Composição, distribuição espaço - temporal e associações de espécies de Gastropoda do infralitoral de fundos inconsolidados da região do Cabo Frio, RJ, Brasil

Abstract

The main purpose of this study was to determine the composition, spacial-temporal distribution and the gastropod associations of upwelling ecosystem of Arraial do Cabo, RJ/Brazil. Monthly, samples were done using an otter-trawl, a rectangular dredge and a van Veen grab at 30, 45 and 60 meters deep, during 1986 to 1988. Some abiotic parameters of the sediment and water near the bottom were analysed. More than 50% of the samples presented water temperatura below 18°C, showing a strong influence of the Central South Atlantic Water in the studied area. The sediment varied from medium sand well sorted to fine sand moderately well sorted. Were collected 915 gastropods of 56 species, recording a new occurrence to the Brazilian coast. A seasonal pattern was not observed in the distribution of the organisms, however a progressive increase of the number of individuals occurred from 1986 to 1988, suggesting a longer seasonal cycle. The highest values of abundance and richness were fond at 30 and 45 meters and the diversity was higher at 45 meters, where the sediment showed intermediate granulometric characteristics in relation to 30 and 60 meters. Clustering analysis allowed the determination of associations to each depth studied. The characterization of the associations was only possible by using data obtained from the three samplers, despite the higher efficiency of the dredge in providing samples of the gastropods.