Physiological effects of cadmium on juvenile Pacific Oysters, Crassostrea gigas, Thunberg

1. "Small" C. gigas spat (2.8 mm) were more sensitive to acute cadmium exposure in seawater than larger spat (3.5 mm), with a 96 hour LCso value of 10.29 and 28.43 mgL-1 total cadmium respectively. 2. Cadmium toxicity to juvenile C. gigas was more closely related to the free cadmium ion concentration than to the total cadmium concentration. The 96 hour LCso in terms of free ion concentration was 0.25 and 0.27 mgL-1 for "small" and "large" spat respectively. 3. EDTA reduced the toxicity of cadmium to C. gigas spat by reducing the external free ion concentration. 4 . Chronic exposure of C. gigas spat to sublethal concentrations of cadmium -retarded growth of both shell and soft tissue; -caused an apparent increase in shell abnormalities; -affected heart contraction rate and caused cardiac arryhthmia; -slowed the rate of filtration of microalgae (spat feed rates); -slowed the behavioural response to tactile and light stimuli; 5. The cadmium bioaccumulation factors of spat exposed to 0, 10, 50 and 250 J..lgL-1 cadmium were 1.5 x 104, 3 x 103, 1.3 x 103 and 1.5 x 103 respectively. These values are similar to those previously reported by Ward (1983) for adult oysters (Saccostrea commercialis ). 6 . Accumulation of cadmium in spat soft tissue was linearly related to the external cadmium concentration. This is similar to the pattern of cadmium accumulation by other species of adult bivalves