Bacteria threatens health of Northwest oyster industry

BREMERTON — West Coast shellfish biologists are engaged in a war against a species of bacteria that has been killing oyster larvae and threatening to cripple the $111 million-a-year shellfish industry.

Experts say the explosive growth of the bacteria may be related to unusual conditions in the Pacific Ocean — including a “dead zone” of low oxygen plus warmer temperatures that spring up unexpectedly.

Last fall, the Vibrio tubiashii bacteria forced the closure of Whiskey Creek Shellfish Hatchery near Tillamook, Ore., a major producer of oyster larvae. The hatchery reopened after construction of a $200,000 water-treatment system.

Vibrio tubiashii is not toxic to humans and it does not harm adult oysters.

The bacteria have taken a lesser toll on oyster production in Quilcene on Hood Canal off Puget Sound, where Taylor Shellfish Farms produces “seed” for commercial growers throughout the region.

Researchers, including Ralph Elston of AquaTechnics in Sequim, are reluctant to blame global warming, but Elston said research is needed quickly to protect oyster hatcheries.

Oyster hatcheries, which produce swimming larvae and tiny oyster “seed” for commercial shellfish farmers, serve as inadvertent incubators for the bacteria, Elston said. It also appears that natural growth is affected.

“As a number of people have said, the hatchery is like the canary in the coal mine,” Elston noted. “We might not know if all the (wild) oyster larvae were to die off one year. It would take time to figure that out.”

In Willapa Bay on the Washington coast, it appears that something has been killing the wild larvae, said Mark Wiegardt, whose family has operated an oyster business there for several generations.

“I don’t think there has been a commercially viable set for the last three years,” Wiegardt said. “At this point, it (Vibrio) is the usual suspect, but nobody has been convicted so far.”

One of the important research needs is a monitoring program to track bacterial growth and identify conditions that trigger the growth, Wiegardt said.

Elston said he has been studying the bacteria intensively since 1998, when Oregon hatcheries first experienced a major die-off of oyster larvae.

“In 1998, we had an El Nino, which brings warm ocean water up the coast,” he said. The National Oceanic and Atmospheric Administration “said it was the strongest El Nino of the century.

“What is interesting to me,” he added, “is that we had the same event last year, when we didn’t have an El Nino to explain it. There was a fundamental heating of the ocean waters in 2007.”

Elston and his collaborators hope to publish a scientific paper that explains the growth of the bacteria in terms of ocean temperature, but broader studies are needed to understand why ocean temperatures might rise unexpectedly.

“I can’t prove this is global warming, but the marked temperature increase is comparable to an El Nino year,” he said.

A low-oxygen dead zone off the West Coast, which has been blamed for the deaths of fish and crabs, also may encourage the growth of bacteria, he said. One idea is that Vibrio produce enzymes that break down the tissues of dead animals, so bacterial growth occurs in proximity to the dead zone.

These connections are not proven, Elston said, but there are plenty of reasons to study the problem — not the least of which is the economic value of the shellfish industry. If conditions are related to global warming, they are likely to increase, he said.

“Our biggest problem is that we need to have something that works,” said Bill Taylor of Taylor Shellfish Farms. “We need to be practical. This is a very complicated issue and we need real answers. We’re just shaking our heads right now.”

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