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Newly hatched larvae of the mud crab R. harrisii and the grass shrimp P. pugio were exposed for 96 h to a range of cadmium free-ion concentrations using metal-buffered seawater. Survival, growth, and molting frequency were monitored. Results show that mud crab larvae are more sensitive to cadmium exposure than grass shrimp larvae. Mud crab larvae experienced decreased survival, reduced growth, and decreased molting frequency at cadmium concentrations in which grass shrimp had high survival and no reduction in growth or molting frequency. In a second series of experiments, newly hatched larvae of each species were exposed for 96 h to a matrix of three cadmium free-ion concentrations and a constant zinc concentration using cadmium-109 and zinc-65 as tracers. Crab larvae showed greater total uptake of cadmium as well as higher accumulation of cadmium in the cytosolic compartment compared to shrimp larvae at cadmium concentrations in which crab larvae suffered adverse toxic effects, as described above. Zinc uptake by both species decreased with increasing cadmium concentration at lower cadmium exposures; however, mean total zinc accumulation was greatest at the highest cadmium concentration. Crab larvae also accumulated more zinc than shrimp larvae at all cadmium concentrations, with a higher percentage of zinc accumulation occurring in the cytosolic compartment as well. These interspecific differences in the metabolism of zinc and cadmium may explain the greater sensitivity of crab larvae to cadmium compared to shrimp larvae.
cadmium, zinc, accumulation, subcellular distribution, larvae, mud crab, Rhithropanopeus harrisii, grass shrimp, Palaemonetes pugio
Environmental scientist, Water Quality Section, Raleigh, NC
Professor of zoology and director, Duke University Marine Laboratory, Beaufort, NC