Three hours north of Boston, the Damariscotta River winds for about 15 miles connecting a fresh water lake to the Maine Coast. Ocean water wins out: the river’s salty. Ideal, it turns out, for oysters. About 80 percent of Maine’s oysters are grown here.

“It’s been a wonderful career,” said Bill Mook, who started growing oysters on this river 33 years ago. “I mean, it’s a gorgeous place.”

He’s sitting on a boat next to one of his leases, a place where flat metal cages form a kind of flotilla in the river. Inside, thousands of tiny oysters are maturing.

Oyster hatchery
Inside this hatchery, oyster growers use an antacid to make the river water less acidic.
Stephanie Leydon WGBH News

The water here is considered pristine, but about ten years ago Mook noticed the impact of an invisible change. Microscopic larvae, which grow inside the hatchery in huge tanks of river water, were failing to form a shell. His business was in jeopardy.

“It was a big problem. We were distraught,” recalled Mook. “We were pulling our hair out trying to figure out what was going wrong.”

Oyster growers from the West Coast — who were hit hard by the same thing years earlier — offered an answer: ocean acidification. It’s the process where carbon dioxide is absorbed in the water and, as the name suggests, makes it more acidic: too acidic for oyster larvae to grow a shell.

“Because of ocean acidification, we now have to buffer the water. It’s like putting Tums in the water. It’s putting antacid in the water,” said Mook.

Because of ocean acidification, we now have to buffer the water. It's like putting Tums in the water. It's putting antacid in the water.
Bill Mook, Mook Sea Farm

Problem solved inside the hatchery. But out on the river, where the oysters grow to full size, it’s more complicated. Mook keeps a careful eye on his crop. He pulled a metal basket full of oysters on board the boat. The edges are razor sharp, in a few months they’ll be ready to sell.

“We’re not seeing any effect so far in how long it takes for them to get to market size,” said Mook. “The big question I have is whether the shells are becoming thinner.”

Ocean acidification works slowly. Mook is trying to stay ahead of changes with help from a University of New Hampshire research team. They’ve developed a water-acid monitoring system that fits inside a black box. The team uses that same black box technology to monitor water conditions around the world. Everything from coral reefs to aqua-culture operations, like Bill Mook’s oyster farm, could be vulnerable.

Maine oysters
Oyster farmer Bill Mook is constantly monitoring the growth of his oysters.
Stephanie Leydon WGBH News

“We see coral reefs that are stating to slow down the rates of growth in Puerto Rico,” said Joe Salisbury, a UNH associate professor of oceanography. “We know that aquaculture is stressed and heroic measures have been made to continue to really make it profitable.”

We know that aquaculture is stressed and heroic measures have been made to continue to really make it profitable.
Joe Salisbury, UNH associate professor of oceanography

Salisbury said collecting enough data to understand the full impact of ocean acidification will take years. But the black box also supplies real-time information, which could help Bill Mook make immediate changes to his business.

“I would like to have some warning and be able to adapt before there’s a problem,” said Mook. “I’ve spent over half my life building this business up and I would like it to continue more than just after I retire.”