OSTRACODE DISTRIBUTION IN LAKES IN THE BAHAMAS AS A RESPONSE TO SEA LEVEL AND CLIMATE CHANGE

Lakes on carbonate platform islands such as the Bahamas display wide variability in morphometry, chemistry, and fauna. These parameters are ultimately driven by climate, sea level, carbonate accumulation and dissolution. A model dividing lakes into either constructional or destructional formational modes has been developed using both qualitative and quantitative data. This model shows that lake formation is influenced by the hydrologic balance associated with climatic conditions that drives karst dissolution as well as the deposition of aeolian dune ridges that isolate basins due to sea-level fluctuations.

The lake model was tested as a predictive tool for faunal distribution, using the microcrustacean group Ostracoda. We used an ostracode database comprised of 11 species from the 32 lakes on San Salvador Island. Ostracode counts included at least 400 right valves per lake. Live/dead studies indicate that the death assemblage faithfully records the living community. A non-parametric multi-dimensional scaling model of the ostracodes show that just like the physical and chemical model, blue holes tend to be similar in species composition and the interdunal depressions and cutoff lagoons also have similar assemblages. The two anomalies in the karsted depression are clustered together. These ostracode communities have either low or no Cyprideis americana—a widespread, cosmopolitan species found in almost all lakes. Instead, they are dominated by Peratocytheridea setipunctata, which is an ecological competitor to C. americana and found in almost all lakes but at higher abundances in the blue holes. While many people attribute species distributions to abiotic drivers, this lake model is able to separate physical versus biological variables and in this case, is able to inform us of an important case of competition that would otherwise not have been detected.