Decreased resistance of eastern oysters (Crassostrea virginica) to a protozoan pathogen (Perkinsus marinus) after sublethal exposure to tributyltin oxide

Anthropogenic environmental stress is a likely contributor to outbreaks of disease due to immunosuppression or increased host vulnerability. Estuarine organisms are exposed to variable concentrations of marine antifouling agents, such as tributyltin (TBT), with higher exposures existing near ports and marinas. Eastern oysters (Crassostrea virginica), inhabiting the northern Gulf of Mexico and the Atlantic coast of North America, are susceptible to a protozoan pathogen, Perkinsus marinus, which has devastated oyster populations and depleted oyster fisheries throughout its range. This study examined the effects of exposure to environmental levels of TBT on susceptibility and survival of oysters when subsequently challenged with P. marinus. Oysters were exposed to TBT (0, 30 and 80 ng/L) in flow-through aquaria for 9 weeks, then moved to static aquaria, where they were challenged with parasites and monitored for an additional 8 weeks for mortality and disease. Results indicated increased infection intensity and oyster mortality in the TBT-exposed treatments relative to unexposed controls. It is hypothesized that TBT exacerbates the infectious disease process and that exposed oysters succumb at lower levels of infection.