Population dynamics of Coenobita clypeatus in Hermitage Bay, Tobago

Terrestrial hermit crabs serve an incredibly important ecological role in seed dispersal and as decomposers along coastal shorelines. They have also become quite popular in the commercial pet trade, with one species, Coenobita clypeatus, being particularly favored. Typically, these hermit crabs are easily captured and removed from the wild with little protection in their native ranges. In Hermitage Bay, Tobago, there is little information about the population numbers, composition, shell preference, and substrate preference of C. clypeatus in their native habitat. In this study, we estimated population size, gastropod shell preferences, and substrate preference conditions when clustering. We conducted mark re-capture surveys in March, July, and December 2023 and collected morphological data from captured hermit crabs. Our results indicate that the estimated population was highest in July, with the variation being significant when using the Schnabel mark re-capture estimation formula. The most common overall shell type, Columbella mercatoria (West Indian Dove Shell), was prevalent among the smaller sized, younger hermit crabs; while the larger hermit crabs preferred Cittarium pica (West Indian Top Shell). The most preferred substrate for these terrestrial hermit crabs were areas with a mixture of sand and dirt, with high amounts of vegetation and leaf waste and low amounts of human litter. These results suggest a predominantly young population and that beach cleanups should focus on removing human litter entirely, while leaving leaf waste and other fallen logs and branches and not using the collected decomposing plant matter for bonfires. This can help maintain a healthy hermit crab population that continues to benefit the coastlines in Tobago as well as other ecosystems.