POLYCHAETE POPULATIONS OF THE SHALLOW SOFT BOTTOMS OFF TERRA-NOVA BAY(ROSS SEA, ANTARCTICA) - DISTRIBUTION, DIVERSITY AND BIOMASS

Diversity, distribution and biomass patterns of polychaetes were studi ed in the shallow soft bottoms off Terra Nova Bay (Ross Sea, Antarctic a). Benthic samples, collected in the austral summer 1989-1990, were s ampled using a Van Veen grab at 14 stations distributed between 23- an d 194-m depth. A total of 5,768 individuals of polychaetes belonging t o 77 species were found. The species richness recorded was high, despi te the few biotopes investigated at Terra Nova Bay in this study, espe cially when compared to that recorded from previous investigations in the same area and from the whole Ross Sea (146 species). Despite the h igh number of species found, only a few species accounted for 76% of t he total abundance: Tharyx cincinnatus (27%), Spiophanes tcherniai (23 %), Leitoscoloplos mawsoni (18%) and Laonice wendellia (5%) were mainl y distributed in the deeper stations (below 100-m depth), while Aglaop hamus ornatus (3%) was the only species abundant in the shallowest sta tions (above 50-m depth), characterized by gravels and coarse sands. S pecies richness, diversity and evenness showed an increase with depth. Abundances ranged between 40 to over 12,000 ind/m(2). Biomass values ranged between 0.9 to 176 g/m(2) (wet weight). A trophic-guild classif ication revealed the occurrence of various feeding categories that wer e, however, numerically dominated by deposit feeders with both discret ely motile epi- and endobenthic forms, and sessile ones. Both the Bray -Curtis similarity and Correspondence (C.A.) analyses showed stations ordered according to depth and to the local dominance of some species. Both poorly and well-structured polychaete assemblages occurred and t hey seemed related to depth-related factors, such as degree of environ mental disturbance (shallowest bottoms vs deep ones), heterogeneity of the substrate and habitat complexity (gravel and coarse sands vs mixe d sediment. The richest and most diverse assemblages of polychaetes we re those occurring below 140-m depth, where the substrate was dominate d by medium sands, often mixed with a mosaic of rocks and boulders.