LEONARD-PINGEL, J.*; ARONOWSKY, A.; ANDERSON, L.C.; Louisiana State University, Baton Rouge; Louisiana State University, Baton Rouge; Louisiana State University, Baton Rouge: Taking the island biogeographic model into the water: are abundance and diversity of encrusters related to hard substrate proximity?

The theory of island biogeography has been used widely since its formulation, most recently finding importance in conservation biology. However, there is a paucity of applications to the marine realm, although marine ecosystems are extremely suitable to the model. In marine systems, where soft sediment bottoms are common, hard substrates represent �islands,� supporting a variety of obligate epiphytic and epizoic taxa (encrusters). Recruitment of individuals onto surrounding hard substrates, in this study mollusc shells, should reflect the island-biogeographic paradigm. Therefore, hard substrates closer to the source �island� should have both a higher abundance of encrusters and a higher diversity of encrusters. In addition, the diversity of encrusting organisms on shells proximal to larger source areas should be higher than that observed for shells proximal to smaller source areas. To test predictions of the island-biogeographic model, we identified hard substrate �islands� in soft sediment habitats within the Gulf of Mexico. Because source areas differed by orders of magnitude in size, we set distance increments for sampling along each transect that were proportional to source size. The results of this study, and those of existing datasets from the Bahamas, Florida, and Mexico, indicate that the presence and size of source �islands� are important predictors of encrustor diversity and abundance on hard substrates in subtidal environments dominated by soft sediments.