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Hatchery-reared juvenile oysters (Crassostrea virginica) were deployed in situ for approximately 1 month from mid-May to mid-June of 1996 at sites that were classified as reference, agricultural, suburban, or urban/industrial. Cellular responses (lysosomal destabilization, glutathione concentrations, lipid peroxidation, heat shock proteins, metallothioneins, and multi-xenobiotic resistance proteins) were analysed, and their efficacy as biomarkers of stress was evaluated. Increased lysosomal destabilization, glutathione depletion, increased lipid peroxidation, and induction of heat shock proteins and metallothioneins were observed at many of the polluted sites, but increases in multixenobiotic resistance proteins were not. Significant correlations between sediment contaminants and lysosomal destabilization or glutathione concentrations were observed. Similarly, there were significant correlations between sediment cadmium and copper levels and metallothioneins. Although elevated lipid peroxidation products and heat shock proteins were observed at some of the contaminated sites, there were no significant correlations with contaminants. These studies suggest that lysosomal destabilization and glutathione depletion are sensitive, robust indicators of contaminant stress. Although lipid peroxidation and heat shock protein responses were not correlated with contaminants, they are still regarded as valuable indicators of stress. These studies demonstrate the value of using a suite of cellular biomarkers to identify and characterize stress responses related to anthropogenic perturbations.

The susceptibility of shellfish to raphidophyte toxicity is not well resolved. This study examined the sublethal cellular responses of eastern oysters Crassostrea virginica exposed to 2 raphidophyte blooms (Chattonella subsalsa or Fibrocapsa japonica). Also, based on the hypothesis that raphidophyte toxicity is related to brevetoxin production, we determined the cellular responses of oysters to purified brevetoxin (PbTx-3) exposure in a separate experiment. We evaluated 3 cellular biomarkers, constituting both cellular damage and detoxification responses: lysosomal destabilization, lipid peroxidation and glutathione concentration. Exposing oysters to water collected from both blooms significantly increased lysosomal destabilization rates in oyster digestive gland when compared to controls, as did exposure to 1 and 10 nM PbTx-3. Glutathione and lipid peroxidation levels were not significantly affected in any treatment. The physiological stress response (i.e. increased lysosomal destabilization rates) in oysters exposed to brevetoxin, C. subsalsa bloom water, or F. japonica bloom water is consistent with that found in oysters exposed to Heterosigma akashiwo (Raphidophyceae) blooms and cultures. The results indicate that oysters are susceptible to raphidophyte and brevetoxin toxicity, and are not solely a vector for neurotoxic shellfish poisoning. The common physiological response to raphidophyte and brevetoxin exposure is consistent with the hypothesized production of brevetoxin by this group, but alternatively may reflect a more general stress response in oysters.

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Sediment toxicity assays were conducted with juvenile Mercenaria mercenaria to compare the results of laboratory assays and in situ deployments. Juvenile clams were deployed for one week at a variety of degraded and undegraded sites in Charleston Harbor, South Carolina. USA, during the summers of 1998, 1999, and 2000. Parallel laboratory assays were conducted with sediments collected from the deployment sites. Mortality and a sublethal endpoint, seed clam growth rate, were used to compare toxicity between reference and degraded sites. Growth rates of field-deployed clams tended to be higher than growth rates for laboratory assays, especially at the reference sites. Field studies indicated a higher potential for toxicity than did the laboratory studies at degraded sites. These studies suggest that laboratory assays may underestimate potential sediment toxicity at degraded sites. However, field growth rates may be affected by natural environmental factors (e.g., pH, dissolved oxygen, and salinity), so regression normalization techniques were used to distinguish the effects of these variables from those of contaminants.