Spatial distribution of macrobenthic fauna on three sandy beaches from northern Rio Grande do Sul, southern Brazil

The spatial distribution of benthic macrofauna on the beaches of Tramandaí, Jardim do Éden and Harmonia, was investigated over five consecutive days in April, 2003. The distribution pattern was also analyzed along with environmental parameters. Three transects were set on each beach, 50 m apart, with four sample stations set along each transect. On every station, three samples of benthic macrofauna were taken daily, with a core sampler with 20 cm diameter. In the midlittoral zone, the polychaete Euzonus furciferus and the isopod Excirolana armata dominated. In the swash zone, tidal migrators, Emerita brasiliensis,Donax hanlevanus and Mesodesma mactroides, were the most abundant species and, on some days, the polychaete Scolelepis gaucha. In the lower zones of the beaches, D. hanleyanus,M. mactroides and the amphipod Puelche orensani dominated. This zonation pattern was found for all three studied beaches, based on the average density of each species, over the five days period. Horizontal variation in the fauna was not found, either inter or intra the studied beaches, possibly due to little variability in slope and homogeneity of sediment grain size presented in the three beaches.