ABSTRACT: The effect of humic acid (HA) on uptake and transfer of Cu by selected marine organisms from the microbial loop was determined. Bacteria grown with and without 15 µg Cu l^-1 and with and without 10 mg Suwannee River Humic Acid (SRHA) l^-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 transfer of Cu from bacteria to copepods. The presence of 10 mg SRHA l^-1 reduced Cu uptake in A. tonsa by an average of 54% and significantly reduced the negative effects of Cu on reproductive success of A. tonsa. The percentage of the total Cu residues in A. tonsa resulting from feeding was estimated 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 residue is due to feeding. Thus, SRHA seems to affect Cu uptake in A. tonsa through binding of free Cu in the water at the same rate as through the food chain. This study demonstrates the importance of complexation of metals by organic matter and trophic transfer processes for organisms critical to estuarine food webs.

KEY WORDS: Trophic transfer · Bioavailability · Humic acid · Zooplankton · Copper

Published in MEPS Vol. 187 (1999) on October 14
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999