The comparison of metal handling strategies in mussels Mytilus edulis and oysters Crassostrea gigas was based on the translocation of these bivalves from a relatively clean site (Bay of Bourgneuf, France) to the metal-rich Gironde estuary, France, whereas resident oysters from the Gironde estuary (feral mussels were absent from this site) were cross-translocated to the clean site for seven months (March to October 1997). Higher levels of metal concentrations (Ag, Cd, Cu, Zn) were observed in specimens from both species in the Gironde estuary. However, no cellular pathology was observed, even in translocated mussels which are not normally present in the studied zone of the Gironde estuary. These observations show that both species cope relatively well with the conditions prevailing in the metal-rich estuary, at least partly as a result of the insoluble storage of bioaccumulated metals in well-defined and localized bioaccumulation structures such as mineralized lysosomes in the kidney of mussels and the digestive gland of both species and granules concentrated in extracellular basal lamina. For both species, recruitment of spat was observed on artificial substrates immersed near the site of translocation in the Gironde estuary. The absence of adult mussels in the metal-rich Gironde estuary may be due to competition with oysters for free surfaces of settlement as well as predation by crabs.
