and vector management arise
from this management objective’s high effectiveness, high acceptability to stakeholders, high
likelihood of success and low level of uncertainty. Voluntary prevention of transport of Styela to the
Poor Knights Islands has a lower anticipated effectiveness but is likely to be significantly cheaper
(Table 5.3). The low scores associated with management objectives that addressed only the Tutukaka
population of Styela, but neglected to consider the potential for its arrival to the Poor Knights Islands
via vectors from the Auckland and Hauraki Gulf regions, arise from an anticipated low level of
effectiveness and high level of uncertainty.
Our model simulations do not permit an evaluation of the efficacy of the various management
objectives in preventing the spread of Styela to the Poor Knights Islands because this HVA was not
contained in the model as a location. However, our evaluation of the various management objectives
(options 1–9) against criteria for pest management provides some guidance. We recommend that any
management strategy adopted to prevent the spread of Styela to the Poor Knights Islands include the
management of vectors. Vector management should not be restricted to vectors originating from
Tutukaka Marina. While this may effectively reduce or prevent transport of Styela from this location
to the Poor Knights Islands, the species would still be able to reach the Poor Knights Islands via
transport on vessels originating from the Hauraki Gulf or Waitemata Harbour 16 . For this reason, we
consider minimising the arrival of high-risk vectors to the Poor Knights Islands, irrespective of their
origin, as the best and most effective option to prevent Styela’s establishment in the HVA. The choice
between a voluntary or mandatory programme will depend on the relative importance of acceptability
to stakeholder, cost and effectiveness in MAFBNZ’s decision making process.
It is unlikely (but not guaranteed) that the small population size of Styela at Tutukaka Marina exerts a
high degree of propagule pressure on resident vectors. However, it is a fortunate circumstance that the
population has remained at a small size where population management is still possible. Because
eventual population growth can not be ruled out we also recommend an attempt at eradicating Styela
from the Tutukaka Marina in addition to a vector management programme.
16
At the time of revising and finalising this Deliverable, Styela was discovered at Marsden Cove Marina in Whangarei
Harbour as part of MAFBNZ’s nationwide target surveillance project RFP106232007. This discovery highlights the
possibility of Styela being spread north by vector traffic from the Hauraki Gulf and Waitemata Harbour.
148 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 5
In summary, we recommend a combination of Options 2 and 6 (attempted eradication and voluntary
vector management) or a combination of Options 2 and 7 (attempted eradication and mandatory vector
management) for preventing the spread of Styela to the Poor Knights Islands HVA.
18. Management objectives and strategies: Lyttelton Port and
Magazine Bay Marina
At the December 2007 workshop, it was agreed that the management plans for Lyttelton Port and
Magazine Bay Marina should be combined. These two locations are situated in close proximity to one
another (< 1 km) and quite possibly linked by water currents. Therefore, the management strategy for
one location should consider the population density and vectors of the other location.
18.1. Status summary
Lyttelton Port
Surveys of the Port of Lyttelton during November and December 2006 indicated that Styela was
widespread and occurred at low to medium densities (≤ 10 individuals per m 2 ) throughout the port.
Styela were found mainly in the upper water column (< 5 m depth) but some individuals were detected
during deeper dives to approximately 10–13 m. “Hot spots” of very high density (11–100 individuals
per m 2 ) occurred on pontoons or wharf pilings at a few discrete locations. One such hotspot, at the A
and B pontoons, is the loading point and berthing area for ferry and tourism vessels. Another hotspot,
on the pontoons near Z wharf, is directly adjacent to where commercial fishing and aquaculture
harvest vessels frequently berth and unload their catch or harvest (see Deliverable 1). Size frequencies
and the apparent population increase since surveys in 2006 and previous surveillance efforts (Gust et
al. 2006a), indicate that Styela populations are well established in the port and have potentially been
present for a considerable period of time. Preliminary work on the genetics of Styela populations in
Lyttelton and Waitemata Harbour suggests that they may be the result of independent introductions
(Goldstien, pers. comm. 2007).
Lyttelton Port is one of New Zealand’s busiest shipping ports and the major commercial port of the
South Island (Inglis et al. 2006). It is frequented by virtually all vessel types – cargo carriers, tankers,
fishing vessels, barges, dredges, cruise ships, pleasure craft - and connected to a wide range of
international and domestic locations (Inglis et al. 2006). Lyttelton Port is connected via vector
movements to three of the four HVAs identified for this project - the Banks Peninsula aquaculture
production area, Akaroa Harbour and the Marlborough Sounds aquaculture production area (see
Deliverable 2). Because of Styela’s short larval phase, direct natural dispersal of the species from
Lyttelton Port (or Magazine Bay Marina) to either of these HVAs is most likely impossible, but could
occur in a stepping-stone manner involving several generations. However, movements of commercial
and recreational vessels, aquaculture vessels and equipment between Lyttelton Port and the HVAs
could facilitate the transport and introduction of Styela to either location.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 149

Deliverable 5
Magazine Bay Marina
During the 2006 surveys, Styela was present at Magazine Bay Marina at low densities (1–10
individuals per m 2 ) throughout the marina, with an area of higher density (10–100 individuals per m 2 )
on vessels, ropes and pilings at Pier B (see Deliverable 1). Of the 34 vessels moored in the marina, a
high proportion (~ 75 %) was visibly fouled and appears to have limited movements (see Deliverable
2). The marina jetties and several of the vessels are in disrepair following a destructive storm in
October 2000. The frequency of vessel movements from and into the marina is very low in
comparison to the port and the majority of voyages are generally restricted to within Lyttelton Harbour
and occasionally around the Banks Peninsula to Akaroa Harbour. Commercial aquaculture harvest
vessels occasionally berth in the marina when moorings within the port are limited, but this occurs
very infrequently. Magazine Bay marina has the lowest vector activity of the three study locations
(Deliverable 2). There are plans to restore and expand the Magazine Bay Marina in the near future,
which would provide new habitat for Styela and, presumably, result in an increase of vector
movements to and from the new marina.
18.2. Options for managing the risk of Styela spread from Lyttelton Port and Magazine Bay Marina
Nine possible management objectives were identified for Lyttelton Port and Magazine Bay Marina.
These are described in Table 5.4 and are summarised in the sections below.
Table 5.4: Styela clava management objectives for Lyttelton Port and Magazine Bay Marina.
Management objectives Focus Strategy
1 No population management (Population) Do nothing to manage the population
2 Local eradication:
“Non-detection over a specified
time by surveys of a specified
level of detection probability”
3 Maintain population at or below
current levels (of abundance or
distribution)
4 Maintain population at or below
specified levels (of abundance
or distribution)
Population Survey and remove entire population, followed by surveillance
and maintenance.
(Vectors) (Should be coupled with management of incoming vectors to
prevent re-introduction of Styela.)
Population Monitor the population with a survey of sufficient power to
determine when the current level of abundance or distribution
(in this case the level detected in the Nov. 2006 survey) has
been reached or exceeded. Control action is implemented if
this level is exceeded by a specified amount (e.g. doubling of
distribution).
Population Monitor the population with a survey of sufficient power to
determine when a pre-specified level of abundance or
distribution has been reached or exceeded. Control action is
implemented if this level is reached or exceeded by a specified
amount.
5 No vector management (Vectors) Do nothing to control the movements or hygiene of potential
vectors coming into, mooring in or leaving the marina and
150 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Management objectives Focus Strategy
6 Minimise spread to HVAs
7 Prevent spread to HVAs
8 Minimise/prevent spread from
marina
9 Combinations of management
options
Vectors:
- outgoing and
bound for HVAs
- incoming
vessels
Vectors:
- outgoing and
bound for HVAs
Vectors:
- all outgoing
vectors
Population +
vectors
travelling to HVAs
Deliverable 5
Voluntary management of infested and potentially infested
vectors departing for the HVAs.
• Use of social marketing to elicit change in vessel hygiene.
• Communication strategy specific to key risk groups
(recreational vessel owners and commercial tourism
operators).
• Encourage an industry code of practice and accreditation
that includes monitoring hull cleaning and antifouling.
Risk profiling
Encourage marina operators to implement their own risk
profiling and management of incoming vessels to enforce
hygiene requirements.
Monitor compliance and outcomes.
Regulatory management:
• Incorporate conditions for vessel hygiene monitoring and
compliance in resource consent for operation of Lyttelton
Port and Magazine Bay Marina.
• Incorporate conditions for vessel hygiene and compliance
in permits for commercial operators visiting the HVAs.
• Implement a controlled or restricted area around the
HVAs where there are strict requirements for vessel
hygiene.
Monitor compliance and outcomes.
As Objective 6 above but includes all vessels and vectors
which depart the marina, regardless of their destination
It is recommended that all population management objectives
be coupled with some level of vector management to reduce
likelihood of re-introduction of Styela and/or to minimise the
possibility of Styela being introduced to the HVAs.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 151

Deliverable 5
18.3. A. Population management options (Lyttelton Port and Magazine Bay Marina)
18.3.1. Option 1: No population management
This option involves no specific management of the Styela population in Lyttelton Port and Tutukaka
Marina or of vectors entering or leaving these locations (Table 5.4).
Effectiveness
Without any management, it is likely that there will be a further increase in the size, density and
distribution of the Styela population within the port and marina over time, and a concomitant risk that
it may be spread to other locations, including the Banks Peninsula, Akaroa Harbour and Marlborough
Sounds HVAs. The time frame and magnitude of any changes in the population size are uncertain.
Practicality
This option requires no additional resources or changes to current management of the port and marina
and their operations.
Acceptability to stakeholders
There are no direct effects of this option on stakeholders, unless Styela populations became large
enough to impact on vessel maintenance and operation. However, because there is increased risk of
Styela spreading to nearby natural habitats and HVAs, particularly aquaculture operations, there is
strong potential for adverse economic outcomes. In this context, doing nothing is likely to be
unacceptable to stakeholders, particularly those who have strong financial connections to potentially
affected environments, such as the aquaculture facilities associated with the Banks Peninsula, Akaroa
Harbour and Marlborough Sounds HVAs.
Likely side-effects
The most immediate side-effect of this option is a potential increase in risk of spread of Styela to
HVAs. MAFBNZ prepared a summary of possible effects of Styela on subcomponents of core New
Zealand values as part of its Organism Impact Statement (OIA) for Styela (Kluza et al. 2005). This
summary is reproduced in Table 5.2. The values encompassed by the Banks Peninsula, Akaroa
Harbour and Marlborough Sounds HVAs include a number of these subcomponents: biodiversity,
habitat, trophic interactions, aquaculture and aesthetics/diving. There is uncertainty over the actual
effects Styela may have on these values; for most values effects are considered to be ‘minor to
moderate’ (Table 5.2). However, Styela could have a ‘major to significant’ effect on aquaculture via
fouling of gear and stock, which may increase operational costs and decrease the value of the product
(NIMPIS 2002). New Zealand’s Greenshell TM aquaculture industry alone has a total market revenue
of NZ$209 million (Burrell and Meehan 2006), and a large proportion of this industry is located in the
Marlborough Sounds and (to a lesser extent) Banks Peninsula HVAs. Severe fouling of these facilities
by Styela would represent a considerable economic risk.
Legality
This option involves no change to the current management regime.
152 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Likelihood of success
Not applicable.
Cost of implementation
There are no direct costs involved with implementation of the ‘do nothing’ option.
Degree of uncertainty
Deliverable 5
The outcome of this strategy is associated with a moderate degree of uncertainty. Styela was first
reported from structures within Lyttelton Port in 2005, but had been collected (but misidentified) from
a dry-docked tug vessel in 2002. Despite Styela’s presence at Lyttelton Port (and possibly marina)
since at least 2002, it has to our knowledge not spread to other artificial or natural habitats within
Lyttelton Harbour 17 (e.g. Diamond Harbour, Corsair Bay and Quayle Island jetties) or Akaroa Harbour
(Gust et al. 2006a, Gust et al. 2006b). Similarly, Styela was discovered at the Tutukaka Marina in
2005 and, in the absence of management action, has neither noticeably increased in local abundance
nor been reported from the Poor Knights Islands.
18.3.2. Option 2: Local eradication
As described in detail during the evaluation of this management objective for the Styela population at
Tutukaka Marina (see above), eradication in practical terms involves the removal of all potentially
reproducing individuals from an area, followed by regular surveillance to ensure that the species
remains absent (Myers et al. 1998, Regan et al. 2006). We defined local eradication of Styela to
mean:
“removal of all detectable individuals from Lyttelton Port and Magazine Bay
Marina and continued non-detection of Styela within these locations for a period
equivalent to at least the length of two generations, when a survey equivalent in
power to that used in this study is implemented.”
Assuming a lifespan of up to 3 years (Kluza et al. 2005), we recommend that any programme to
declare eradication using this definition would need to continue for at least 6 years. Styela occurs at
low to moderate densities throughout the port and marina, with hotspots of very high density in both
locations. There are several factors that would pose significant challenges in eradication attempts for
Styela at Lyttelton Port and Magazine Bay Marina. First, the size of these locations and diversity of
substrates (e.g. several thousand piles, 100s of metres of breakwalls and up to 100 vessels in Lyttelton
Port) would require a very large-scale operation. Second, the low water clarity (i.e. poor visibility) in
Lyttelton Harbour and considerable depth (Lyttelton Port: 13 m) means that the use of SCUBA diving
to detect and remove Styela will be inefficient and possibly inadequate, particularly at the port.
Coutts and Forrest (2005) evaluated eradication tools for Styela as part of a MAFBNZ funded project.
They conclude that hand-picking of Styela by divers is only feasible for small populations in locations
17 Field observations for MAFBNZ’s nationwide target pest surveillance project RFP106232007.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 153

Deliverable 5
with reasonable visibility. For areas with large amounts of artificial habitat and a widespread
distribution of Styela at moderate densities they recommend that:
“Where possible, structures and vessels infected with Styela should be removed from the water for
land-based treatment. Applicable methods […] may include water blasting, natural air drying,
immersion in freshwater, and exposure to acetic acid or chlorine. Immersion in an acetic acid bath
would be a suitable method for structures such as moorings that can be lifted temporarily (e.g., for a
few minutes) and re-deployed.
Where artificial structures cannot be practically or cost-effectively removed (e.g., wharf piles, floating
pontoons, large vessels) and in situ treatment is necessary, the most feasible approach […] is wrapping
with impermeable plastic. Mortality within the wraps could be accelerated through the addition of
acetic acid or chlorine. Hand removal of Styela may also be appropriate where densities are low.
For artificial structures that cannot we wrapped, such as concrete or rip-rap walls, and for natural
habitats, other approaches will be necessary. Possible methods include hand removal, smothering with
sediment and steam sterilisation.”
Eradication of Styela from Lyttelton Port may only be possible via two methods. One option would be
in situ wrapping of piles and pontoons (also referred to as ‘encapsulation’; optionally enhanced by the
injection of chlorine or acetic acid between piling/pontoon and wrapping sheet), steam sterilisation or
equivalent methods for vertical walls and breakwalls, and removal and treatment of smaller structures
such as ropes and ladders. Coutts and Forrest (2005) found all of these methods to be effective in
killing Styela in a specified area. An alternative option may be the closure of the port entrance
(i.e. isolation of the port basin) and the treatment of all port water with appropriate chemicals. This
has been done successfully during the eradication of the black-striped mussel (Mytilopsis sallei) from
three Darwin marinas in 1999 using 187 tons of liquid sodium hypochlorite and 7.5 tons of copper
sulphate (Ferguson 2000). While a combination of encapsulation, removal from water and steam
sterilisation would be a suitable option for eradicating Styela from Magazine Bay Marina, chemical
treatment of marina water would not be an option as this facility is not enclosed and chemicals
released within the marina would be dispersed via currents into adjacent habitats. Chemical treatment
would also not be an option for Cashin Quay and the Coal Terminal of Lyttelton Port. Both sites are
located outside the port basin and would need to be treated using a combination of encapsulation
(Cashin Quay) and steam sterilisation or equivalent methods (breakwalls near Coal Terminal).
Effectiveness
Eradication of Styela from Lyttelton Port and Magazine Bay Marina will only stand a chance of being
effective if two conditions are met. Firstly, eradication would need to be attempted at both locations.
Because port and marina are situated only approximately 1 km from another, both are within reach of
each others’ propagules, and treatment of a single location may result in re-infection by larvae
dispersed from the neighbouring population. Second, eradication would need to be coupled with an
effective and comprehensive vector management programme. Lyttelton Port receives approximately
130 commercial ship arrivals from the Port of Auckland each year, where Styela is present,
widespread and unmanaged (Deliverable 2). Arrivals also occur from other locations where Styela is
established, including ports in Australia and northeast Asia (Inglis et al. 2006). Also persistence of
Styela within the marina or port on infected resident vessels, or “transmission” of Styela from visiting
154 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 5
vessels to susceptible local vessels is possible under this option, as it contains no measures to manage
vectors. Eradication without vector management (this management objective) would have a high
likelihood of resulting in re-establishment of Styela in the port, resulting in moderate longer-term
effectiveness of this management objective.
As discussed above for the Tutukaka Marina, the effectiveness of an eradication campaign is
particularly contingent on an ongoing powerful surveillance programme and the immediate
availability of resources for incursion response if re-establishment occurs during the monitoring
period.
Practicality
Eradication is only feasible when the following criteria can be met (Bomford and O'Brien 1995):
• all reproductive animals are at risk of removal and can be detected at low densities
• the rate of removal from the population exceeds the rate of increase
• immigration to the population is zero, and
• there is general public acceptance of the control programme.
At Lyttelton Port and Magazine Bay Marina, the most significant challenge for this strategy involves
detection of all individuals before they become reproductive. The water clarity at both locations is
very poor (at times 0.3 m Secchi depth, see Deliverable 1) which means that all surfaces may have to
be treated under the assumption that they may contain Styela. One particular challenge will be the
treatment of pilings associated with wharves 1–7. These wharves are used on either side, and are built
upon a continuous array of vertical piles. Under each wharf are approximately 10 ‘hidden’ rows of
piles (each row containing up to 75 piles) that are not readily accessible. Wrapping of these piles
(> 1,000 in total) would have to be done by driving a small vessel under the wharf or by divers
dragging wrapping material under the jetty. An additional challenge is presented by old derelict piles,
which have often broken off below the water surface and can thus not be seen. These structures
present an entanglement issue and thus a hazard to divers. They are usually located between rows of
newer piles and their proximity to the water surface makes them a hazard for driving a small boat
under the wharves. Yet, they are suitable habitat for Styela and would have to be located, inspected
and treated in the same manner as regular piles that are visible from the surface. Lyttelton Port
contains hundreds of such submerged, derelict piles.
Encapsulation of piles and pontoons is an effective option but has little practicality because of the
large number of piles in the port (estimate: 2,000) and the logistical constraints the port’s water depth
poses on pile wrapping by divers. The limitation of deep ascents that can be made per diver per day
means that large rotating dive teams are required for this work.
Wrapping of permanent structures and removal from the water of smaller structures may be
complemented by the use of larval monitoring techniques in the surveillance plan. Refer to the
evaluation of the effectiveness of eradication of Styela at the Tutukaka Marina for details on these
techniques.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 155

Deliverable 5
Acceptability to stakeholders
The effectiveness of treatment methods for marine pest control is often inversely related to the
acceptability of these methods to stakeholders (Kuris and Thresher 2004). This is likely to be the case
for chemical treatment of Lyttelton Port, which will have a high level of effectiveness but will very
likely be unacceptable for a range of stakeholders because of (i) the potential environmental impact of
the operation, and (ii) the temporary closure of the port required for the application of chemicals to the
port’s isolated water body. Use of encapsulation and sterilisation treatments is likely to have a higher
acceptability to stakeholders in the port and marina.
Likely side-effects
The environmental effects associated with encapsulation would be minimal, provided the plastic wraps
do not leach chemicals under immersion and provided they are removed at the end of the treatment.
Because of the quantities of wrapping materials required, we recommend the use of recyclable plastics
to minimise the impacts associated with their eventual disposal as landfill. Wrapping of piles and
other structures is likely to kill all fouling organisms growing on these surfaces. While this is
undesirable for native species, a positive side effect is that all or most other non-indigenous species in
the port would also perish. One possible advantage of the wrapping treatment would be that piles
could be left wrapped for an extended period because (i) the wrapping material may deter fouling
organisms or (ii) in the event of another pest incursion the wraps could be removed, effectively
resulting in a second eradication campaign. The additional injection of acetic acid or chlorine
underneath the wraps is unlikely to have any environmental impact because both substances quickly
neutralise when in contact with seawater.
Pile and pontoon wrapping would affect the operation of the port and marina as dive teams need to
operate safely and away from vessel traffic and loading operations. However, this impact would be
very localised and restricted to an area within approximately 50 m of where wrapping takes place.
Because of the low usage of the Magazine Bay Marina the impact at this location may be negligible.
Closure of the port and chemical treatment of the port basin water would have a major impact on the
operations of the port. The entire facility would need to be shut down for the period of the treatment
(we estimate a minimum of 1 week), which is likely to be associated with considerable financial losses
incurred by the port operator (Lyttelton Port Company), operators of commercial vessels frequenting
the port, and associated industries dependent on the port for import or export of goods. The
environmental impact associated with chemical treatment of the port basin are likely to consist of the
death of the entire resident biota of Lyttelton Port and, possibly, the death of organisms in areas
adjacent to the port following re-opening and flushing of the facility. Copper sulphate is toxic to
marine organisms but has no known impacts on human health at the doses used for eradicating the
black-striped mussel. In Darwin, for example, it was deemed safe for divers to inspect submerged
surfaces a few days following the marinas’ treatment with chlorine and copper sulphate (Ferguson
2000). However, the use (and required concentration) of copper sulphate for killing Styela has not yet
been examined.
Legality
As Styela clava is an Unwanted Organism, its removal and disposal would require approval from
MAF Biosecurity NZ under the Biosecurity Act 1993. Isolation and chemical treatment of the port
156 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

asin water would result in the mortality of all or the majority of resident organisms. A resource
Deliverable 5
consent for this operation will be required from the regional council (Environment Canterbury) and the
Environmental Risk Management Authority (ERMA). Dead fish are likely to float to the surface and
will have to be captured and disposed of on land, which will also require consent from the regional
council and, likely, the Ministry of Fisheries. Chemical treatment of Cullen Bay Marina in Darwin
resulted in 4 tons of dead fish that had to be removed and disposed of (Ferguson 2000).
The closure of all port operations required for chemical treatment of port basin water would require
prior negotiations to determine who carries the economic losses associated with the eradication
campaign. Because of the diversity of stakeholders in the port (Lyttelton Port Company, local
engineering and provedoring companies, shipping companies, and others) this is likely to be a
complex undertaking and may be associated with legal disputes.
Likelihood of success
Eradication campaigns have been successful on a number of occasions, and exclusively when the
target species had been discovered shortly following its establishment at the location when its
abundance and density were restricted (Anderson 2005, Culver and Kuris 2000, Ferguson 2000). In
contrast, attempts to eradicate well-established invaders have usually been unsuccessful (Glasby et al
2005, Hewitt et al 2005, Coutts and Forrest 2007). Styela is widespread throughout the Lyttelton Port
and Magazine Bay Marina and both facilities contain a large amount of inaccessible habitats (see
discussion of practicality). We believe that encapsulation of structures in the port will stand only a
small chance of eradicating Styela, and that complete eradication from the port can only be achieved
via chemical treatment of the port basin. A combination of encapsulation, removal from water and
steam sterilisation, in combination with follow-on monitoring, would stand a moderate likelihood of
success of permanently removing Styela from Cashin Quay, the Coal Terminal and the Magazine Bay
Marina.
Cost of implementation
The costs involved in the actual eradication attempt and the regular post-eradication monitoring of
adult and larval Styela are likely to be considerable. Accurate costing of eradication approaches is
beyond the scope of this Deliverable, but we provide some estimates for guidance.
The Lyttelton Port and Magazine Bay Marina contain an estimated 264,700 m 2 and 9,700 m 2 of
artificial habitat (Deliverable 1). We estimate that there are approximately 2,000 piles within the port,
with an average depth of 8 m (i.e. 16,000 linear meters of piles). A further ~500 piles with an average
depth of 4 m (i.e. 2,000 linear metres) are located within the Magazine Bay Marina. There are no
pontoons at the Magazine Bay Marina, and approximately 750 m 2 of pontoon habitat within the port.
Pannell and Coutts (2007) estimate the cost of pile wrapping (including removal) at $14.20 per linear
metre, and the cost for pontoon wrapping at $150 per 9 m 2 (Coutts and Forrest 2005; Pannell and
Coutts 2007). On the basis of these estimates, wrapping of piles and pontoons in the Lyttelton Port
and Magazine Bay Marina would cost approximately NZ$256,000 and $12,500, respectively. In
addition to that, costs would arise for steam sterilisation (or equivalent method) to treat approximately
1,000 m of breakwall (average depth 8 m) and for the removal, treatment and reinstallation of
approximately 250 tire fenders, ladders and miscellaneous other structures from the water. We have
no cost estimates for these items.
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Deliverable 5
Chemical treatment of the port basin water would require the closure of the Lyttelton Port for
approximately one week. Determination of the financial losses associated with this closure is beyond
the scope of this Deliverable. However, Lyttelton Port is the South Island’s main shipping port and
we envisage that losses incurred by its closure would be considerable. In Darwin, where marinas
colonised by the black-striped mussel were closed off and treated using chemicals, the entire campaign
(pre-treatment survey, purchase and administration of chemicals, post-treatment survey, public
awareness campaign, vector management) had a combined cost of AU$2.2 million (Ferguson 2000;
Bax et al 2001). This did not include any economic losses incurred by the marinas’ operators or
associated maritime industry.
In addition to the actual eradication campaign, regular surveillance of port and marina would be
required for up to 6 years. A survey of both locations with the equivalent power of the survey used for
Deliverable 1 would require a team of six people, a small research vessel and a period of nine working
days. Using the estimates of Hayes et al. (2005) as this would result in $31,500 per survey, not
including transport, accommodation and associated field expenses. (As stated for the discussion of
this management objective for Tutukaka Marina, Hayes et al.’s estimates are based on a cost of $500
per person per day and given present day personnel costs they represent a considerable underestimate).
Additional use of larval monitoring techniques would cost around $2,300 per survey if a gene probe
was used to screen plankton samples, or ~$2,500 per survey if larval collectors were deployed and
monitored.
Styela become reproductively mature at between 2 and 7 months of age (Kluza et al. 2005). To
ensure that any new recruits are detected early, visual surveys should initially be carried out at least
quarterly, so that new individuals can be removed before they reach reproductive maturity. Once
sequential surveys begin to return no individuals it may be possible to reduce the frequency of survey
to 6-monthly.
For a discussion when to stand-down monitoring and eradication operations refer to our evaluation of
eradicating Styela from the Tutukaka Marina (Option 2 in previous section).
Degree of uncertainty
The degree of uncertainty associated with this management objective is most likely because many
habitats in the port are highly inaccessible and Styela is widely spread through the entire area.
Uncertainty can be minimised through the use of a well-designed and rigorous detection and
monitoring programme. Sensitivity and associated variation of monitoring surveys for particular
population sizes can be calculated for a given methodology and sampling effort. Uncertainty can
therefore be quantified a priori (Hayes et al. 2005).
18.3.3. Option 3: Maintain population at or below current level
This management objective is very similar to Option 2, except that the objective is not to remove
Styela completely, but to ensure that it becomes no more abundant than it is currently or at the time of
the surveys associated with Deliverable 1 (5.4). If the population approaches or exceeds this
threshold, control action is implemented. Because of the low visibility within both port and marina,
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Deliverable 5
manipulation of Styela density via hand-picking by divers is not feasible. The treatment method we
recommended above (wrapping of piles, pontoons and other structures) is not sensitive to density but
targets all Styela (and other fouling organisms) contained within the treatment area. For this reason,
population size should be specified as the measure of abundance linked to a treatment threshold. If
this is done, population size can be manipulated by wrapping a corresponding proportion of piles and
structures depending on how far the threshold has been exceeded. Alternatively or additionally, a
spatial population distribution pattern may be specified as the threshold unit, allowing particular areas
of the marina to be targeted (e.g. the ‘hotspots’ of high Styela abundance, such as the pontoons
comprising A and B jetties and the pontoons located between Z Berth and Gladstone Pier). However,
because current knowledge about the relationship between Styela density and inoculation risk is
limited and there is uncertainty regarding the influence of the proximity of vessels to Styela
populations, the usefulness of this approach is not known. A specified catch-per-unit-effort (CPUE)
may also be considered as a threshold measurement in place of a population size. This threshold
should be set by MAFBNZ, in consultation with a Technical Advisory Group. The frequency of
survey will be determined by the proximity of the population level to the threshold. At population
levels well below the threshold, sampling may be conducted at a lower frequency, with an increase in
frequency as the threshold is approached to improve precision of population estimates.
Effectiveness
The effectiveness of this management objective in preventing the spread of Styela to the HVAs is less
than that associated with Option 2 (eradication), particularly in the absence of vector management.
Infection of resident vectors with Styela can still occur, as can the species’ subsequent transport to any
of the HVAs. Because there is no knowledge of the relationship between population size (or density)
and inoculation pressure to resident vectors, the decision on an ‘appropriate’ or ‘acceptable’
population size at Lyttelton Port and Magazine Bay Marina is likely to be uninformed and arbitrary.
Practicality
As for Option 2 regarding the use of encapsulation treatments. Closure and chemical treatment of the
port basin is not applicable for this management objective.
Acceptability to stakeholders
As for Option 2 regarding the use of encapsulation treatments.
Likely side-effects
As for Option 2 regarding the use of encapsulation treatments.
Legality
As for Option 2 regarding the use of encapsulation treatments.
Likelihood of success
The success of the control action will be evaluated by the sequential surveys. If a given population
reduction effort is unable to maintain the population below the threshold level, then the strategy will
need to be re-evaluated, potentially with implementation of alternate control methods. Given a robust
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Deliverable 5
survey and monitoring regime, this management objective is likely to be associated with a moderate
likelihood of success.
Cost of implementation
The costs for this option will be considerably less than those for Option 2. An initial delimitation
survey is necessary to determine the level by which populations of Styela in Lyttelton Port and
Magazine Bay Marina exceed those described here in Deliverable 1. This will determine the control
effort required in the first instance (refer to Option 2 for cost estimates per pile or pontoon unit).
However, unlike an eradication campaign, where there is an anticipated stand-down of operations once
successful eradication has been declared, the costs of monitoring for this option are ongoing. As a
control option, it requires ongoing financial support and, therefore, would need long-term budgetary
support to be effective. Long-term, we expect this option to be comparable in cost to eradication.
Degree of uncertainty
The degree of uncertainty associated with the effectiveness of this management objective in
preventing the spread of Styela to the HVAs is likely to be higher than that for Option 2. This
management objective assumes that a reduced population size will reduce the risk of Styela being able
to reach the HVAs. However, there is a lack of information on the relationship between local
population size and inoculation risk of susceptible vectors residing at the marina.
18.3.4. Option 4: Maintain population at or below a specified level (other than current level)
This management objective is similar to Objective 3 (above), except that the threshold is set at a level
other than the current level (Table 5.4). The population is monitored using surveys with a specified
probability of detection and active management is implemented if a specified threshold is approached
or exceeded.
The task of setting the threshold value and unit is complex and careful consideration should be given
to ensure that it is acceptable and manageable. For example: the threshold may be set at a level higher
than current which will allow the population to increase beyond the existing abundance and/or
distribution before being controlled. Once this option is implemented it is unlikely that a change to a
more conservative strategy (e.g. local eradication) would be possible. The choice of threshold value
should be associated with some knowledge of how it relates to the inoculation risk of locally moored
vectors by Styela or the likelihood of its dispersal into adjacent natural coastal environments.
Currently such knowledge does not exist.
Effectiveness
The choice of threshold unit (population size vs. density) and threshold size (or density) will affect the
outcome and the tools required to control the population should it exceed the threshold. Hand-picking
of Styela by divers is unfeasible given the turbidity of Lyttelton Harbour, and encapsulation does not
allow manipulation of Styela density. We therefore suggest that population size is selected as the
threshold unit at these locations. If the threshold is approached or exceeded, active management is
implemented to reduce the population to a lower level. Suitable active management tools for Lyttelton
Port and Magazine Bay Marina include encapsulation, steam sterilization and temporary removal of
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Deliverable 5
structures from water for treatment (e.g., water-blasting or chemical). Refer to Options 2 and 3 for
detail.
Re-introduction of Styela on vessels entering Lyttelton Port or Magazine Bay Marina, and/or
persistence of Styela within the marina on infected resident vessels is possible under this option, as it
contains no measures to manage vectors. The effectiveness of this management objective to prevent
the spread of Styela to HVAs may be further compromised if Styela is “transmitted” from infected
visiting vessels to susceptible local vessels.
Practicality
As for Option 3.
Acceptability to stakeholders
As for Option 3.
Likely side-effects
As for Option 3.
Legality
As for Option 3.
Likelihood of success
As for Option 3.
Cost of implementation
This option may be more expensive than Objective 3 (maintaining the population at the current level),
due to the cost of active management of a potentially larger population.
Degree of uncertainty
As for Option 3.
As described in Objective 3 there is the option to manage some areas of the port and marina in a
different way to other areas. For example, control could be targeted at areas where potential vectors to
the HVAs berth or depart from. However, propagule pressure to suitable settlement substrates can be
high throughout yachting marinas (Floerl and Inglis 2003), and current knowledge about the
relationship between Styela density and inoculation risk is inadequate to support this strategy.
The advantage of setting the threshold at a level other than current is that at locations where Styela is
currently abundant the threshold can be set at a lower level to reduce and maintain the population at
the threshold. Conversely, if there was evidence that the risk of spread of Styela to HVAs would not
significantly increase if the current population increased to a certain degree then the threshold could be
set a level higher than current to delay or avoid management costs. However, again, this information
is currently not available and in its absence we do not recommend the use of an arbitrarily chosen
population threshold size (e.g. 50 % of the current population size at Lyttelton Port) as a management
strategy.
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18.4. B. Vector management options (Lyttelton Port and Magazine Bay Marina)
The options evaluated in this section are treated as exclusive and assume an absence of population
management. Combinations of vector and population management options are evaluated in a separate
section below.
18.4.1. Option 5: No vector management
This option involves no management of vectors entering or leaving Lyttelton Port and Magazine Bay
Marina (Table 5.4).
Effectiveness
Without vector management, vessels carrying Styela will be able to enter and leave the the port and
marina unnoticed. In the absence of population management, particularly at Lyttelton Port, it is likely
that Styela will eventually become transported to the either of the Banks Peninsula, Akaroa Harbour
and Marlborough Sounds HVAs via infected vectors leaving the port. This likelihood would be
nullified (Option 2) or reduced (Options 3 and 4) if population management is adopted and successful.
However, irrespective of population management, a lack of vector management at Lyttelton Port
would be unable to prevent the arrival of Styela on vessels from Auckland and Hauraki Gulf, where
Styela is widespread and abundant. In the right circumstances, larvae released by Styela on these
vessel may be able to colonise adjacently moored local vessels and aquaculture vectors that
subsequently travel to the HVAs.
Practicality
This option requires no additional resources or changes to current management of the marina and its
operations.
Acceptability to stakeholders
As in Option 1.
Likely side-effects
As in Option 1.
Legality
As in Option 1.
Likelihood of success
Not applicable.
Cost of implementation
There are no direct costs involved with implementation of the ‘do nothing’ option.
Degree of uncertainty
As in Option 1.
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18.4.2. Option 6: Minimise spread to HVAs
Deliverable 5
Minimising the risk of spreading Styela from Lyttelton Port and Magazine Bay Marina to the Banks
Peninsula, Akaroa Harbour and Marlborough Sounds HVAs (referred to as ‘the HVAs’ from hereon –
not including the Poor Knight Islands HVA) can involve two dimensions of voluntary management.
Firstly, management of infected or potentially infected vessels departing from Lyttelton to the HVAs.
Secondly, risk profiling of incoming vectors to prevent inoculation of resident vessels with Styela
(Table 5.4).
Because of the diversity of shipping and industry sectors using Lyttelton Port and Magazine Bay
Marina (commercial, aquaculture, tourism, recreational) and the different operational and economic
characteristics associated with each, separate vector management strategies may be required for each
sector.
(a) Commercial sector
Commercial vessels that travel between Lyttelton and the HVAs include merchant vessels, fishing
vessels, the Diamond Harbour ferry, towed barges and maintenance vessels such as dredges.
Minimising the potential of spreading Styela to HVAs via these vessels can be achieved by eliciting
changes in vessel maintenance. Such changes could include: (i) evaluation of appropriateness of
current antifouling paints used (possibly change to a more appropriate product), (ii) (where
appropriate) increased frequency of antifouling paint renewal to lower the risk of colonisation by
Styela, and/or (iii) regular inspection and (where required) manual cleaning of vessel hulls involving
appropriate containment of fouling material. Pro-active behaviour of owners and operators can be
elicited through the use of social marketing aimed at increasing awareness of the risks an invasion by
Styela may pose to the values encompassed by the HVAs.
(b) Aquaculture sector
Styela can be transported from Lyttelton to the HVAs via vectors associated with the aquaculture
industry, including harvesting and maintenance vessels, towed barges and farming equipment.
Minimising the risk of spreading Styela via the aquaculture sector can be achieved via a
communications / social marketing exercise that helps aquaculture operators identify which processes
associated with their operations have the potential to facilitate the spread of the species (e.g. regular
commutes between Banks Peninsula HVA and Lyttelton Port during mussel harvesting seasons, and
subsequent transfer of harvesting vessels to Marlborough Sounds HVA). As for commercial vessels,
aquaculture operators could: (i) evaluate the appropriateness of current antifouling paints used on their
vessels and other submerged equipment (possibly change to a more appropriate product), (ii) (where
appropriate) increase the frequency of antifouling paint renewal to lower risk of colonisation by
Styela, and/or (iii) regularly inspect and (if required) manually clean vessel hulls and farming
equipment with appropriate containment of fouling material. In particular, any vessels or equipment
that pass through Lyttelton Port during transfer between aquaculture facilities (e.g. harvesting vessels
operating in both the Marlborough Sounds and Banks Peninsula HVAs) should be maintained in a way
that the likelihood of colonisation by Styela is minimised.
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(c) Tourism sector
Tourism vessels that travel between Lyttelton and the HVAs include sightseeing vessels and sailing
charters. As for the other sectors, the potential of these vessels to facilitate the transport of Styela to
the HVAs can be minimised by eliciting changes in vessel maintenance. Such changes could include:
(i) evaluation of appropriateness of current antifouling paints used (possibly change to a more
appropriate product), (ii) (where appropriate) increased frequency of antifouling paint renewal to
lower the risk of colonisation by Styela, and/or (iii) regular inspection and (if required) manual
cleaning of vessel hulls involving appropriate containment of fouling material. Pro-active behaviour
of owners and operators can be elicited through the use of social marketing aimed at increasing
awareness of the risks an invasion by Styela may pose to the values encompassed by the HVAs.
(d) Recreational vessels
Recreational vessels travelling between Lyttelton Port, Magazine Bay Marina and the three HVAs
have the potential to transport Styela to these locations. Recreational vessels residing at Magazine Bay
Marina are generally poorly maintained and in many cases fouling assemblages can be seen from the
surface (Deliverable 2). The risk of transporting Styela can be minimised by eliciting changes in
vessel maintenance. Such changes could include: (i) evaluation of appropriateness of current
antifouling paints used (possibly change to a more appropriate product), (ii) (where appropriate)
increased frequency of antifouling paint renewal to lower the risk of colonisation by Styela, and/or
(iii) regular inspection and (if required) manual cleaning of vessel hulls involving appropriate
containment of fouling material. Pro-active behaviour of recreational vessel owners can be elicited
through the use of social marketing aimed at increasing awareness of the risks an invasion by Styela
may pose to the values encompassed by the HVAs.
Participation of all sectors in voluntary vector management schemes may be enhanced by the
development of industry codes of practice with regard to minimisation of the risk of spreading marine
pest organisms. For example, the aquaculture industry has already established environmental codes of
practice, whose adoption is used by facility operators for marketing and demonstrating the quality of
their product. The high commercial relevance of a certified “pest-free” farming environment would
make the development of a biosecurity related accreditation particularly feasible for the aquaculture
industry.
Vector management measures may also be initiated by the port and marina operators. The
development of risk profiling and management procedures for incoming vectors by operators of the
Lyttelton Port and the Magazine Bay Marina would further help reduce the risk of spreading Styela to
the HVAs. The arrival of Styela on the hulls of visiting vessels could, in the right circumstances,
result in the inoculation of adjacently moored vessels that may subsequently visit the HVAs. Such
importation of Styela may compromise the efficacy of population management efforts if carried out in
conjunction with vector management. Styela is widespread throughout the Auckland and Hauraki
Gulf regions and may arrive at Lyttelton via transport on merchant vessels or maintenance vessels
such as dredges (see Deliverable 2).
Again, different shipping sectors (commercial, aquaculture, tourism, recreational) will need to be
managed in different ways. In broad terms, however, Lyttelton Port and Magazine Bay Marina could
adopt risk profiling schemes that allow them to (i) screen resident and incoming vessels and other
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Deliverable 5
vectors for their potential to transport Styela to the HVAs (survey of travel and maintenance history),
and (ii) inform operators of high-risk vectors of their threat to biosecurity and assist with solutions for
convenient and cost-effective vector hygiene. Options for this include: assistance with organising for
in-water cleaning using approved technology that ensures containment of biological material,
assistance with local haul-out (or dry-docking) and antifouling paint renewal, and offering integrated
berthage and maintenance packages (haul-out or dry-docking and antifouling paint renewal) to long-
term residents or frequent visitors. The implementation of such programmes could be made attractive
to operators of port and marina through the establishment of an accreditation system that certifies
awareness of and commitment to biosecurity of the facility. Examples of such accreditation systems
already exist for recreational marinas (e.g. the Blue Flag system for marinas worldwide;
www.blueflag.org).
To determine the likely success of this management option, it is important to monitor rates of
compliance among all sectors with the voluntary measures.
Effectiveness
Adoption of voluntary vector management measures as described above would most likely reduce the
frequency at which Styela is transported to the HVAs and, presumably, the species’ likelihood of
becoming established in these locations. The effectiveness of this management objective will be
influenced by the level of participation among vessel, aquaculture, tourism and port and marina
operators. Species invasions are highly stochastic processes (Sakai et al 1998) and even rare
transportation events can result in the establishment of new populations (Buchan and Padilla 1998).
We suggest that vector management can be a very powerful tool to minimise the potential for Styela to
reach the HVAs, provided it is practised by all or the majority of vessel owners and operators. Natural
dispersal of Styela to the Akaroa Harbour and (in particular) the Marlborough Sounds HVAs is
unlikely and would require a considerable number of larval generations. Vector management will be
more effective in preventing the spread of Styela to these HVAs than population management.
However, Styela is able to disperse naturally to the Banks Peninsula HVA, and both population and
vector management are likely to be required to prevent the arrival of Styela at this HVA.
Practicality
The development of an effective voluntary vector management programme will require the approval
and commitment of all sectors – commercial, aquaculture, tourism, recreational – as well as the port
and marina operators. The main objectives of such a programme can be identified through workshops
between MAFBNZ, representatives of the various sectors, Lyttelton Port and Magazine Bay Marina
management and, possibly, the antifouling paint industry. This may require a considerable initiative.
Significant participation in a voluntary programme will only be achieved via effective communication
and marketing strategies specifically targeted at the various sectors.
Acceptability to stakeholders
We anticipate acceptability of the programme to be high because participation in it is voluntary.
Likely side-effects
We expect small direct adverse effects to be associated with this management objective. More
frequent application of antifouling paints, and a higher incidence of in-water hull cleaning by
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Deliverable 5
scrubbing or brushing may result in higher concentrations of antifouling toxins in marina water and
sediments, which can have adverse effects on resident non-target biota (Comber et al. 2002,
Katranitsas et al. 2003, Thomas et al. 2002). Any potential effects on water and sediment chemistry,
and local biota, can be minimised by promoting the use of non-toxic antifouling paints (Johnson and
Gonzalez 2007, Johnson and Miller 2002). Increased in-water removal of biofouling resulting from
improved hull maintenance must be accompanied by appropriate containment and disposal of the
material on land.
Legality
This option involves no change to the current management regime. However, clarification would be
needed on the obligations (if any, under the do-nothing approach) of vessel owners and operators who
observe Styela on their vessels, and the implications for knowingly translocating an Unwanted
Organism.
Likelihood of success
Even though this management option could be effective in preventing the spread of Styela to the
HVAs, the likelihood of achieving the required level of participation across all sectors is relatively
low. Participation of recreational and tourism vessel operators, as well as the aquaculture industry, is
likely. However, the overriding importance of economic incentives for commercial shipping may
prevent participation of a large proportion of merchant vessel operators. This may compromise this
management option’s potential to prevent the spread of Styela particularly to the Marlborough Sounds
HVA, which received a larger number of commercial vessel arrivals from Lyttelton per year than the
Banks Peninsula or Akaroa Harbour HVAs (see Deliverable 2).
Cost of implementation
The initial costs associated with this management objective are for the development of effective social
marketing and communications strategies targeting the various shipping and industry sectors. Initially,
the specific objectives of the vector management strategy should be identified by MAFBNZ in
consultation with scientific experts. Additional costs will arise through periodic monitoring of
compliance and the outcomes of the strategy. Resources should be available for a periodic review
process, the results of which can be used for refining elements of the campaign (e.g. poor compliance
of particular sectors) or developing new information material to update stakeholders. We anticipate
the cost to MAFBNZ associated with the implementation of a voluntary vector management
programme to be considerably less than the costs required for population control. The majority of
foreseeable costs will be associated with staff time and possibly the outsourcing of the development of
social marketing and communications strategies and associated information materials.
Degree of uncertainty
Given high levels of participation among sectors, the achievement of this management objective for
the Marlborough Sounds and Akaroa Harbour HVAs will be associated with a moderate level of
uncertainty. Because natural dispersal of Styela to the Banks Peninsula HVA is possible in the
absence of population management, and can undermine the effectiveness of any vector management
efforts, the achievement of this management objective for the Banks Peninsula HVA is associated with
a high level of uncertainty.
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18.4.3. Option 7: Prevent spread to HVAs
Preventing the spread of Styela to the Banks Peninsula, Akaroa Harbour and Marlborough Sounds
Deliverable 5
HVAs would require the implementation of mandatory measures that result in the exclusion of
infected or potentially infected vectors from these locations (Table 5.4). The specific methods
involved in preventing fouling and transport of Styela on vessel hulls are similar to those described in
Option 6 above. However, this management objective requires legislation to be developed and
implemented instead of voluntary measures.
(a) Commercial sector
Prevention of transport of Styela from Lyttelton to the HVAs can be achieved through the
establishment of mandatory guidelines for vector hygiene that are incorporated into the licences or
resource consents of vessels travelling from Lyttelton to the HVAs.
(b) Aquaculture sector
A code of practice for prevention of transfer of Styela could be developed for/by the aquaculture
industry, with compliance required for any vessels frequenting Lyttelton Port or Magazine Bay Marina
and any of the HVAs. Most aquaculture vectors are owned by facility operators, and compliance with
hygiene guidelines specified in the code of practice could be tied to the resource consents for facilities
within the HVAs. A code of practice for the aquaculture industry should provide guidelines to prevent
the spread of Styela by movements of service vessels and barges, as well as through transfers of
aquaculture stock and equipment between production facilities.
(c) Tourism sector
Prevention of transport of Styela from Lyttelton to the HVAs can be achieved through the
establishment of mandatory guidelines for vector hygiene that are incorporated into the licences or
resource consents of tourism vessels travelling from Lyttelton to the HVAs.
(d) Recreational vessels
The establishment of mandatory guidelines for recreational vessels is more difficult to achieve because
operation of these vessels is not tied to a licence or resource consent. However, mandatory
notification of the intention to travel to the HVAs could be made a requirement for any recreational
vessel using Lyttelton Port and Magazine Bay Marina. A vessel’s potential for spreading Styela to the
HVAs could be assessed by the notified authority (e.g. port or marina operators, harbour master) based
on the travel and maintenance history reported.
Preventing the spread of Styela from Lyttelton to the HVAs could also to some extent be made the
responsibility of the port and marina operators. Port and marina could be required to set up a
monitoring system for vessels frequenting the HVAs that tracks the hull maintenance schedule of these
vessels and notifies their owners and operators when maintenance is due. An optional measure would
be the inclusion of hull surveys in the port and marina’s monitoring programme that result in
mandatory hull maintenance for vessels that fail the inspection requirements. Mandatory hull
inspections have been used by the Northern Territory Fisheries Authority in Australia following the
black-striped mussel incursion at Darwin marinas. From a managerial perspective, this exercise was
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Deliverable 5
considered very useful as several dozen cases of non-indigenous species introduction were intercepted
through mandatory hull cleaning (A. Marshall, pers. comm.).
As discussed for the Poor Knight Islands HVA, an additional option is the implementation of a
controlled and/or restricted area around the Marlborough Sounds, Banks Peninsula and Akaroa HVAs
that is only accessible to vessels that are compliant with requirements for vessel hygiene. Any
regulations relating to vector hygiene should be meaningful, reasonable and defensible, and be
developed by MAFBNZ in consultation with experts on biofouling, the antifouling paint industry and
representatives of shipping and industry sectors associated with Lyttelton Port, Magazine Bay Marina
and the HVAs.
Effectiveness
The criteria determining the effectiveness of this management objective are the same as those
described for Option 6. In this case, effectiveness in preventing the spread of Styela to the HVAs can
be assumed to be very high as mandatory exclusion of infected and potentially infected vectors from
the HVAs will prevent any introduction of Styela to these locations from Lyttelton. However, as for
Option 6, arrival of Styela at the HVAs via vector originating from other sources of the species (e.g.
Auckland) will remain possible. The likely incidence of non-compliance and illegal visits to the
HVAs by potentially infected vessels can not be easily determined.
The effectiveness of a mandatory vector management programme can be determined – and increased –
by regular compliance monitoring and the development of disincentives for non-compliance (e.g.
fines, suspension of licences, etc.).
Practicality
The practicality of this management objective is lower than that of Option 6 because of the large
number of stakeholder groups and management authorities that need to be involved in the policymaking
process.
Acceptability to stakeholders
The effectiveness of management measures for marine pests is often inversely related to the
acceptability of these measures to stakeholders (Thresher and Kuris 2004). Vector management may
pose a high level of inconvenience on owners and operators of vessels, aquaculture and tourism
operations and port and marina. Improved vessel management can translate into significant additional
costs arising from an increase in the frequency of antifouling paint renewal (and associated haul-out or
dry-docking costs) and economic losses incurred through vessel inactivity during treatment. We
anticipate the acceptability of this management objective to stakeholder to be lower than for
population management. Acceptability will be particularly low for operators of large commercial
(merchant and fishing) vessels because of the high costs associated with increased maintenance and
losses in income during maintenance periods.
Likely side-effects
As for Option 6.
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Legality
Deliverable 5
Adoption of this management objective would require the development of legislation that facilitates
the development, implementation and monitoring of the vector management programmes discussed
above. This is likely to be a complex task requiring input and cooperation of several agencies,
including the Marlborough District Council, Tasman District Council, Nelson City Coucil,
Environment Canterbury and Banks Peninsula District Council. The powers and responsibilities of
these agencies and MAFBNZ in a management programme as described above need to be established.
Likelihood of success
We expect this option to be associated with a very high likelihood of success in particular if access to
the Poor Knights Islands is restricted to vessels with demonstrably low or no potential to transport
Styela. This option would have the advantage of also targeting vectors arriving from areas other than
Tutukaka Marina, such as the Hauraki Gulf region where Styela is abundant and widespread.
Cost of implementation
The costs associated with this management objective will be higher than those associated with Option
6 because of the addition of policy making. All cost items discussed for Option 6 will be incurred,
with the addition of the costs involved in translating a voluntary management programme into a
mandatory one that potentially involves several government authorities.
Because this management objective requires the development of communication strategies, awareness
campaigns, etc., in the same manner as described for Option 6, it may be feasible to commence with a
voluntary vector management programme and decide on the adaptation of mandatory guidelines when
levels of compliance, effectiveness and potential problems of the voluntary programme have been
quantified and reviewed. One possible shortcoming of this approach is, however, that the accidental
introduction of Styela to the HVAs during the trial period of the programme may not be reversible.
Degree of uncertainty
If vector management is mandatory and vessel owners and operators visiting the HVAs have no
choice, the degree of uncertainty associated with this management objective is likely to be low.
18.4.4. Option 8: Minimise/prevent spread from Lyttelton Port and Magazine Bay Marina
This management objective aims to prevent or minimise the spread of Styela from Lyttelton Port and
Magazine Bay Marina by targeting all outgoing vectors belonging to all shipping and industry sectors,
regardless of their destination. Minimising spread from the port and marina would require the
implementation of the voluntary vector management programme described for Option 6, but extended
to all outgoing vectors. Preventing spread of Styela from the port and marina would require the
implementation of mandatory vector maintenance guidelines described in Option 7, for all outgoing
vectors. The advantage of this strategy would be that the risk of spreading Styela to other, non-HVA
locations, is reduced. At present, Lyttelton has the only confirmed Styela population in the South
Island.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 169

Deliverable 5
Effectiveness
As for Options 6 and 7.
Practicality
As for Options 6 and 7.
Acceptability to stakeholders
As for Options 6 and 7.
Likely side-effects
As for Options 6 and 7.
Legality
As for Options 6 and 7.
Likelihood of success
As for Options 6 and 7.
Cost of implementation
As for Options 6 and 7.
Degree of uncertainty
The degree of uncertainty for the spread of Styela to the HVAs associated with this objective is higher
than the uncertainty associated with management objectives outlined in Options 6 and 7. Management
objectives that aim to minimise or prevent the spread of Styela to the Banks Peninsula, Akaroa
Harbour and Marlborough Sounds HVAs target potentially high-risk vessels from all locations, not
just the Lyttelton port and marina. Measures that prevent the spread from the Lyttelton Port and
Magazine Bay Marina may be successful, but can not control the fact that Styela may become
transported to the HVAs, particularly the Marlborough Sounds HVA, by vessels from Auckland and
the Hauraki Gulf. As shown in Deliverables 2 and 3, movement of commercial and recreational
vessels between the Auckland region and ports and marinas within the Marlborough Sounds HVA
occur frequently.
18.5. C. Combined vector and population management options (Lyttelton Port and Magazine Bay
Marina)
18.5.1. Option 9: Combination of population and vector management
This management objective would combine population management (eradication or maintenance of
population at/below current or other levels; Options 2–5) with vector management at Lyttelton Port
and Magazine Bay Marina (minimisation/prevention of spread to the HVAs, or prevention of spread
from port and marina; Options 6-8).
170 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

A combination of population and vector management at Lyttelton Port and Magazine Bay Marina
could, for example, consist of the adoption of Option 3 and Options 6 or 7 (maintenance of current
population size and reduction/prevention of arrival of vectors carrying Styela at the HVAs).
Effectiveness
Deliverable 5
The effectiveness of this combined approach is likely to be higher than for the exclusive use of a
single measure, which can leave ‘loopholes’ for Styela. A combination of population and vector
management as the management objective has distinct advantages because: (i) population management
at the Lyttelton port and marina will reduce the rate at which locally moored vectors become colonised
by Styela, and (ii) vector management will minimise the rate at which Styela is transported.
Particularly favourable approaches are those that minimise or prevent the arrival of high-risk vectors at
the HVAs, as this would also target vectors arriving from other known sources of Styela (e.g.
Auckland and Hauraki Gulf regions). Population management at Lyttelton port and marina without
vector management can not prevent the transport of Styela to the HVAs from other sources.
Practicality
The level of practicality associated with this management objective depends on the combination of
population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above).
Acceptability to stakeholders
The level of acceptability associated with this management objective depends on the combination of
population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above).
It is possible that the use of population management will result in an increased willingness of
stakeholder groups to partake in voluntary vector management programmes.
Likely side-effects
The magnitude of side effects associated with this management objective depends on the combination
of population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above).
Legality
The legality of this management objective depends on the combination of population and vector
management measures used: refer to the appropriate combination of management objectives among
Options 2–4 and 6–8 above).
Likelihood of success
The likelihood of success of this management objective depends on the combination of population and
vector management measures used: refer to the appropriate combination of management objectives
among Options 2–4 and 6–8 above).
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 171

Deliverable 5
Cost of implementation
The costs associated with this management objective depend on the combination of population and
vector management measures used: refer to the appropriate combination of management objectives
among Options 2–4 and 6–8 above). They will be higher than the cost of only population or only
vector management.
Degree of uncertainty
The degree of uncertainty associated with this management objective depends on the combination of
population and vector management measures used: refer to the appropriate combination of
management objectives among Options 2–4 and 6–8 above). We suggest uncertainty will be lower for
a combined approach than for only population or only vector management.
18.6. Recommended approach for Lyttelton Port and Magazine Bay Marina
Evaluation of the nine management objectives against criteria to be considered for the development of
pest management plans under The Biosecurity Act 1993 resulted in the highest relative rankings for a
combination of population management and a voluntary vector management programme that
minimises the human-assisted spread of Styela to the Marlborough Sounds, Banks Peninsula and
Akaroa Harbour HVAs (score of 66; Option 9a in Table 5.5). Different factors contributed to the
lower desirability of the other strategies. Mandatory vector management may be very effective, but
will not be acceptable to particular shipping and industry sectors (e.g. merchant vessels). Doing
nothing may be equally unacceptable because of the potential impacts Styela may have on aquaculture
operations. Attempted eradication of Styela from Magazine Bay Marina and – in particular - Lyttelton
Port is likely to be very expensive, highly unacceptable, associated with significant side-effects and
stands a high chance of being unsuccessful given Styela’s widespread distribution in these locations
and the size of the area that would need to be treated.
As for the case of the Poor Knights Islands HVA, we recommend a well-designed, comprehensive
vector management programme as the best immediate step to prevent the establishment of Styela in
the Marlborough Sounds and Banks Peninsula aquaculture production areas and Akaroa Harbour. We
emphasise that it is important, particularly for the Marlborough Sounds HVA, that all potentially highrisk
vectors are targeted, including those arriving from other areas where Styela is known to be present
(e.g. Auckland and Hauraki Gulf). Negligence of these vectors may lead to the introduction of Styela
to the HVAs and compromise the efficacy of all other management efforts.
We suggest that additional population management at Lyttelton port and marina may help to further
reduce the risk of spreading Styela to the HVAs. Eradication of Styela from the port (and therefore
also the marina) is probably unfeasible (cost and high uncertainty of success). Reducing or
maintaining current population sizes may be a feasible approach that can be achieved and that may
reduce propagule pressure on resident vectors travelling to the HVAs. However, we recommend that
any population management is preceded by experiments that examine how the risk of vector
colonisation by Styela varies throughout the port. Are vessels moored adjacent to hot-spots of Styela
at higher risk of becoming colonised than vessels moored in area of low abundance? The assessment
of the relationships between population size (or density), distance from reproductive adults and the
frequency at which susceptible vectors become colonised will help justify the feasibility and determine
the best format of population management for Styela in Lyttelton.
172 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Deliverable 5
Table 5.5: Evaluation of management objectives for Styela at Lyttelton Port and Magazine Bay Marina based on pest management criteria listed in The Biosecurity Act 1993 (Forrest et
al 2006). Values in brackets indicate relative weighting of criteria (e.g. ‘2’ = rank score multiplied by 2). Relative ranking system: 0 = unfavourable; 5 = favourable.
Option 1: No population
management
Effectiveness
(weighted x 3)
Practicality
Acceptability to
stakeholders
(weighted x 2)
Likely side-effects
(weighted x 2)
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 173
Legality
Likelihood of success
(weighted x 3)
Cost of
Implementation
(weighted x 3)
Degree of uncertainty
(weighted x 2)
1 5 1 1 5 0 a 5 3 38
Option 2: Local eradication 3 1 2 1 2 2 1 2 31
Option 3: Maintain population
at/below current levels
Option 4: Maintain population at
or below specified level
2 3 3 3 3 4 1 2 43
2 3 3 3 3 4 4 2 52
Option 5: No vector management 1 5 1 1 5 0 b 5 3 38
Option 6: Minimise spread to
HVAs
4 3 5 4 5 3 4 3 65
Option 7: Prevent spread to HVAs 5 2 1 4 2 5 3 4 61
Final score

Deliverable 5
Option 8a: Minimise spread from
marina (voluntary)
Option 8b: Prevent spread from
marina (mandatory)
Option 9a: Combination of
population and voluntary vector
management
Option 9b: Combination of
population and mandatory vector
management
Effectiveness
(weighted x 3)
Practicality
Acceptability to
stakeholders
(weighted x 2)
Likely side-effects
(weighted x 2)
174 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand
Legality
Likelihood of success
(weighted x 3)
Cost of
Implementation
(weighted x 3)
Degree of uncertainty
(weighted x 2)
4 3 5 4 5 3 4 2 63
5 2 1 4 2 5 3 3 59
5 3 4 4 5 4 3 3 66
5 2 1 4 2 5 2 4 58
a We evaluated the likelihood of success to prevent the transport of Styela to the HVAs via the do-nothing approach.
Final score

18.7. Discussion of simulation model results
Deliverable 5
We here summarise the results of the epidemiological model simulations. For detailed results refer to
Appendix 7.
The results obtained from the model simulations indicate that, over a period of 10 years, the spread of
Styela around New Zealand is largely unaffected by population or vector management in Lyttelton.
After 10 years, Styela had become established in a similar number of locations, irrespective of
management approach (do-nothing, population reduction by 50 %, or vector management). The
sequence at which HVA locations became colonised by Styela was consistent for all simulated
scenarios, with the Marlborough Sounds HVA becoming colonised soonest. In all 400 replicate model
runs, Styela became established in four of five HVA-associated model locations (Nelson, Havelock,
Waikawa Bay, Akaroa). Some positive trends are worth noting, however. Vector management and
population reduction resulted in a 5-% and 8-% decrease in the frequency at which Styela was
transported to the HVAs, respectively. While this did not prevent the species’ establishment at the
HVAs in the long term (10 years), it reduced the rate at which model locations became colonised
during the initial 6 years of the simulated period.
These results are most likely explained by the localised adaptation of the management approaches
considered here. To reflect the actual nationwide distribution of Styela (as of 2007), our model
incorporated Styela populations in Auckland and Lyttelton. However, population and vector
management were simulated only for Lyttelton but not for Auckland. The 11 model locations that
comprise the Auckland region account for 35.3 % of the total artificial habitat associated with all
model locations, and for 36 % of all yachts in the model. In comparison, Lyttelton Port and Magazine
Bay Marina comprise 1.1 % of total habitat and 0.9 % of all vectors. Our results show that, if
management measures are exclusively applied to a single source population of Styela in a heavily
inter-connected transport network with multiple established populations then this management
programme will most likely have no or low effectiveness. Our results therefore support our evaluation
of the nine management objectives in the previous sections that highlight the importance of preventing
the arrival of all high-risk vectors at the HVAs, not only high-risk vectors originating from Lyttelton
or Tutukaka. The potential influence of vector or population management at Lyttelton Port, Magazine
Bay Marina and, most likely (though not examined by the model) Tutukaka Marina on the spread of
Styela to the HVAs is likely to be compromised if movements of high-risk vectors originating from the
expansive Auckland and Hauraki Gulf populations of Styela are not managed.
Based on the evaluation of the nine different management objectives (Options 1–9 above) and the
results of the model simulations, we recommend the development of a comprehensive vector
management programme for preventing the spread of Styela to the Marlborough Sounds, Banks
Peninsula and Akaroa Harbour HVAs. While preventing the transport of Styela to the latter two
HVAs will be relatively easy to achieve, protection of the Marlborough Sounds HVA will be difficult,
as this region receives a high and diversity volume of vector traffic from both of New Zealand’s
largest sources of Styela – Lyttelton Harbour and the wider Auckland and Hauraki Gulf regions.
Because voluntary participation of large commercial vessels (merchant, tanker, cargo, etc.) in
increased hull maintenance is unlikely due to the considerable associated costs, mandatory guidelines
may be required to prevent transport of Styela on these ships.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 175

Deliverable 5
The efficacy of vector management could be optimised through additional population management,
such as maintenance of Lyttelton Styela populations at ‘safe’ levels. However, we recommend that
any population management at Lyttelton Port and Magazine Bay Marina is preceded by research into
the relationship between population size and propagule pressure to adjavent susceptible vectors.
Without such information, no meaningful choice of “safe” or “acceptable” population density can be
made.
18.8. Conclusions
Our evaluation of management objectives for both Tutukaka and Lyttelton populations of Styela and
the results from the model simulations indicate that the most feasible approach is likely to be the
exclusion of high-risk vectors from the HVAs that are to be protected and preserved. In both cases,
synchronous population management will most likely maximise the effectiveness of the overall
management programme. Our evaluations indicate that there are ways of excluding Styela from the
HVAs, but they may not be cheap, acceptable to stakeholders or free of associated side-effects. At the
writing of this report, there is no definite knowledge on the presence or absence of Styela from the
four HVAs. We recommend that the initiation of any comprehensive management programme to
prevent the establishment of Styela in the HVAs should be preceded by efforts to ascertain that the
species has not yet become established in these locations.
18.9. Available methods for population management of Styela
In the preceding sections we discussed and evaluated nine optional management objectives for
preventing the spread of Styela from Tutukaka Marina, Lyttelton Port and Magazine Bay Marina to the
four high-value areas. As we mentioned in our discussion of population management options, there is
a range of technologies available for treated submerged surfaces fouled by Styela. We provide a
detailed discussion of the various treatment methods in Appendix 7.2, including an avaluation of cost,
effectiveness, advantaged and disadvantages.
19. Acknowledgements
We acknowledge the capable field assistance of all the divers and boat people associated with the
surveys including: Martin Flanagan, Chris Woods, Lindsay Hawke and Matt and Kathy Comnee. We
thank the managers of Lyttelton Port, Magazine Bay Marina and Tutukaka Marina for access to their
facilities. We acknowledge the excellent GIS development by Ude Shankar and ongoing assistance,
advice and expertise from Helen Hurren. Many thanks to Don Morrisey for reviewing drafts of this
manuscript and his perceptive, constructive criticism.
176 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

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184 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 1
Major man made habitats present in Tutukaka Marina: piles, pontoons and break-walls.
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 185

Appendices
Appendix 2
Beneath a representative wharf in Lyttelton Port illustrating the wooden and concrete sleeve pier
piles, some of the major man made habitats present at this location.
186 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 3
Magazine Bay Marina photo illustrating construction of walkways and berth fingers.
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 187

Appendices
Appendix 4
Beaufort scale definitions.
Beaufort
number
Wind speed
(knots)
Wave height
(feet)
Definitions 14 Effects observed on the sea
0 < 1 - Calm Sea is like a mirror
1 1-3 0.25 Light air
2 4-6 0.5 - 1 Light breeze
3 7-10 2-3 Gentle breeze
4 11-16 3½ - 5 Moderate breeze
5 17-21 6-8 Fresh breeze
6 22-27 9½-13 Strong breeze
7 28-33 13½-19 Near gale
8 34-40 18-25 Gale
9 41-47 23-32 Strong gale
10 48-55 29-41 Storm
Ripples with appearance of scales; no foam
crests
Small wavelets; crests of glassy appearance,
not breaking
Large wavelets; crests begin to break;
scattered whitecaps
Small waves, becoming longer; numerous
whitecaps
Moderate waves, taking longer form; many
whitecaps; some spray
Larger waves forming; whitecaps everywhere;
more spray
Sea heaps up; white foam from breaking
waves begins to be blown in streaks
Moderately high waves of greater length;
edges of crests begin to break into spindrift;
foam is blown in well-marked streaks
High waves; sea begins to roll; dense streaks
of foam; spray may begin to reduce visibility
Very high waves with overhanging crests; sea
takes white appearance as foam is blown in
very dense streaks; rolling is heavy and
visibility is reduced
188 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 5.1
Appendices
Companies contacted during collection of vector data collected for the Tutukaka Marina. Entries in
bold type denote operations with whom contact was attempted on several occasions but that did not
contact us back or provide any information. PKI = Poor Knights Islands.
Vessel name Vessel type Mooring location Last
Destinations HVAs
antifouling
visited
Cara Mia Commercial fishing Tutukaka Marina Nov-06 Offshore fishing PKI
vessel
sites
Pacific
Commercial dive Tutukaka Marina Feb-07 PKI PKI
Hideaway vessel
Marlin Blue Commercial dive Tutukaka Marina Oct-05 PKI PKI
vessel
Whangarei
Norseman Commercial dive
vessel
Tutukaka Marina May-06 PKI PKI
Rumblefish Commercial dive
vessel
Tutukaka Marina Jan-07 PKI PKI
Blue Striker Commercial fishing Tutukaka Marina Dec-06 Offshore fishing PKI
vessel
sites
Calypso Commercial dive
vessel
Tutukaka Marina Aug-06 PKI PKI
El Tigre Commercial dive
vessel
Tutukaka Marina Aug-06 PKI PKI
Bright Arrow Commercial dive
vessel
Tutukaka Marina Jun-06 PKI PKI
Hendrick J Commercial dive
vessel
Tutukaka Marina Nov-06 Tui, Waikato No
Perfect Day Commercial dive
vessel
Tutukaka Marina Sep-06 PKI PKI
Cave Rider Commercial dive
vessel
Tutukaka Marina Sep-06 PKI PKI
Arrow Commercial dive
vessel
Tutukaka Marina (unknown) (unknown) (unknown)
CDiver Commercial dive
vessel
Tutukaka Marina (unknown) (unknown) PKI
PK Charters Commercial dive
vessel
Tutukaka Marina (unknown) (unknown) PKI
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 189

Appendices
Appendix 5.2
Companies contacted during collection of vector data collected for the Lyttelton Port. Entries in bold
type denote operations with whom contact was attempted on several occasions but that did not contact
us back or provide any information.
Vessel name Vessel type Mooring location Last antifouling Destinations HVAs visited
St George Mussel barge Z Wharf Every 12/15
months
Banks Peninsula,
Marlborough Sounds
Marlborough
Sounds
Pelican Dredge Z Wharf Mar-07 Timaru, Tauranga, Marlborough
Taranaki and Nelson Sounds
Tardis Mussel harvester Z Wharf Nov-06 Banks Peninsula, Banks
Marlborough Sounds Peninsula,
Marlborough
Sounds
Argos Georgia Commercial fishing Z Wharf Apr-05 Sub Antarctic Islands (unknown)
Southern Commercial fishing No. 2 or No. 3 May-06 (unknown) (unknown)
Progress
Wharf
Sharp Shooter Commercial fishing No. 2 or No. 3 Nov-06 (unknown) (unknown)
II
Wharf
Ida Marion Commercial fishing Dry dock Wharf Nov-06 Banks Peninsula Akaroa
Cressy Commercial fishing Dry dock Wharf Dec-05 Banks Peninsula Akaroa
Frontier Commercial fishing Dry dock Wharf Dec-05 Banks Peninsula Akaroa
Claymore Commercial fishing No. 6 Wharf Oct-06 (unknown) (unknown)
Marlene Commercial fishing No. 6 Wharf Sep-06 Akaroa Akaroa
Shemara Commercial fishing No. 2 or No. 3 Jan-07 Nelson, West coast Marlborough
Wharf
North Island
Sounds
Austro Carina Commercial fishing No. 5 Wharf Jun-06 Picton, Timaru, Marlborough
Wellington
Sounds
Canopus Commercial fishing Lyttelton
Fisherman’s Wharf
Oct-05 Akaroa Akaroa
Aotea Commercial fishing Lyttelton
Fisherman’s Wharf
Jan-07 Akaroa Akaroa
Latitude Commercial fishing No. 5 Wharf Dec-06 Auckland Marlborough
Sounds
Robert H Commercial fishing No. 5 Wharf Mar-07 Banks Peninsula Akaroa
Emma Lady Sailing charter vessel Lyttelton
Nov-06 Banks Peninsula (unknown)
Hamilton
Fisherman’s Wharf
Silver Foam Commercial fishing Lyttelton
Fisherman’s Wharf
Jul-05 Akaroa Akaroa
Ivan Golubets Commercial fishing Lyttelton May-06 (unknown) (unknown)
Mainstream Commercial fishing Lyttelton (unknown) Nelson Marlborough
Sounds
Snark Commercial fishing Lyttelton
Fisherman’s Wharf
Dec-06 Banks Peninsula Akaroa
Genesis Tourism /
Inner Harbour Pile Nov-06 Banks Peninsula Akaroa
maintenance /
research vessel
Moorings
Waipapa Tourism vessel Kaiapoi river Feb-07 (unknown) (unknown)
Paranui Tourism vessel Kaiapoi river Dec-05 (unknown) (unknown)
Black Diamond Ferry B Jetty / pontoon Aug-06 Banks Peninsula (unknown)
Canterbury Cat Tourism vessel B Jetty / pontoon Aug-06 Banks Peninsula Akaroa
Onawi Tourism vessel B Jetty / pontoon Aug-06 Banks Peninsula (unknown)
Fox II Sailing charter vessel Inner Harbour Pile
Moorings
Oct-06 Akaroa Akaroa
Oyster Sailing charter vessel Inner Harbour Pile Oct-06 Banks Peninsula (unknown)
190 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendices
Vessel name Vessel type Mooring location Last antifouling Destinations HVAs visited
Albatross Tug
Moorings
No. 5 Wharf Feb-07 Akaroa Akaroa
Phoenix Inflatable work vessel No. 5 Wharf Mar-07 Banks Peninsula (unknown)
Eleni Commercial fishing Lyttelton
Fisherman’s Wharf
Nov-06 Akaroa Akaroa
Lady Waiana Commercial fishing Lyttelton
Fisherman’s Wharf
Mar-06 Banks Peninsula (unknown)
Crusader Commercial fishing/ Lyttelton
Mar-07 Banks Peninsula (unknown)
maintenance vessel Fisherman’s Wharf
Strathallan Charter vessel Lyttelton
Fisherman’s Wharf
Apr-07 Banks Peninsula Akaroa
Phoenix Commercial fishing Lyttelton
Fisherman’s Wharf
Feb-07 Banks Peninsula Akaroa
Harrold Hardy Commercial fishing Lyttelton
Fisherman’s Wharf
Dec-05 Banks Peninsula (unknown)
Angitu Charter vessel Lyttelton
Fisherman’s Wharf
Aug-06 Banks Peninsula (unknown)
Pegasus II Fishing charter vessel Inner Harbour Pile
Moorings
Feb-07 Banks Peninsula Akaroa
Tug Lyttelton Historic / charter
vessel
No. 2 Wharf Sep-06 Banks Peninsula (unknown)
Port of Lyttelton
Tug
Tug Tug Jetty Apr-06 Confined to Port (unknown)
Port of Lyttelton
Tug
Tug Tug Jetty Apr-06 Confined to Port (unknown)
Sumner
Lifeboat (back-up Tug Jetty Dec-06 Banks Peninsula (unknown)
Lifeboat
Tug)
Canterbury Pilot vessel Tug Jetty Nov-06 Banks Peninsula (unknown)
Argos Helena Commercial fishing Z Wharf Oct-06 Sub Antarctic Islands (unknown)
Hood Williams Pile driving barge (unknown) 5 yrs previous Confined to Port (unknown)
Pantas 1 Commercial fishing (unknown) (unknown) (unknown) (unknown)
Independent 1 Commercial fishing Z Wharf (unknown) (unknown) (unknown)
Altair II Commercial fishing (unknown) (unknown) (unknown) (unknown)
Malakhov
Kurgen
Commercial fishing Gladstone Pier (unknown) (unknown) (unknown)
Kapitan Rusak Commercial fishing (unknown) (unknown) (unknown) (unknown)
Aleksandr Commercial fishing (unknown) (unknown) (unknown) (unknown)
Ksenofontov
Oyang 77 Commercial fishing (unknown) (unknown) (unknown) (unknown)
Oyang 97 Commercial fishing (unknown) (unknown) (unknown) (unknown)
Oyang 70 Commercial fishing (unknown) (unknown) (unknown) (unknown)
Seafort Commercial fishing (unknown) (unknown) (unknown) (unknown)
Governor Commercial fishing (unknown) (unknown) (unknown) (unknown)
Narvora Commercial fishing (unknown) (unknown) (unknown) (unknown)
Mercury Commercial fishing (unknown) (unknown) (unknown) (unknown)
Stephen John Commercial fishing (unknown) (unknown) (unknown) (unknown)
Marie Ann Commercial fishing (unknown) (unknown) (unknown) (unknown)
Triton Commercial fishing (unknown) (unknown) (unknown) (unknown)
Belize Charity cruises (unknown) (unknown) (unknown) (unknown)
Service barge Ship maintenance Dry dock Wharf (unknown) (unknown) (unknown)
barge
Service barge Ship maintenance
barge
Dry dock Wharf (unknown) (unknown) (unknown)
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 191

Appendices
Appendix 5.3
Companies contacted during collection of vector data for the Magazine Bay Marina.
Vessel name Vessel type Mooring location Last antifouling Destinations HVAs visited
Storm Cat Commercial
fishing vessel
Magazine Bay
Marina
Dec-2006 Northern Pegasus
Bay
Marlborough
Sounds
192 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 5.4
Companies contacted during collection of vector data for the Poor Knights Islands HVA.
Company / owner Vessel name Location Operations HVAs visited
Cara Mia Charter Cara Mia Tutukaka Marina Fishing charters Poor Knights Is.
Pacific Hideaway Charters Pacific Hideaway Tutukaka Marina Dive charters Poor Knights Is.
Marlin Blue Fishing Charters Marlin Blue Tutukaka Marina Fishing charters Poor Knights Is.
Poor Knights Liveaboard NZ
Ltd
Appendices
Norseman Tutukaka Marina Dive charters Poor Knights Is.
Bluezone Aquaventure Rumblefish Tutukaka Marina Dive charters Poor Knights Is.
Blue Striker Fishing Charters Blue Striker Tutukaka Marina Fishing charters Poor Knights Is.
Dive! Tutukaka Calypso Tutukaka Marina Dive charters Poor Knights Is.
Dive! Tutukaka El Tigre Tutukaka Marina Dive charters Poor Knights Is.
Dive! Tutukaka Bright Arrow Tutukaka Marina Dive charters Poor Knights Is.
Dive! Tutukaka Perfect Day Tutukaka Marina Dive charters Poor Knights Is.
Dive! Tutukaka Cave Rider Tutukaka Marina Sightseeing charters Poor Knights Is.
Dive! Tutukaka Hendrick J Tutukaka Marina Dive charters None
Dive Poor Knights CDiver Tutukaka Marina Dive charters (unknown)
(unknown) PK Charters Tutukaka Marina Dive charters (unknown)
Yukon Charters Arrow Tutukaka Marina (unknown) (unknown)
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 193

Appendices
Appendix 5.5
Companies contacted during collection of vector data for the Marlborough Sounds HVA.
Company/Owner Vessel name Location Operations
Vessel
description
HVAs and Styela source
locations visited
Nelson Ranger St George (unknown) Service vessel 23m Lyttelton; Havelock, Port
Fishing Co.
Underwood
ASL Contracting Te Au Miro Havelock Mussel farming 25m
Golden Bay, Picton, Waikawa
Harvester Bay Marina, Havelock
Westland (unknown) Mussel farming 11m Barge Golden Bay, Picton, Waikawa
tow
Bay Marina, Havelock
Keri Moana (unknown) Mussel farming 15m
Golden Bay, Picton, Waikawa
Harvest/Dump
barge
Bay Marina, Havelock
Keri iti (unknown) Mussel farming 17m Mussel Golden Bay, Picton, Waikawa
work boat Bay Marina, Havelock
Charolin (unknown) Mussel farming 10m Mussel Golden Bay, Picton, Waikawa
work boat Bay Marina, Havelock
Hikapu hunter (unknown) Mussel farming 10m
Golden Bay, Picton, Waikawa
Runabout Bay Marina, Havelock
Solly Arista-cat Takaka (unknown) (unknown) Golden Bay, Croisilles Harbour
Stray-cat (unknown) (unknown) (unknown) Golden Bay, Croisilles Harbour
Marlborough Mussel Intrepid Havelock Mussel farming 26m Havelock, Elaine Bay, Okiwi
Company
Bay, Pelorous Sound, Queen
Charlotte Sound
Okiwi Spirit (unknown) Mussel farming 25m Havelock, Elaine Bay, Okiwi
Bay
Hebberd Marine
Farms
(unknown) (unknown) (unknown) (unknown) (unknown)
MacLab (unknown) (unknown) (unknown) (unknown) (unknown)
Port Mussel Co (unknown) (unknown) Mussel farming (unknown) (unknown)
Apex Marine Farms Beverley S (unknown) (unknown) 16m Picton, Oyster Bay, Port
Underwood
Kai Kouti (unknown) (unknown) 18m Picton, Oyster Bay, Port
Underwood
194 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 5.6
Appendices
Companies contacted during collection of vector data for the Banks Peninsula and Akaroa HVAs.
Area of facilities indicated in hectares.
Company/Owner Vessel
Black Cat
Company
Pigeon Bay
Aquaculture Ltd
Te Wharau
Investment Ltd
Sea-Right
Investments Ltd
Akaroa Salmon
(NZ) Ltd
Ocean Marine
Farms Ltd
Marlborough
Mussel Company
Ltd
Location Operations Area Vessel
Styela sources
name
description visited
Black Cat Akaroa Scenic cruises Passenger
boat
Lyttelton
Cat II Akaroa Scenic cruises Passenger
boat
Lyttelton
Clipper Akaroa Scenic cruises Passenger
boat
Lyttelton
(unknown) Pigeon Bay Mussel farming 29 6m Speedboat None
Omega Mussel farming 12m Barge Lyttelton
St George Mussel farming 23m
Harvester:
Lyttelton
(unknown) Menzies Bay Mussel farming 6 Small
runabout
None
Tardis Mussel farming Harvester Lyttelton
(unknown) Wainui (Akaroa) Paua farming 5 11m barge None
Belinda Titoki & Lucas Bays Salmon farming 6 6.7m Trailer None
Anne (Akaroa)
boat
(unknown) Scrubby Bay, Big Mussel farming ~100 Local
None
Bay, Port Levy
maintenance
vessel
St George Mussel farming 23m Harvester Lyttelton
(unknown) Pegasus Bay& Port Mussel farming (unkno (unknown) (unknown)
Levy
wn)
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 195

Appendices
Appendix 5.7
Copies of the questionnaires used to survey vessel, aquaculture facility and port/marine owners and
operators.
Aquaculture Facility
Operator Questionnaire:
A. Vessel information:
A1. Please list & describe the vessels (maintenance / service / harvesting) that you use, or that frequent your facility
(vessel type, length):
A2 (a) Do these vessels visit / frequent:
Port of Lyttelton
Magazine Bay Marina, Lyttelton
Tutukaka Marina, Northland
Marlborough Sounds: Picton / Waikawa Marina / Havelock
Port of Nelson
Port of Auckland
A2 (b) If “yes” for A2a: Please complete for each vessel that visits the areas
Vessel Port / marina Frequency of
visits
A3. Where do the vessels tend to berth within these areas?
Residence time
of visits
A4. Do the vessels proceed directly from these areas to your facility? Y / N
If not which other locations do they visit first?
A5. Do the vessels ever visit other aquaculture facilities?
Where? How often? For what reason?
A6. How often are your vessels cleaned? Where? How?
B. Equipment / Stock / Spat information:
B1. Where do you source your equipment / spat from?
B2. How is it transported to / from your facility?
B3. Do you ever transfer equipment to locations outside your facility?
Where to? How? How often?
B4. Where does your harvested stock go once it leaves your facility?
How? How often?
C. Facility information:
Date:
Interviewer:
Aquaculture facility:
Interviewee:
Purpose of visits
196 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

C1. What is the overall area of your facility?
C2. What types of structures make up your facility?
(e.g. pontoons, floats, piles, moorings etc)
C3. What is the approx. length / area of each structure?
D. Unwanted Species:
D1. Do you implement any measures to prevent the transport of unwanted species? If yes, please explain:
D2. Have you ever observed Styela clava within your aquaculture facility?
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 197

Appendices
Harvester Vessel Operator Questionnaire:
1. Name of vessel:
2. Vessel length:
3. Approx. date of last antifouling?
How often is vessel cleaned?
4. Which marine farms does your vessel service?
(or if not keen on divulging this info: Which areas / bays within the Marlborough Sounds does vessel visit to collect
harvest?
How often are farms / areas visited?
5. Where is the harvest offloaded?
How often is port (or ports?) visited?
Residence time in port(s)?
6. Does your vessel ever visit farms in the Banks Peninsula Aquaculture Production Area? (probably not but good to
double check..)
6 (a) Does your vessel ever visit / frequent:
Port of Lyttelton
Magazine Bay Marina, Lyttelton
Tutukaka Marina, Northland
Port of Nelson
Port of Auckland
6 (b) If “yes” for A6a: Please complete for each port / marina:
Port / marina Frequency of visits Residence time of
visits
7. Where do the vessels tend to berth within these areas?
8. Do you ever transfer equipment (rather than harvest)?
Where to/from? How often?
Date:
Harvester:
Interviewee:
Purpose of visits
198 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Questionnaire for Port of Lyttelton:
Vessels use of facility:
Recreatio
nal
vessels:
Commercial vessels:
Tourism
vessels*
Ferries Fishing
vessels
# Vessels
currently
present at
facility
# Vessels
regularly at
facility but
not currently
present
(* include: wildlife & harbour cruises, cruise ships, dive & fishing charters)
(** Include: facility maintenance / service vessels, dredge etc)
Contact details for vessel operators / owners:
Unique
NIWA ID:
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 199
Pilot /
Tug
Merchant
Ships
Vessel type: Vessel name: Contact name: Contact details:
(table extended as required)
Other**
(Note: if contacts not available for some vessels, please ask port / marina authority for information to complete vessel
operator / owner form)
Submerged / floating structures within port / marina:
C1. For PERMANENT structures:
Structure type Pontoon Barge Other
(please state)
What length / area is currently present at facility?
Length of time in place?
Sourced from…?
How were they transported? (floated in sea or by land?)
Any more planned for the facility?
If yes:
Where will they be sourced from?
How will they be transported?
C2. For TEMPORARY structures:
Date:
Interviewer:
Interviewee:
Structure type Pontoon Barge Other
(please state)
What length / area of substrates are temporary?
When will they be removed?
Where will they be moved to?
How will they be transported?
Will they be cleaned before they are moved?
How and where will they be cleaned?

Appendices
C3. Are there any structures that were “PRESENT UNTIL RECENTLY”?
Structure type Pontoon Barge Other
(please state)
What types / length / area of substrates were removed?
Where were they located?
When were they removed?
Where were they moved to? How were they moved?
Were they cleaned before they were moved? How?
Where?
Lyttelton Port “hot-spots”
At the following locations Styela clava has been found in elevated densities:
Pontoons between Z wharf & Gladstone Pier
Pontoons A & B
Tug Berth
No. 2 Wharf
Please provide the following information for vessels that berth regularly at these locations, or have berthed there during last 6
– 12 months:
Location / berth Vessel name & type Frequency & duration of
stay
(table extended as required)
Next port of call on departure
from berth
200 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Questionnaire for Magazine Bay Marina:
A. Vessels use of facility:
Recreationa
l vessels: Tourism
vessels
Commercial vessels:
Ferries Fishing
vessels
# Vessels
currently
present at
facility
# Vessels
regularly at
facility but
not currently
present
(** Include: facility maintenance / service vessels, dredge etc)
B. Contact details for vessel operators / owners:
Unique
NIWA ID:
(extend table as required)
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 201
Pilot /
Tug
Mercha
nt Ships
Vessel type: Vessel name: Contact name: Contact details:
Other**
(Note: if contacts not available for some vessels, please ask port / marina authority for information to complete vessel
operator / owner form)
C. Submerged / floating structures within port / marina:
C1. For PERMANENT structures:
Structure type Pontoon Barge Other
(please state)
What length / area is currently present at facility?
Length of time in place?
Sourced from…?
How were they transported? (floated in sea or by land?)
Any more planned for the facility?
If yes:
Where will they be sourced from?
How will they be transported?
C2. For TEMPORARY structures:
Date:
Interviewer:
Port / Marina:
Interviewee:
Structure type Pontoon Barge Other
(please state)
What length / area of substrates are temporary?
When will they be removed?
Where will they be moved to?
How will they be transported?
Will they be cleaned before they are moved?
How and where will they be cleaned?

Appendices
C3. Are there any structures that were “PRESENT UNTIL RECENTLY”?
Structure type Pontoon Barge Other
(please state)
What types / length / area of substrates were removed?
Where were they located?
When were they removed?
Where were they moved to? How were they moved?
Were they cleaned before they were moved? How?
Where?
202 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Questionnaire for Tutukaka Marina:
A. Vessels use of facility:
# Vessels
currently
present at
facility
# Vessels
regularly at
facility but
not currently
present
Recreationa Commercial vessels:
l vessels: Tourism Ferries Fishing
vessels
vessels
(**Include: facility maintenance / service vessels, dredge etc)
B. Contact details for vessel operators / owners:
Unique
NIWA ID:
(extend table as required)
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 203
Pilot /
Tug
Vessel type: Vessel name: Contact name: Contact details:
Merchant
Ships
Other*
*
(Note: if contacts not available for some vessels, please ask port / marina authority for information to complete vessel
operator / owner form)
C. Submerged / floating structures within port / marina:
C1. For PERMANENT structures:
Structure type Pontoon Barge Other
(please state)
What length / area is currently present at
facility?
Length of time in place?
Sourced from…?
How were they transported? (floated in sea
or by land?)
Any more planned for the facility?
If yes:
Where will they be sourced from?
How will they be transported?
C2. For TEMPORARY structures:
Date:
Interviewer:
Port / Marina:
Interviewee:
Structure type Pontoon Barge Other
(please state)

Appendices
What length / area of substrates are temporary?
When will they be removed?
Where will they be moved to?
How will they be transported?
Will they be cleaned before they are moved?
How and where will they be cleaned?
C3. Are there any structures that were “PRESENT UNTIL RECENTLY”?
Structure type Pontoon Barge Other
(please state)
What types / length / area of substrates were
removed?
Where were they located?
When were they removed?
Where were they moved to? How were they
moved?
Were they cleaned before they were moved?
How? Where?
D. Lyttelton Port “hot-spots”
At the following locations Styela clava has been found in elevated densities:
Pontoons between Z wharf & Gladstone Pier
Pontoons A & B
Tug Berth
No. 2 Wharf
Please provide the following information for vessels that berth regularly at these locations, or have berthed there during last 6
– 12 months:
Location / berth Vessel name & type Frequency & duration of
stay
(extend table as required)
Next port of call on
departure from berth
204 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Questionnaire for vessel operators/ owners:
General information
A1. Unique NIWA ID: ____________
A2. Vessel name: _____________________________
A3. Vessel type: (please circle)
Recreational yacht / launch
Tourism vessel
(incl. harbour cruises, dive boats, fishing charters, cruise ships)
Ferry / water taxi
Pilot / Tug / facility maintenance vessel / dredge
Commercial fishing vessel
Merchant ship
Aquaculture service vessel
Other (please state):
A4. Vessel length: ____________
A5. Does vessel carry ballast water? Y / N (please circle)
A6. Approx date of last anti-foul: ____________
Vector information:
B1. Where is your vessel berthed? How frequently does your vessel visit this port / marina? (please circle)
one-off / weekly / monthly / annually / other (please state)
B2. What is the residence time of your vessel in this port / marina?
B3. Does your vessel visit any of the following areas: (please circle)
Banks Peninsula Aquaculture Production areas
Akaroa Harbour
Marlborough Sounds Aquaculture Production areas
Poor Knights Islands Marine Reserve
Port of Auckland
Visitors to “High Value Areas” (HVA):
C1. Please complete if answered “yes” to B3.
HVA Last port of call
before visit to
Banks Peninsula
Aquaculture Production
areas
Akaroa Harbour
Marlborough Sounds
Aquaculture Production
areas
Poor Knights Islands Marine
Reserve
HVA
Duration of
visit
Purpose of visit Frequency of
visits
C2. Please complete if vessel visits Aquaculture production areas / facilities:
Date:
Interviewer:
Interviewee:
Appendices
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 205

Appendices
Name of Aquaculture area /
facility
Visitors to Port of Auckland:
D1. Number of trips per month/year:
D2. Average duration of visits:
Duration of visit Frequency of visits Purpose of visit
206 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 6.1
Appendices
Hydrodynamic particle dispersal model simulation from release point in the Port of Lyttelton under
calm conditions.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 207

Appendices
Appendix 6.2
Hydrodynamic particle dispersal model simulation from release point in the Port of Lyttelton under
north-east winds.
208 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 6.3
Appendices
Hydrodynamic particle dispersal model simulation from release point in the Port of Lyttelton under
south-east winds.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 209

Appendices
Appendix 6.4
Hydrodynamic particle dispersal model simulation from release point in the Port of Lyttelton under
south-west winds.
210 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 6.5
Appendices
Hydrodynamic particle dispersal model simulation from release point in thePort of Lyttelton under
north-west winds.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 211

Appendices
Appendix 7.1
CONCEPT AND OUTPUT SUMMARY OF NIWA’S EPIDEMIOLOGICAL MODEL.
Model concept
The model was based on conventional SIR models that are common in studies of the epidemiology of
human or animal diseases (Bjornstad et al 2002; Wonham et al 2004). These models divide hosts
(individuals) in a population into three groups that are either “susceptible” (S) or “resistant” (R) to a
disease, or have become “infected” (I) by it. Toxic antifouling paints provide yacht hulls with a
temporary “resistance” to fouling organisms by deterring or killing larvae that attempt to settle on
them (Christie and Dalley 1987). This resistance diminishes over time, with a concomitant increase in
the hulls’ susceptibility to fouling (Floerl et al 2005). Yacht hulls, therefore, repeatedly progress
through a series of states in which they are either: (1) protected by the antifouling paint (R), (2)
susceptible to becoming colonised by Styela (S), or – possibly - (3) infected with Styela (I). In our
simulations, newly painted yachts began as resistant, but became susceptible to fouling over time.
Depending on their travel and maintenance schedule, yachts residing within infected locations either
became infected with Styela or remained susceptible without becoming infected, or the antifouling
paint was renewed (resistant) before infection could occur. Manual cleaning of susceptible or infected
yacht hulls did not result in resistance to renewed colonisation but in the removal of Styela from the
hull (if present) and the retention of the susceptible state for the yacht.
Model parameterisation
In this section we provide a summary of the model and its parameterisation. For full details on the
origin of source data and mathematical derivations of parameters in the model refer to Floerl et al (in
press).
1. Data on travel and maintenance patterns of yachts around New Zealand
Patterns of yacht movements and yacht maintenance around New Zealand were obtained from a
questionnaire survey of approximately 1,200 domestic and international yachts in 2002 - 2004. These
sample numbers represent approximately 5 % of all permanently moored New Zealand yachts and
approximately 40 % of all international yachts arrivals to New Zealand during the study period.
Data from the questionnaires were used to construct a probability matrix of yacht movements between
36 coastal locations around New Zealand. The locations included all New Zealand yacht harbours
(marinas) and ~ 80-90 % of available mooring facilities (Fig. A7-1). Where several marinas or
mooring facilities were in close proximity to one another they were combined into a single location
(e.g. Wellington and Tauranga). The total number of domestic and international yachts in the model
was set at 9,702 and 450, respectively, based on average occupancy figures for each marina obtained
from interviews with the owners or operators and figures on annual arrivals of international yachts to
New Zealand (New Zealand Customs, pers. comm. 2004).
2. Habitat availability, probability of establishment and yacht susceptibility to fouling
Each of the 36 model locations provided berthing space for between 23 and 1,832 yachts.
Measurements undertaken during previous studies indicated that this translated into associated fouling
212 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendices
habitat sizes (vertical pilings and floating pontoons) of 391 m 2 to 31,144 m 2 per location. Because the
model was originally developed for coastal yacht marinas and mooring locations the habitat associated
with each location was restricted to the floating jetties or arrays of piles found in marinas and coastal
mooring sites, respectively. The location “Lyttelton” contained the combined yacht numbers and
habitat size estimates of the Magazine Bay Marina and the marina located in the Port’s Inner Harbour.
However, it did not contain the large amount of artificial habitat associated with the Port’s commercial
wharves and facilities that were surveyed as part of Deliverable 1. These limitations were
communicated to MAFBNZ during the December 2007 workshop.
Model runs were initiated by “seeding” Lyttelton and Auckland (Auckland consisted of 11 component
locations; Fig. A7-1) with resident populations of Styela. In Lyttelton, the population size at t = 0 was
derived from the average population density estimates presented in Deliverable 1 and set at 0.11 % of
available habitat. No quantitative population size estimates exist for Styela in the Waitemata Harbour;
however, the species is known to be widely spread and abundant in some locations. All 11 component
locations (marinas and mooring facilities) of the Auckland region were therefore seeded with the same
population density of Styela as the Lyttelton port and associated marinas. In both Lyttelton and
Auckland the resident population of the invader was set to double in size every 12 months. We
limited the maximum area that Styela was able to occupy in each infected location to 25 % of the
available habitat.
At t = 0 in the model, the distribution of antifouling paint ages and associated susceptibility to fouling
of all yachts in all 36 locations was set at the frequency distribution of paint ages derived from the
questionnaire responses. Over time, antifouling paint age and susceptibility to fouling increased for
each yacht. The relationship between antifouling paint age and susceptibility to fouling was derived
from data collected during in situ surveys of yacht hulls in Australia and New Zealand in 1999 – 2003
(Floerl 2002; Floerl et al 2005). Renewal of the antifouling paint “reset” susceptibility to zero (i.e. R).
In addition, yachts were randomly assigned probabilities for manual hull cleaning based on a
frequency distribution derived from the yacht survey.
The probability of establishment of the NIS at a new (uninfected) location was defined as the number
of infected yachts that needed to reside in an uninfected location for 1 day to result in a 1 % chance of
establishment on that day. The model was parameterised such that the residency of 10 yachts infected
with Styela in an uninfected marina for 1 day resulted in a 1 % probability of Styela becoming
established in this marina on that day.
An initial sensitivity analysis determined that the values used for population growth rate in infected
locations and probability of establishment in uninfected locations have a strong effect on the spreading
rate of the modelled species. Therefore population growth rate and establishment probability were
kept constant in all simulations described here. The actual growth and transmission rates of Styela in
New Zealand are unknown. However, our aim was to evaluate patterns of spread under different
management approaches and no claim is made that the timing of modelled spreading events is
representative of the real world.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 213

Appendices
Auckland:
Westhaven Marina
Halfmoon Bay Marina
Westpark Marina
Bayswater Marina
Pine Harbour
Viaduct Harbour
Bucklands Beach
Tamaki Estuary
Hobson West Marina
Okahu Harbour
Devonport
Milford Marina
Kawau and
Waiheke Is.
Nelson
Lyttelton
Akaroa
Dunedin; Port Chalmers
Kerikeri
Opua; Russell
Tutukaka
Whangarei
Mahurangi
Great Barrier Is.
Gulf Harbour
Coromandel Harbour
Whitianga
Thames
Tauranga
Napier
Wellington
Picton; Waikawa Bay;
Havelock
Fig. A7-1: Yachting locations contained in the epidemiological model. Locations in bold font were used as source
locations of Styela in the model.
214 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

RESULTS
Summary of simulation results
Appendices
After a simulated period of 10 years, Styela originating from Lyttelton and Auckland had successfully
established in an additional 23 coastal locations around the South and North Islands, irrespective of
whether no management, population management or vector management had been undertaken
(Table A7-1; Fig. A7-2). The rate of spread to nationwide coastal locations was generally highest
between years 1 and 6 of the 10-year simulation period, and levelled off considerably during the final
3 years (Fig. A7-2). Gulf Harbour, Picton, Opua, Great Barrier Island and Tauranga were
consistently the first five locations to become infected with Styela; infection of the former four
locations generally occurred in ≤2 years. The relative sequence of infestation of the six HVAassociated
model locations (Picton, Waikawa Bay, Nelson, Havelock, Tutukaka and Akaroa) was
similar for the three management options, with the Marlborough Sounds becoming infected soonest of
the four HVAs of interest (Table A7-1). Vector management and population reduction of Styela in
Lyttelton respectively resulted in an average of 4.7 % and 8.3 % fewer arrivals of infected yachts to
HVA locations than when no management occurred. Yet, for most of the model locations associated
with HVAs the 95 % confidence intervals of the timing of Styela establishment under no, vector or
population management overlapped, indicating no significant differences.
Throughout the 10-year period, vector management (reducing the proportion of yachts susceptible to
fouling by Styela) did not result in a significantly lower spreading rate (number of new infected
locations per unit time) than when no management occurred, as indicated by the largely overlapping
95 % confidence intervals (Table A7-1). However, population management resulted in an apparent
temporary reduction in the spreading rate. A one-off reduction in Styela density in Lyttelton by 50 %
resulted in a lower number of new infected locations on a nation-wide scale between approximately 1
and 6 years from the start of the simulations (Fig. X2). Unfortunately, the lower number of infected
locations was not associated with the HVAs. Instead, population management in Lyttelton resulted in
lowered infection probabilities for Napier, Thames and Port Chalmers (Fig. A7-1).
Over a simulated period of 10-years, five of the six model locations associated with HVAs (Akaroa,
Nelson, Havelock, Waikawa Bay and Tutukaka) had a 100 % probability of becoming colonised by
Styela irrespective of the presence or absence of management. The infection probability of Picton
(Marlborough Sounds HVA) was reduced by 6.5 % and 8.7 % under vector or population management
in Lyttelton, respectively.
We were unable to examine the spread of Styela to the Poor Knight Islands HVA because they were
not locations in the model. In simulations where Styela was eradicated from Tutukaka each time it
became infected, on average 3.9 %, 1.4 %, 0.4 % and 0.8 % fewer infected yachts arrived at Opua,
Russell, Kerikeri (north of Tutukaka) and Mahurangi (south of Tutukaka) over a 10-year period than
when Tutukaka remained unmanaged. The number of infected yacht arrivals to Whangarei was not
affected by Tutukaka management. Under both simulated scenarios (management or no management
of Styela in Tutukaka) all locations adjacent to Tutukaka (Opua, Russell, Kerikeri, Whangarei and
Mahurangi) became infected with Styela in 100 % of model runs.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 215

Appendices
Table A7-1: Sequence of infection of model locations over a 10-year period under no management, vector management or population management (density reduction) in Lyttelton, and
population management (eradication) in Tutukaka. Numbers indicate the time in years until a location became infected with Styela (average of 100 model runs (± 95 %
confidence interval). Locations in bold are associated with the four HVAs.
(a) No management (b) Vector management (Lyttelton) (c) Population reduction (Lyttelton) (d) Tutukaka eradication
1 Gulf Harbour 1.12 ± 0.10 1 Gulf Harbour 1.18 ± 0.11 1 Gulf Harbour 1.45 ± 0.12 1 Gulf Harbour 1.10 ± 0.10
2 Picton 1.25 ± 0.11 2 Picton 1.41 ± 0.12 2 Picton 1.67 ± 0.13 2 Picton 1.29 ± 0.10
3 Opua 1.40 ± 0.14 3 Great Barrier Is. 1.64 ± 0.17 3 Opua 1.74 ± 0.15 3 Opua 1.44 ± 0.14
4 Great Barrier Is. 1.54 ± 0.16 4 Opua 1.69 ± 0.16 4 Great Barrier Is. 1.93 ± 0.16 4 Great Barrier Is. 1.45 ± 0.13
5 Tauranga 2.06 ± 0.15 5 Tauranga 2.24 ± 0.14 5 Tauranga 2.67 ± 0.15 5 Tauranga 2.16 ± 0.16
6 Waikawa Bay 2.42 ± 0.16 6 Nelson 2.49 ± 0.15 6 Nelson 2.75 ± 0.17 6 Nelson 2.26 ± 0.15
7 Nelson 2.46 ± 0.15 7 Waikawa Bay 2.53 ± 0.16 7 Waikawa Bay 2.87 ± 0.17 7 Waikawa Bay 2.33 ± 0.15
8 Waiheke Is. 2.90 ± 0.19 8 Akaroa 3.05 ± 0.22 8 Akaroa 3.25 ± 0.21 8 Akaroa 2.77 ± 0.20
9 Akaroa 2.93 ± 0.20 9 Mahurangi 3.13 ± 0.21 9 Wellington 3.53 ± 0.18 9 Wellington 2.96 ± 0.16
10 Kerikeri 2.98 ± 0.21 10 Wellington 3.17 ± 0.16 10 Kerikeri 3.54 ± 0.23 10 Waiheke Is. 2.97 ± 0.18
11 Whangarei 3.06 ± 0.21 11 Waiheke Is. 3.20 ± 0.17 11 Waiheke Is. 3.54 ± 0.19 11 Whangarei 3.15 ± 0.20
12 Wellington 3.07 ± 0.18 12 Whangarei 3.27 ± 0.23 12 Whangarei 3.65 ± 0.21 12 Kerikeri 3.18 ± 0.21
13 Kawau Is. 3.35 ± 0.23 13 Kerikeri 3.35 ± 0.25 13 Mahurangi 3.69 ± 0.18 13 Kawau Is. 3.20 ± 0.24
14 Mahurangi 3.35 ± 0.22 14 Whitianga 3.60 ± 0.22 14 Tutukaka 3.81 ± 0.25 14 Tutukaka 3.34 ± 0.27
15 Tutukaka 3.36 ± 0.26 15 Kawau Is. 3.61 ± 0.24 15 Whitianga 3.88 ± 0.24 15 Mahurangi 3.42 ± 0.19
16 Whitianga 3.47 ± 0.19 16 Tutukaka 3.74 ± 0.28 16 Kawau Is. 3.92 ± 0.24 16 Whitianga 3.47 ± 0.19
17 Dunedin 3.84 ± 0.20 17 Coromandel Harb. 4.32 ± 0.28 17 Dunedin 4.41 ± 0.20 17 Dunedin 4.03 ± 0.19
18 Coromandel Harb. 4.04 ± 0.25 18 Dunedin 4.35 ± 0.20 18 Coromandel Harb. 4.53 ± 0.29 18 Coromandel Harb. 4.04 ± 0.23
19 Russell 4.92 ± 0.21 19 Russell 5.22 ± 0.25 19 Russell 5.34 ± 0.21 19 Russell 4.89 ± 0.22
20 Havelock 5.39 ± 1.03 20 Thames 5.74 ± 0.30 20 Havelock 5.41 ± 0.99 20 Thames 5.46 ± 0.25
21 Thames 5.49 ± 0.27 21 Havelock 6.43 ± 0.86 21 Thames 5.92 ± 0.30 21 Havelock 5.97 ± 0.77
22 Napier 7.19 ± 0.93 22 Napier 7.05 ± 0.80 22 Napier 6.98 ± 1.09 22 Napier 7.18 ± 1.01
23 Pt Chalmers 7.50 ± 0.26 23 Pt Chalmers 8.16 ± 0.26 23 Pt Chalmers 8.05 ± 0.29 23 Pt Chalmers 7.93 ± 0.26
216 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

No. new infected locations (± (± 95% 95% C.I.) C.I.)
24
18
12
6
0
0 2 4 6 8
10
Time (years)
No management
Vector management
Population reduction
Appendices
Figure A7-2: Simulated spread of Styela around New Zealand under three different management approaches. At
t = 0, Styela populations cover 0.11 % of habitat in Lyttelton and Auckland. The simulated vector and
population management measures are restricted to Lyttelton port and marinas. Data on the y-axis
indicate the number of model locations where Styela established over time. For each management
approach, bold lines represent the mean of 100 simulations and thin dotted lines represent the upper
and lower 95 % confidence intervals.
DISCUSSION
The results obtained from the model simulations indicate that, over a period of 10 years, the spread of
Styela around New Zealand is largely not affected by population or vector management in Lyttelton.
A similar number of model locations became infected irrespective of management approach.
However, in particular cases a 50-% reduction of the Styela population at Lyttelton Port and Magazine
Bay Marina resulted in delayed establishment of the species at further locations. These results are
most likely explained by the localised adaptation of the management approaches considered here. To
reflect the actual nationwide distribution of Styela (as of 2007), our model incorporated Styela
populations in Auckland and Lyttelton. However, population and vector management were simulated
only for Lyttelton but not for Auckland. The 11 model locations that comprise the Auckland region
account for 35.3 % of the total artificial habitat associated with all model locations, and for 36 % of all
yachts in the model. In comparison, Lyttelton Port and Magazine Bay Marina comprise 1.1 % of total
habitat and 0.9 % of all vectors. Our results show that, if management measures are exclusively
applied to a single source population of Styela in a heavily inter-connected transport network with
multiple established populations then this management programme will most likely have no or low
effectiveness. However, this conclusion is based on the simulation of a single population management
effort (a one-off reduction in Styela density) and one single vector management option. Other
approaches, such as the maintenance of the reduced population at Lyytelton over time, or a
combination of vector and population management, may yield different results but were not evaluated
by our model.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 217

Appendices
The population growth rate of Styela in colonised locations and the rate of transmission of Styela from
infected yacht hulls to uninfected marinas were chosen arbitrarily and may not be representative of
real conditions. Previous sensitivity analyses indicated that the simulated spreading rate is highly
sensitive to variation in these two parameters. While the patterns (e.g. sequence of infection of
locations, differences between management approaches) obtained from the model runs may be
realistic, the actual number of new locations in which Styela established per year is probably not.
The model outputs include patterns that correspond to observations made on Styela’s distribution in
the past 3 years. Gulf Harbour was consistently the first location to become infected in the model.
Styela was recorded from Gulf Harbour by NIWA staff in 2005. The model also indicated that Styela
is likely to establish in the Marlborough Sounds HVA sooner than in the other three HVAs. Vessels
colonised by Styela have been reported from this HVA on more than one occasion, even though no
established individuals have yet been detected. Opua is another location that consistently features
amongst the first four infected locations. Also here, Styela has been recorded on several vessels
associated with this location. The evidence described here is of course correlative but might warrant
consideration of Great Barrier Island for surveillance of Styela. Great Barrier Island was consistently
the third or fourth infected location in all simulations (infection occurred < 2 years from the model
start). The island is a major destination for recreational vessel traffic from the Auckland region and
there is evidence that many yachts reside there on their way to the Poor Knight Islands HVA (Floerl,
unpubl. data 2003-2005).
Because the Poor Knight Island HVA was not a location in the model we were unable to determine the
effect of population management in Tutukaka on the risk of spread of Styela to the Poor Knight
Islands. However, this HVA receives frequent vector traffic from the Auckland region. In the
absence of population and/or vector management for Styela in Auckland we suggest that the risk of
infection of the Poor Knight Islands may be more than negligible even if Tutukaka is managed.
218 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendix 7.2
POTENTIAL TOOLS FOR THE MANAGEMENT OF STYELA POPULATIONS
Appendices
We describe a wide variety of treatment options previously tested in marine environments that could
potentially be used to control Styela or other non-indigenous species on artificial structures and natural
habitats. We summarize eleven types of treatment method currently available to attempt Styela
control with assessment of their costs, limitations and notes on their practical implementation. In
Table A7-2 we compare the treatment options and summarize key aspects of the methods, including
the most appropriate structures for their implementation, their acceptability to stakeholder and
presumed chances of success. We also highlight any potential legal issues, application issues, benefits
or known side-effects of their use, and where available outline estimates of the approximate cost per
unit area to treat surfaces for Styela infestation.
Plastic wrapping
Many artificial structures cannot be removed from the water so they must be treated in situ. The most
successful and cost-effective treatment method currently available is to encapsulate them with a
physical barrier such as impermeable plastic (polyethylene). When applied correctly, wrapping
impedes water flow and depletes available dissolved oxygen and food. This produces an anoxic
environment which can result in complete mortality of all encapsulated biota (Coutts and Forrest
2005).
Wrapping wharf piles in plastic was found to eliminate all encapsulated biota in an attempted
eradication of the sea squirt (Didemnum vexillum) in New Zealand (Pannell and Coutts 2007), and the
snowflake coral (Carijoa riisei) in Hawaii (Montgomery 2007). However it was not 100% lethal to
biota in cases where the wrapping had been damaged by berthed ships, or failed to completely prevent
water exchange (such as on complex wharf structures with multiple cross-beams). In addition,
pontoons wrapped in impermeable plastic resulted in the mortality of Styela clava (Coutts and Forrest
2005) and D. vexillum (Coutts and Forrest 2007).
Wrappings can remain on wharf piles for extended periods (up to 12 months) providing additional
protection from re-infestion (e.g. during the species spawning season). Should the outside of
wrappings become re-infested, their removal provides a second treatment option. In New Zealand it
cost ~NZ$11 per linear meter to treat wharf piles, with the removal and disposal of plastic costing an
additional NZ$3.20 per linear meter of pile (Pannell and Coutts 2007). The C. riisei eradication
attempt in Hawaii cost around US$100,000, although they used a lot of volunteer time (but travel and
a per diem was paid) (S. Pelleteri, pers comm.). Three key issues related to the use of plastic
encapsulation methods are: 1) disposal of the collected organic material and the plastic wraps, 2) the
plastic may tear loose and become an environmental and/or navigational hazard, and 3) the plastic
needs to be well sealed to mitigate the release of offensive odours generated by the decaying
organisms.
Plastic wrapping with chemicals added
In areas where structures are in high use, and rapid treatment is required, chemicals such as acetic acid
or chlorine can be added inside the wrapping to accelerate mortality. The addition of chemicals within
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 219

Appendices
plastic wrapping treatments has been trialled and found moderately effective in a variety of marine
pest management attempts. For example, the addition of 4% acetic acid within wrapped pontoons
achieved 100% Styela mortality in 10 minutes (Coutts and Forrest 2005). Wharf piles infested with
the Asian kelp (Undaria pinnatifida) were sterilised using bromine compounds applied inside PVC
sleeves (Stuart 2002). The black-striped mussel (Mytilopsis sallei) and Asian green mussel (Perna
viridis), were detected on the hulls of three apprehended illegal fishing vessels in Darwin Harbour in
2006. The vessels were wrapped in a PVC sheath (35 m x 14 m) and chlorine was added (400 ppm) to
kill the marine pests (Department of Primary Industry Fisheries and Mines 2006). In addition, vessels
infested with D. vexillum were successfully treated in situ using plastic encapsulation and the addition
of chemicals at a cost of $NZ 560 per vessel (Coutts and Forrest 2007).
A less successful attempt was made to sterilise steel pontoons and fuel barges infested with U.
pinnatifida using sodium hypochlorite in Big Glory Bay, New Zealand. These pontoons were
wrapped in plastic and sodium hypochlorite granules were placed within the sheeting. Although the
treatment initially appeared successful, new sporophyte growth was later detected. The barges were
subsequently either antifouled or burnt (Stuart and Chadderton 1997).
The use of chemicals contained within plastic wrapping was useful in some cases. However, most
chemicals are readily diluted in saltwater reducing concentration and efficacy, thereby requiring large
doses and lacking selectivity. Some chemicals that contain metal ions, such as copper compounds, can
also persist for a long time, and may continue to have residual toxic effects long after the target
invader has been eliminated (by bio-accumulation within other animals in the food chain). The use of
chemicals for future programs should ensure that chemicals will be contained and neutralised within
the plastic wrappings prior to their release to the surrounding environment, and are not likely to cause
on-going toxic effects.
Desiccation
An effective method to treat some infested structures is to remove them from the water (e.g. drydocking
of vessels). A recent attempt to desiccate D. vexillum colonies in New Zealand used cranes
to lift jetties or pontoons clear of the water while mussel floats were placed every 2 metres beneath the
structures to float them out of the water. The structures remained afloat for two weeks. However, this
method proved to be very labour intensive and caused damage to some jetties pontoons (Coutts and
Forrest 2005).
As mussels and oysters can survive for extended periods out of water, desiccation has been found to be
a cost effective and environmentally friendly method to control fouling species on aquaculture farms.
Mussel infrastructure (e.g. moorings, warps, floats, and backbones) can be removed from the water,
desiccated and later returned to the same location, or in some cases replaced with new materials.
However, there is a possibility that some individuals may survive for extended periods of time out of
the water (such as amongst dense clusters of mussels). It was found that Styela can survive air
exposure from 17 hours to 6 days, depending on ambient temperature and humidity (Coutts and
Forrest 2005).
Although this method is cost-effective, environmentally friendly and can be applied above-water,
often specialized gear may be required to remove vessels and it may inconvenience port operations.
220 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Appendices
Also given that Styela is robust to prolonged periods of desiccation the structures would probably need
to be removed from the water for up to a week to ensure 100% mortality.
Complete removal and immersion in either acetic acid or chlorine baths are also considered
appropriate for treating moorings, ropes, and floats as similar methods have been adopted to treat
unwanted organisms in aquaculture operations around the world (Coutts and Forrest 2005). For
example, to eradicate U. pinnatifida, ropes and mooring chains attached to infested structures were
removed from the water and soaked in a chlorine bath for 24 hours, and then allowed to sun dry
(Stuart and Chadderton 1997).
Rotating brushes
Removing a vessel from the water (e.g. dry-docking) can be expensive so some vessel owners remove
vessel fouling in-water using scrapers or brushes. Unfortunately, most in-water hull cleaning does not
allow for the collection of the fouling material released into the surrounding environment. This
method has been restricted or banned in some countries as a result. Diver operated portable rotating
brush systems are being trialed in New Zealand that claim to remove and collect 100% of the
biofouling while cleaning vessel hulls. Experimental trials have found that these claims are not
entirely true. While the diver operated portable rotating brush system is highly effective in removing
biofouling ( often > 90%), a small amount of material often remains (usually calcareous tubeworms)
(Hopkins and Forrest, In review). There are additional issues related to divers and hoses knocking
fouling material off during the operation, and the difficultly these machines have in cleaning the
‘nooks and crannies’ on a vessels hull. Furthermore, it is possible that the scrubbing operation may
actually stimulate fouling organisms to spawn during or after removal. A related method attempted to
remove Didemnum vexillum from the hull of a vessel using an underwater vacuum device and special
cutter, but this was deemed to be too labour intensive and ineffective for the colonial ascidian mats
(Coutts 2002).
Steam sterilisation
In-situ steam sterilisation has been tested as a method to treat Undaria pinnatifida on natural
substrates (Blakemore and Forrest 2007). Unfortunately, the apparent inability of the equipment to
achieve temperatures high enough for 100% mortality limits its utility. Reduced mortality is
particularly notable on surfaces with structural complexity, such as rocky reef areas or in many natural
habitats or situations with well developed fouling communities. To achieve complete mortality using
steam sterilisation alone it is suggested that temperatures >60 o C are maintained for several tens of
seconds (Blakemore and Forrest 2007). The application of this method will be most practical for new
infestations or those that are restricted spatially, as effort can then be concentrated in localised areas
(Blakemore and Forrest 2007). For example, the use of heated water was used to successfully
eradicate Undaria pinnatifida gametophytes on a sunken vessels hull in the Chatham Islands, New
Zealand over a four week period. This work comprised sterilising sections of the vessel hull by
attaching a plywood box to the side of the hull with magnets. Industrial electrical elements within the
box, powered by a diesel generator on the surface support vessel, heated the encapsulated water to
70°C. A flame torch was used for inaccessible areas such as near the seafloor and for areas with heavy
fouling (Wotton et al 2004).
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 221

Appendices
Suction devices
The use of a diver-operated suction device was trialled to eliminate the seaweed Caulerpa taxifolia in
New South Wales, Australia (Creese et al 2004), and has also been used in Croatia and the Spanish
Mediterranean (Meinesz et al 2001). In Australia, biomass was removed by a large, diver-operated
airlift connected to a barge where a settlement and filtration system was mounted. In Hawaii an
underwater vacuum cleaner was trialled to “suck” up invasive algae species such as gorilla ogo
(Gracilaria salicornia). This system is designed not to harm marine life that is inadvertently sucked
into the system and traps loose fragments, which reduces the risk of spreading the algae during
transport. The use of suction devices to collect targeted organisms is cost effective for small isolated
patches on the seafloor but is slow and organisms can block the suction equipment. It also requires
equipment such as pumps, generators and filters as well as several crew to operate it, and is only
feasible over areas of sandy sediments as underwater visibility is reduced when used over muddy
sediments. In addition, some material collected may be difficult to contain and require safe disposal or
subsequent treatment.
Pressure spraying
High pressure (>2000 psi) spraying was found to be effective in dislodging U. pinnatifida
gametophytes from fissures and crevices and was suggested to have the potential to keep equipment,
such as buoys, free of biofoulers (Forrest and Blakemore 2006). However, the use of blasting and
high-pressure water jets is expensive and time consuming, is generally only applicable to above-water
applications, and considerable care needs to be taken to prevent the release of fouling species back
into the marine environment. A water blasting tunicate mitigation technique has been trialled to
remove sea-squirts (Ciona intestinalis and Styela clava), from mussel lines on Canadian aquaculture
farms. Although useful for treating C. intestinalis, this technique had limited success even when used
at higher pressures to treat Styela. The difficulties arise because Styela has a much stronger test than
C. intestinalis and requires very high pressure to either damage it, or dislodge individuals from their
attachment points. At these high pressures the spray also damages both the mussels and their socking
attachments (K. Heasman, Cawthron, pers. comm.).
Fresh water immersion
Fresh water immersion was found to be 100% effective to control U. pinnatifida on seed mussel
ropes, without affecting mussel health (Forrest and Blakemore 2006), but the use of freshwater in the
marine environment can be logistically difficult. Styela clava can also tolerate freshwater exposure for
up to 24 hours and their survival may be enhanced if immersion of structures leads to a salinity
increase in the treatment water (Coutts and Forrest 2005). Few examples exist of using freshwater
immersion to reduce the risk of marine species being transported. However to prevent the introduction
of invasive species between coral reefs via infested dive gear, all dive equipment used in the North-
West Hawaiian Island coral reef ecosystem reserves is subject to a 24-hour freshwater soak prior to
use, and is given a 10 ppm chlorine freshwater immersion between reefs in the reserve (Anon 2005).
Removal by hand
It is possible to remove some sessile or sedentary marine organisms by hand picking or scraping. This
technique typically requires divers and it is often only practical to clear small areas since operations
222 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

over large areas can be labour intensive and cost-prohibitive. Over small areas this method is very
selective and typically requires few resources. For example, the mussel (Perna canaliculus) was
physically removed and buried by divers when a small population (12-24) were found attached to a
razor shell during a research dive in Gulf St Vincent, South Australia in 1996. Dredging and
additional dives found one more individual and its removal was thought to have completed the
eradication (Primary Industries and Resources South Australia 1999).
Appendices
Divers also physically removed 30,000 Northern Pacific seastar (Asterias amurensis) around Hobart in
1993 (Goggin 1998) and an additional 21,000 in 2001 (C. Sutton, CSIRO, pers. comm.), but these
attempts were ultimately ineffective in controlling the population. An eradication was attempted
around Holbourne Island, Australia, where divers injected ≈8000 starfish with copper sulphate, but
only eliminated ≈70% of the population (Birkeland and Lucus 1990). Localised control of subtidal
Undaria pinnatifida populations have also been attempted, which relies on divers detecting and
manually removing visible sporophyte stages of the seaweed, but is rarely successful (Hewitt et al
2004). Another issue with many of the techniques requiring divers is the potential danger they are
exposed to while conducting surveys or treatments. Considerable threats include becoming entangled
in ropes, plastic etc, and threats from passing vessel traffic. Furthermore, poor underwater visibility
may result in reduced search sensitivity and it is unlikely that all individuals will be detected,
particularly as population densities decline or if small and cryptic organisms are targeted.
Smothering
A variety of materials such as plastic, rubber, jute matting, spoilage or salt have previously been used
to smother invasive marine species. For example PVC plastic was used on the seabed to smother
Caulerpa taxifolia (Meinesz et al 2001; Creese et al 2004) and Didemnum vexillum (Coutts and
Forrest 2007; Pannell and Coutts 2007). Some workers have also added bleach beneath the plastic
(Williams and Schroeder 2004). This approach is similar to plastic encapsulation with chemicals
added, but is appropriate to sea-bed habitats. In the French Mediterranean mats soaked in copper
sulphate (ion-exchange textile covers) have been placed over beds of Caulerpa taxifolia - the
chemicals then leach from the mats and kill the algae (Uchimura et al 2000). Using salt to smother C.
taxifolia has also been successful at small scales (4 m² areas) at a site in Sydney Harbour, Australia
with divers spreading salt by hand (4 cm thick, ~50 kg/m²) (Creese et al 2004). For larger areas, salt
dispensed from a barge has found to be effective in treating C. taxifolia on soft sediments in water <
6m deep (Glasby et al 2005). In areas > 6m the salt was found to disperse too much before reaching
the substratum, and was ineffective at inducing widespread mortality.
Coutts and Forrest (2007) smothered rip-rap (rock used to stabilise the shore) with sheets of Bidum
A24 grade geotextile fabric to treat an infestation Didemnum vexillum. Unfortunately this method
failed to eradicate the target pest on the rip-rap as gaps remained in the joins between the sheets that
allowed the colonies to survive and reproduce. Similarly, the process of smothering C. taxifolia in
New South Wales (Australia) did not succeed in areas of uneven seabed or on rocky substrata.
When attempting to smother an area of seabed, some water exchange is often inevitable due to tidal
movement, therefore the material should continue for ~10 meters outside the boundary of the affected
area. The success of smothering can be dependent on a number of factors including the size of the
area, maintaining the smothering for a prolonged period and exposure (e.g. it can be difficult to anchor
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 223

Appendices
plastic in exposed areas). For example, in Humboldt Bay, California, USA an attempt to eradicate the
seagrass (Zostera japonica) by covering it with plastic failed as the strong tides in the area pulled the
sheets away (Rushton 2005).
Habitat modification
Modifying the characteristics of a habitat such as increasing or lowering the salinity are methods of
habitat modification. This type of treatment is usually only applicable to small, relatively enclosed
water bodies with limited tidal flows. Habitat modification methods are non-selective and will often
result in the death of non-target species, accordingly it is imperative to ensure that there is general
public support for the attempt and understadning of the implications before it begins. In Australia, the
salinity of a coastal lagoon was raised by adding 1000 tonnes of sea salt (NaCl) to treat four ha of
Caulerpa taxifolia as a preventive measure to stop its spread to additional estuaries (Ian Peebles, pers,
comm. cited in Global Invasive Species Program 2004). To successfully eradicate C. taxifolia the
salinity of West Lake, Australia, was artificially reduced to ~10 psu for several weeks by diverting low
salinity urban storm-water into the 1.2 km 2 lake (Murphy and Schaffelke 2003). Another example of
the successful use of this technique was the eradication of the seastar (Asterias amurensis) from
Henderson Lagoon (Australia) by dredging the lagoon mouth, and stressing the organism with
brackish water (13 ppt) (C. Sutton, pers. comm.).
Another well known example of habitat modification success was the eradication of the black striped
mussel (Mytilopsis adamsi) from three marinas in Darwin Harbour, Australia at a cost of Aus$2.2
million. To prevent the spread of the mussel to other states quarantine was quickly established to
control the movement of vessels and any item in contact with contaminated water. To eradicate this
species, workers closed the entrance gates to the marinas, poured over 187 tons of liquid sodium
hypochlorite and 7.5 tons of copper sulphate into the water, and required vessel owners to pump the
solution through their water pipes. The solution contacted all vessels and submerged structures,
killing the mussels in 15-18 days. Because the chemicals are general biocides, most other marine life
in the marinas was killed as well, but ecosystems were apparently recovered by 2000 (Ferguson 2000;
Bax et al 2002).
Classical biological control is an additional, but risky option to the incursion response tools described
above. However it is generally considered unlikely in marine environments, with extreme specificity
in pest-parasite, or pest-predator relationship is required for success without affecting non targeted
organisms. We did not consider biological control amongst the list of 11 potential management tools
since it is unlikely to be acceptable to the public, due to the considerable risk and unknown impacts of
an introduced parasite or predator on diverse assemblages in a novel environment. Terrestrial
examples of failed biological control attempts are also well known, such as the introduction of the
cane toad to control cane beetles in Australia. Previous failures such as this are likely to make the
general public understandably dubious about the potential risks of classical biological control. In
addition we know of no obvious predator or parasite species that would be considered for a candidate
for biological control of Styela in New Zealand waters.
224 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Table A7-2: Comparison of treatment methods, appropriate structures, acceptability and chance of success, legal issues, application issues, benefits, side effects, and approximate cost
per unit area (if available) to treat Styela clava
Treatment Structures/ habitats Stakeholder
acceptability and
chance of success
Plastic
encapsulation
Plastic
encapsulation
with chemicals
(e.g. acetic
acid/chlorine)
- Wharf piles
- Jetties/pontoons
- Vessels
- Buoys
- Seabed (smothering)
- Jetties or pontoons
- Vessel
- Wharf piles
Desiccation - Buoys
- Vessels
- Aquaculture
equipment
- Ropes, chains, tyres
Acceptability: High
Success: High
Acceptability:
Moderate
Success: High
Acceptability: High
Success: High
Appendices
Legal issues Application issues Benefits Side effects Indicative costs
(NZ$)
- Resource consent
may be required
- OSH certified
commercial divers
required
- Resource consent
issues related to the
safety and disposal
of chemicals
- Permission required
to remove gear
(e.g. mooring buoys,
vessels)
- Plastic dispenser
required
- Relatively simple to
deploy and can “setn-forget”
- Slow acting
(e.g. days/weeks)
- May inconvenience
port operations
- Fast acting
- Safety gear required
- Requires attention to
ensure effective
concentration
- Applied above-water
- Specialised gear
may be required to
remove vessels
(e.g. dry dock)
- May inconvenience
port operations
- 100% effective if
applied correctly
- Cost-effective
- Structures/habitats
can be treated in-situ
- Can remain on for
long periods and
may act as a
secondary treatment
- Can quickly treat
structures that are in
heavy use (e.g.
vessels, pontoons)
- Minimise any larval
release
- Cost-effective
- Environmentally
friendly
- Unselective
- May emit offensive
odours
- Disposal issues
(plastic and collected
biota)
- Diver safety issues
- Potentially
hazardous
- Collateral damage
- Can be expensive
- Disposal issues
- Potentially corrosive
- Diver safety issues
- Removal of some
structures (e.g.
vessels) may be
expensive
- Some organisms can
survive for extended
periods out of water
- Wharf piles ($11 to
treat & $3.20 to
remove per lineal m)
- Jetty/pontoon ($611)
- Vessel mooring
($176)
- Vessel ($560)
- Seabed >50m
($600/m)
- Pontoon (3x3m)
$160
- Cost will vary
depending on the
structure treated
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 225

Appendices
Treatment Structures/ habitats Stakeholder
acceptability and
chance of success
Rotating brushes
(that collect
fouling)
Steam sterilisation - Wharf piles
- Seafloor
- Vessels
Suction devices - Vessels
- Seabed
- Seaweed beds
- Vessels Acceptability:
Moderate
Success: Moderate
Acceptability: High
Success: Low
Acceptability:
Moderate
Success: Low
Legal issues Application issues Benefits Side effects Indicative costs
(NZ$)
- Resource discharge
consent required
- OSH certified
commercial divers
required
- OSH certified
commercial divers
required
- Resource discharge
consent may be
required
- OSH certified
commercial divers
required
- Specialised brushes,
pumps and collection
bags required
- Not all fouling may
be removed/
collected
- Brushes may not
access ‘nook and
crannies’ on a hull
- Specialised
equipment required
- Not effective on nonuniform
surfaces
- Labour intensive
- Only practical over
small areas
- Specialised
equipment required
- Labour intensive
- Only practical over
small areas
- Not all fouling may
be removed
collected
- Quick (e.g. 30m
vessel in 4 hours)
- Can be done in-situ
- Fouling material
collected on the
surface (90%)
- Environmentally
friendly
- Can target specific
areas
- Discharge of fine
particulate to the
environment
- May remove adults
or stimulate the
release of
propagules or
fragments into the
water column
- Diver safety issues
- Collateral damage
- Diver safety issues
- May
fragment/redistribute
species
- Can miss species
- Diver safety issues
- Vessel (30m) $5000
226 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand

Treatment Structures/ habitats Stakeholder
acceptability and
chance of success
Pressure spraying - Buoys
Acceptability: High
- Vessels
Success : High
Freshwater - Aquaculture
equipment
Hand removal
(e.g. picking,
scraping)
- Scientific equipment
- Vessels
- Wharf piles
- Vessels
- Seaweed beds
Smothering - Seaweed beds
- Rip-rap
- Seabed
Acceptability
Moderate
Success: Moderate
Acceptability High
Success: Low
Acceptability: High
Success: Low
Appendices
Legal issues Application issues Benefits Side effects Indicative costs
(NZ$)
- Issues related to
disposal of removed
fouling
- OSH certified
commercial divers
required
- OSH certified
commercial divers
required
- Simple to apply
- Applied above-water
- Effectiveness
depends on water
pressure
- Logistical issues
involved if large
amounts required
- Requires good
underwater visibility
- May require
repeated treatments
- Limited to a small
area
- Labour intensive
- Labour intensive
- Specialised
equipment may be
required
- Only practical over
small areas
- Requires good
underwater visibility
- Cost-effective
- Can be applied
quickly
- Cost-effective
- Environmentally
friendly
- Selective (low
collateral impact)
- Does not require
complex equipment
- Environmentally
friendly
- May
fragment/redistribute
species
- Some species (e.g.
mussels) can survive
for extended periods
in freshwater
- Not all targeted
species may be
collected
- Diver safety issues
- Collateral damage
- Diver safety issues
- Seaweed bed
($1.50/m 2 )
- Divers spreading salt
($8/m 2 )
- Barge/divers
spreading salt
($33/m 2 )
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 227

Appendices
Treatment Structures/ habitats Stakeholder
acceptability and
chance of success
Habitat
modification
- Enclosed water
bodies
Acceptability:
Moderate
Success: Low
Legal issues Application issues Benefits Side effects Indicative costs
(NZ$)
- Resource consent
required
- Only possible in
certain situations
- May require
chemicals
- Can potentially treat
a large area
- Large collateral
impact
- Mytilopsis adamsi
eradication in Darwin
($2.4 million)
228 • Assessment of population management options for Styela clava MAF Biosecurity New Zealand