Epifaunal assemblages of the eastern Great Australian Bight: Effectiveness of a benthic protection zone in representing regional biodiversity

This paper describes the epifaunal macro-invertebrate assemblages of the continental shelf in the eastern Great Australian Bight (GAB) in relation to environmental factors, including water depth and sediment type. Patterns of species composition are used to assess the effectiveness of the Benthic Protection Zone (BPZ) of the GAB Marine Park in representing regional biodiversity. A total of 753 kg of benthos belonging to 797 species and 10 phyla were collected in 65 5-min tows using a 1.8 m wide and 0.6 m high epibenthic sled, fitted with a 50 mm mesh bag. Results suggest that the eastern GAB supports one of the world's most diverse soft-sediment ecosystems. Sessile, suspension-feeding organisms (primarily poriferans, ascidians and bryozoans) dominated samples, and collectively comprised over 96% of the biomass and 74% of the species collected. Correlation analyses revealed a significant positive relationship between species richness and biomass and highlighted a general decline in both parameters with increasing depth and percentage mud in sediments. Six epifaunal assemblages identified in this study were correlated with depth and sediment type. Large total biomasses and high numbers of species were recorded in inner shelf waters of the western Eyre Peninsula, which support high levels of plankton production, and at the Head of the Bight, where sediments are fine grained. All six of the assemblages and 54% of the species collected were found in the BPZ, suggesting that the zone may effectively represent the epifaunal assemblages of the continental shelf in the eastern GAB.