According to scientists at the Woods Hole Oceanographic Institution, 30% of the world’s carbon dioxide (CO2) emissions, known to be a leading cause of global warming, are being absorbed by the ocean. Small coincidence that over the past 50 years of global  industrialization, rising CO2 emissions have also led to a 30% increase in the average acidity of ocean surface water.

This phenomenon is just starting to attract the attention– and alarm– of policymakers and the shellfish industry.  I talked to Scott Doney and Sarah Cooley at WHOI to find out why.

How does ocean acidification happen?

When CO2 in the atmosphere combines with seawater (H2O), the molecules combine to form carbonic acid (H2CO3). This acid is weak and dissociates rapidly in basic seawater, releasing hydrogen ions. When these ions combine with the carbonate ions already present in the water to form bicarbonate, they rob coral and shellfish of the materials they need to grow their shells and skeletons.

Scientists estimate that the pH of seawater has decreased by about 0.1 units– a 30 % decline on the logarithmic pH scale– and could decline by 0.3-0.5 units more in the next 100 years, as CO2 levels rise. Over time, they warn, the ocean’s ability to absorb CO2 could diminish the development of coral reefs and marine organisms with calcium carbonate shells, with side effects reverberating throughout the ecosystem.

Scott Doney, of WHOI, explains the connection between CO2 and your favorite seafood dinner

The question is when, and where, said Dr. Doney. Using carbon emissions projections from the Intergovernmental Panel on Climate Change, he predicted that acidity levels in the ocean will double by mid-century, and carbonate ions could decline by half.

Carbon dioxide, if you look at it as a pollutant, is very long-lived, lasting from hundreds to thousands of years. It will also continue to grow through the mid-century, with no good indication that we’ll be able to stabilize it.  We’ve now increased atmospheric carbon dioxide to a range that hasn’t been seen since 800,000 years ago,  judging from ice cores.

-Scott Doney

In a 2008 paper, Drs. Cooley and Doney indicate that bivalves, such as scallops and oysters, would feel the effects of acidification more heavily than sea urchins or crustaceans, such as lobsters, shrimp, and crabs, due to their use of a more soluble form of calcium carbonate in their shells. The effects of acidification on fish is not known, but should be studied, Dr. Doney said.

“There’s no indication that this will destroy sea life, but it certainly will diminish and dislocate some species,” he said.

Calling for additional research into the socio-economic, as well as biological and political ramifications of ocean acidification, Drs. Doney and Cooley, with WHOI marine policy specialist Hauke Kite-Powell, are investigating the impacts on the shellfish industry in the Northeast.

The economic effects of ocean acidification will be felt locally, the scientists say. In New Bedford, the top American port for shellfish, they found:

• By 2060, a 25 % loss in shellfish populations would decrease landing revenues by $67 million a year, or $2.2 billion
• Losses in primary revenue from commercial harvests—or the money that fishermen receive for their catch—could add up to as much as $1.4 billion within 50 years
• In comparison, a 25 % decrease in the seafood employment sector contributed to a dramatic economic decline from in New Bedford from 1992 to 1999, when 20 % of residents were living below the federal poverty level

The Bigger Picture

Dr. Doney’s research also takes a look at the global picture, especially at areas of the developing world that are dependent on viable fisheries.

“As with so many aspects of environmental degradation, the Third World is often hit hardest, and is the least resilient,” he said. “We want to make the connections with fishing communities and how they can adapt.”

Acidification could be the death blow for coral reefs, which are already impacted by pollution and overfishing, Dr. Doney said, which will have an impact on coastal erosion, fish habitat, and tourism.

Regions that are impacted by acid rain and nutrient runoff might already be experiencing the effects of acidification, he added. While a connection between nitrogen loading and acidity has not been thoroughly studied, Dr. Doney warned that algal blooms from excess nitrogen release CO2, “an unfortunate synergy” that could occur on Cape Cod.