The longitudinal distribution of copepods in Corumba Reservoir, State of Goias, Brazil

The assessment of factors that determine the spatial distribution of zoopla nkton abundance is a central issue in zooplankton ecology. Since these fact ors are, in the most cases, spatially autocorrelated, especially in reservo irs, it is frequently difficult to isolate the primary causes that explain the variation in zooplankton abundance. In this paper, the spatial variatio n of copepods in Corumba Reservoir (Goias, Brazil) was studied. Sets of var iables were used to model copepod abundance variation: limnology (abiotic v ariables), phytoplankton and spatial position of sampling sites. The copepo d assemblage was composed of Thermocyclops minutus, Thermocyclops decipiens , Mesocyclops longisetus and Notodiaptomus iheringi. Along the reservoir's main axis, abundance increases, albeit not linearly, towards the lacustrine zone. High abundance, similar to that found in the lacustrine region, was also observed in the lateral arms. These patterns were very similar for dif ferent years and seasons. Copepods were significantly correlated with phyto plankton and geography. After controlling for the effect of space, the rela tionship between copepods and phytoplankton was not significant (partial Ma ntel test). This result indicates that hydrology is the primary process tha t controls not only the abundance of copepods, but also limnological featur es and food resources, which are commonly used to explain variations in zoo plankton abundance.