Differences in chemical composition between two species of Daphnia and some freshwater algae cultured in the laboratory1

Abstract

Daphnia pulex Leydig, 1860, and Daphnia magna Straus, 1820, were cultured in spring water in glass aquaria and fed every day or two with a monoculture of Euglena gracilis Klebs and occasionally with a mixed algal culture containing mainly Chlorophyceae. Daphnia and algae were harvested weekly and accumulated over 3 months. Samples were analyzed by X‐ray emission and optical emission spectroscopy. Fifty‐three elements were detected in the spring water and 54 in the plankton. On a dry weight basis, both species of Daphnia contained higher concentrations of Na, Ca, Sc, La, Nd, Zr, Cl, Br, and Ni than the algae; the algae had accumulated, on the average, more K, Cu, Ag, Be, Mg, Zn, Hg, Al, Si, Sn, Pb, Ti, P, As, Mo, I, Fe, Mn, and Co than had the Daphnia. The concentrations of Ca and Cl were 2.1 and 3.2 times higher, respectively, in D. magna than in D. pulex.