<b>Soft bottom benthic macro-invertebrates assemblages on the continental shelf and upper slope of southernBrazil</b>

Abstract

Benthic macro-invertebrates assemblages on the continental shelf and upper slope of southern Brazil (31º15´- 34º30´ S) were identified and the biotopes distribution and faunal abundance were related with environmental conditions. An Inner shelf (11-38 m) Association which occurs south of 32ºS was discriminated from others by the sandy substrate. The highest biomass was related with sandy bottoms which favor the presence of large epibenthic psammophilic species and the availability of particulate matter, leading to the total biomass of 82% by the deposit feeder Encope emarginata. The Middle Shelf Southern Association (40-75 m) is influenced by the flow of Sub Antarctic Shelf Water in winter, which determines low bottom water temperatures (12- 14°C) and high phytoplankton productivity. In addit ion, the increased nutritional quality of the substrate probably supports high numbers of infaunal deposit feeders (polychaetes, ophiurids). In the North Middle and Outer Shelf Association (50-150 m muddy substrates and winter temperatures above 15ºC) predominate. The discrimination between meridional and septentrional middle shelf associations was related to temperature effects, determining the prevalence of cryophilic and thermophilic species, respectively. A general change of the fauna of the the Upper Slope Association (150-500m) occurred owing to environmental conditions which characterize the beginning of deep benthos.