Co-occurring factors affecting ghost crab density at four sandy beaches in the Mexican Caribbean

Abstract

Human pressure can cause a decrease in the abundance of beach macrofauna, especially supralittoral crustaceans. In studying the life history traits of supralittoral crustaceans, human impact and beach features (e.g. beach slope, grain size, swash width) are often considered separately. Ghost crabs are widely accepted as ecological indicators of beach quality and condition since their abundance decreases at disturbed beaches; moreover, ghost crabs can respond to natural drivers. This study aims to determine factors affecting the density of the ghost crab Ocypode quadrata in the Mexican Caribbean. We studied the spatiotemporal variation of the density of ghost crabs at two urbanized and two reference beaches by counting crab burrows on all beaches during six sampling periods. Our results indicate that physical features of the beach are significantly correlated with burrow density, and burrow density varies substantially between urbanized and reference beaches. The greater variation of burrow density accounted for beach disturbance, followed by beach morphodynamic features. Based on these results, our study confirms that the ghost crab is a relevant biological indicator species and is useful for guiding beach management criteria in the Mexican Caribbean. Our findings demonstrate that temporal replications must be included when using ghost crabs as ecological indicators.