Kris Holderied, who directs the National Oceanic and Atmospheric Administration’s Kasitsna Bay Laboratory, says the ocean’s increasing acidity is “the reason fishermen stop me in the grocery store.”

“They say, ‘You’re with the NOAA lab, what are you doing on ocean acidification?’ ” Holderied said. “This is a coastal town that depends on this ocean, and this bay.”

This town in southwestern Alaska dubs itself the Halibut Fishing Capital of the World. But worries about the changing chemical balance of the ocean and its impact on the fish has made an arcane scientific buzzword common parlance here, along with the phrase “corrosive waters.”

In the past five years, the fact that human-generated carbon emissions are making the ocean more acidic has become an urgent cause of concern to the fishing industry and scientists.

The ocean absorbs about 30 percent of the carbon dioxide we put in the air through fossil fuel burning, and this triggers a chemical reaction that produces hydrogen, thereby lowering the water’s pH.

The sea today is 30 percent more acidic than pre-industrial levels, which is creating corrosive water that is washing over America’s coasts. At the current rate of global worldwide carbon emissions, the ocean’s acidity could double by 2100.

What impact it is having on marine life, how this might vary by geography and species, and what can be done about it if humans do not cut their carbon output significantly are some of the difficult questions scientists and policymakers are seeking to answer.

The decline in pH will likely disrupt the food web in many ways. It is making it harder for some animals, such as tiny pteropods and corals, to form their shells out of calcium carbonate, while other creatures whose blood chemistry is altered become disoriented and lose their ability to evade predators.

To study what is happening off the West Coast, Gretchen Hofmann, a professor of marine biology at the University of California at Santa Barbara, has recruited everyone from sea-urchin divers to Bureau of Ocean Energy Management, Regulation and Enforcement officials.

She calls it “an all-hands-on-deck moment in our country, and it’s happening before our eyes.”

The NOAA has started tracking changes in the ocean’s pH over time in eight coastal and coral reef ecosystems, ranging from the Gulf of Maine to coastal Hawaii, and is evaluating its impact on more than two dozen commercially important species, such as red king crab, summer flounder and black sea bass.

“One of the primary questions is how is the chemistry of the water changing and how variable is that change across the water we’re responsible for, which is a lot of coastline,” said Libby Jewett, director of the program.

Federal and state authorities are searching for ways to cope with a problem whose obvious solution — slashing global carbon emissions — remains elusive. A blue-ribbon panel established by outgoing Washington Gov. Chris Gregoire (D), which will issue its recommendations in November, is examining local contributors such as agricultural runoff. Federal officials and scientists, meanwhile, are trying to determine which species may be able to adapt to more acidic seas and explore what other protections could bolster fish populations under pressure.

In the 1970s, NOAA senior scientist Richard Feely and his colleagues began talking about measuring carbon concentrations in the ocean, the way Charles David Keeling had charted atmospheric carbon from a station in Hawaii’s Mauna Loa starting in 1958. Keeling pushed the oceanographer to refine his methods before taking any measurements, and Feely conducted his first transect of the Pacific Ocean in 1982.

By the late 1990s, scientists such as the National Center for Atmospheric Research’s Joan Kleypas were demonstrating that the sea’s declining pH posed a threat to marine life . At first, scientists assumed that the growing acidity of the ocean would dismantle ecosystems around the world in a uniform way, by dissolving the coral reefs that provide essential habitats and impeding the development of the smallest organisms that form the basis of the food web.

But now, scientists are beginning to tease out a more complex picture, in which some parts of the world could be more vulnerable and others may demonstrate resilience. Water from the deep ocean normally comes up and spills over the continental shelf in a process called upwelling; in the Pacific Northwest this water is increasingly acidic, killing oyster larvae that farmers are growing. Much of Alaska’s waters already have lower pH levels, because the water is colder and cold water can hold more carbon dioxide, and the water that reaches the Arctic has been circulating around the planet, absorbing CO2 along the way.

According to NOAA supervisory oceanographer Jeremy Mathis, “It doesn’t take much to push it past the thresholds we’re concerned about.”

And last year, a team of researchers led by Oregon State University professor George Waldbusser found that the pH in the lower part of the Chesapeake Bay is declining at a rate that’s three times faster than the open Pacific Ocean, partly because of increased nutrient runoff from farming and other activities. This stream of nutrients causes phytoplankton to take more carbon dioxide out of the upper Bay; as the plankton release CO2 as they move to the lower Bay, it increases carbon concentrations and lowers the overall pH.

A.J. Erskine, aquaculture manager for the Kinsale, Va.-based Bevans Oyster Co. , and Cowart Seafood Corp. in Lottsburg, Va., said they started focusing on the issue when “two years ago we were seeing production losses, and we didn’t know where it was from.”

Six shellfish hatcheries in Virginia have used state funds to conduct their first year of water chemistry monitoring and hope to do more; Erskine said they suspect nutrient runoff from the land contributes to the problem.

Oyster farmers off the coasts of Washington and Oregon were the first to see how ocean acidification threatened their business. Alan Barton, an employee at Oregon’s Whiskey Creek Shellfish Hatchery, suspected that lower pH waters were killing off oyster larvae, or spat. Working with Oregon State University and NOAA researchers, they were able to prove it was the case, and now time their intakes to ensure that their oysters are exposed to less-acidic water.

“The scientists helped provide an adaptation strategy to help that industry, and it worked,” Feely said, adding that a $500,000 ­investment in pH-monitoring equipment “saved that industry $34 million in one year,” in 2011.

But Feely and Jewett acknowledged that tackling the problem in the open ocean will be harder. Jewett said that if they can identify which species are most vulnerable, “we can try to be even more protective of them for the future” by limiting their catch.

The die-off of oyster larvae in the Pacific Northwest has implications for oyster growers in places as far away as Homer, Alaska, since they traditionally buy their spat from Washington and Oregon farms. Out on the Homer spit, a slim strip of land jutting out into Kachemak Bay, the Kachemak Shellfish Growers cooperative office now boasts a small hatchery where it hopes to produce 3 million spat this year.

“We just can’t rely on the Lower 48 anymore,” said co-op manager Sean Crosby, whose group recieved $150,000 in federal funds over the past two years to start up and run the hatchery. “Even though we’re not seeing ocean acidification in Kachemak Bay, we’re feeling its effects.”

Alaska and the NOAA are jointly funding four buoys throughout the state to monitor pH levels, while other NOAA scientists are testing how species such as surf smelt would likely gain from a lower pH because they thrive under those conditions, while others, including dungeness crab, would lose.

These species interact with each other, which is why ocean acidification could have such large ripple effects. The highly vulnerable pteropods, for example, can make up as much as 40 percent of the diet of Alaska’s juvenile pink salmon.

“When you ask why does ocean acidification matter, often we’re interested because of the fish we eat and the things we make money off of,” said Shallin Busch, a research ecologist at the NOAA’s Northwest Fisheries Science Center.

Other species, such as purple sea urchins off California’s coast, have shown some genetic capacity to adapt to more acidic conditions, in part because they are periodically exposed to corrosive waters. Hofmann described her job as seeking an answer to the question, “Will there be sushi?”

“The question is, can they adapt quickly enough in this rapidly changing environment?” Hofmann asked. “And the answer, at least in the case of sea urchins, could be yes.”