Ocean acidification, the chemical transformation that occurs when large amounts of carbon dioxide are absorbed into marine waters, imperils Alaska's fishing-dependent economy, says a new study funded by the National Oceanic and Atmospheric Administration.

Commercial fishermen who depend on the ocean for their income and subsistence fishermen who depend on it for their diets will be harmed by the documented ocean changes, says the study, accepted for publication in the journal Progress in Oceanography.

Hardest hit among the 29 population centers in Alaska, the study says, will be communities arcing the southern coastline of the state -- in southeastern Alaska, the Prince William Sound area and the Alaska Peninsula and Bristol Bay areas.

Species most vulnerable to acidification, according to this and other studies, are shellfish, which build up calcium shells. Numerous past studies have shown that tanner and red king crab, two species important to Alaska commercial fishermen, have difficulty developing and even surviving in more acidic waters. But also at risk are salmon, which eat pteropods, tiny shell-bearing creatures.

As a result, communities dependent on shellfish harvest and salmon fishing stand to lose the most from acidification, the study says.

Less vulnerable, the study says, are bottom-dwelling species like pollock and the communities that depend on them.

Jeremy Mathis, an oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle, director of the University of Alaska Fairbanks' ocean-acidification research program and a lead author of the study, said it was different from other analyses of acidification.

Other studies have been "hard science" and "earth science," he said, looking directly in the water and at species living there.

This study focused on factors like "food security, employment opportunity, the size of the economy," he said. "This is an economic-social study," focusing on people, he said.

One surprise, said co-author Steve Colt, an economist at the University of Alaska Anchorage, was that Anchorage is among the communities with an economy at risk from acidification. Many residents of Alaska's largest city are commercial fishermen targeting species vulnerable to acidification, and those Anchorage-dwelling fishermen tended to have big catches and high earnings.

Anchorage, as Alaska's economic and financial hub, is sensitive to economic problems elsewhere in the state, Mathis pointed out.

Another surprise, said Colt, was that fishing-dependent Kodiak Island was found to be less vulnerable than expected. Colt said that hunting and subsistence harvests of marine mammals provided some diversity to residents' diets, and thus an alternative to food sources at the highest risk from acidification.

"An important strategy for adaptation or whatever you want to call it, coping, is to make sure you safeguard the resources that may not be directly affected by acidification, but may be affected by other stressors," he said.

Ocean acidification is a phenomenon paralleling greenhouse gas-driven climate change. Much of the carbon dioxide emitted into the atmosphere is absorbed by the world's oceans, and over time it has changed the water's chemistry, making it more acidic and corrosive.

A variety of physical conditions make acidification more pronounced in waters off Alaska than in the rest of the world.

"It's all about geography," Mathis said. The world's ocean currents end their cycles here, depositing carbon dioxide from elsewhere, he said. "The coastal waters of Alaska sit right at the end of the ocean conveyor belt," he said. That means carbon dioxide from the rest of the world's oceans is deposited in waters off Alaska, and it does not take much additional carbon dioxide to trigger effects.

Alaska waters are also preconditioned for acidification because cold water more effectively holds carbon dioxide than warm water, he said. "Obviously, we don't have a shortage of cold water in Alaska," he said.

More localized factors also build up carbon dioxide levels in Alaska waters, he said. Those factors include melt of sea ice, melt of glacial ice and decay of organic matter, he said.

The Alaska community study was the first of what is expected to be a series produced by the Synthesis of Arctic Research program, which is funded by NOAA and the Bureau of Ocean Energy Management.