Effect of Commensal Hydroids on Hermit Crab Competition in the Littoral Zone of Texas

Abstract

IN Galveston Bay, Texas, the hermit crab Clibanarius vittatus is the dominant animal on many shallow mud and sand flats. During the winter the hermits Pagurus longicarpus and Pagurus pollicaris migrate into the region dominated by Clibanarius and remain there until the following spring. Hermit crabs engage in ritualized fights¹ in competition for gastropod shells which are a necessary protection from predators. In both laboratory and field encounters, Clibanarius are very aggressive in competition for shells and are usually able to win shell fights with Pagurus, even if exceeded in size. As suitable unoccupied shells are extremely rare, Pagurus are at a potential disadvantage in competition with Clibanarius for this resource.