The chemical composition of two species of Daphnia, their algal food and their environment

Abstract

Since the elements of which plankton are composed enter the food chain, it was thought interesting to devote a study to their chemical composition. Daphnia magna and D. pulex were reared in a laboratory for three months maintained on a monoculture of E. gracilis supplemented occasionally with a mixed algal culture. These plankton were raised in spring water. A complete chemical analysis revealed the plankton and the rock from which the spring water flowed to contain 54 detectable elements, while the concentrated water had only 53. Major differences were noted between the two species of Daphnia in their ability to accumulate K, Na, Ca, Sr, P, S, Cl, and Co. The Daphnia and algae contained different amounts of Na, K, Mg, Ca, Zn, Al, Sc, La, Nd, Sn, Ti, P, S, Cl, Br, I, Fe, Mn, Ni, Zr, Cu, Ag, Be, Si, Pb and Hg. The composition of the Daphnia is governed by the mixed algal culture and the spring water. The Daphnia reject E. gracilis; the latter does not contribute to their chemical composition. Aside from supplementary additions of N, P, K and Cl to the algal cultures their composition is governed by that of the spring water.