Assessment of population management options for Styela clava

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