Hydrobiologia 373/374: 297–310, 1998. J.-C. Amiard, B. Le Rouzic, B. Berthet & G. Bertru (eds), Oceans, Rivers and Lakes: Energy and Substance Transfers at Interfaces. © 1998 Kluwer Academic Publishers. Printed in Belgium. 297 Influence of the level of oxygenation in sediment and water on copper bioavailability to marine bivalves: laboratory experiments and translocation experiments in the field Herman Hummel 1 , Paolo Magni 1,∗ , Claude Amiard-Triquet 2 , Florence Rainglet 2 , Roel Modderman 1 , Yvette van Duijn 3 , Marcel Herssevoort 3 , Johan de Jong 3 , Linda Snitsevorg 4 , Maaike Ytsma 4 , RoelofBogaards 1 & Lein de Wolf 1 1 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Vierstraat 28, 4401 EA Yerseke, The Netherlands 2 Universit´ e de Nantes, CNRS, Facult´ e de Pharmacie, Laboratoire d’ Ecotoxicologie, 1, Rue Gaston-Veil, 44035 Nantes Cedex, France 3 Polytechnical Faculty, Hogeschool Rotterdam & Omstreken, Kluyverweg 4, 2629 HT Delft, The Netherlands 4 Van Hall Institute, Hereweg 99, 9721 AA Groningen, The Netherlands ∗ Present address: Department of Bioresource Science, Kagawa University, 761-07 Miki, Kagawa, Japan Key words: bivalves, oxygen, condition, copper, bioavailability, translocation, sediment, silt fraction Abstract 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 were compared, translocated and exposed to different levels of oxygen in the laboratory. Cockles showed no significant differences in condition and copper content between animals from light (= more oxygenated) and dark (= less oxygenated) sediments. Baltic clams also showed no differences in condition, but the clams had a higher copper content (concentration as well as body burden) in dark than in light sediments. During the translocation experiments no significant changes occurred. In the laboratory experiments the level of oxygen had no effect on the condition 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 μm) was higher in dark sediments than in light sediments. The copper content in the sediment was positively related to the silt and organic carbon content. We argue that the relation between coloration (= degree of oxygenation) of sediments and the copper content of Baltic clams could be indirect: due to a higher silt fraction and/or organic content at some places on a tidal flat, these places are more hypoxic and therefore darker, whereas simultaneously these places have a higher copper concentration because of more copper-complexing sites (and surface), whereby the higher copper concentration in the sediment relates to a higher copper concentration in the clams. Introduction Variations of metal content in bivalves can be related to several environmental and internal ecophysiolog- ical factors, such as temperature, salinity, sediment grain size or tissue weight (Bryan, 1980, 1984; Lu- oma, 1983, 1989; McLusky et al., 1986; Forstner, 1987, 1990; Millward, 1995). The influence of the oxygenation level in sediment and water is mostly referred to with much reservation, because of the com- plex interrelation of oxygen-levels with e.g. acidity and sulphide levels (Theede, 1985; Forstner, 1990; Di Toro et al., 1992; Ankley et al., 1994). At lower oxygen levels in water the carbon-dioxide levels will