ABSTRACT
ABSTRACT Tropical zooplankton communities have quite different structural properties when compared to temperate counterparts. The aim of this study is to assess the effects of nutrient influx, oxygen deficit and invertebrate predation on the structure of tropical zooplankton. Three reservoirs in of tropical South America were selected as study cases. The effects of long-term eutrophication on zooplankton community were investigated on a small urban reservoir, the Pampulha Reservoir. This system suffered a steady increase in its trophy along the last
272 Restoration and Management of Tropical Eutrophic Lakes
decade. A data set consisted of monthly samples of zooplankton and major limnological factors such as nutrients N and P taken between the years of 1993 and 1998 were used. The effect of a spatial gradient of trophy was investigated in one of the largest tropical reservoirs of Brazil, the Furnas Reservoir (1440 km2). A data set consisted of twelve sampling points located in one of the reservoir axis (Sapucai River) of 220 km that were visited every three months between 1999 and 2000. Finally, the effect of oxygen deficit and invertebrate predation (Chaoborus brasiliensis) on the structure of crustacean zooplankton were investigated in a small, urban but protected mesotrophic artificial lake. The lake was located inside a dense Eucaliptus forest. A data set of a complete annual cycle (1999-2000) was used in the analysis. Zooplankton suffered similar modifications in its structure, considering both the temporal and spatial scale. The influx of nutrient caused the disappearance of calanoids, and biomass increase of some cyclopoids (specially of Thermocyclops). Further, it was also demonstrated that oxygen and invertebrate predation are key factors in structuring the vertical distribution of zooplankton and the water column of a tropical lake.
