Abstract:

The planktonic communities composed of rotifers and crustaceans of two tropical karstic lakes in the Yucatan Peninsula, Mexico, with similar origin but different trophic state were analyzed. Both systems, the meso-eutrophic (El Padre) and oligotrophic (Minicenote) were considered as monomictic lakes. The abundance, temporal distribution of species, richness and diversity were measured and discussed in relation to the influence of abiotic factors and the presence of a natural predator. These analyses indicated that these tropical systems were not homogenous for several of these measures at both spatial scales and during the annual cycle analyzed, despite their reduced temperature variation compared to temperate lakes. The results indicated that the dynamics in the zooplankton community were related to the environmental factors, the opportunistic species (with maximum densities related to resource maxima), and the exploitative competition between the dominant herbivorous species. Independently of the trophic condition, the abundance, richness, and diversity were lower during the mixing period. During the annual cycle studied in the meso-eutrophic system, the key environmental parameters related to plankton abundance were pH and temperature whereas in the oligotrophic system, oxygen concentration was important. In both lakes, richness and diversity were related to conductivity, although in the oligotrophic lake the relation was negative whereas in the meso-eutrophic lake it was positive. No relationship was found between the abundance of the studied predator (Chaoborus sp.) and the changes in the abundance, diversity and richness of zooplankton in the systems.

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