A massive subtidal aggregation of hermit crabs in Surprise Atoll lagoon, New Caledonia

Abstract

Many hermit crab species can form large aggregations, sometimes numbering thousands of individuals (e.g., Gherardi and Vannini 1992). Research suggests that such clustering behavior can reduce predation risk and positively influence feeding, reproduction, and shell exchange. While clustering is well documented among lineages inhabiting terrestrial and intertidal zones, it remains poorly studied at subtidal depths where the greatest hermit crab diversity exists. The limited work that has examined this behavior across multiple habitats found clustering to be rare or entirely absent among species occupying subtidal depths (including in six Dardanus species; Barnes and Arnold 2001, but see Ramsay et al. 1997). Here, we report clustering behavior in the subtidal hermit crab species Dardanus scutellatus (H. Milne Edwards, 1848) that formed a massive aggregation of tens of thousands of individuals from 10 to 15 m depth (Fig. 1). Observations were made at approximately 0830 hrs, November 24, 2 ...