Bioavailability and trophic transfer of humic-bound copper from bacteria to zooplankton

The effect of humic acid (HA) on uptake and transfer of Cu by selected mari ne organisms from the microbial loop was determined. Bacteria grown with an d without 15 mu g Cu 1(-1) and with and without 10 mg Suwannee River Humic Acid (SRHA) 1(-1) were fed to Uronema sp. The Uronema were subsequently fed to Acartia tonsa to determine the effect of humic acid on the uptake and t ransfer of Cu from bacteria to copepods. The presence of 10 mg SRHA 1-1 red uced Cu uptake in A. tonsa by an average of 54% and significantly reduced t he negative effects of Cu on reproductive success of A. tonsa. The percenta ge of the total Cu residues in A. tonsa resulting from feeding was estimate d by exposing A. tonsa to the same conditions with and without pre-exposed Uronema as food. The results indicate that approximately 50% of the Cu resi due is due to feeding. Thus, SRHA seems to affect Cu uptake in A. tonsa thr ough binding of free Cu in the water at the same rate as through the food c hain. This study demonstrates the importance of complexation of metals by o rganic matter and trophic transfer processes for organisms critical to estu arine food webs.