Distribution patterns in the biomass of macrozoobenthic communities in Admiralty Bay (King George Island, South Shetlands, Antarctic)

The distribution patterns of macrozoobenthic communities as shown by the biomass of the higher taxa were investigated in Admiralty Bay. Material was collected at depths ranging from 4 to 500 m (102 quantitative samples), representing the full depth range of this basin and including areas characterized by the different levels of glacial influence. Five community groups were distinguished by multivariate analysis (clustering, MDS) based on the Bray--Curtis similarity index. In the Ezcurra Inlet, the area characterized by intensive glacial processes resulting in a high sedimentation rate, the distribution of biomass was not depth related, but was associated with the intensity of glacial disturbance along the axis of the fjord. The innermost part of this fjord, which receives strong outflows from glaciers, had a low biomass value (2.9 g/0.1 m²) and was dominated by polychaetes. The middle part of the fjord which is not so heavily disturbed had higher biomass values (46.1 g/0.1 m²) due to the dominance of bivalves. A clear depth gradient of biomass distribution was observed in bottom areas located far from glaciers, in the central basin of the bay, with three zones within the depth ranges 4-30, 40-380, and 400-500 m. The highest mean biomass values (92.5 g/0.1 m²) were found in the middle sublittoral (40-380 m) dominated by ascidians. In the shallow and deep assemblages, the biomass was lower (33.8 g/0.1 and 30.9 g/0.1 m² respectively), most probably associated with the ice disturbance in the shallows and lower food supply in the deepest part of the shelf.