Researchers Find Link in Oyster Deaths

It’s no secret that pearl oysters can easily fall victim to pollution and changing water temperatures, but a recent study suggests that changes in water temperature can make oysters even more susceptible to pollution.

The study, which was conducted on non-pearl-producing oysters in the eastern waters of North America, found that even relatively low levels of heavy metal pollution can interfere with the oysters’ metabolic processes. To add to the dilemma, the effects of this pollution become particularly notable when coupled with high seasonal temperatures. The combined effect is strong enough to lead to fatal weakness and disease, which helps to explain documented oyster declines in the wild.

The researchers, a team from the University of North Carolina led by ecophysiologist Inna Sokolova, investigated both the heavy metal cadmium and temperature, finding that independently they decrease the efficiency of the oyster’s mitochondria — the place where stored food is turned into the energy living cells run on. Cadmium can also cause an increase in the production of reactive oxygen species — dangerous metabolic by-products — while higher temperatures hamper the cellular processes that normally prevent the compounds from causing damage.

“We have looked at oysters’ metabolism, and have found out that their respiration rate increases when they are exposed to cadmium at environmentally relevant levels, as the organism spends more energy on basal maintenance,” Sokolova said in a release.

“Metabolism also increases when they are exposed to higher temperatures. At some point, when they are exposed to both cadmium and higher temperatures, their metabolism can not go up any more and they start dying because they have hit the maximum level.”

Even if certain levels of pollutants have been determined to be tolerable, and some oysters have evolved to handle warm water temperatures for a few months, the combination of the two pushes the oysters to a crisis point where any further change can make their survival unlikely. Current environmental stresses on oysters might be partially responsible for recent outbreaks of disease that have already decimated many eastern oyster beds.

“Metabolic dysfunction can certainly contribute to disease susceptibility,” Sokolova said. “A host-parasite relationship is always a two-sided story, and the outcome is dependent on the invasiveness and abundance of the parasite and the host’s ability to ward the parasite off.”

Posted: January 4, 2007

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