The ecological and zoogeographical significance of the sub-Recent Ostracoda off Cabo Frio, Rio de Janeiro State, Brazil

An environmental analysis based on the ostracod fauna was carried out on 43 sediment samples collected during the Geocosta Rio II Expedition to the northern continental margin of State of Rio de Janeiro, between the town of Cabo Frio and the Saquarema Lagoon (22°55′/23°5′S; 42°00′/42°20′W), Brazil. From a total of 67 species, 31 are considered to be new and are left in open nomenclature. Sedimentological and bathymetric parameters were compared with the relative frequency, dominance, diversity (Shannon-Wiener and Margalef indexes) and abundance of species in order to evaluate the environmental impact of those parameters on the distribution and occurrence of ostracods in the study area. Most of the recorded species are typical of the Southern Brazilian Subprovince (lat. 22/21° to 31/30°S), but have their southernmost occurrences in the adjacent Platensian/Uruguayan/Pelotensis Subprovince (lat. 31/30° to 36°S). In spite of the shallow depth from which the samples were recovered, the ostracod fauna is thus characterized as a cool-water assemblage; waters in the area may be cool because of extensive upwelling.