Abstract
SUMMARY: 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 (Ω) 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 Ω 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 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 threezone 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.
Highlights
Our results suggest that beach morphodynamics is the best predictor for the variability of macroinfaunal community composition
Variations in macroinfaunal structure are more perceived between morphodynamically extreme beaches: species richness, abundance and biomass all tend to be highest in dissipative beaches (McLachlan, 1990, 1996; Defeo et al, 1992; Jaramillo and McLachlan, 1993; McLachlan et al, 1993; Borzone et al, 1996)
(summer), UNA, PEC, FOG and PER; coarse sand was found at ACU, JAC, MAS
Summary
Tide amplitude, wind action, grain size, slope and swash climate are the most important factors in their physical characterization (McLachlan, 1990; McArdle and McLachlan, 1992; McLachlan et al, 1993). Interactions among these factors generate morphodynamic gradients, with reflective beaches with coarse sand, steep slope and a narrow surf zone at one extreme, and dissipative beaches with fine sand, a gentle slope and a wide surf zone at the other (Short and Wright, 1983). The abundance and biomass of a population may increase in the more reflective beaches, that is, in the opposite direction from the expected trend for the community, as observed for Pseudorchestoidea brasiliensis (Gómez and Defeo, 1999). Defeo et al (2001), testing the swash-exclusion hyphothesis in populations of the mole crab Emerita brasiliensis, found no significant differences in most parameters of population and reproductive biology between dissipative and reflective beaches
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