Studies on a Population of Daphnia magna

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Abstract
A description is given of the fluctuation in population composition, size of parthenogenetic females, egg production, hemoglobin content and density of epibionts on the carapace in a population of Daphnia magna in a sludge settling tank at Hampton Waterworks. In the early summer the size of the parthenogenetic females and the egg production fluctuated together, while egg production and hemoglobin concentration fluctuated inversely. In winter both hemoglobin concentration and egg production were low. Males produced more hemoglobin more quickly than females, and lost it more quickly. Other spp. of Daphnia in the same settling tank were D. curvirostris, D. obtusa, D. pulex and D. longispina. On one occasion the last 3 were all taken together with D. magna. Epibionts recorded were Colacium vesiculosum, Rhabdostyla pyriformis, Intrastylum invaginatum f. daphniae, Carchesium sp., Acineta sp., Amoebidium parasiticum, Cocconeis placentula and Synedra sp. Epistylis anastatica, normally epibiotic on copepods was found sparsely on D. pulex. There was an inverse relation between the density of Colacium and that of peritrichs on the carapace of Daphnia magna. Infection with an amoeboid parasite, Pansporella perplexa, was found. Degree of infection at different ages and reproductive states was examined, and revealed a specific difference in the degree of infection of Daphnia magna and D. curvirostris, the former being heavily infected and the latter practically uninfected.

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