Are ghost crabs ( Ocypode spp.) smaller on human-disturbed sandy beaches? A global analysis

Testing ghost crabs as indicator species usually fail to depict the mechanisms behind low burrow densities in urban coasts, neglecting individual traits as diagnostic variables. We conducted meta-analyses to compare the diameter of ghost crab burrow openings across gradients of human disturbances. Length–weight regressions were calculated, hypothesizing that crabs condition differ between beaches with high and low disturbance. The dataset regarding burrow opening diameter included 78 beaches (latitudes between 36° N and 30° S), and length–weight regressions were calculated based on 1,172 crabs data from 11 beaches (latitudes between 23° N and 30° S). Mean burrow diameter was smaller in high disturbance beaches, but a linear relationship with the level of human modification was not found in our gradient analysis. The higher the number of stressors acting locally, the greater the negative effects on burrow diameter. The body condition of ghost crabs was lower in high disturbance beaches; this result challenges the hypothesis that ghost crabs are smaller on disturbed beaches merely because individuals die before reaching adult ages. Our results have implications within the scope of ghost crab ecology, particularly regarding the inclusion of trait variation in investigations of mechanisms underlying spatial contrasts and in application of ecological-disturbance indicators.