ASSIMILATION AND REGENERATION OF TRACE-ELEMENTS BY MARINE COPEPODS

Assimilation efficiencies (AE) of five trace elements (Am, Cd, Co, Se, and Zn) and carbon by neritic copepods (Acartia tonsa and Temora long icornis) feeding at different food concentrations and on different foo d types (diatoms, green algae, flagellates, dinoflagellates, and Fe ox ides) were measured with radiotracer techniques. Food concentration ha d little influence on AEs of C, Cd, Co, and Se within a range of 16-80 0 mu g C liter(-1). AEs of Am and Zn were highest at low food concentr ations (16-56 mu g C liter(-1)) but remained relatively constant when food levels exceeded 160 mu g C liter(-1). Different algal diets had n o major influence on AEs, which generally were in the order Cd > Se > Zn > Co > Am. Metals (Cd, Co, and Zn) were assimilated from Fe oxides with 50% less efficiency than from algal cells. Element regeneration i nto the dissolved phase was a significant route for the release of ing ested elements by copepods and increased with increased food concentra tion. Element regeneration rates for Cd, Se, and Zn were comparable to the regeneration rates of major nutrients such as P (30-70% daily). R etention half-times of elements in decomposing fecal pellets ranged fr om <1 d (Cd) to >10 d (Am). The efficient assimilation and regeneratio n of Cd, Se, and Zn can significantly lengthen the residence time of t hese elements in ocean surface waters.