ECOLOGICAL PATTERNS IN THE BENTHIC MACROBIOTA ACROSS THE CONTINENTAL-SHELF OFF CENTRAL CHILE

The upper sublittoral benthic macrobiota off central Chile (36 degrees 32'S) was sampled on six cruises during 1984 and 1985, at four fixed benthic stations. The aim of this study was to learn about bathymetric and seasonal patterns of distribution and abundance of macrobenthos, including the macro-infauna and the sulfur bacteria Thioploca spp., an d their relationship to oceanographic variables, in particular, dissol ved oxygen. Biotic data were analyzed by different approaches and meth ods, including community attributes, diversity indices, and ordination analyses: principal component analysis (PCA) and non-metric multidime nsional scaling (NMDS). The relations between environmental variables and the biota were explored by PCA and correlation analyses. Results s how significant declines with depth in the number of macrofaunal speci es, numerical abundance and biomass. Shannon-Wiener diversity differen ces were not significant however. According to a biomass distribution analysis, prokaryotes appear associated with the deeper bottoms. The c ommunity ordination disclosed three depth-associated biotic assemblage s. Species in these assemblages do show seasonal and bathymetric patte rns of abundance and distribution and, despite the variability of the former, the latter appear to be shaped by dissolved oxygen content in the water close to the bottom.