EFFECTS OF CADMIUM ON SURVIVAL, OSMOREGULATORY ABILITY AND BIOENERGETICS OF JUVENILE BLUE CRABS CALLINECTES-SAPIDUS AT DIFFERENT SALINITIES

Juvenile blue crabs, Callinectes sapidus, from the Barataria estuary ( Louisiana, USA) were exposed to a range of dissolved cadmium concentra tions at 2.5 and 25 parts per thousand to determine their response to cadmium. 21-Day LC(50)s were an order of magnitude lower at 2.5 parts per thousand (19 mu g liter(-1)) than at 25 parts per thousand (186 mu g liter(-1)). Crabs were exposed to Cd levels of 0,50 and 100 mu g li ter(-1) for measurements of feeding, respiration and excretion rates. Respiration was the primary component (($) over bar x = 86.2%) of the energy expenditure budget in all cases, relative to excretion. Rates o f energy expenditure did not vary with cadmium concentration at either salinity, and were much lower than those of energy consumption and ab sorption. Scope for growth paralleled energy consumption and absorptio n. Scope for growth did not vary as a function of cadmium concentratio n at 25 parts per thousand; scope for growth at 2.5 parts per thousand was significantly lower in crabs exposed to 50 and 100 mu g liter(-1) Cd relative to control crabs. Cadmium levels of up to 100 mu g liter( -1) do not stress juvenile blue crabs at 25 parts per thousand; but at 2.5 parts per thousand, these same levels of Cd result in mortality a nd sub-lethal stress. This finding is important since nursery grounds for juveniles of this species often lie in low salinity, estuarine wat ers, and high dissolved cadmium levels have been reported in Louisiana estuaries.