Phytoplankton of cenotes and anchialine caves along a distance gradient from the northeastern coast of Quintana Roo, Yucatan Peninsula

This work details the taxonomic composition of suspended algae (phytoplankton and tycoplankton) communities in five cenotes (sinkholes) and two anchialine caves in northeastern Quintana Roo, Mexico. The sample set of cenotes are Casa, Nohoch Nah Chich, Maya Blue, Cristal, and Carwash, as well as the two associated caves leading from the cenotes of Maya Blue and Cristal. The site distribution represents a distance gradient with respect to the coastline with which we observe the effects of tidal movement and the mixing of waters (e.g. saline water and freshwater) on the composition of the suspended algae communities. Two sample sets were taken, one at the end of the dry season (March-April 1995) and the second at the end of the rainy season (September-October 1995) with the goal of comparing the contrasting climatic conditions of the region. A total of 79 species were identified, of which, diatoms were the most important with respect to species richness with a total of 75% of species. The floristic composition is very similar between the freshwater cenotes. The distance of a cenote site with respect to the coastline was a determining factor in the species composition. Casa Cenote is the most distinct of the sample set for the presence of marine species due to its proximity to the coastline. The tides are a large determining factor of the floristic composition of Casa Cenote with 24% all species identified in this study found exclusively in this system. The anchialine system species are transported from the cenotes and the adjacent cave systems. The largest percentage or species (95%) are freshwater, and only 5% of the total number of identified species are of marine origin. It is recognized that the most distant cenotes from the coast, Carwash and Cristal, as well as Maya Blue and Nohoch Nah Chich, are the most similar, despite being part of different cave systems. In these inland systems the marine species decreased drastically (2.4% in Nohoch Nah Chich and no marine species in the remaining cenotes). Marine species are found at the halocline of the caves.