Limnetica 40

Suitable sampling methods must be used to accurately characterize Rotifera assemblages. The present study tested the efficiency of plankton net mesh size in Rotifera studies based on the assemblage parameters of richness, abundance, and biomass. Samples were taken in the Cachoeira River Basin (CRB), Brazil, using plankton nets with two different meshes (20 and 65 μm). A total of 69 Rotifera species were recorded, distributed among 10 families and 17 genera.  We recorded 16 exclusive species in the 20 μm mesh net, representing 23.2% of Rotifera richness. There were significant differences in the richness, abundance, and biomass captured by the two meshes. The abundances of all individual taxa where higher with the 20 μm mesh net, a pattern repeated for their frequencies of occurrence. That pattern was not observed for biomass, however, as the biomasses of eight species were greater using the 65 μm mesh net than the 20 μm mesh. The analysis of indicator species (IndVal) selected seven species as indicators of the 20 μm mesh. Smaller rotifers were underestimated in terms of all parameters analyzed (richness, abundance, and biomass) when the 65 μm mesh was used.