BIOGEOGRAPHIC PATTERNS OF BENTHIC INVERTEBRATE MEGAFAUNA ON SHELF AREAS WITHIN THE SOUTHERN OCEAN ATLANTIC SECTOR

Bioregionalisation of Antarctic and Southern Ocean shelf communities ideally incorporates a range of data on physical, environmental and biological properties. Analysis of the benthic invertebrate megafaunal assemblages of shelf habitats within the Atlantic sector, from scientific survey trawl catches, reveals distributional patterns. For the northern Antarctic Peninsula and the South Shetland Islands, the data indicate a two-layered pattern based on standardised total biomass data and the composition of phyla that contribute to that biomass. An examination of physical oceanographic data reveals a pattern of shelf faunal zonation: the benthic invertebrate communities on the northern shelves of the South Shetland Islands and the northern Antarctic Peninsula can apparently be separated into zones based on the physical properties of the Antarctic Circumpolar Current and the Weddell water masses that meet and mix in this region. Evident at smaller spatial scales are the effects of disturbance regimes, whether by iceberg scouring or historical commercial bottom trawling. Patterns of benthic invertebrate biomass are also described for the South Orkney Islands, as well as general patterns of phylum-level composition for South Georgia, the South Sandwich and Bouvet Islands. These regions are generally echinoderm-dominated, compared to the hexactinellid sponge-dominated northern Antarctic Peninsula region.