Inter-individual variations in cadmium and zinc biodynamics in the scallop Chlamys nobilis

Intraspecific variability in the bioaccumulation of metals has been widely recorded in marine invertebrates, including marine bivalves. In the present study, we used biokinetic modelling and metal subcellular partitioning approaches to understand the intraspecific variability of metal bioaccumulation (Cd and Zn) in the scallop Chlamys nobilis as a model organism. Significant individ- ual differences in metal body burdens were found in C. nobilis. Cd concentrations varied by 3-fold and concentrations of Zn varied by 10-fold for individuals with similar body sizes. Contrasting metal biokinetics and metal subcellular partitioning were observed in different individuals. There was no significant relationship between the metal body burden and the dissolved metal uptake rate or the dietary assimilation efficiency in the individual scallops. However, a significant negative relationship was found between the metal efflux rate and the respective metal body burden, suggesting that efflux rate plays a key role in determining the intraspecific differences in the metal body burden in the tissues of scallops. Subcellular partitioning was closely related to the metal body burden in the scallops as well. A lower efflux rate or a higher proportion of metals stored in non-toxic form con- tributed to higher metal body burdens in individual scallops. Intrinsic variation may provide a popu- lation with more plasticity to counteract spatially or temporally abrupt environmental changes, and may be important for survival of microevolutionary events. Our results provide important information for interpreting the variability observed in natural environments.