This project studies the biogeography of bacteria and archaea colonizing several anchialine caves, pits, caletas, and Caribbean seawater in Quintana Roo, Mexico. We explore the horizontal and vertical distributions of these communities to constrain the biogeochemical potential of the Yucatan carbonate aquifer, the largest of its kind in the world. The purpose of this study is to understand whether the dispersal of biogeochemically significant microorganisms is uneven in this important aquifer.