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THE LOCATION: Gulf of Maine

THE STORY: The Ocean, CO2 and New England Shellfish

Chad Coffin worries about Maine's mudflats. In certain spots, these low-lying coastal wetlands have become acidic enough to kill young clams. Polluted runoff, caused by elevated carbon dioxide levels and ocean acidification, a phenomenon driven by fossil fuel emissions that makes seawater more corrosive, are the guilty parties.

Chad Coffin digging for clams

Chad Coffin digging for clams.

Putting used shells back into the seafloor can buffer the acidity from this double whammy, effectively giving a Tums to the ocean. But when Coffin, who is president of the Maine Clammers Association, asked the state legislature to make the necessary rule changes to do it, they wanted to see studies that had not yet been funded.

"Ocean acidification is a deep concern, and we're interested to see if we can add any tools to our arsenal to fight it," Coffin explains. "From what little we know, this is one of the only things we have to fight back. We need a weapon. We need to know more."


The Gulf of Maine, along with the lucrative fishing banks off of Massachusetts, is incredibly rich and contains bountiful fishing grounds. But colder, high-latitude waters are naturally rich in carbon dioxide. Plus, native shellfish populations already struggle to cope with nutrient pollution from farms, lawns, streets and septic systems. These nutrients fuel plant growth, producing even more carbon dioxide.

Scientists believe polluted runoff and global fossil fuel emissions are giving the region's waters a double-dose of carbon dioxide, causing greater damage than from either source alone.

With declining groundfish populations, about 80 percent of revenue from New England fisheries comes from shellfish. In lab studies, oysters, soft shell clams, bay scallops, mussels and other shellfish raised in more acidic seawater have shown they develop at a slower pace, produce deformed shells or die in greater numbers. Additionally, New England's rich maritime history brings millions of tourists to its iconic fishing communities each year.

Algae Blooms

Pollution from fertilizers and leaky sewage systems cause algae to bloom. The algae decompose and raise acidity.

Freshwater Input

More than 60 rivers pour freshwater, which is more acidic than seawater, into the Gulf of Maine.


Colder waters hold more carbon dioxide, leading to higher acidity.

Vulnerable Species

Lab studies show that many types of valuable shellfish, such as eastern oysters, hard clams, soft shell clams, mussels and bay clams, have fared poorly in CO2-rich waters.

Acidification Hotspot

Credit: Illustrations of sea life © B. Guild Gillespie / www.chartingnature.com

illustration of lobster and clams

Credit: Illustration © B. Guild Gillespie / www.chartingnature.com


The Gulf of Maine seafood and tourism industries at a glance:

  • 2nd is where Massachusetts ranks among U.S. states in value of seafood landings, bringing in $478.8 million in 2010
  • 3rd is where Maine ranks among U.S. states in value of seafood landings, bringing in $375 million in 2010
  • 4,500 Maine fishermen depend on one possibly vulnerable species – lobster
  • $13.6 billion in sales were indirectly generated by Maine's tourism industry in 2004
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