Spatial distribution of Polychaeta in intertidal sandy beaches at São Sebastião (SP)

Abstract

Five sandy beaches of Sao Paulo, Brazil, were sampled in order to determine whether different beach morphodinamics support different macroinfaunal compositions. Density and diversity patterns of Polychaeta from five beaches were compared with some physical and chemical characteristics of those sites. Two patterns were distinguished through examination of diagrams based on muitivariate techniques: (1) in protected beaches with high sand content there is the dominance of Laeonereis acuta : (2) in very protected beaches with high silt and clay content there is the dominance of smaller species. Organic-rich sediments supported a more diverse fauna showing the importance of this source of food on occurrence of many deposit-feeding species. It is suggested that low salinity can determine L . acuta abundance, due to high correlation between this parameter and the density of this specie. The dominance of smaller species on finer sediments, Heteromastus filliformes and Sternaspis capillata , could be due to mechanisms of exploitation of food resources. Principal component analysis showed that sand, silt-clay as well as organic contents and salinity were the most important variables accounting for the spatial variability of polychaetes on the studied beaches.