SHELL DYNAMICS AND MICROHABITAT SELECTION BY STRIPED LEGGED HERMIT-CRABS, CLIBANARIUS-VITTATUS (BOSC)

Hermit crabs respond to odors signaling potential shell availability b y (1) withdrawing if they are in relatively large shells; (2) fleeing if the shells are ones they would occupy if given choices; (3) investi gating if the shells occupied are relatively small. We used these beha vioral responses as measures of shell fit to assess shell resources of Clibanarius vittatus (Bose). From analysis of responses we conclude s hell resources are dynamic. Behavioral tests suggest many crabs occupi ed relatively large shells in the spring and relatively small shells i n the fall. Crabs in shells in which they would remain when presented with excess shells never comprised more than 30% of the population at any time of the year. Behavior of subpopulations of crabs from sand/mu d and oyster reef habitats and crabs on land or in water at low tide w as determined. In the fall, crabs whose behavior indicated they occupi ed relatively small shells for their size were found mainly in sand/mu d habitats and remained in the water at low tide. Crabs whose behavior suggested shells they occupied that fit well were rare. The few that were found were found mainly in sand/mud habitats and were equally dis tributed on land and water. Crabs behaving as if shells were large for their size were found distributed evenly throughout oyster reef and s and/mud habitats and on both land and in water at low tide. Distributi onal results could not be explained by reduced mobility. Movement stud ies showed that even crabs in weighted shells should not be trapped by a receding tide. We postulate crab habitat choice is a behavioral adj ustment that compensates for imperfect shell fit.