Fish community structure dynamics in cenotes of the Biosphere Reserve of Sian Ka'an, Yucatan Peninsula, Mexico

Cenotes are permanent aquatic systems formed by geomorphologic processes (karst), located in the Yucatan Peninsula. Many of these oligotrophic systems are connected superficially to wetlands during the wet season. We describe the fish community structure in 4 cenotes during the rainy and dry seasons over a 4-year period and relate it to limnetic dynamics in each cenote. We sampled cenotes to describe morphology, water physicochemical characteristics, primary production, and invertebrates and fish abundance and richness. We did not find differences in physicochemical variables between seasons but we did find differences among years and among cenotes. We found 11 fish species (25% of the total richness reported for the Biosphere Reserve of Sian Ka'an) from 5 families: Cichlidae, Poeciliidae, Characidae, Pimelodidae and Synbranchidae. We noted little seasonal or inter-annual variation of fish species richness. But there were higher differences of fish species richness and abundances among cenotes. Fish community structure was correlated with temperature, transparency, pH, dissolved oxygen, chlorophyll a, periphyton and zooplankton abundance. Results showed that physicochemical variables and fish community structure are not affected by seasonal hydrology dynamics, suggesting that cenotes are stable aquatic systems compared to the surrounding wetlands. Other limnetic factors such as cenote morphology are also related to fish community structure.