The costs of moulting in Daphnia; mineral regulation of carbon budgets

1. Zooplankton differ in their elemental contents. For the essential elemen ts calcium (Ca) and phosphorus (P), Daphnia spp. have particularly high con tents, and thus high demands, compared with other cladocera and copepods. 2. There are recent indications that the growth of zooplankton, notably Dap hnia, may be directly constrained by the availability of P and Ca. 3. Major pools of P and Ca are associated with the carapace, and the moulti ng process represents a constant drain of these elements, as well as carbon (C), from the animals. 4. The demands for P and Ca for moulting may pose constraints on the carbon accumulation in the animals, and thus the extensive needs for these elemen ts may translate into a total loss of C transported in the pelagic food web . 5. While the costs of moulting are substantial for the zooplankton, the exp ort of minerals bound in the moult will play only a minor role for the epil imnetic element budgets in most lakes.