Application 124771 - Ministry of Fisheries

CAWTHRON INSTITUTE | REPORT NO. 2134 MAY 2012
5.3. Enrichment stages
The biological and physico-chemical data from each grab sample were used to
assess and compare the relative enrichment stage (ES) of each grab sample
(Figure 7). No significant difference between the ES of grab samples at control and
reference farm sites (F1,40 = 0.12, p > 0.05) was observed. All sites, except Control site
2, were mildy enriched regardless of type (‘control’ or ‘farm’), with average ES scores
of 2.03 (s.e. ± 0.85) across all control sites and 2.07 (s.e. ± 0.74) at reference farm
site.
Enrichment Stage (ES ± 1 s.e.)
3.5
3
2.5
2
1.5
1
0.5
0
Con 1 Con 2 Con 3 Con 4 Con 5 Con 6 Farm
1
Figure 7. Average enrichment stages (ES) from replicate grab samples at control and reference
farm sites (see Appendix 2 for raw data used to calculate ES).
5.4. Epibiota from video transects
Video transects were used to determine the dominant substrata, the extent of mussel
shell drop-off and the characteristic epibiota at each site (Table 2, Figures 8 and 9)
Dense mussel shell drop-off was found to extend no more than 25-40 m from the farm
edge of all reference farms (see maps in Appendix 6), but sparse clumps of mussels
were observed out to 100 m at some sites, possibly due to the repositioning of farms
over time. Epifauna species associated with mussel drop-off, and the food and solid
substratum it provides, were common at farm sites (Figure 8, Table 2). A variety of
sessile organisms were observed living on mussel shell beneath farms (Figure 9 A-D),
including solitary ascidians (Pyura pachydermatina and the invasive Styela clava),
bryozoans (including Watersipora cucullata and Bugula sp.), finger and mat forming
sponges, bivalves, calcareous polychaetes, small feather hydroids (unknown species)
and seaweeds (including Codium sp.). Mobile fauna observed beneath farm sites
included fish (mainly leatherjackets, Parika scaber, and spotty wrasse Notolabrus
Farm
2
Farm
3
Farm
4
Farm
5
Farm
6
Farm
7
Farm
8
15