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    On biogeographic patterns of benthic invertebrate mega fauna on shelf areas of the Southern Ocean Atlantic sector

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    S.J. Lockhart and C.D. Jones (USA)
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    The ideal approach to bioregionalisation of Antarctic and Southern Ocean shelf communities incorporates a range of data on physical, environmental and biological properties, as well as the interaction of these properties. Here, benthic invertebrate megafaunal communities of shelf habitats within the Atlantic sector of the Southern Ocean were analysed quantitatively from scientific survey trawl catches in order to identify and characterise such communities for comparative purposes at a fine spatial scale, with an ultimate aim of determining broad patterns of distribution. The region for which the greatest complexity of data was available, the northern Antarctic Peninsula and the South Shetland Islands, reveals a two-layered pattern based on the standardised total biomass data and the composition of phyla that contributes to that biomass. In terms of biomass, the shelf area adjacent to the northern of the Antarctic Peninsula represent an extreme compared to the relatively sparse South Shetland Island shelf. The situation is reversed at each region’s easternmost shelves. In terms of composition, the demarcation occurs where the sponge dominated communities most frequently encountered on both shelf systems rather abruptly decline westwards on the shelf north of the South Shetlands off western King George. By referencing physical oceanographic data for the region, a pattern of shelf faunal zonation emerges. Patterns of benthic invertebrate biomass are also described for the South Orkney Islands, as well as general patterns of composition at the level of phyla for South Georgia, the South Sandwich Islands, and Bouvet Island. These latter regions are generally echinoderm dominated, relative to the hexactinellid sponge dominated northern Antarctic Peninsula region.