GILCHRIST, S.L.: A Seven Year Study of Shell Distribution and Use by Coenobita clypeatus on Bailey’s Cay, Roatan, Honduras

Bailey’s Cay is a small volcanic island surrounded by seagrass and coral reefs. It is covered with lithophytic vegetation interspersed by volcanic rock. Individuals of Coenobita clypeatus, found commonly on the island, obtain empty gastropod shells from the rocky intertidal and fringing beaches. As in similar studies, larger shells were less frequently available than smalls shells and shell fragments. To examine how influxes of shells impact the population structure of hermits on the island, approximately 70,000 gastropod shells of various sizes were added to the island over a seven-year period. Particular attention was given to increasing the availability of larger and heavier shells. For different shell types added, shell sizes and weights were measured and shells were marked before release. Shell sizes and types were evenly distributed in three sampling areas. Hermit crabs were sampled each year, noting types of shells used and changes in population size. In the first three years of the study, larger crabs were more numerous than noted in the initial study of population structure. Hurricane Mitch completely inundated the Cay for three days. No crabs in the largest category were collected from the Cay in the two subsequent years despite shell availabilty. The current trend is an increase numbers for all size classes.