Variation in cadmium uptake by estuarine phytoplankton and transfer to thecopepod Eurytemora affinis

The pathways of cadmium (Cd) uptake and transfer within an estuarine plankt onic community from the Patuxent River, Maryland, USA, were investigated us ing an assemblage of natural phytoplankton and the copepod Eurytemora affin is Poppe. The experiment was carried out in October 1992 in replicated 500- liter, flow-through, fiberglass tanks. Growth rate, species composition, an d Cd loading affected the accumulation of Cd by the phytoplankton. Uptake o f Cd by phytoplankton was proportional to the amount of Cd available in the water column. Partition coefficients (Kd) for phytoplankton uptake average d 4.4 x 10(4). As metal loading rates and phytoplankton species composition changed during the 12-d experiment, Cd partitioning declined. Transfer of Cd to E. affinis occurred from Cd-laden phytoplankton, with levels in the c opepods being approximately the same as, or somewhat less, than in the phyt oplankton. Some Cd uptake occurred in copepods exposed to dissolved Cd only ; however, the uptake was considerably less than that seen from food. Thus, Cd content of higher trophic levels, such as copepods, can be affected by the degree of Cd incorporation in their food source, and by ecological fact ors regulating phytoplankton ingestion.