Relationships between a hermit crab and its shell resource: spatial patterns within a seagrass-dominated landscape

Abstract

Abundance patterns of the hermit crab Pagurus maclaughlinae and its gastropod shell resources were compared to one another across the shallow subtidal landscape within Tampa Bay, Florida at a landscape (4.88 ha) and a sub-landscape (1 m 2 ) scale. Specifically, we investigated whether the spatial abundance patterns of P. maclaughlinae over time could be explained by the abundance patterns of either future resources (i.e. live gastropods) or present resources (i.e. empty gastropod shells). The seagrass landscape was sampled for seagrass, hermit crabs, live gastropods and empty gastropod shells during the spring and fall of 1994 and 1995. The distribution of P. mac- laughlinae could be explained by the distribution of its gastropod shell resources when the spatial organization of both P. maclaughlinae and these resources were compared across the landscape. Physical measures of the dominant seagrass Halodule wrightii (i.e. canopy height and shoot density) appeared to be unrelated to the distribution of P. maclaughlinae and either of its shell resources (pre- sent or future) across the landscape. These results suggest that hermit crabs track their 'limited' resources (i.e. gastropod shells) when viewed over the spatial scales examined here. Furthermore, our results suggest that the spatial distribution of future, as well as present resources, adds insight into patterns of hermit crab abundance.