Daily variation of macrobenthic fauna on an exposed sandy beach of Rio Grande do Sul, Brazil

This work aims to verify the daily zonation of benthic macrofauna in Harmonia beach north coast of Rio Grande do Sul state, for five consecutive days. Biological data was collected with a PVC core (20 cm diameter) along three transects distant 50 m each other, with four levels and three samples in each level. First level was always 8 m above the superior limit of swash zone and the last one was 1 m depth. There were also daily data collection of beach topographical profiles, which indicated a pronounced erosion process in the fifth day. Benthic macrofauna organisms showed a regular pattern of zonation along all days, with intertidal zone marked by the presence of the isopod Excirolana armata and the polychaeta Euzonus furciferus.Swash zone was represented by a high abundance of the hippid crab Emerita brasiliensis, the pelecypod Donax hanleyanus and the polychaeta Scolelepsis gaucha. Surf zone and breaker zone didn't show differences in species composition, being dominated by juvenile of D. hanleyanus, Mesodesma mactroides, the amphipode Phoxocephalopsis zimmeri and the polychaeta Hemipodus olivieri. Results indicated that benthic macrofauna zonation pattern was regular, although some changes in species position along the transect was observed, mainly due to swash zone variation.