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Can Chesapeake Oysters Evolve Their Way Out of Trouble?

The Chesapeake Bay's oyster colonies are in bad shape. But a new, disease-resistant population has emerged. Natural selection to the rescue! We hope.

When colonialists first settled in the Chesapeake Bay, oyster reefs made of old shells piled so high that they threatened to sink ships sailing into the harbor. In the late 1800s, the bay’s oyster population could filter enough water in three or four days to fill the entire Chesapeake Bay; now there are so few oysters in the bay that it would take a year for them to perform the same task. The population currently stands at one percent of historic levels.

Both state and federal governments have been stepping up their efforts to revitalize the bay’s oyster colonies. A boom in oysters would help both the bay and the people who live on it. Oysters filter water, and the Chesapeake Bay, long a dump for Baltimore’s industries, needs cleaning. And a thriving oyster population would mean more oysters available to eat, creating jobs for oyster fishermen.

Revitalizing the oyster population is not so simple, though. One group of researchers has been breeding oysters in a lab and dumping them into streams that feed the bay, hoping some of them will thrive. But new research suggests a different approach to rebuilding oyster populations: help those that are helping themselves.

Oyster fishing was once a major Maryland industry, and over-harvesting played a role in decimating the bay’s oyster population. Loss of habitat and the impact of agricultural runoff on the Chesapeake Bay’s condition also contributed. Parasites that carry oyster-killing diseases, though, hit the oysters hard. The problem began in the late 1950s, when a parasite (which likely came from Asia) infected the Chesapeake Bay. In the first years of the epidemic, oysters suffered from a 90 percent mortality rate.

But over time, some oysters have developed a resistance to these parasites. Ryan B. Carnegie and Eugene M. Burreson of the Virginia Institute of Marine Science looked at data collected over five decades and concluded that oysters living in saltier, parasite-infested areas of the bay were no longer succumbing to the disease the parasite carried, even as the population of parasites in the water increased.

The problem, as Carnegie and Burreson argue, is that restoration efforts in the Chesapeake Bay aren’t focused on those saltier areas or their hardy inhabitants. Instead, they have tended to prefer growing oysters in less salty nurseries where disease does not pose a threat. But when those oyster larvae are transplanted into the main bay, they’re usually being sent to their deaths: They have few defenses against the diseases that have been killing them off for decades.

Instead of growing vulnerable oysters in safe havens and sending them into danger, why not focus on the disease-resistant oysters? They’ve already proven they can survive in adverse conditions. More oysters means a cleaner bay, more jobs for the people that harvest them, and, assuming disease-resistant oysters taste just as good as their less evolved brethren, more fresh oysters for East Coasters to chow down on.

Picture courtesy of flickr user Chesapeake Bay Program

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