SEATTLE — Oyster growers in the Pacific Northwest have already been stung by changes in ocean chemistry linked to greenhouse-gas emissions.
Now, a new study led by Seattle researchers finds communities in Southwest and Southeast Alaska that rely on the sea for food and jobs are also likely to be hit hard over the coming decades.
The analysis, published this week in the journal Progress in Oceanography, is among the first to examine the potential social and economic impacts of ocean acidification — sometimes called global warming’s twin.
Just as carbon dioxide from power plants, factories and cars diffuses into the atmosphere, the gas is also absorbed by the world’s oceans. As a result, scientists say the average pH of seawater has become slightly lower, or more acidic, since the start of the industrial era.
That effect is expected to intensify in the future — and some places are more vulnerable than others.
The Alaskan waters that yield much of the U.S. commercial-seafood catch are near the top of that list, said lead author Jeremy Mathis, of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Lab in Seattle.
Carbon dioxide dissolves more readily in cold water, and the Bering Sea and Gulf of Alaska are already naturally CO2-rich.
“It doesn’t have that far to go before it reaches this critical threshold where the water can become corrosive,” Mathis said.
That’s what scientists say occurred along the Washington and Oregon coasts beginning in the mid-2000s. Naturally low pH levels dropped even further, killing oyster larvae in hatcheries that drew water from the Pacific.
The industry solved the problem by closing intake valves when pH is low, but some companies also shifted operations to Hawaii.
Many Alaskan communities, where people live off the seafood they catch, don’t enjoy that flexibility, Mathis said. If crab or salmon populations crash, people will see their main source of protein, and economic well being, diminish.
In identifying the most vulnerable communities, the researchers examined incomes, educational levels, educational opportunities and job diversity.
They also looked at which seafood species dominate local economies and diets, and how those species are likely to be affected by changing ocean chemistry.
Red king crab, for example, appear to be very sensitive to small changes in acidity that can make it harder to build shells. In laboratory tests, larvae died at a high rate when exposed to pH levels that now occur some times of the year in the Bering Sea.
By 2100, those conditions are expected to be common. “The waters of the Gulf of Alaska and the Bering Sea and the Arctic Ocean will be corrosive to shellfish throughout the year,” Mathis said.
Salmon are less sensitive to pH, but are still at risk because of possible effects on their food. Tiny creatures called pteropods, which are eaten by a wide range of fish, are already being harmed by water corrosive to their shells along the West Coast and other places.
Many of these problems were detailed last year in a series of stories by The Seattle Times.
Drawing on existing studies of the impacts of changing pH on marine creatures, the researchers used computer models to estimate potential impacts on harvests by the year 2100. In some places, like Dillingham on Bristol Bay, they found some catches could drop by as much as 70 percent.
But Tuesday’s study contains few numbers, and no estimates of potential economic impacts. That’s because there are so many unknowns, said co-author Steve Colt, professor of economics at the University of Alaska Anchorage.
“We just don’t know enough about all the links in the chain, starting with the ocean chemistry and going through the various levels of the food chain and even getting from potential changes in fish abundance and distribution to the economic impact to communities,” he said.
Instead, the researchers calculated a relative risk index. Communities most at risk are colored red on a map — and are concentrated in the southeast and southwest portions of the state.
For example, Petersburg, an island community in Southeast Alaska where many Washington-based fishing boats operate, ranks high in the red category because it is so dependent on seafood and has few other job opportunities.
Even without hard figures, the study is one of the first attempts to bridge the gap between scientific research on ocean acidification and its potential impacts to people, said Scott Doney, chairman of the Marine Chemistry and Geochemistry Department at Woods Hole Oceanographic Institution in Massachusetts.
“This brings it home to the level of talking to community leaders, political leaders and business leaders in Alaska to say here are the areas we think are the most vulnerable,” said Doney, who was not involved in the project.