Greenhouse gas suspected in oyster woes

The collapse began rather unspectacularly.

In 2005, when most of the millions of Pacific oysters in this tree-lined estuary failed to reproduce, Washington’s shellfish growers largely shrugged it off.

In a region that provides one-sixth of the nation’s oysters — the epicenter of the West Coast’s $111 million oyster industry — everyone knows nature can be fickle.

But then the failure was repeated in 2006, 2007 and 2008. It spread to an Oregon hatchery that supplies baby oysters to shellfish nurseries from Puget Sound to Los Angeles. Eighty percent of that hatchery’s oyster larvae died, too.

Now, as the oyster industry heads into the fifth summer of its most unnerving crisis in decades, scientists are pondering a disturbing theory. They suspect water that rises from deep in the Pacific Ocean — icy seawater that surges into Willapa Bay and gets pumped into seaside hatcheries — may be corrosive enough to kill baby oysters.

If true, that could mean shifts in ocean chemistry associated with carbon-dioxide emissions from fossil fuels may be impairing sea life faster and more dramatically than expected.

And it would vault a key Washington industry to the center of international debate over how to respond to marine changes expected to ripple through and undermine ocean food webs.

Scientists seeking to explain what’s plaguing these coastal oysters say the link to more corrosive water is strong but anecdotal. It could be just one of several factors.

But the possibility leaves some shellfish farmers uneasy about more than just their future business.

Indications that ocean acidification may already play a role in the decline of oysters are a “sign of things being out of balance, and that scares the living daylights out of me,” said third-generation oysterman Brian Sheldon.

Ruffling his 8-year-old son Jebediah’s head, he added, “For this guy.”

Pacific oysters aren’t native to Willapa Bay, but shellfish growers have farmed them here since the 1920s. It’s about the only place left on the West Coast where growers look to the wild to get their oysters.

Normally, oysters spawn in the water, producing larvae that swim and eventually attach to a hard surface — typically other oyster shells. This creates oyster seed, called a “set.” These succulent mollusks are then moved by hand throughout the bay and take two to five years to fatten up.
But somewhere between the larval stage and settling on a shell, these embryonic oysters are dying. And since only a few young have survived since 2005, “we’re running out of oysters in the bay,” said Bill Dewey, spokesman for Taylor Shellfish Farms. “Growers are scrounging for whatever they can find.”

Standing ankle-deep in sea-water on a south Willapa sandbar earlier this month, Sheldon, owner of Northern Oyster Co., watched his workers gather shellfish at low tide from one of the few places that still had some: a state “oyster reserve,” a sort of shellfish bank growers can lease and draw upon to subsidize their own crops.

For the first time since his grandfather started the company in 1934, Sheldon plans this year to spend thousands buying oyster seed — larvae attached to shells — from hatcheries, rather than counting solely on wild reproduction. He expects he’ll make only half as much as he would in a normal year.

“It perplexes me that we are still, as a country, and really, globally, denying that there is something going on,” he said.
Researchers at first blamed an explosion of Vibrio tubiashii, an ocean-borne, larvae-killing bacteria. When researchers sampled the marine waters that get sucked directly into the hatcheries from the sea, they found bacteria counts nearly 100 times above normal. Even after installing extensive microbe-killing ultraviolet water-treatment systems, larvae died.

Then they noticed the water’s pH — the scale measuring acidity and alkalinity — sometimes dropped below normal, becoming more acidic.
Seawater typically is slightly alkaline, but when oceans absorb carbon dioxide from the atmosphere — as they have by the hundreds of billions of tons since the Industrial Revolution — they become more corrosive.

Climate modelers predicted greenhouse gases would make marine waters more acidic by century’s end. They expected to notice it first in deep water. But two years ago, oceanographers Richard Feely and Chris Sabine, both with the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory in Seattle, found more acidified waters already reaching the surface.

Corrosive waters can dissolve clamshells, eat away at corals and kill fish eggs.

The Arizona Daily Star online, 21 June 2009. Article.

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