Isopod assemblages on the continental shelf and upper slope from the southwestern Atlantic

Composition and distribution of isopod assemblages on the shelf and upper slope from the Sao Paulo northern coast, southeastern Brazil, were studied from sixty-nine dredge hauls and fifty four van Veen grab samples taken between 10 and 600 m depth. Data from both samplers were binary transformed for community analysis. Multivariate methods for classification and ordination, as Cluster Analysis and Canonical Correspondence Analysis, were employed in such studies. Forty-eight species were discovered in the area, 21 of them new to science. From those new species 71% were found as deep as 50 m, and the Anthuridea was the most diverse group. Clustering analysis disclosed three distinct groups. Group 1 comprises the inner shelf assemblage, which is influenced by warm and light water — the Coastal Water (CW). Species from this group are Politolana eximia, Politolana sp, Cristaserolis laevis, Paranthura sp. 1 and Colanthura sp. Group 2 comprises the outer shelf plus shelfbreak assemblages, and is situated within a transitional area under both the CW and the South Atlantic Central Water (SACW) influence. Accalathura crenulata and Joeeropsis sp. dominate it. Group 3 characterizes the slope, is always within the SACW domain, and Gnathia ricardoi, Bathygnathia magnifica, Eisothistos sp., and Metacirolana sp. are the most frequent species. The isopod assemblage structure in the shelf and upper slope appears to be determined primarily by hydrodynamics and factors linked to depth and less controlled by sediment composition. It is suggested that the slope is probably an upper limit for deep-living isopods in the region.