Zoogeography of Holocene Podocopina (Ostracoda) from the Brazilian Equatorial shelf

This study reports on the Holocene ostracods of the Brazilian Equatorial sh elf from French Guiana to near Natal, almost 1400 km in length. This part o f the Western Atlantic Tropical Province, where the mouths of the Amazon an d Para rivers separate two zoogeographical units, has distinct oceanographi c and sedimentologic features. Three hundred and thirty nine samples were s tudied from the REMAC (legs 4, 5, 5A and 6) and the GEOMAR projects (legs I , II and III). The ostracod fauna includes 74 species, of which 37 have bee n previously described (mostly from other areas). The remaining 37 species are left in open nomenclature although 26 of them are probably new. Twelve species are confined to the northwest and 16 to the southeast of the mouths of the Amazon and Para rivers. The inner shelf of the northwestern region is a barren zone resulting from turbid freshwater discharged by the Amazon and Para rivers. Most of the studied species live at water depths of less t han 100 m; 28 species inhabit waters shallower than 75 m, and 18 species li ve in waters shallower than 50 m. Although Brazilian ostracods have many ge nera and species in common with Holocene ostracods elsewhere in the tropica l Atlantic, diversity differs greatly. For example, diversity on the Brazil ian Equatorial shelf is lower than elsewhere in the Western Atlantic Tropic al Province, but higher than in the Eastern Atlantic Tropical Province. Fau nal similarities between these provinces are at the generic rather than spe cies level; exceptions are few and consist of conservative Tethyan species that are cosmopolitan. (C) 1999 Elsevier Science B.V. All rights reserved.