AIM: To test the effect of fish exclusion over zooplankton and phytoplankton in a shallow lake in the floodplains of the Cuiabá River in Brazil's Pantanal; METHODS: Fishes and two classes of zooplankton sizes were excluded using mesocosms (100 µm and 200 µm mesh openings). The experiment lasted nine days with sampling at the beginning, six and nine days after the start of the experiment. Zooplankton and phytoplankton densities were compared among exclusion treatments and the open water which was considered as control areas by a Repeated Measures Analysis of Variance; RESULTS: The zooplankton composition and densities differed considerably between the exclusion treatments and the control areas, with a predominance of Cladocera and Copepoda in the exclusion treatments and a predominance of Rotifera in the control areas. During the experiment, the composition of the phytoplankton assemblage showed no difference between the exclusion and the control. However, there was a marked reduction in the density of the Cyanophyta and Chlorophyta algae among the exclusion treatments; CONCLUSIONS: The increase in density and the variation in the zooplankton composition suggest that these organisms are controlled by the fish and demonstrate that the zooplankton may exert control over the density of phytoplankton.
top-down control; zooplankton; shallow lake; Pantanal; trophic cascade
