Copepod assemblages in a highly complex hydrographic region

Community structure and diversity patterns of planktonic copepods were investigated for the Southwestern Atlantic Ocean between 34 and 41°S. Our objectives were (1) to define copepod assemblages, (2) to accurately identify their association to different water masses/hydrodynamic regimes, (3) to characterize the assemblages in terms of their community structure, and (4) to test if frontal boundaries between water masses separate copepod assemblages. Biogeographic patterns were investigated using multivariate analysis (cluster and ANOSIM analyses). Biodiversity patterns were examined using different univariate indexes (point species richness and taxonomic distinctness). Five regions of similar copepod assemblages were defined for our study area each one corresponding to different environments (freshwater, estuarine, continental shelf, Malvinas and Brazil current assemblages). These assemblages have major community structure differences. In spite of the complex oceanographic scenario of our study area, that can lead us to expect a pattern of copepod communities with diffuse boundaries, we found a strong spatial correspondence between these limits and the presence of permanent frontal structures.