COEXISTENCE IN A HERMIT CRAB SPECIES ENSEMBLE

¹ Duke University Marine Laboratory, Beaufort, North Carolina 28516

The shell exploitation of hermit crabs inhabiting a subtidal region of Beaufort Harbor (N. C.) was studied to determine the importance of shell resource partitioning in allowing the coexistence of the hermit crabs. The three most abundant species (Pagurus annulipes, P. longicarpus, and P. pollicaris) partition the 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 (P. annulipes and P. longicarpus). Specimens of four other hermit crab species were collected (Pagurus brevidactylus, Pagurus impressus, Paguristes hummi, and Petrochirus diogenes). Individuals of these species are more prevalent offshore. In Beaufort Harbor they use relatively small shells or shells which tend to be overlooked or shunned by the other species.

Experiments on shell selection, interspecific fighting, and substrate selection were conducted to determine the mechanism by which habitat differences and shell resource partitioning are maintained. Differences in shell preference and substrate preference were found between P. longicarpus and P. annulipes. However, no interspecific shell fighting dominance was observed for P. longicarpus, P. annulipes, and P. pollicaris.

Coexistence of individuals of the seven species of hermit crabs collected in Beaufort Harbor is made possible by a combination of habitat differences, shell size partitioning, and shell species partitioning in descending order of importance. The shell partitioning of the three most abundant species is 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 are maintained in part by a preference for shell debris by P. annulipes.