Species richness and distribution patterns of echinoderms in the southwestern Atlantic Ocean (34-56°S)

Abstract

The aim of this study was to compile and analyse available historical information on echinoderms in the southwestern Atlantic Ocean in order to make a synthesis of present taxonomical knowledge, to identify patterns of geographical distribution of echinoderm assemblages and to test the validity of the current zoogeographic scheme for this group. This study was conducted on the Argentinean continental shelf, southwestern Atlantic Ocean (34-56°S). An intensive research on geo-referenced data was carried out to make a knowledge synthesis on echinoderm species and thus create a historical database. Multivariate analysis was used to analyse the faunal composition through latitudinal and bathymetric gradients as well as echinoderm associations. The results confirmed the existence of two faunal associations that correspond to the traditional zoogeographic scheme established for the Argentine Sea: the Argentinean and Magellan Provinces. The Argentinean Province had 46 widely distributed species. Of the 86 species recorded in the Magellan Province, a high percentage (25%) were also found in Antarctic waters, suggesting a strong connection between the echinoderm fauna of this province and the Antarctic Region. The species richness between 34 and 56°S in the Atlantic Ocean showed a significant increase in reference to latitude, with the highest values being recorded between 46 and 56°S. In view of the high percentage of shared species with Antarctica, considered a hot-spot region in terms of echinoderm diversity, the pattern of distribution of species richness observed in our study area could correspond to a dispersion of this species from Antarctic to sub-Antarctic regions.