Eighteen years ago, farmed oyster larvae began disappearing in mass die-offs, mystifying hatchery managers in the Pacific Northwest and threatening a thriving part of the region’s economy.
…
The culprit turned out to be an increasingly acidic ocean, and research efforts to solve the mystery have propelled Washington State to the forefront of the world’s efforts to understand and offset the shifting chemical composition of the seas.
Now, the global race against ocean acidification is intensifying as carbon dioxide levels in the seas increase. A recent study found that the world’s oceans crossed a “planetary boundary” in 2020, and warned that things were worse than previously thought. Researchers said the deteriorating conditions could “result in significant declines in suitable habitats for important calcifying species,” including coral reefs and bivalves.
“We are seeing a very significant change in the rate of acidification,” said Dr. Richard Feely, a chemical oceanographer with the National Oceanic and Atmospheric Administration in Seattle who has been studying the problem since it first surfaced, and an author on the recent paper. “The rate of change has shown much faster change over the last 50 years than it did over the previous 200 years. The expectation is, as we continue to release carbon dioxide into the atmosphere, that rate will continue to increase.”
…
Operations at Taylor Shellfish farms.
And as the rate of acidification rises, scientists are considering drastic, controversial options to try to stem the damage that is weakening the skeletons of coral reefs, the habitats of millions of species and the shells of bivalve animals and zooplankton, essential to the marine food chain.
One of the earliest successful remedies was the introduction of sodium carbonate, to the seawater in the hatcheries. Now, experts are exploring much more extensive countermeasures: adding minerals along shorelines to wash alkaline water into the sea; building high-tech facilities that strip acid out of the ocean; and breeding new kinds of oysters resistant to higher acid levels.
…
Without mitigation, ocean acidification will have a significant impact on the shellfish industry and on consumers, according to a government study published in 2020. Nearly all of the oysters consumed by Americans are farmed.
…
Research has shown that acidification occurs from two sources along the West Coast. As humans pump carbon dioxide into the atmosphere, the amount taken up by the oceans increases. Some 30 percent of the carbon emitted during the industrial era has been absorbed by the oceans.
The California Current — cold, nutrient-rich water that flows from the north Pacific along the west coast to Mexico — is the second source of carbon. During the spring and summer, winds blow surface water away from the coast, and it is replaced by deeper, cold, nutrient-rich water. This water is one of the keys to the productivity of oyster beds here.
But decaying vegetation in the water also produces carbon dioxide, contributing to much higher levels of acidification when the California Current upwelling makes its seasonal appearance. A study published in 2019 found that the waters off the West Coast were acidifying faster than anywhere else in the world.
…
Acidification changes the ocean’s chemistry, specifically the saturation point of the two main minerals needed to build oyster shells: calcite and aragonite, a form of calcium carbonate. If the oyster larvae do not have sufficient aragonite, they either starve or succumb to predators.
“The lethal effects on shellfish really occur in the larval stage,” said Terrie Klinger, a professor of marine ecology at the University of Washington and co-director of the Washington Ocean Acidification Center.
Early on, growers and scientists built monitoring stations at the hatcheries so that they could respond to rising levels by injecting a buffer of sodium carbonate, reducing the acidity. Oyster farms are now moving nurseries to less acidic waters when possible.
…
But the future of oyster farming is uncertain. “The concern in the years ahead is that the ocean chemistry conditions are going to get worse and affect the animals on our farms in the ocean where we don’t have the ability to treat the water like we do in the hatchery,” Mr. Dewey said.
Another possible complication for the commercial farms concerns the Pacific oyster, which was introduced to the region from Japan in the 1920s because it was easy to grow. “There is speculation but no clear evidence that the Pacific oysters favored by the commercial industry are more sensitive to acidification because they evolved in a different setting where they were less likely exposed to corrosive waters associated with west coast upwelling,” said Jan Newton, an oceanographer and co-director of the Washington Ocean Acidification Center at the University of Washington.
Researchers have also found that domesticated oysters may have lost some of their ability to evolve in response to changing ocean conditions.
“There are two effects that are important to marine organisms,” Dr. Feely said. “One is the changing temperature itself, and the other one is acidification. With the larval stages of organisms, the combined effects of acidity and temperature effect is worse than any one of the two effects by itself.”
Treating water in the oyster hatcheries is merely a stopgap measure. Aside from shellfish, acidification is taking its toll on other sea life, including tiny pteropods (sea slugs and snails) and krill. That is causing a decline in food sources and critical nutrients for salmon and other fish.
Researchers have documented the disintegration or even lack of formation of shells on pteropods, and have observed krill having difficulty forming shells.
Mussel shells also appear to be growing thinner, as do those of Dungeness crabs, according to a recent study.
Research has also shown that acidification affects the sense of smell of crabs and other marine creatures, hampering their ability to locate their prey.
…
Researchers are exploring other ways to adapt to changing waters. They are breeding oysters that may be more resistant to acidic waters. Farmers are considering the possibility of natural refuges to grow oysters, including planting thick stands of eelgrass that soak up carbon dioxide near the farms.
…
Jim Robbins, The New York Times, 7 July 2025. Full article.
