TESTING A MODEL FOR LAKE FORMATION AND OSTRACODE DISTRIBUTION ON CARBONATE PLATFORMS—AN EXAMPLE FROM THE BAHAMAS

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, and 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 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 52 lakes that were used in constructing the lake model. Ostracode counts were at least 400 right valves per lake. Live/dead studies indicated that the death assemblage faithfully records the living community. A non-parametric multi-dimensional scaling model using the ostracodes show that just like the physical and chemical model, blue holes tend to be very similar in species composition. The interdunal depressions and cutoff lagoons 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 Hemicyprideis 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 vs. biological variables and in this case, is able to inform us of an important case of competition happening that would not have been normally detected.