A year's survey conducted at a seagrass (Halodule wrightii Ascherson) bed and an adjacent bare sand area, on Codó Beach, Ubatuba, southern Brazil, showed that the macrobenthic species composition was different at the two habitats. Surface deposit feeder infaunal polychaetes were the dominant species in the Halodule site and omnivorous/carnivorous and filter feeder polychaetes, in the bare sand. These differences could be explained mainly by the characteristics of the sediment and the stability of the bottom and, secondly, by the presence of Halodule. The presence of vegetation has no effect on density of macrobenthos, probably due to the small size of Halodule plants, which do not support an abundant epifauna. Despite that fact, both number and diversity of species were higher in the seagrass area than in the unvegetated site, as was epifaunal abundance. Significant patterns of temporal fluctuations of macrobenthos abundance and species diversity were not observed, but diversity was the highest in Spring at both habitats. The temporal fluctuations of abundance differed in the two habitats. At the unvegetated site instability of the substrate seems to be responsible for the observed fluctuations in densities. At the Halodule site only light fluctuations occurred, though they did not follow those of macrophyte biomass. Macropredator effects are suggested to be one of the controling factors of macrobenthos density at the vegetated habitat.
zoobenthos; seagrass; Halodule; Ubatuba; Brazil