Utilization of gastropod shells by hermit crabs (Decapoda: Anomura: Paguridae) in Japan as related to characteristics of domicile shell

Abstract

Abstract The relative proportions of gastropod shells occupied by the hermit crabs Pagurus dubius (Ortmann, 1892), P. filholi (De Man, 1887), P. lanuginose De Haan, 1849, and P. nigrofascia Komai, 1996 on a boulder shore at Asamushi, northern Japan differ significantly from those of the living gastropods that leave behind their empty shells after death. There is a difference in the frequencies of the shells of Omphalius rusticus (Gmelin, 1791) and Chlorostoma turbinatum A. Adams, 1853, which resemble each other in shape, between the proportions of shells occupied by the living gastropods and those of their empty shells occupied by hermit crabs. The three species of hermit crabs that were dominant at the study site showed no difference in shell selectivity between the two gastropod species in the laboratory. This result indicates that shell selection by hermit crabs cannot be responsible for the difference in composition between availability and utilization observed in the field. The empty shells of O. rusticus are thicker and heavier than those of C. turbinatum, suggesting that the former last longer than the latter, as shell durability against compressive force decreases as shell thickness is reduced. These observations suggest that the difference in the period for which these empty gastropod shells remain intact accounts for the difference in composition between their availability and utilization by hermit crabs.