PALEOECOLOGICAL SHIFTS IDENTIFIED THROUGH BIVALVE ASSEMBLAGES FROM THE BOWDEN AND PORT MORANT FORMATIONS IN THE PLIOCENE AND PLEISTOCENE

Identifying ecological shifts in Caribbean bivalve populations can help identify potential environmental and habitat changes that may have occurred during the Late Pliocene and Early Pleistocene in Jamaica and the Caribbean as a whole. Bivalve ecology has been used in other studies focused on the southwestern Caribbean to demonstrate environmental shifts, and this study aims to prove a similar point by cohesively tying together a narrative of ecological change in the Caribbean. Samples were collected from the Bowden and Port Morant Formations in southeast Jamaica in order to quantify the changes in the taxonomic and ecological diversity of bivalves from the Late Pliocene to the Pleistocene. Approximately 10,000 bivalves from 50 bulk samples, with a total of 94 different genera, were counted and identified for this study. Results indicate a dramatic shift in the taxonomic composition of these two bivalve assemblages. Nonmetric multidimensional scaling (NMDS) distinguishes the Port Morant and Bowden formations across the X axis, showing them to have very different taxonomic assemblages. The Bowden Formation represents a turbidity flow, making it a useful compilation of various ecological sites in that time period. It is predominantly filled with Trigoniocardia and other genera that are consistent with soft sandy substrates. In contrast, the Port Morant samples are dominated by Chione, Mytilopsis, and members of the Lucinidae family. These bivalve genera are indicative of seagrass beds and distinctly different than the shell assemblage from the Bowden. This change in the most common genera found, such as the high Chione concentration in the Port Morant Formation, may represent a transition from sandy substrates to seagrass bed habitats. Reef and seagrass environments increased in abundance in the southwestern Caribbean in response to environmental changes (e.g. increases in temperature, salinity, and decreases in planktonic productivity), causing ecological change in the bivalve communities. The changes in the northern Caribbean may also be a response to these regional environmental changes. Further investigation of molluscan assemblages from the northern Caribbean may shed light on the possibility of ecological turnover throughout the Caribbean that resulted in new habitats and new benthic communities.