A MECHANISTIC MODEL OF CONTAMINANT-INDUCED FEEDING INHIBITION IN DAPHNIA-MAGNA

Particles in water ubiquitously carry a net negative charge. It was hy pothesised that the interaction between suspended particles and pollut ants in water results in a process of adsorption that can be related t o the charge of the pollutant concerned, and that this is a potential route of pollutant uptake by aquatic animals such as particle-grazing zooplankton. Experiments with the alga Chlorella vulgaris were conduct ed to test the hypothesis that pollutant-induced feeding inhibition in the cladoceran Daphnia magna was dependent on this mechanism. Using c ompounds differing in charge, results supported the hypothesis that, w hile all compounds were capable of causing feeding inhibition, electro positive species such as cadmium induced effects close to the chronic no-effect concentration, whereas electronegative species such as vanad ium induced effects only at or close to lethal levels. It was suggeste d that for those compounds capable of causing feeding inhibition at su blethal concentrations, this inhibition would be a key mechanism impai ring reproduction and growth, with potential consequences for grazing animals at population and community levels in natural ecosystems.