Shell use by megalopae of the hermit crab Pagurus filholi

The close relationship between hermit crabs’ fitness and the size and species of gastropod shells they occupy is largely based on studies of young and adult crabs. When hermit crabs settle as megalopae, they too require a shell, but there are few studies of shell selection and use by this early life stage. We examined shell selection by megalopae and early juveniles of the hermit crab Pagurus filholi for three gastropod shell species, Nassarius fraterculus, Batillaria cumingii, and Homalopoma sangarense, all common in the study area and used by young and adult P. filholi. The early crab life stages did not prefer any shell species. Shell species had no significant effect on the survival of megalopae or early juveniles that were exposed to high water temperatures, nor on crab growth rates or vulnerability to predators. Under desiccating conditions, megalopae and early juveniles had significantly lower survival in Homalopoma shells than in Batillaria shells. These results suggest that variation in fitness across shell species has not selected for shell species preferences by early life stages of P. filholi perhaps explaining why they occupy shell species more equitably compared to later life stages for which fitness varies with the species of shell they occupy.