SPECIFICITY IN THE ASSOCIATION BETWEENHYDRACTINIA ECHINATAAND SYMPATRIC SPECIES OF HERMIT CRABS

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Abstract
Field and laboratory methods were used to investigate the degree of specificity in the symbiotic associations between several species of hermit crabs and the colonial hydroid. Sympatric species [4] of hermit crabs in Bogue Sound, North Carolina [USA], exhibited distinct differences in their patterns of association with H. echinata. H. echinata occurred most frequently on shells occupied by the crabs Pagurus longicarpus and P. pollicaris, but rarely on shells occupied by P. annulipes and P. brevidactylus. Seasonal fluctuations in the abundance of H. echinata corresponded with fluctuations in the abundance of P. longicarpus and P. pollicaris. The species of gastropod shell inhabited by the crabs appeared to play only a minor role in the pattern of association with H. echinata. Shell-selection experiments in the laboratory revealed that P. longicarpus and P. pollicaris tended to select Hydractinia-coveredshells while naked P. annulipes rejected Hydractinia-covered shells even when offered only such shells. The presence of Hydractinia coupled with the shell-selection behavior of the hermit crab species studied tend to partition the gastropod shell resource in Bogue Sound, thus reducing competition among the 4 sympatric crab species.