Abundance of planktonic ciliates in a cascading reservoirs of the Paranapanema River, Brazil - DOI: 10.4025/actascibiolsci.v26i4.1532

Abstract

The present study aimed to investigate the spatial and temporal distribution patterns of density and biomass of the planktonic ciliates, in a reservoir serie of the Paranapanema River (22^o 18’ - 23^o 35’ S; 49^o 30’ - 52^o 50’ W). We intend to test the hypothesis that, along reservoirs serie, there is a decrease of abundance from river towards the dam. Samplings were carried out in seven reservoirs, during 2001, in two distinct hydrological periods, at subsurface of the lacustrine region, using a Van Dorn bottle (5 liters). Aliquots from one liter were obtained and fixed with a fixing solution compounded by alkaline lugol, formaldehyde and sodium tiosulfate. Obtained values for ciliates abundance (density and biomass) in different reservoirs (0.4 to 16.6 cells.mL^-1; 0.23 to 20.7 µg.C.L^-1, respectively) were inferior to results found in eutrophic environments, but similar to those registered in oligo-mesotrophic environments. Analysis of the abundance distribution results, along reservoirs serie, did not corroborate the hypothesis of decreasing density and biomass from upstream to dowstream, due to an expectancy of a possible oligotrophication downriver. In relation to different functional groups of ciliates, it was verified the dominance of Oligotrichida, mainly small sized individuals (< 30 µm).