Counting and measuring ghost crab burrows as a way to assess the environmental quality of beaches

Abstract

Despite controversies, the non-destructive indirect method of counting and measuring the burrows of ghost crabs remains the best option for assessing the environmental quality of beaches. In order to better conserve and manage local populations and their environments, we evaluated the occurrence of the ghost crab Ocypode quadrata at 39 beaches, characterized according to the degree of human presence and by physical factors. Three main groups of beach variables-low, moderate and high – were identified according to the degree of human presence coupled with natural factors. The modes of access and cleaning best discriminated the beaches. Amongst physical features, only “trail beaches” and “restricted access beaches” significantly differed from other beaches. The drift and effluent beach zones with lesser human presence showed the highest numbers/densities of burrows. Older crabs, inferred by the largest burrows, were found less frequently at all beaches, the drift zone being the major aspect for their presence. Despite the great variability in the distribution of ghost crabs, they are sensitive to low environmental quality and their adequacy for assessing environmental quality was confirmed.