Assessment of population management options for Styela clava

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