FUNCTIONAL SHIFT IN GASTROPOD ASSEMBLAGES REFLECTS CHANGING HABITATS IN THE CARIBBEAN NEOGENE

The closure of the Central American Seaway led to changes in the physical environment and a shift in habitats that restructured benthic communities in the Caribbean. Through the use of quantitative analyses and ecological samples, a picture is emerging of how diverse groups, including bivalves, bryozoans, and corals, responded to environmental change. However, a quantitative study of the ecological response of gastropods has not yet been completed. Gastropods are a taxonomically and ecologically diverse group, giving them the potential to tell a nuanced ecological story. To this end, we have collected approximately 30,000 gastropods from quantitative bulk samples of 29 faunules spanning nearly 11 million years. These gastropods have been taxonomically identified and placed into functional groups based on diet and, where possible, substrate preference. Here, we present preliminary results from 10 of the faunules. Analyses of gastropod functional groups show no significant change in the relative abundance of predatory gastropods or the relative abundance of suspension feeding gastropods through time. However, the relative abundance of herbivores does increase through time, in particular, herbivores that graze on rock or hard substrates show a substantial increase in the youngest samples. The increase of herbivores on hard substrates supports the hypothesis that the growth of coral reefs played an important role in the restructuring of benthic shelf communities. No change in the predatory and suspension feeding gastropods may suggest that a decrease in planktonic productivity did not have a large influence on gastropods, and that other forms of primary productivity easily replaced lost planktonic productivity. On the other hand, it is possible that broad functional groups may not provide enough insight into the ecological changes of gastropods during this time, and that parsing the functional groups, particularly predatory gastropods, will yield different results. However, these initial results support the hypothesis that habitat shifts, particularly the increasing abundance of coral reefs in the Caribbean, drove ecological shifts in the gastropod faunas.