The egg production rates of Acartia tonsa were studied using two main experiments. In the first, two different species of diatoms, Rhizosolenia fragilissima and Thalassiosira weissflogii, both differing in size, were fed to A. tonsa adults. Egg production rates decreased significantly in the R. fragilissima treatment compared to the T. weissflogii treatment. In the second set of experiments, increased A. tonsa adults grown in increased nutrient and metal treatments were compared to those growing in control treatments. Egg production rates decreased in the nutrient plus metal treatments.