The increasing acidification of the oceans is measured in pH units, but its impacts on people will be measured in dollar signs, says Sarah Cooley. Commercial and recreational fishing, tourism, the protection of shorelines by coral reefs—all could be harmed by ocean acidification that is already well under way. Not to mention the hard-to-quantify-but-significant cultural and lifestyle changes that communities will have to make to adapt to changing marine ecosystems.

In other words, ocean acidification is not just a problem for corals and other marine life. It has the potential to change the way humans feed themselves, earn their livings, run their communities, and live their lives.

“What goes around comes around,” said Cooley, a postdoctoral researcher at Woods Hole Oceanographic Institution (WHOI). “Ocean acidification is definitely an anthropogenic problem [resulting from human activities] but it will come back and influence human communities.”

A marine chemist by training, Cooley sought a way after graduate school to apply her scientific know-how to socioeconomic problems. Working with WHOI marine chemist Scott Doney and Hauke Kite-Powell from the WHOI Marine Policy Center, she is trying to predict what ocean acidification will do to the marine resources that people living in New England, or western Africa, or island nations depend on, and she is looking toward what we can do to prepare for those changes and perhaps mitigate the worst of them.

“We’re working on ways to put a dollar value on the potential losses that could occur due to ocean acidification, so we can go to policy-makers and say, ‘It’s going to cost X many dollars in lost jobs and lost fishing revenues, but if we do Y money’s worth of planning now, we’ll be in good shape,’ ” she said.

Shell game

Like climate change, ocean acidification is a global problem that results from the enormous increase of carbon dioxide, or CO 2 , released into the atmosphere, primarily from burning fossil fuels. Although ocean acidification and global warming stem from the same source, they are different problems, said Cooley; acidification is a matter of simple chemical reactions that have been understood for more than 100 years. Excess CO 2 in the air dissolves in seawater and forms carbonic acid and, through a series of other reactions, reduces the amount of carbonate in seawater.

That is bad news for many of the so-called calcifying sea creatures that use carbonate and calcium to build their shells or skeletons. “The waters are becoming less and less welcoming for shelled organisms,” Cooley said.

Experiments done at WHOI and elsewhere show that in seawater containing high levels of CO 2 ,corals have difficulty making new skeleton and may have existing skeleton dissolve away; many calcifying plankton struggle; mollusks such as oysters and scallops find it harder to build and maintain shells; and juvenile mollusks grow more slowly and have more abnormalities and lower survival rates. Among calcifying organisms, only crustaceans such as crabs and lobsters appear to tolerate low carbonate levels; some even make thicker exoskeletons under such conditions. On the whole, though, more acidic seas and lower carbonate levels could spell trouble for hundreds of species, the ecosystems they belong to—and the human communities that depend on them.

‘Not just a dollar thing’

In a paper in the December 2009 issue of Oceanography, Cooley and her coauthors described how ocean acidification could endanger some “ecosystem services”—the benefits to human societies provided by healthy ecosystems. Coral reefs, for instance, bring tourism income, protect shorelines from erosion, and provide habitat for fish that may be the main source of protein for local people.

Trying to put a dollar value on the benefits provided by coral reefs is difficult, said Cooley. “If my property doesn’t get destroyed by storms because the reef is there, does that save the entire property value? How do I count it over time? Do I amortize it? It’s a squishy thing to value.”

Squishy or not, one thing is certain: The figure is very, very high. Cooley found that the worldwide value of shoreline protection by coral reefs has been estimated at $9 billion a year; shoreline protection plus reef-supported fisheries was valued at $30 billion a year.

For island nations, the exact figure could be less important than the proportion of the economy that depends on the reefs. In 2006, direct income from coral reef tourism provided 15 percent of the gross domestic product of the Caribbean island of Tobago. Add indirect income—“dinners tourists ate, tchochkes they bought, umbrella drinks they bought”—and the total comes to 30 percent of the GDP. “Without that [reef tourism], the economy of Tobago would be one-third smaller,” Cooley said. “And how many people would be out of work?”

Healthy reefs and mollusk populations also are a key element in the cultures of many island and maritime societies. “Quality of life is not just a dollar thing,” Cooley said. “Even if we can’t put this into an equation, there’s still an intrinsic value that we need to preserve.

“Think about coming to Cape Cod. You go into every gift shop, and there’s the little shell-related doodads. If [in the worst-case scenario] there’s no more scallops because they’ve all been acidified, well then there are no more shell-related doodads, and we will have lost something on the Cape.”

People, protein, and pressures

Cooley found that ocean acidification’s likely impacts on the seafood industry are easier to predict. According to the Food and Agriculture Organization of the United Nations, the first-sale value of ocean fisheries worldwide was more than $91 billion; aquaculture of marine organisms generated another $79 billion.

Although the oceans are global, ocean acidification isn’t uniform, and its effects are not the same everywhere and on every species. Fisheries that depend heavily on mollusks, such as those in New England, would likely be hit harder. Fisheries in Hawaii and Alaska should be less vulnerable, because mollusks make up a tiny fraction of the catch there.

Then again, Cooley said, the finfish catch may also decline, because many of the fish we like to eat, such as haddock, halibut, herring, flounder, and cod, depend heavily on mollusks for their own nourishment. Even top predators, the animals that eat the haddock, herring, and cod, could be affected. Swordfish, tuna, shark, and salmon are on that list.

Cooley said ocean acidification might be especially harmful to island nations and parts of the developing world where seafood is a major source of protein. Established models show that carbonate will become increasingly scarce in the oceans over the next 90 years, squeezing most calcifying organisms into a shrinking zone of tropical waters where carbonate levels will be highest (though still much lower than today’s levels). Working with estimates of human population growth and food needs, Cooley determined that tropical regions will come under simultaneous stresses from ocean acidification and increasing demand for dietary protein. These stresses occur in combination with other environmental pressures, such as temperature rise, watershed changes, and pollution.

“We’re layering pressure upon pressure, and as a result, in 20 years or 30 years—within our kids’ lifetime—things are not going to be the same any more,” said Cooley. In particular, “more people may be going hungry.”

Coping with the changes

Ocean acidification won’t lead to empty oceans, Cooley said. Some animals will tolerate higher acidity; some may even thrive on it. But there will probably be fewer species overall, and the mix of species in a given locale will almost certainly change. Already, along the coast of Washington state, upwelling currents have brought more acidic water from offshore into near-shore areas and are suspected to have contributed to a drop in shellfish hatchery yields. At the same time, in a nearby coastal area, a pH decrease of about half a pH unit was associated with a shift from a thriving community dominated by mussels and calcifying algae to one dominated by seagrasses, non-calcifying algae, and invertebrate species that don’t make shells—and that humans don’t like to eat. Similar changes have been observed elsewhere.

“The world is probably going to march on without these species, but it might be darn uncomfortable” for us, forcing our economic and cultural systems to change, she said. “The [natural] communities are going to be very, very different. And different might be OK—maybe. There still is an ecosystem to be had. But a lot of the things that we really enjoy, that our communities depend on, are not going to be there. We may be able to find other awesome things about the new communities, but chances are, the options will be limited.”

The only long-term remedy for ocean acidification is to reduce the amount of CO 2 we discharge into the atmosphere. That will involve the same sorts of actions touted to combat climate change: conserve energy, use renewable energy sources, and so forth. But, Cooley said, even if we were to end CO 2 emissions tomorrow, there is so much already in the atmosphere that the oceans would continue to acidify for centuries to come.

In other words, we have no choice but to deal with ocean acidification.

“We need to make adaptations first, as we look toward [longer-term] solutions,” Cooley said. One example, she said, is establishing and maintaining marine protected areas that provide refuges for species that might be under a number of stresses. Another is to shift from single-species to ecosystem fisheries management strategies—for example, to focus less exclusively on managing one species, such as cod, and instead consider the many factors, such as weather, human-caused pressures, and interactions with other organisms, that affect the ecosystem where the cod live.

Aquaculture operations, which could become a major source of protein for human communities, could begin cultivating species that are fairly resistant to ocean acidification; or they could join forces to adjust the pH of ocean water brought into their facilities.

“I think it’s feasible if several aquaculturists were to get together now and think, ‘OK, in the next 10 years we want to do a larger facility that treats incoming water before we rear the spat. That’s going to be a better use of our resources than competing individually and some of us going out of business,’ ” Cooley said.

Global problem, regional answers

And when people are put out of work by ocean acidification and other pressures on ocean ecosystems, said Cooley, “we need to have community measures in place to retrain them and help them move into [jobs] that are equally valuable for themselves and the community.” If a person who has lost his maritime job “is flipping burgers or greeting people at a big-box store, is he going to be a happy guy? No, because he went into fishing as a career because he loved the water and he loved doing that. And some kind of dramatic shift from what his traditional role has been may not be all that satisfying to him.”

Any proposed strategies will have to be regional, because impacts from ocean acidification are regional, said Cooley. Policy-makers and communities in each locale will have to ask, “How are we going to manage our fisheries in the face of this additional pressure? There’s definitely no one-size-fits-all answer, unfortunately.”

Cooley said she’s glad communities and policy-makers are starting to think about ocean acidification.

“Our ultimate goal is to talk to people about ocean acidification and how it might affect their endeavors,” she said. “One of the best currencies to do that, no pun intended, is economics. Because people always want to know when their interests are at stake.”

This work is supported by the National Science Foundation and the WHOI Marine Policy Center.