The use of population aspects of the ghost crabs as indicators of anthropogenic impact on urban beaches of the Brazilian Semiarid Coast

Abstract

To assess the effects of urbanization on populations of Ocypode quadrata along the semiarid Brazilian coast, four urban beaches with varying levels of usage and one rural beach as a reference were analyzed. Each beach was morphologically characterized, considering tidal range (m), beach slope, beach length (m), sand grain size (ɸ), and Urbanization Index (UI). On each beach, four transects were marked perpendicular to the waterline, each 10 meters wide and spaced 10 meters apart, extending from 5 meters below the high tide line to the base of the dune (when present) or anthropogenic structures. The burrows were counted and measured. In general, no significant differences were found in burrow abundance or mean diameter, despite the differing beach uses. Only one significant difference was observed in the mean burrow diameter of ghost crabs between Sabiaguaba and Canto Verde beaches. The heavier vehicle traffic on Sabiaguaba Beach appears to have impacted juvenile crabs. Comparing the abundance and size of burrows did not prove to be a reliable indicator of anthropogenic impacts when comparing beaches with varying levels of urbanization along the semiarid Brazilian coast.