Application 124771 - Ministry of Fisheries

MAY 2012 REPORT NO. 2134 | CAWTHRON INSTITUTE
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index, was also similar between farm and reference sites, with the most even samples
(i.e. closest to 1 in the index) being Control site 6 (0.97) and Farm site 1 (0.89).
Species diversity was calculated using the Shannon Wiener diversity index, and
averaged between 2.15 and 2.9 at Control sites (3 and 1 respectively) and between
1.93 and 2.89 at Farm sites (4 and 1). A complete list of biological indices can be
found in Appendix 2 and a complete taxa list can be found in Appendix 3.
The dominant infauna taxa across all sites were the window shell (Theora lubrica),
various species of polychaetes (e.g. Heteromastus filiformis, Prionospio multicristata,
Prionospio yuriel and Sphaerosyllis sp.), brittle stars, and oligochaete worms (Table
1). The dominant epifauna taxa by abundance were Phoxocephalidae amphipods,
Decapoda larvae (unidentified), Cumaceans and Melitidae amphipods.
Patterns in infaunal community composition were further explored using multivariate
statistical techniques (Figure 6, see Appendix 1 for Simper analysis). In addition to
being distinguished by the low total abundance and taxa richness, multivariate
analysis showed the infaunal community at Control site 2 was different to the other
stations; due mainly to a greater abundance of the nut clam, Nucula gallinacea and
Phyllodocidae polychaetes, and the near absence of polychaete worms like
Sigalionidae sp., Cossura consimilis and Prionospio yuriel. This group was also
differentiated by lower abundances of a number of invasive bivalve (Theora lubrica),
the capitellid worm (Heteromastus filiformis) and the polychaete worm (Sphaerosyllis
sp).
The infauna communities from the control and farm grab samples were generally
separated at the 35% level of similarity (Figure 3). The majority of samples from the
control sites and individual grabs from four farm sites (Li 292, 362, 379, and 396),
were differentiated by greater numbers of polychaetes (Neonesidea sp., Sigalionidae,
Cossura consimilis and Aglaophamus species), but also by lower abundances of most
taxa found in the majority of farm samples. Grab samples from farm sites and
individual grabs from Control site 1, 4 and 6, were grouped by higher abundances of
polychaete worms including Prionospio multicristata, Prionospio yuriel, and the
capitellid worm (Heteromastus filiformis), but also had greater numbers of the invasive
marine bivalve (Theora lubrica).
The differences in infauna communities found between farm and control sites are
indicative of a mildly enriched benthic environment beneath farms resulting in greater
abundances of opportunistic species. However, in most cases the subtle differences
observed were in the abundance of species, rather than their presence or absence.
This suggests that infauna communities in the wider environment are already exposed
to mild enrichment through natural sedimentation processes.