Meeting Abstract

P1.35  Thursday, Jan. 3  Hermit Crab Use of Octopus Middens GILCHRIST, S.L.; New College of Florida gilchrist@ncf.edu

Octopuses are common predators on reefs in the Caribbean. Among prey items that they consume are both gastropods and hermit crabs. In the Bay Islands of Honduras, members of Octopus vulgaris and O. briareus use dens on reefs and in surrounding sea grass areas. At Roatan, O. briareus is the most common species on the back reef while O. vulgaris is most common around Cayos Cochinos. Both species create middens near den sites which attract hermit crabs. Octopus briareus tends to use crevices and holes in the reef as dens while O. vulgaris creates dens from rubble. At Plantation Beach Reef of Cayos Cochinos Grande, middens rarely contain crab carapaces while at Bailey�s Cay Reef of Roatan, carapaces are major components of middens. At both sites, where gastropods constitute a large percentage of midden materials, hermit crabs can be found using shells discarded by octopuses and leaving behind shells at the middens. At Plantation Beach Reef, density of octopuses was relatively high during the summer of 2006 and the middens had little overlap in debris while during the summer of 2005 octopus density was lower and there was greater overlap in midden contents. Hermit crabs were found almost exclusively around middens containing gastropod shells suggesting that they are able to detect differences in the types of debris available. Artificial middens created from depositing shells near potential den sites showed that some visual cues may attract hermit crabs. Artificial middens baited with both shells and decaying gastropod flesh attracted not only hermit crabs but other crustaceans. Some of these crabs cracked or peeled gastropod shells at the middens, effectively decreasing the size of the resources available to hermit crabs.