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 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 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,” said Barton, who manages Whiskey Creek, which 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 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 taking in that amount — more than one-quarter of the greenhouse gas that has accumulated 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 otherwise, 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 only add to the oceans’ problems, which include warming temperatures and expanding low-oxygen “dead zones.”