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 (22o 18’ - 23o 35’ S; 49o 30’ - 52o 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).
Highlights
The traditional concept of classical food chain in aquatic environments has been recently supplemented through the new paradigm of microbial loop (Laybourn-Parry, 1994), which suggests that bacteria and protozoans have primary paper in production, transferring and maintenance of organic matter inActa Scientiarum
Lansac-Tôha et al 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, as well as identify biotic and abiotic factors intervening on determine those patterns
Considering the reservoir position, in Paranapanema River, we verified that, in general, there was an increase in density toward middle of the reservoir seri, with higher abundance values in Canoas I Reservoir, and following a decrease, and once again, an increase in the end cascade
Summary
The traditional concept of classical food chain in aquatic environments has been recently supplemented through the new paradigm of microbial loop (Laybourn-Parry, 1994), which suggests that bacteria and protozoans have primary paper in production, transferring and maintenance of organic matter inActa Scientiarum. Biological Sciences pelagic region (Azam et al, 1983) This concept, jointly to scientific and technological advances of microbial ecology through the advent of epifluorescence microscopy (Caron, 1983; Hobbie et al, 1997), brings on the development of new studies on these communities during last three decades. Protozoans are the principal bacteria consumers and, in turn, they are predated by large sized zooplankton (Sherr and Sherr, 1988, Laybourn-Parry, 1992). Many times, they constitute in dominant trophic link through picoplanktonic and nanoplanktonic production is transferred to high trophic levels (Hwang and Health, 1997). According to Gifford (1985), ciliates have been found feeding on preys of different sizes, from bacteria to organisms of their own size
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