The adverse effects of cryptochirid crabs (Decapoda: Brachyura) on Siderastrea stellata Verril, 1868 (Anthozoa: Scleractinia): causes and consequences of cavity establishment

In marine environments, a wide range of small, cryptic invertebrates are specialist inhabitants of sessile Scleractinian corals, the exclusive hosts of cryptochirid crabs which reside in the cavities of infested coral colonies. These cavities likely affect coral growth, especially when crabs colonize the surface of the corals early in their development. The spatial distribution of cryptochirids on hosts has not yet been fully assessed, but this information has important implications for competitive interactions between crabs. This study aims to analyse the structure and spatial distribution of the Brazilian gall crab Kroppcarcinus siderastreicola on Siderastrea stellata. Crabs inhabited 21% of the colonies that were sampled. The relationship between coral size and cavity size was determined by using Spearman's correlation. The results confirm the assumption that crabs negatively influence coral growth rates. In addition, the relationship between the mean distance between cavities and coral size indicates that the establishment of new crabs may be affected by the occupation of previous crabs.