The accumulation of cadmium by the shore crab Carcinus maenas (L.) is to some extent dependent upon the calcium concentration of the external medium. This effect is apparently independent of the overall salinity of the external medium and may at least partially explain previous reports of a ‘salinity effect’.

Haemolymph cadmium has a highly significant inverse relationship with the external calcium concentration. This effect is less obvious with other tissues, although the whole body cadmium has a significant inverse correlation with the external calcium concentration. Both the haemolymph and gill show a significant inverse relationship between tissue cadmium and calcium.

When postmoult animals were exposed to 20μ-mol l−1 Cd in 100% s.w., high concentrations of both calcium and cadmium appeared in the haemolymph. Postmoult animals in cadmium-free sea water generally had a lower haemolymph calcium concentration than intermoult animals, and the rise in haemolymph calcium seen in the presence of cadmium may indicate some degree of competition for ‘deposition sites’ between these two metals.

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