Combined effects of 3,4-dichloroaniune and food concentration on life-table data of two related cladocerans, Daphnia Magna and Ceriodaphnia Quadrangula

Life-table relations of two seasonally competing cladocerans, Ceriodaphnia quadrangula and Daphnia magna, were investigated, using 3,4-dichloroaniline (DCA) as stressor. Screening tests revealed that Ceriodaphnia was about one order of magnitude more sensitive to DCA than Daphnia. Therefore, in Daphnia life-table experiments were performed at 5, 20 and 80 μg/L DCA, whereas in Ceriodaphnia 2, 5 and 10 μg/L DCA were applied. Each concentration was combined with three food levels (1*103, 5*103, and 2.5*104 cells/mL Scenedesmus subspicatus). Reproduction was found to be the most sensitive parameter to DCA. In comparison to controls, about the same egg numbers were produced but failed to hatch. Overall, reproduction was more affected at lower food levels. At low food levels, DCA delayed the first reproduction only in Daphnia. In contrast to Ceriodaphnia, growth and filtration rates of Daphnia were inhibited. DCA decreased the survival probability only in Ceriodaphnia. Consequently, the decrease in intrinsic rate of natural increase in Daphnia, evoked by DCA, was due to the inhibition in reproduction rather than to higher mortality, whereas in Ceriodaphnia both lower survival and lower reproduction contributed to a strong decline in intrinsic rate at DCA concentrations higher than 5 μg/L.