Daphnia galeata life history response to heterogeneous food conditions anddissolved chemicals in the Rimov Reservoir

Laboratory cultivation experiments were carried out in order to determine t he response of D. galeata to food conditions and dissolved chemicals in the water collected in three contrasting sites of the Rimov Reservoir. There w ere two types of cultivation media: (1) lake water with natural seston, fil tered through a 40 mum mesh size sieve, (2) lake water filtered through a m embrane filter 0.45 mum (or 0.22 mum), with Scenedesmus subspicatus culture added to a concentration of 1.0 mg POC l(-1). In the treatment with natura l seston, the parameters investigated (body length, filtering setae length, clutch size, egg volume and postembryonic development time) were determine d mainly by the food level, which was higher in the upper part of the reser voir than near the dam. In one series, significantly larger clutches and sm aller eggs together with longer postembryonic development (PED) were detect ed in daphnids cultivated in hypolimnetic water, compared to those in epili mnetic water. As particulate carbon concentrations were similar, this indic ates that in that case food quality played a role shaping life histories in Daphnia. In some of the experiments with the filtered water, there was a d etectable effect of dissolved chemical(s), which induced shorter PED and sm aller primiparae in the animals cultivated in water from the upper part of the reservoir.