Hermit crab shell use patterns: response to previous shell experience and to water flow

Abstract

Gastropod shells serve as a portable shelter for hermit crabs and provide protection for their otherwise vulnerable, soft abdomens. This study investigates the effect of prior shell experience and water flow on hermit crab shell selection. Research at Bodega Bay, California, examined shell selection in Pagurus granosimanus (Stimpson) and Pagurus samuelis (Stimpson) as a function of previous shell occupancy. Laboratory experiments found that when Pagurus granosimanus was presented two weight-matched shells of Olivella biplicata (Sowerby) and Tegula funebralis (Adams), it was significantly more likely to choose the shell species that it was collected in. Survey data yielded different shell use patterns between Pagurus granosimanus and Pagurus samuelis, with Pagurus samuelis using almost exclusively Tegula funebralis and Pagurus granosimanus using Olivella biplicata and Tegula funebralis at one site while using Tegula brunnea (Philippi) at another site. It was also found that Pagurus granosimanus is found deeper in the intertidal than Pagurus samuelis. Research conducted on Mo'orea, French Polynesia, examined the effect of water flow on shell selection by hermit crabs. Population surveys and laboratory experiments were combined to determine if Calcinus seurati (Forest) from high flow and low flow environments select shells of different weight. It was found that Calcinus seurati collected from a high flow site selected significantly heavier shells than those collected from the still water site. Laboratory experiments also showed a tendency for Calcinus seurati to select heavier shells in a high flow treatment than in a no flow treatment. Reef crest populations of Calcinus gaimardii (Edwards) and Calcinus elegans (Edwards) were also surveyed and compared with Calcinus seurati survey data. A significant difference in shell weight was found between Calcinus gaimardii and Calcinus seurati from the still water site. No other significant differences were found among species. Regression analyses indicate a correlation between hermit crab weight and shell weight for all three Mo'orean species.