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 the Whiskey Creek Shellfish Hatchery had perished.
It took 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 that the larvae could not form their 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 — we're changing the chemistry of the oceans," said Barton, who manages Whiskey Creek, which supplies three-quarters of the oyster seed to independent shellfish farms from Washington to California.
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 even the 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 has built up in the atmosphere, primarily from the burning of fossil fuels.
By the end of the century, said French biological oceanographer Jean-Pierre Gattuso, "The oceans will become hot, sour and breathless."
He was one of 540 scientists from 37 countries who gathered 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 also have been exploring ways to restore the ocean's alkalinity through such artificial means as spreading vast amounts of limestone or other minerals on the ocean surface. It's not 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 slosh onto the continental shelf off California, Oregon and Washington. "We found corrosive water everywhere we looked, particularly off California and Oregon," he said.
A few years ago, the shellfish industry became alarmed that 80 percent of oyster larvae at hatcheries were not surviving. A strain of bacteria was initially blamed.
But after Feely found evidence of corrosive waters reaching the West Coast, industry officials asked him and other scientists if there might be a connection to the die-offs. Sure enough, 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 particularly sensitive in their first few days of life. As acidity rises in the ocean, the abundance of calcium carbonate — a mineral they need to build their shells — is gradually reduced. At extremely high levels of acidity, lab experiments show, seawater no longer provides this material and can cause existing shells of corals, snails and other animals to dissolve.
Now, the Whiskey Creek hatchery tries to balance the acidity of its waters by adding soda ash. Costs have increased and production has never fully recovered.