Anchialine ponds in the Bahamas (i.e., those with subterranean connections to the sea) often support communities that are more typical of shallow marine environments (e.g., reefs and estuaries). Anchialine communities are replicated within and among islands and their biotic and abiotic environments can vary considerably over time and space. By comparing macroalgal population dynamics in anchialine and non-anchialine sites, we are attempting to better understand how marine communities respond to large-scale environmental change. For example, in some anchialine habitats, Acetabularia crenulata, A. calyculus, and Batophora oerstedii (all Dasycladacea) form "mats" of growth that are far larger and denser than those from nearby marine and estuarine sites. Such mats can even be found in ponds that exhibit extreme abiotic fluctuations—fluctuations that have no apparent analogs in non-anchialine sites. An example is Reckley Hill Settlement Pond on San Salvador Island where salinity can vary from one-half to more than twice the average for seawater (35ppt) depending on seasonal precipitation. Yet, Dasyclad communities thrive there. Have they adapted to persist in novel conditions, or do they die back and recolonize later? We are using population genetics, abiotic stress trials (e.g., altered salinity), and physiological methods to better understand how Dascyclad populations from anchialine and non-anchialine systems cope with abiotic stress.
Results/Conclusions
We have conducted preliminary community surveys of Dascyclads from nine anchialine ponds on three Bahamian islands. Preliminary results suggest that Batophora oerstedii is common, having been identified in eight of the nine ponds. In contrast, Acetabularia spp. are apparently absent or rare in five of the nine ponds, but are abundant in the other four. While we have yet to test stress tolerance of populations from anchialine ponds, results from a recent undergraduate study of salinity tolerance in A. crenulata from Florida suggest that marine populations grow best at 35-53ppt with a more than sixty-percent reduction in growth rate at higher (61 – 70ppt) and lower (17 – 27ppt) salinities. Forthcoming trials will extend this work to anchialine communities and should should help us to better understand whether inland Dasyclads respond to stress differently than their marine and estuarine counterparts. Because Dasyclad algae are primary producers, such responses could scale up to affect other trophic levels. As such, anchialine Dasyclad communities in the Bahamas could be natural stress labs for investigating the community and ecosystem effects of climate change and other anthropogenic threats to near-shore marine environments.