METAL ACCUMULATION IN THE CLAM TRIDACNA-CROCEA UNDER NATURAL AND EXPERIMENTAL CONDITIONS

Clams (Tridacna crocea) were collected from three sites in the Torres Strait along a transect from the mouth of the heavily polluted Fly Riv er towards the south. The concentrations of Cu, Cd and Zn in different organs of the clams were determined and, with the exception of Cd lev els in the gills and mantle, were found to decrease with increasing di stance from the river outfall. The levels of metals in the clam tissue s, however, fall within a similar range of values found in control cla ms collected from Orpheus Island. In addition, the rates of metal bioa ccumulation in clams were studied under laboratory conditions. Experim ents carried out with either Cd (0.20 mg/l) or Cu (0.06 mg/l) in seawa ter revealed a linear uptake of metal throughout the experimental peri od in different clam organs. The highest accumulation rates were found in the kidney and the lowest in the muscle. The accumulation rate of Cd was higher in the mantle than in the gills, whereas the inverse was found for Cu. Cu treatment resulted in significant expulsion of the s ymbiotic zooxanthellae from the mantle, a recognized stress response. In clams collected from the wild, the concentration of renal metal-bin ding proteins (metallothionein-like proteins) increased with the level s of total metal in the kidneys, and indirectly reflected the environm ental levels.