Effect of food type on the acute and chronic toxicity of copper to Daphnia magna

SUMMARY. Daphnia magna was maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin‐enriched algae were less sensitive to a chronic copper stress than animals fed a trout‐granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size and r, the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal‐fed animals, 0.12 for animals reared on trout‐granules). In contrast to chronic toxicity, 72 h LC50 values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental conditions.