MEPS 565:131-147 (2017)  -  DOI: https://doi.org/10.3354/meps11991

ABSTRACT: Ghost crabs are important sandy beach dwellers whose bioindicator potential depends on a broader understanding of the relationship between environmental and biological parameters. We analyzed variations in ghost crab populations both directly (abundance, size, and sex ratio) and indirectly (burrow occupation rate and size differences between crabs and burrows) in relation to their across-shore distribution and their relationship with beach features. Nine pristine areas with distinct morphodynamics and wave exposure levels were sampled quarterly over 1 yr. Across-shore variability was recorded with larger crab sizes, lower occupation rates, and proportionally more females landwards. Storm surge period was a determining factor with respect to ghost crab populations, causing individuals to contract their distribution landwards and increases in burrow occupation rate and mean crab size estimates. Beach features influenced population parameters, with crab density and mean size tending to increase towards smaller grain sizes and with steeper slopes in the crab’s range of occurrence favoring crab abundance. Burrow occupation rate differed according to slope and crab density. Our results revealed an intrinsic variability of ghost crab populations over time and among and within beaches that may be a source of bias in environmental studies. Therefore, these phenomena should be considered in the design of monitoring strategies and impact assessment protocols. This study also emphasizes the need for a cautionary approach in data interpretation of crab number and size based on burrow estimates.

KEY WORDS: Morphodynamics · Wave exposure · Abundance · Size · Indicator species ·Monitoring