Phosphorus Release Patterns and the Effects of Reproductive Stage and Ecdysis in Daphnia magna

Abstract

Rates of continuous phosphorus release by individual Daphnia magna (0.3 – 0.9 mg dry weight) were measured using high performance liquid chromatography components in conjunction with a specially designed incubation flow cell. Within the temporal resolution of the technique (3 min), phosphorus release often appeared pulsed rather than only steady. We found significant variation in release rates among the different stages of an individual's parthenogenetic reproductive cycle. Rates observed for animals carrying more mature embryos were lower than those earlier in the reproductive cycle. Rates of phosphorus release observed at and after ecdysis averaged 6.7 times higher than rates observed at other times.Key words: phosphorus, excretion, reproductive stage, ecdysis, Daphnia magna