SEMIQUANTITATIVE STUDY OF MACROBENTHIC FAUNA IN THE REGION OF THE SOUTH SHETLAND ISLANDS AND THE ANTARCTIC PENINSULA

During the BENTART 95 Expedition, 24 Agassiz trawls for macrozoobentho s sampling were carried out at depths of 40-850 m, from north of Livin gston Island to the Antarctic Peninsula. The samples were analysed usi ng a semi-quantitative method, and with the resulting numerical data, transformed into a six-point scale, we constructed a Bray-Curtis simil arity matrix. A total of 74,624 specimens, belonging to 38 taxonomic g roups, were collected. The most abundant group was Polychaeta Sedentar ia, with 36% of the total, whereas the highest relative masses were fr om Ascidiacea (23%), Echinoidea Regularia (18%) and Ophiuroidea (16%). The maximum number of specimens recorded was 15,600 ind./50 l. Cluste r analysis separated stations located in Foster Bay (Deception Island) , characterised by low taxonomic richness and high relative mass (aver age: 26.7 kg). A zonation of ascidians, regular sea urchins and ophiur oids was observed at Deception Island. clearly related to depth and su bstratum type. The remaining stations were separated into two groups. The first one comprised the shallowest stations (40-130 m), dominated by sessile active filter-feeders, belonging to Ascidiacea, Demospongia and Bryozoa, and probably related to high primary production zones. T he second group comprised deeper stations and was dominated by classes exhibiting a diversity of trophic strategies: Ophiuroidea and Asteroi dea, to 400 m, and Polychaeta Sedentaria at greater depths.