DID CARIBBEAN GASTROPOD ASSEMBLAGES FUNCTIONALITY SHIFT AS A RESPONSE TO ECOLOGICAL CHANGE IN THE LATE NEOGENE?

The closure of the Central American Seaway (CAS) around 3.5 Ma resulted in increased salinity, decreased upwelling, and decreased productivity in the Caribbean Sea. These changes to the physical environment drove shifts in the ecology of nearshore benthic marine communities. Although mollusks of the Plio-Pleistocene Caribbean are well-studied, quantitative, functionally based analysis of gastropods from bulk samples has not previously been done. Here, we present data on gastropod functional groups from the Southwestern Caribbean (SWC) to determine if they display a shift in dominant trophic groups that could be linked to productivity changes concurrent with the closure of the CAS. Quantitative bulk sampling has yielded over 14,000 gastropod specimens from 28 faunules in Panama and Costa Rica. We compared changes in relative abundance of trophic groups of gastropods from these samples to test for changes in trophic structure before and after the closure of the CAS. Preliminary results show a significant decrease in abundance of browsing carnivores (W= 1, p= 0.057) and herbivores that prefer fine-grained substrates (W= 2, p = 0.069), and a significant increase in predatory carnivores (W= 15, p= 0.059) and herbivores that prefer rock or coral substrates (W= 14, p= 0.069). The observed shift in herbivores reflects a shift in dominant habitats; biogenic habitats (coral reefs and/or seagrass meadows) became more abundant in the Caribbean after closure of the CAS, while soft substrates became less common. This interpretation is supported by data from similar research on bivalves from the SWC. The increase in predatory carnivores was unexpected based on previous studies of gastropods. We plan further analyses of the data to test these initial findings. Understanding changes in gastropod assemblages, and comparing them to changes seen previously in bivalve assemblages, will help to provide a robust understanding of how Caribbean ecology changed during the late Neogene.