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Rising ocean acidity tips delicate balance

Los Angeles Times
Published:   |   Updated: March 18, 2013 at 06:26 PM
LOS ANGELES -

Peering into the microscope, Alan Barton thought the baby oysters looked normal, except for one thing: They were dead. Slide after slide, the results were the same. The entire batch of 100 million larvae at Whiskey Creek Shellfish Hatchery perished.

It took several years for the Oregon oyster breeder and a team of scientists to find the culprit: a radical change in ocean acidity.

The acid levels rose so high the larvae could not form protective shells, according to a study published this year. The free-swimming baby oysters would struggle for days, then fall exhausted to the floor of the tank.

"There's no debating it," said Barton, manager of Whiskey Creek that supplies three-quarters of the oyster seed to independent shellfish farms from Washington to California. "We're changing the chemistry of the oceans."

Rising acidity doesn't just imperil the West Coast's $110 million oyster industry. It ultimately will threaten other marine animals, the seafood industry and health of humans who eat affected shellfish, scientists say.

The world's oceans have become 30 percent more acidic since the Industrial Revolution began more than two centuries ago. In that time, the seas have absorbed 500 billion tons of carbon dioxide that built up in the atmosphere, primarily from the burning of fossil fuels.

By taking in that amount — more than one-quarter of greenhouse gas in the atmosphere — the oceans have buffered the full effects of climate change, scientists say: Temperatures have not risen as much as they would have, glaciers haven't melted as fast.

Yet the benefits are coming at a cost to marine life, especially oysters, clams and corals that rely on the minerals in alkaline seawater to build their protective shells and exoskeletons. The ill effects of the changing chemistry add to the oceans' problems, which include warming temperatures and expanding low-oxygen "dead zones."

By the end of the century, French biological oceanographer Jean-Pierre Gattuso said, "The oceans will become hot, sour and breathless."

He was one of 540 scientists from 37 countries who met last month in Monterey, Calif., to discuss their findings on oceans in a "high-C02 world."

The full brunt of ocean acidification won't hit for decades. But scientists say the only sure way to avoid the worst is to significantly reduce carbon emissions.

Some have been explored ways to restore the ocean's alkalinity through artificial means, such as spreading vast amounts of limestone or other minerals on the ocean surface. It's not yet clear whether either approach is realistic.

The West Coast provides a jarring glimpse of what lies ahead if trends continue, said Richard A. Feely, a chemical oceanographer for the National Oceanic and Atmospheric Administration.

Feely and a team of scientists have been tracking particularly acidic waters as they well up from the deep ocean and wash onto the continental shelf off California, Oregon and Washington. "We found corrosive water everywhere we looked, particularly off California and Oregon," he said.

The cold, nutrient-laden waters from the deep sea are naturally more acidic than surface waters. Human contributions of CO2 only add to that acidity.

A few years ago, the shellfish industry became alarmed that 80 percent of oyster larvae at hatcheries were not surviving. Initially, they blamed an aggressive strain of bacteria.

After Feely found evidence of corrosive waters reaching the West Coast, industry officials asked him and other scientists if there was a connection to the die-offs. And scientists found a link by studying the Whiskey Creek hatchery at Netarts Bay, Ore., whose larvae were bathed in acidic waters drawn in by intake pipes.

Oyster larvae are very sensitive in their first few days of life. As ocean acidity rises, the abundance of calcium carbonate, which they need to build shells, is gradually reduced. At extremely high levels of acidity, lab tests show, seawater no longer provides this material and can cause shells of corals, snails and other animals to dissolve.

Now, the hatchery tries to balance the acidity of its waters by adding soda ash. Costs are up and production hasn't fully recovered.

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