Combined influence of human disturbance and beach geomorphology on Ghost Crab, Ocypode cursor, burrow density and size in the eastern Mediterranean

Abstract

Ghost Crabs, Ocypode cursor (Linnaeus, 1758), are used as a bioindicator species to evaluate the ecological condition of sandy beaches. Studies using Ghost Crabs as bio-indicator have often focused on the influence of human disturbance and beach geomorphology, separately. However, the relative importance of these variables should be assessed to maintain community structure. Here, I used an indirect burrow examination technique to understand whether Ghost Crabs respond to human disturbance stronger than to geomorphological properties of the sites. I analysed sand compaction rate, sand grain size, beach width, and beach slope as geomorphological features and urbanization index as a measure of human disturbance on each site. I further examined Ghost Crab burrows by counting and measuring the openings. Ghost Crabs showed lower population density and individual body sizes as a response to human disturbance, and the level of this response was partly related to the geomorphological features of the sites. However, human disturbance explained approximately 72% of the variation in the Ghost Crab burrow density and about 70% of the variation in the burrow size, alone. The findings of this study corroborate the use of Ghost Crabs as an efficient bioindicator species of human disturbance on sandy shores to achieve efficient beach management, yet suggest that managers and scientists should combine the influences of geomorphological features of the beaches and the degree of human disturbances in their ecological assessments.