Biogeography of Brazilian prosobranch gastropods and their Atlantic relationships

Abstract

Aim The present study uses marine prosobranchs from shallow waters (down to 200 m) as a model to determine biogeographical units along the Brazilian coast and to investigate changes in assemblages along the Western Atlantic. Location Western Atlantic Ocean. Methods The composition and species distribution of prosobranchs were determined using secondary data and information gathered from Brazilian scientific collections. The similarities among the areas were calculated using the Sørensen, Simpson and Ochiai Indices, and were illustrated using dendrograms constructed by unweighted pair group method using arithmetic averages. Ordination analysis was performed using non-metric multi-dimensional scaling based on the similarity matrices. Results As a result of the compilation performed, 700 marine prosobranch species distributed in 81 families from shallow waters were recorded in Brazil. The results show a clear correlation between geographic distance between areas and their faunal similarity. There is a gradual latitudinal variation in marine prosobranch assemblages along the Brazilian coastline. The coastal areas sustain richer gastropod assemblages than the oceanic islands. Main conclusions Considering the results of cluster and ordination analyses, this study proposes to divide the Brazilian coast into four regions: (1) Guyanese Province (Amapa state), (2) North-eastern Brazil Area (from the mouth of the Amazon to southern Bahia, Brazil), (3) South-eastern Brazil Area (from southern Bahia to Santa Catarina, Brazil, transition zone), and (4) Argentinian Province (Rio Grande do Sul state). The North-eastern and South-eastern Brazil Areas belong to the Brazilian Province. The Brazilian insular areas are biogeographical units distinct from the other regions studied. Each island has its own composition of marine prosobranchs from shallow waters, while they share species with other coastal and island environments