Hermit crabs in a mangrove swamp: the structure of Clibanarius laevimanus clustering.

To address the question of hermit crab clustering, 11 clumps composed of Clibanarius laevimanus were studied in the mangal of Mida Creek, Kenya in 1988. Hermit size and sex were analyzed, as well as the type, dimensions, and status of their shells. Empty gastropod shells constituted a limiting factor on the population studied; the architectural traits which seemed to be favored by the hermits were those associated with a defence against crab predators (high weight and narrow apertures). Differences in either the availability of adequate shells or in the services provided by the housing in question explained the observed diversity in both the type and the mass of shells occupied among the examined population categories. Furthermore, each clump showed homogeneity with respect to the dimensions of the hermits participating in it, and immature and adult specimens were partitioned among three cluster types. It is suggested that clustering might be classified as a social phenomenon, because hermits are attracted by similarly sized conspecifics, interact through an elaborate communication system, and because most benefit from a chain process in shell exchange.