Reconstructing the biokinetic processes of oysters to counteract the metal challenges: physiological acclimation

Oyster Crassostrea hongkongensis, a widely cultivated oyster species in Southern China, can accumulate metals (especially for Cu and Zn) to extraordinarily high concentrations (up to 3% of body dry weight). It remains unknown how they were acclimated to contaminated environment and built up such high metal concentrations in their bodies. A seven month transplantation experiment was conducted to rebuild the physiological process of acclimation in oysters to illustrate how they cope with increasing metal bioavailability. The metal concentrations increased substantially in the transplanted oysters from a reference site to a contaminated site. Our results showed that metal biokinetics in the oysters changed dramatically after suffering from metal stress. The clearance rate, dissolved uptake rate (for Cd and Zn), and metal assimilation efficiency (for Zn) was depressed, while the metal efflux rate (for Zn) was enhanced in the contaminated oysters. Beside the change of metal homeostasis, the oysters were able to sequester metals into subcellular nontoxic forms and maintain a low portion of metals distributing in the metal-sensitive fraction. This comparative bioaccumulation study of C. hongkongensis suggested that adjustment of metal biokinetics played an important role in the survival of oysters in metal contaminated environment.