Oyster larvae hit by bacteria

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, Vibrio tubiashii, may be related to unusual conditions in the Pacific Ocean including a "dead zone" of low oxygen plus warmer temperatures that spring up unexpectedly.

The bacteria forced the closure last fall 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.

The bacteria have taken a lesser toll on oyster production in Quilcene on Hood Canal, 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. Long-term studies could address the mysteries of the ocean.

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 (natural) 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 natural 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.

U.S. Rep. Norm Dicks, D-Wash., has been working with the U.S. Department of Agriculture to obtain temporary funding to boost research until more money can be provided in the next federal budget, said his spokesman, George Behan.

Vibrio tubiashii is a relative of the bacteria that can cause illness in humans. But tubiashii is not toxic to humans and it does not harm adult oysters. It can be lethal, however, for free-swimming oyster larvae and for seed oysters under 2 millimeters (about the size of a pin head).

Elston said he has been studying the bacteria intensively since 1998, when Oregon hatcheries first experienced a major die-off of oyster larvae. Elston and other researchers found that 1998 was associated with nutrient-rich upwelling along the coast, which brings pathogens up to the surface.

"In 1998, we had an El Niño, which brings warm ocean water up the coast," he said. "NOAA (the National Oceanic and Atmospheric Administration) said it was the strongest El Niño 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 Niño 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 Niño 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.

Not all hatcheries are feeling the effects of the bacteria, said Robin Downey, executive director of the Pacific Coast Shellfish Growers Association.

"Up to this point, our hatcheries have operated fairly well," she said. "We have had a few blips, but we don't know enough at this point to really explain the problem."

Downey said news reports a few weeks ago tended to be overly alarmist, and she found herself responding to hypothetical questions from reporters.

"What I'd like to say is that we have some brilliant scientists coming together to work on this problem and find solutions. Whiskey Creek has gone to lengths that none of the others have."

The hatchery installed a $200,000 treatment system, based on filtering and killing the bacteria, removing the toxic proteins and finally replenishing the water with "good" bacteria to hold future infections in check.

Shellfish growers passed the hat and came up with $40,000 to support studies at Whiskey Creek. Researcher Alan Barton joined the effort, coming over from Oregon State University's Molluscan Broodstock Program.

Bill Taylor of Taylor Shellfish Farms in Shelton said all growers are watching the work at Whiskey Creek. While oyster hatcheries have their ups and downs, Vibrio tubiashii may have been responsible for problems that went unidentified in the past.

"Our biggest problem is that we need to have something that works," Taylor said. "We need to be practical. This is a very complicated issue and we need real answers. We're just shaking our heads right now."

Taylor's Quilcene oyster hatchery has experienced production problems not seen at the company's hatchery in Hawaii. Still, the shortage of oyster seed may begin to affect the market for shucked oysters later this year, because the company is putting more effort into the lucrative market for single ("half-shell") oysters.

"We sell a lot of seed to people all over the world," Taylor said. "A lot of people depend on us. I don't know that we will supply everyone's needs, but we should be able to supply a good portion of what people need.

"It's tough, because you know that water conditions can change overnight," he said. "It's like trench warfare."

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Information from: Kitsap Sun, http://www.kitsapsun.com/