Gulf oysters face less immediate danger from ocean acidification than northern bi-valves, study says

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Don’t break out the Tabasco sauce to celebrate just yet, but oysters in Mobile Bay and other estuaries along the Gulf of Mexico are facing less danger from ocean acidification over the next few decades than bi-valve molluscs (oysters, clams, mussels, scallops) in colder water, according to a new study titled “Vulnerability and Adaptation of U.S. Shellfisheries to Ocean Acidification.”

Robert 'Bubba' Morrison shows off his morning catch of oysters at Cedar Point in Coden, AL on Dec. 16, 2014

Robert ‘Bubba’ Morrison shows off his morning catch of oysters at Cedar Point in Coden, AL on Dec. 16, 2014

The study, published this week in the peer-reviewed journal Nature Climate Change, examined bi-valve fisheries throughout the U.S. to predict the likely impacts of ocean acidification, which can impede the molluscs’ ability to grow hard shells.

Robert 'Bubba' Morrison shows off his morning catch of oysters at Cedar Point in Coden, AL

Robert ‘Bubba’ Morrison shows off his morning catch of oysters at Cedar Point in Coden, AL

While oysters in the Gulf of Mexico were not likely to see as much acidification in the next few decades as coldwater areas, the area rated higher than most in terms of social vulnerability if those thresholds were reached. A high level of dependence on a single species puts the area at greater risk of fishery problems, said Lisa Suatoni, Oceans Program Senior Scientist for the Natural Resources Defense Council and one of the study’s four primary investigators.

“Our analysis shows acidification will harm more than ocean creatures,” Suatoni said. “It will have real impacts on people’s lives. It will pinch pocketbooks, it will put livelihoods at risk, and it will alter the fabric of communities all across the country.”

Ocean acidification occurs as seawater absorbs carbon dioxide from the atmosphere, changing the pH of the water. As the concentration of CO2 in the atmosphere increases, the pH of seawater drops, making it more difficult for bi-valve molluscs to survive.

According to the National Oceanic and Atmospheric Administration, about 25 percent of man-made carbon emissions are absorbed through seawater, causing measurable changes in seawater chemistry.

The NOAA paper states that “Initially, many scientists focused on the benefits of the ocean removing this greenhouse gas from the atmosphere. However, decades of ocean observations now show that there is also a downside — the CO2 absorbed by the ocean is changing the chemistry of the seawater.”

Because this absorption occurs faster in cold water, the study’s authors estimate that waters in the Gulf of Mexico will not drop to unsafe pH levels for oysters until after 2099. This is in stark contrast to fisheries in Alaska, and the Pacific Northwest, where pH levels have already dropped enough to inhibit shell growth. According to the study, acidification has already cost Pacific oyster fisheries $110 million, as it has become especially difficult for young oysters to take hold and develop in the more acidic waters.

Of course, ocean acidification is just one of many threats to oysters in Mobile Bay. Nitrogen pollution from agricultural runoff and declining water quality from untreated storm water and sewage all cause their own havoc on oyster populations.

“That’s really where the Gulf states’ risk comes in,” Suatoni said. “The nutrient pollution can change the ocean chemistry too, on top of the broader acidification due to carbon emissions.”

In the Florida Panhandle, decreasing freshwater flow from the Apalachicola River is being blamed for the near-total collapse of that area’s oyster fishery.

Nature Climate Change is produced by Nature Publishing Group, which publishes dozens of scientific journals on a wide range of topics. The shellfish study was conducted at the National Socio-Environmental Synthesis Center, which is funded through an award to the University of Maryland from the National Science Foundation.

More information on the study is available at the NRDC web site.

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