Living with constraints: food quality effects on zooplankton
Copepods and daphniids exhibit different grazing patterns, which affect the seston size distribution. I have studied whether the grazing of one guild could be beneficial for the other guild. Daphniids grew faster on seston previous manipulated by copepods than on seston which was not manipulated. Seston manipulated by daphniids was a poor food source for Daphnia and thus, growth declined. When marine copepods were feeding on plankton previously manipulated by copepods their growth potential (RNA:DNA) decreased with increasing copepod densities. In the laboratory I studied the effect of fatty acids and phosphorus (P) on Daphnia magna life-history and stoichiometry. D. magna had low EPA saturation threshold for growth (0.04 µg EPA L-1) and high storage capacity. However for P, daphniids had high requirements but only small storage capacity. P storage could not be utilised, whereas EPA storage could compensate periods of poor food quality.