Structure and dynamics of benthic megafauna on the continental shelf offshore of Ubatuba, southeastern Brazil

Abstract

Two water masses influence the seabed: South Atlantic Central Water (SACW) and Coastal Water (CW). The first penetrates towards the coast during summer months, and retreats offshore in the winter. Distribution, density and biomass of the benthic megafauna show two domains: inner shelf and outer shelf, both separated by a front. High abundance of the brachyuran crab Portunus spinicarpus characterizes the frontal system and occasionally changes the structure of the inner and outer shelf assemblages. Water masses and sea depth are the main factors structuring the benthic megafauna communities. Clustering analysis disclosed four assemblages: 1) coastal communities within the CW domain; 2) inner shelf communities influenced by a mixed zone with CW predominant, 3) frontal zone communities where SACW was predominant, 4) outer shelf communities within the SACW domain. Species diversity was almost homogeneous on the entire shelf except in the frontal zone where it sharply decreased. The common species, both perennial and seasonal, showed a consistent pattern of dominance through the study period. Adjustments occur within the community whereby some species increase in abundance when others decrease, maintaining a stable pattern. -from Author