ACCUMULATION OF TRACE-ELEMENTS IN A MARINE COPEPOD

We measured assimilation efficiencies (AEs) from ingested algal food, uptake rates from the dissolved phase, and efflux rate constants of fi ve trace elements (Ag, Cd, Co, Se and Zn) in the marine copepod Temora longicornis. AEs of Ag, Cd, Co, Se, and Zn from two diatom diets were 13, 35, 14, 59, and 61%, respectively. AEs of metals from ingested na tural seston collected during the spring phytoplankton bloom in Long i sland Sound were comparable to AEs from diatoms. The assimilation of a ll trace elements within the T. longicornis gut took longer (4-15 h) t han the gut passage time of ingested food particles. The rate constant of metal uptake from the dissolved phase was highest for Ag, followed by Zn > Cd > Co > Se. Efflux rate constants for all trace elements ra nged from 0.08 to 0.30 d(-1), indicating that metals were regenerated at a very fast rate in these animals. Generally, the efflux rate of me tals was higher following uptake from food than uptake from the dissol ved phase. The retention half-times of trace elements in copepod carca sses were 0.6-3.3 d. A bioenergetic-based kinetic model was used to qu antify the relative importance of metal uptake in copepods from differ ent pathways. The model indicates that under conditions typically enco untered by copepods in nature, >50% of Zn and >98% of Se in copepods a re obtained from ingested food. For Ag, Cd, and Co, >50% accumulates f rom the dissolved phase. The relative importance of trace element upta ke from the dissolved phase vs, particulate ingestion in the overall m etal uptake depends greatly on the metal AE, the feeding rate of copep ods, and the partition coefficient of metals in ingested food particle s.