Metal accumulation and condition of transplanted zebra mussel (Dreissena polymorpha) in metal polluted rivers

Abstract

Zebra mussels (Dreissena polymorpha) originating from a drinking water reservoir were exposed at seven sites in metal polluted watercourses in Flanders (Belgium), including to a cadmium and zinc pollution gradient. At each site one cage, containing twenty-five mussels, was exposed for six weeks. Mussels were collected after 10, 21 and 42 days. At each sampling, five mussels were taken from each cage and analysed for metal content and condition. Significant metal accumulation in zebra mussel was measured as a function of time at all sites for at least one metal. However, a steady state in accumulation was not always reached. Depending on the site, extremely high levels of cadmium, copper, nickel and zinc were measured in the mussels. Despite differences in metal accumulation, no significant differences in two condition indices were observed among the different sites. When data of all the sites were pooled there was no significant relationship between the condition and the metal load in the mussels, although a threshold could be distinguished. However, when this relationship was examined for the separate rivers, significant relationships were found. This indicates that besides metal pollution other environmental factors such as food availability affect the mussel condition.