Interactive effects of xenobiotic, abiotic and biotic stressors on Daphnia pulex—Results from a multiple stressor experiment with a fractional multifactorial design

•Impact of toxic substances for aquatic communities cannot be solely derived by single exposure tests.•The identification of interactive effects between abiotic, biotic and man-made stresses can be assessed with multifactorial test designs.•The results show clearly that multiple stress factors affect organisms integratively. Pollutant effects on aquatic key species are confounded by multiple abiotic and biotic stressors. To better discriminate and understand the intrinsic and environmental correlates of changing aquatic ecosystems, we untangle in present study how the effects of a low-dosed fungicide on daphnids (via different exposure routes) becomes modified by increasing temperature and the presence of a predator. Using a fractional multifactorial test design, the individual growth, reproduction and population growth rate of Daphnia pulex were investigated under exposure to the fungicide pyrimethanil at an environmental relevant concentration – either directly (via the water phase), indirectly (via food), dually (via water and food) or for multiple generations (fungicide treated source population) – at three temperatures and in presence/absence of the predator kairomones of Chaoborus flavicans. Our results clearly illustrate that multiple stress factors can modify the response of an aquatic key species to pollutants. The environmentally relevant exposure of the contaminant via food or the medium is of same importance. Nevertheless, temperature and the presence of a predator are the dominant factors controlling the reproduction of D. pulex. We conclude that sublethal pyrimethanil pollution can disturb the zooplankton community at suboptimal temperature conditions, but the effects will become masked by low temperatures or if chaoborid larvae are present.