Carbon, nitrogen, and phosphorus content of freshwater zooplankton

The amounts of C, N, and P in relation to dry weight were measured in natural populations of crustacean zooplankton from a humic lake. The elemental composition within a given species showed little seasonal variation, and experimental starvation or feeding did not cause any significant changes in the P content. C constituted 48±1% of dry weight with only minor variation among species. The mean C : N : P atomic ratios reflected large interspecific differences in P and N content and ranged from 212 : 39 : 1 in Acanthodiaptomus denticornis to 85 : 14 : 1 in Daphnia longispina. Comparisons with published measurements indicate that this pattern is quite general and probably constitutional. These findings suggest that the species composition of the zooplankton community can have strong influence on the N : P ratio of recycled nutrients and thereby affect resource competition between phytoplankton species.