Impacts of two introduced suspension feeders in Port Phillip Bay, Australia

This study examined the impacts of 2 of the most common epibenthic suspension feeders, Sabella spallanzanii and Styela clava, in Port Phillip Bay, by transplanting individuals from the surrounding habitat into 2 x 2m experimental plots. Densities in the plots represented naturally occurring densities, ranging from 0.5 to 10 individuals per m-2 for Sabella and from 0.5 to 5 individuals per m-2 for Styela. At the completion of the 10 week experimental period the numbers of alive and dead Sabella and Styela in each plot were counted. The infauna in each plot was sampled by inserting 2 metal cylinders to a depth of 15cm into each plot. The sediment within each cylinder was vacuumed to a depth of 10cm into a 1mm mesh bag using a diver-operated, water-driven suction device. The total area in each plot that was sampled was 0.2m2 (cylinder diameter = 35.5cm). Macrofauna were counted and identified in the laboratory to the lowest possible taxon, which was mostly Family. There were significant effects on individual taxa at Sabella and Styela densities greater than 1-2 individuals per m-2, which are densities greater than those typically recorded in Port Phillip Bay. There was a significant negative relationship between Sabella density and the abundance of lumbrinerid polychaetes and gammarid amphipods, and between Styela density and the abundance of lumbrinerids, tanaids, crustaceans as a group, and the bivalve Laternula rostrata.