The effects of gastropod shell availability and habitat characteristics on shell utilization by the intertidal hermit crab Pagurus longicarpus Say

The shell utilization patterns of two intertidal populations of the hermit crab, Pagurus longicarpus Say, were studied. The populations differed with respect to the physical characteristics of their habitats and the availability of empty gastropod shells. The first population was in an estuary connected to Narragansett Bay. This population had few, if any. empty shells available in the area. The second population was in a rock-cobble area directly on Block Island Sound. There were large numbers of empty gastropod shells available for this population. The consistently high gastropod mortality on this shore appears to be caused by the animals being washed up on the beach, where they die due to desiccation.Data from samples collected from June to November of both 1974 and 1975 showed that there were distinct differences in the shell utilization patterns of the two populations. A greater proportion of the animals collected from the estuary population inhabited damaged shells and/or shells with symbionts compared to the individuals from the population with large numbers of empty shells available.The results of shell selection experiments indicated that individuals from both populations inhabited less than preferred shells. The population with large numbers of empty shells available was qualitatively shell-limited because of the effect of physical factors on the morphology of the gastropod species of that area. In addition, the shell selection experiments showed that individuals from the two areas had significantly different shell preferences. This result may be explained by the effects of the environment on the growth rates of the hermit crabs and/or as an indication that shell preferences may vary in response to the physical factors of a given habitat.