Asteroids Asterias rubens (Linneaus, 1758) were exposed in the field to various concentrations of waterborne or dietary Cd (from contaminated mussels). Cadmium uptake, and subsequent loss, kinetics were studied for 45 d for each. Dietary (110 µg Cd g-1 dry wt of the prey) and waterborne (5 and 20 µg Cd l-1) Cd was significantly accumulated in the 3 measured body compartments: pyloric caeca, body wall, and skeleton. Waterborne Cd (1 µg Cd l-1) was also significantly accumulated in the body wall but not in the pyloric caeca or the skeleton. Dietary Cd accumulation occurred in all body compartments. In the pyloric caeca, a steady state equilibrium was reached within 20 d, the concentration at steady state ranging from 3 to 9 µg Cd g-1 dry wt according to the exposure mode. The body wall and the skeleton accumulated Cd linearly during the exposure period at a rate of 0.07 to 0.25 µg Cd g-1 dry wt d-1 according to the exposure mode. Cadmium loss kinetics were fitted by inverse exponential functions to all body compartments, except to the skeleton where the loss was generally nonsignificant. Results indicate that there is a Cd flux through the asteroid body from the digestive system to the body wall where Cd is slowly incorporated to the skeleton. Concentration factors calculated for the pyloric caeca fit the range of values previously reported from laboratory experiments and thus validate them in field conditions. Thus A. rubens may be considered a valuable bioindicator of Cd contamination.
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