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(213) Impact of pesticides on grazing efficiency. Montenegro, K.1,2, Bengtsson, G.1, Hansson, L.-A.1, 1 2 ABSTRACT- Survivorship has been used for many years as an ecotoxicological endpoint to demonstrate the effects of chemicals on organisms. Endpoints based on behavioural traits, e.g. predator avoidance, feeding behaviour and locomotory behaviour may be more sensitive and give more insights in patterns of sublethal toxicity. Grazing efficiency in zooplankton which may affect primary productivity and nutrient cycling as a consequence of cascading through aquatic food webs, was addressed as a behavioural endpoint in this study. The grazing efficiency of Daphnia pulex was measured by exposing Scenedesmus sp. to a range of densities of zooplankton which were first exposed to pesticides, either through water or through phytoplankton. The net growth rate was inversely related to the density of zooplankton. Phytoplankton biomass was estimated from the Cha content and the Glyphosate and DDE concentrations in Daphnia and Scenedesmus from parallels uptake experiments with a radiolabelled source. The exposure to pesticides reduced the grazing efficiency of zooplankton especially when they were contaminated from water. Key words: pesticides, grazing efficiency, phytoplankton |
