THE HABITAT SPECIFICITY OF PATCHINESS: SPATIAL VARIABILITY OF SEAGRASS-ASSOCIATED MOLLUSK DEATH ASSEMBLAGES IN SAN SALVADOR, BAHAMAS

Seagrass habitats are important because of their diversity, productivity, and ability to support wider ecosystem functions. Their significance is increasingly recognized among conservationists and ecosystem managers. Seagrass habitats can also be valuable to paleoecologists, as they are host to a diverse array of preservable marine invertebrates, which may record signals of both regional and local environmental change. In order to fully utilize faunal assemblage information obtained from fossilized marine ecosystems, such as seagrass habitats, paleontologists must first understand the degree of spatial heterogeneity in these systems. We were interested in whether the spatial patchiness in the mollusk fauna of seagrass habitats is comparable to the spatial patchiness in mollusks of other types of marine habitats. We addressed this question using mollusk death assemblages from San Salvador, Bahamas.

San Salvador is located on the eastern edge of the Bahamaian archipelago. It is an ideal locality for addressing questions about carbonate marine systems, including paleontological questions about taphonomy and paleoecology, due to its relatively low level of anthropogenic disturbance and the easy accessibility of its marine habitats. We sampled 12 distinct sites circling the island and covering a variety of marine habitat types, including reefs, open sand, open seagrass, and seagrass filled lagoons.

We found that mollusk death assemblages varied considerably throughout the island. The seagrass sites generally had a greater density of mollusks, with certain taxa dominating the assemblages (e.g. Cerithium sp.), however samples from these sites also generally displayed as much spatial patchiness as the samples from other habitat types, indicating that seagrass habitats are not more homogeneous than other marine habitats. These results suggest that paleontologists who are interested in seagrass habitats need to sample in ways that are consistent with the way other marine habitats are sampled, keeping in mind the degree of spatial variation that may be present among seagrass-associated mollusk faunal assemblages.