Reproduction as one of the main causes of temporal variability in the elemental composition of zooplankton

Abstract

With the aim to determine the contribution of development and reproduction to the variability in the elemental composition of zooplankton, we measured the carbon (C), hydrogen (H), nitrogen (N), and phosphorus (P) elemental composition of the planktonic crustacean assemblage in an alpine lake for a whole seasonal cycle. The species included three distinct living modes: a cladoceran, Daphnia pulicaria; a cyclopoid copepod, Cyclops abyssorum; and a calanoid copepod, Diaptomus cyaneus. For the three species, reproduction was the main cause of elemental variability. Adult females of the three species lost from 32% to 48% of their initial absolute C and H content during reproduction, which corresponded to a similar decrease in their lipid and carbohydrate content. The N content did not change in any of the three species, nor did the protein and chitin content. Daphnia and Diaptomus lost 35% and 56%, respectively, of their initial absolute P content during reproduction, whereas the P content of Cyclops did not change. The three species stored energy compounds under unfavorable conditions for later use in offspring production, but only Diaptomus and Daphnia mobilized stored P. Corresponding stoichiometric changes with re- production included a decrease in C:N ratio for the three species; an increase in N:P ratio for Daphnia adult females and adults of Diaptomus; and a C: P ratio increase in Diaptomus females and decline in Cyclops females. Differences in C: P ratio changes corresponded with differences in allocation to their respective reproductive tissues. Diaptomus males and Daphnia females did not change their C: P ratio with reproduction.