Acidity in ocean killed NW oysters, new study says
Researchers said Wednesday they have conclusive evidence that ocean acidification is at least partly responsible for killing oysters on the West Coast.
Seattle Times environment reporter
It's been eight years since baby oysters started dying by the billions at an Oregon hatchery and in Washington's Willapa Bay.
In 2009, top scientists drew global attention when they said evidence suggested the culprit might be changing ocean chemistry from the same greenhouse gases that contribute to global warming. They just couldn't prove it — until now.
Researchers said Wednesday they can definitively show that ocean acidification is at least partly responsible for massive oyster die-offs at the hatchery in Netarts Bay, Ore.
It's the first concrete finding in North America that carbon dioxide being taken up by the oceans already is helping kill marine species.
"This is the smoking gun for oyster larvae," said Richard Feely, an oceanographer and leading marine-chemistry researcher with the National Oceanic and Atmospheric Administration in Seattle and one of the paper's authors.
Said Alan Barton, another of the paper's authors: "It's now an incontrovertible fact that ocean chemistry is affecting our larvae."
In a paper published this week in the journal Limnology and Oceanography, the scientists studied the water that gets pumped from the Pacific Ocean into the Whiskey Creek Hatchery, which supplies baby shellfish for most of the West Coast's $110 million-a-year oyster industry.
Here's why: Since 2005, wild oysters along the Washington coast and at the hatchery had been dying inexplicably in their larval stages. At first the suspect was a bacterial disease, but hatchery workers soon noticed that the die-offs only occurred after high winds drew water from the ocean deep.
Unlike the complex mechanics of climate change, ocean acidification is just basic chemistry. Scientists long had predicted that as carbon dioxide from fossil fuels gets taken up by the seas, ocean waters — typically slightly alkaline — would slide closer to the acidic side of the pH scale. They just expected it would take 50 to 100 years.
But Feely and other top researchers in 2007 and 2008 had discovered that the pH of marine waters along the West Coast had dropped decades earlier than expected.
Netarts Bay naturally experiences a wide range of ocean-chemistry fluctuations, and the Northwest's regular wind-driven upwelling events are what drive nutrients to the surface, making the West Coast one of the world's most-productive marine systems. But Feely and other scientists began to suspect that deep water was the real problem.
Because deep, dark water is so far removed from sunlight and photosynthesis, it already contains more carbon dioxide than surface water. The researchers suspected that when ocean acidification from greenhouse gases was added in, the pH of water was pushed over the edge for some oyster species.
There were reasons to think they were right. The Pacific oyster, an import from Japan, is particularly vulnerable to more acidic waters. Its shells are formed from an easily eroded form of calcium carbonate and its larvae get more exposure to marine waters than those of native oysters, like the Olympia.
So, to be certain, the scientists took water from the hatchery and controlled it for temperature and bacteria and pollutants. They let oysters grow in water from the surface and water that upwelled from the deep.
But only when the wind blew and drew corrosive waters from the deep just as oysters were spawning did the shellfish not survive to adulthood.
"We'd develop the eggs and that egg development would look good, but they'd grow a little bit and two days later they'd still be the same size and two days after that they'd all be dead," Barton said.
Burke Hales, an Oregon State University chemical oceanographer and the study's lead author, said they found that the corrosive water was most dangerous just before the oysters developed their shells.
"It's not that the shell dissolved," he said. "It's that their ability to make shells was very critically affected."
The most significant part of their work, scientists said, was that they were using real marine water under normal conditions, not seawater manipulated based on computer models.
"This is not just some lab experiment," Barton said. "This is real ocean water — from today, not from some predicted future — impacting shell formation. It's a pretty important finding."
Said George Waldbusser, a professor of ocean ecology and biogeochemistry at Oregon State University: "We're not talking about something we may see a few hundred years into the future. It's now."
For now, the hatchery has been able to grow oysters again by controlling when it takes in water and by adding in calcium carbonate when needed. But the oyster industry in general is gravely concerned about the future in part because ocean chemistry problems are expected to get worse.
Not only is ocean acidification expected to grow more severe in coming years, but one predicted impact of climate change is more frequent upwelling events.
"There are things that could compound all these issues," Waldbusser said.
Craig Welch: 206-464-2093 or email@example.com. On Twitter @craigawelch.