Composition, structure and zonation of intertidal macrofauna in relation to physical factors in microtidal sandy beaches at Río de Janeiro State, Brazil

Abstract

The intertidal macroinfauna of fiftheen exposed sandy beaches located in Rio de Janeiro State was studied to determine species richness, density, biomass and zonation. Morphodynamic influence on biological parameters is also evaluated in this paper. Dean´s morphodynamic index (?) ranged from reflective to intermediate values and mean grain size ranged from fine to coarse sands. A total of 17 species were identified, with the crustaceans Emerita brasiliensis, Excirolana braziliensis and Pseudorchestoidea brasiliensis being the most abundant species. Species richness had a significant positive linear relationship with W values, swash period and slope, and a negative relationship with grain size. Significant positive relationships were also observed for total density with the swash period and slope, total biomass with slope, density of Emerita brasiliensis with swash period and slope and biomass of Emerita brasiliensis>/i> with slope. Zonation analysis showed that two or three biological zones could be recognised, with the two-zone pattern being observed in most of the beaches. This pattern consisted of a lower zone characterised by Emerita brasiliensis, Donax haleyanus and Hemipodus oliveri; and an upper zone characterised by Excirolana braziliensis, Pseudorchestoidea brasiliensis and Phaleria testacea. The three-zone pattern as a disruption of the general two-zone pattern and its formation was attributable to the variation in the distributions of P. brasilensis and E. braziliensis. Our results suggest that beach morphodynamics is the best predictor for the variability of macroinfaunal community composition.