COEXISTENCE IN A HERMIT CRAB SPECIES ENSEMBLE

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Abstract
The shell exploitation of hermit crabs inhabiting a subtidal region of Beaufort Harbor, North Carolina [USA], was studied to determine the importance of shell resource partitioning in allowing the coesitence of the hermit crabs. The 3 most abundant spp. (Pagurus annulipes, P. longicarpus and P. pollicaris) partition size range. The size ratio between the larger species (P. pollicaris and P. longicarpus) was 1.7 and the size ratio between the smaller species (P. annulipes and P. longicarpus) was only 1.2. Differences in shell species utilization were significant only for the smaller species. Specimens of 4 other hermit crab spp. were collected (Pagurus brevidactylus, Pagurus impressus, Paguristes hummi and Petrochirus diogenes). Individuals of these species are more prevalent offshore. In Beaufort Harbor they used relatively small shells or shells which tended to be overlooked or shunned by the other species. Experiments on shell selection, interspecific aggression and substrate selection were conducted to determine the mechanism by which habitat differences and shell resource partitioning were maintained. Differences in shell preference and substrate preference were found between P. longicarpus and P. annulipes. No interspecific shell fighting dominance was observed for P. longicarpus, P. annulipes and P. pollicaris. Coexistence of individuals of the 7 spp. of hermit crabs collected in Beaufort Harbor was possible by a combination of habitat differences, shells size partitioning and shell species partitioning in descending order of importance. The shell partitioning of the 3 most abundant spp. was maintained by differences in maximum crab size at sexual maturity and by differences in shell species preference. Habitat differences between P. annulipes and P. longicarpus were maintained in part by a preference for shell debris by P. annulipes.

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