ASSIMILATION OF METALS IN MARINE COPEPODS AND ITS BIOGEOCHEMICAL IMPLICATIONS

Laboratory experiments employing gamma-emitting radiotracers assessed the retention efficiency of ingested metals in the calanoid copepod Anomalocera patersoni and the retention of excreted metals in fecal pellets. Adult copepods ingested the haptophyte Isochrysis galbana labeled with Cd-109, Zn-65, Hg-203, Am-241 and Pu-237 at a rate of 3.79 mg algal C g-1 animal dry wt h-1. Average retention efficiencies were 30% for Cd, 48% for Zn, 21% for Hg, 4.5% for Am, and 0.8% for Pu. Algal cells resuspended into unlabeled seawater retained metals to varying extents, with depuration curves conforming to a 2-compartment model; Cd was lost most rapidly. The fecal pellets produced by animals feeding on radioactive I. galbana lost essentially all of their Cd-109, Zn-65, Am-241, and Pu-237 to unlabeled seawater within 1 d. Hg-203 was lost most slowly, again conforming to a 2-compartment model; its retention half time was about 25 d in the slowly exchanging pool. Bacterial activity did not appear to have an effect on metal retention in the fecal pellets. The retention efficiencies suggest that Cd, Zn, and Hg should be recycled by copepods in surface waters as part of the organic cycle in the sea, while the transuranic elements should be defecated and removed from surface waters by sinking biogenic debris.