Bacteria targeting prized Northwest oysters

An invisible microbe that thrives in warm ocean water has undermined the Pacific Northwest's prized oyster supply, killing billions of young larvae that mature into the succulent shellfish known across the world.

The bacterium, Vibrio tubiashii, is related to another species that can sicken people who eat raw shellfish. This one doesn't bother people — it kills shellfish in their larval stage, before they latch onto rocks to grow.

An explosion of the microbe late last summer shut down an Oregon shellfish hatchery that is one of the largest on the West Coast, supplying larvae to about 70 oyster growers the way seed companies provide crop seed to farmers.

The microbe also is the likely culprit in the disappearance of recent generations of wild oysters from usually prolific estuaries such as Willapa Bay on the southern Washington coast.

"We're in a state of panic," said Robin Downey, executive director of the Pacific Coast Shellfish Growers Association, based in Olympia. "There is no other word for it."

Scientists have rushed to devise filters that can strain the lethal bacterium out of water flowing through hatcheries.

Researchers say the rise of bacteria might be tied to the same unusual ocean conditions — possibly connected to global climate change — causing the suffocating "dead zones" that have appeared off the Oregon coast in recent summers.

The bacteria, long known in coastal waters at low levels, seem to have taken off in the same areas and about the same times as the dead zones. But it's unclear what conditions have caused the bacteria to thrive.

"It's safe to say it's probably all of Oregon and parts of California and Washington," said Ralph Elston, a veterinarian with Aquatechnics in Sequim who works with shellfish hatcheries.

Oysters grow for a few years before they're big enough to eat, so those showing up in restaurants now predate the recent bacterial boom that killed young oysters. Growers predict the loss of those generations of oysters will shrink supply and probably drive up prices later this year.

"It's going to have some major effects on the industry in the next year or so," said Bill Taylor of Taylor Shellfish Farms, which hatches and grows oysters on Washington's Hood Canal and also has been hammered by the bacteria this spring. "There's not going to be enough marketable oysters to sell."

Besides oysters, geoducks grown farther north on the West Coast are at risk. Clams and mussels seem less vulnerable, though fisheries officials have noticed a lack of young razor clams along some areas of the coast.

West Coast growers produce more than $100 million worth of commercial shellfish each year, with oysters by far the largest share. Cultivated oysters are mainly Pacific oysters, originally imported from Japan and different from native West Coast oysters.

But researchers said the bacteria probably also are affecting wild shellfish.

Oyster larvae suddenly disappeared from Willapa Bay last year, said Alan Trimble, a University of Washington researcher who works at the bay. He suspects the bacteria contributed to poor reproduction of native oysters and razor clams in bays and coastal beaches.

"When the larvae die in the water column, it isn't just Pacific oysters; the others disappear also," he said in an e-mail from Namibia, where he is on leave.

That could affect the rest of the marine food chain, because many other forms of marine life eat young shellfish.