INFLUENCE OF THE LEVEL OF OXYGENATION IN SEDIMENT AND WATER ON COPPERBIOAVAILABILITY TO MARINE BIVALVES - LABORATORY EXPERIMENTS AND TRANSLOCATION EXPERIMENTS IN THE FIELD

The effects of differences in the level of oxygenation of sediment or water on the condition and copper content of two bivalves, the Baltic clam Macoma balthica and the cockle Cerastoderma edule, were assessed. Specimens from four intertidal flats in the Netherlands and France we re compared, translocated and exposed to different levels of oxygen in the laboratory. Cockles showed no significant differences in conditio n and copper content between animals from Light (= more oxygenated) an d dark (= less oxygenated) sediments. Baltic clams also showed no diff erences in condition, but the clams had a higher copper content (conce ntration as well as body burden) in dark than in light sediments. Duri ng the translocation experiments no significant changes occurred. In t he laboratory experiments the level of oxygen had no effect on the con dition or copper content of the Baltic clam. The only factor affecting the copper content of Baltic clams was the addition of copper to the water or sediment. The copper, organic carbon and silt fraction (< 16 mu m) was higher in dark sediments than in light sediments. The copper content in the sediment was positively related to the silt and organi c carbon content. We argue that the relation between coloration (= deg ree of oxygenation) of sediments and the copper content of Baltic clam s could be indirect: due to a higher silt fraction and/or organic cont ent at some places on a tidal flat, these places are more hypoxic and therefore darker, whereas simultaneously these places have a higher co pper concentration because of more copper-complexing sites land surfac e), whereby the higher copper concentration in the sediment relates to a higher copper concentration in the clams.