Observations on the plankton of some Costa Rican lakes

Thirty lakes in Costa Rica were sampled for phytoplankton and 17 of these for zooplankton, in July-August 1991. Chemical and physical parameters were determined in-situ or from samples taken in the same period. Phytoplankton and zooplankton did not appear to influence the composition of each other and fish appeared to have no influence on either. Plankton taxa and community richness showed little correlation with lake chemistry, geography, morphology or other biota present. Phytoplankton richness tended to decrease with lake elevation and Secchi disk depth and increase with pH and turbidity. In 14 lakes at higher elevation and a tendency to be turbid and unstratified, chlorophytes were the most abundant division. Copepods dominated in 7 lakes which were mostly shallow, turbid and of low alkalinity. Seven lakes that were deeper and at low to middle elevation were dominated by Cladocera and insect larvae dominated 2 small turbid lakes.