Bacterioplankton from cenotes and anchialine caves of Quintana Roo, Yucatan Peninsula, Mexico

The seasonal fluctuation of bacterioplankton densities were evaluated in fi ve cenotes and two anchialine caves of Quintana Roo, northeastern Yucatan P eninsula. Bacterioplankton densities were extremely low (5.8 +/- 0.35 x 10( 2) - 8 +/- 0.48 x 10(3) cells/ml), even for oligotrophic environments. Non seasonal differences were detected in the cenotes, however, in the caves ba cterial counts were higher in the rainy season. Bacterial densities were lo wer in the cenotes (5.8 +/- 0.35 x 10(2) - 4.3 +/- 0.26 x 10(3) cells/ml), and higher in the caves (2.7 +/- 0.16 x 10(3) - 8 +/- 0.48 x 10(3) cells/ml ). Rainwater percolation, rich in forest soil particulate (POM) and dissolv ed organic (DOM) matter into the caves, seems to promote higher bacterial d ensities. In addition, surface bacteria entering groundwater in the same wa y as POM and DOM could also be augmenting bacterial densities in the caves. Low groundwater nutrient (0.05 - 1.7 mu M total P, 34.89 - 250.9 mu M tota l N) concentrations as well as reduce bacterial densities characterizes the cenotes and caves as ultra- to oligotrophic environments.