Microbial hotspots in anchialine blue holes: initial discoveries from the Bahamas
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Inland blue holes of the Bahamas are anchialine ecosystems with distinct fresh and salt water layers, and anoxic or microoxic conditions at depth. Scientific cave diving and geomicrobiology exploration of blue holes are providing a first glimpse of the geochemistry and microbial life in these vertically stratified karst features. We hypothesized that two geographically adjacent, sunlit blue holes on Abaco Island would have comparable biogeochemistry and microbial life. Water samples were analyzed using in situ multiparameter dataloggers and field and laboratory tests, and diver-retrieved microbial samples were analyzed using nucleic acid analysis. Microbial 16S rRNA genes were dominated by members of the anoxygenic phototroph clade Chlorobi, with smaller numbers of Deltaproteobacteria, in both blue holes. However, spatial distributions of microbial biomass and species present within these major clades were significantly different. We also found that differences in the intensity of solar insolation, terrestrial and marine inputs, water residence time, depth to the halo/chemocline, and cave passage geometry strongly influence geochemical changes with depth. The biogeochemical diversity of inland blue holes in the Bahamas make them valuable as natural laboratories, repositories of microbial diversity, and analogs for stratified and sulfidic oceans present early in Earth’s history.
KeywordsBlue holes Anchialine caves 16S rRNA clone libraries Microbial ecology Bahamas
We are indebted to expert divers J. Heinerth, K. Broad, W. Skiles, T. Morris, A. Milowska, L. Hinderstein, T. Thomsen, and G. Stanton whose enthusiasm, skill, and powers of observation enriched this study in many facets. We also thank N. Shiel-Rolle and P. Swart for assistance in the field, T. Hanson for valuable discussions on the ecology of anoxygenic phototrophs, and D. Jones and K. Dawson for laboratory analyses. This study was greatly facilitated by N. Albury and K. Tinker of The National Museum of the Bahamas/The Antiquities, Monuments and Museums Corporation (AMMC), and by the Abaco-based non-governmental organization Friends of the Environment. This project was funded by the National Science Foundation’s Biogeosciences Program (EAR 0311854 to J.L.M.) and Biodiversity Inventories Program (DEB 0315903 to T.M.I.), as well as by a National Geographic Society Expeditions Council grant to K. Broad and by the AMMC. This article is dedicated to the memory of explorers and conservationists Agnes Milowska and Wes Skiles. Their contributions to cave diving science will long be remembered.
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