Shellfish harvesters plagued by acidic ‘dead muds’

They’re called dead muds.

Rising levels of carbon dioxide in the atmosphere combined with unregulated nitrogen pollution are having a deadly effect on Maine’s shellfish, some researchers say.

Scientists are starting to measure the impact of increasingly acidic waters on coastal organisms, and what they’ve found is alarming. Formerly fertile shellfish flats are becoming uninhabitable wastelands of dreck.

The phenomenon is another threat to Maine’s shellfish industry, estimated to be worth $60 million annually.

“They call them dead muds,” said Mark Green, an oyster grower and marine science professor at St. Joseph’s College in Standish. “The darker muds and sulfur-rich muds don’t have any clams, and those are the flats that have lower pH levels. Places where historically there have been great harvests that supported clammers for decades, you now see water quality changes that are reflected in the mud.” The more acidic the water, the lower the pH.

In these places, researchers aren’t finding dead or unhealthy shellfish. They’re finding nothing at all. It is a complete eradication.

“If you put a larval shellfish in a mud flat that has a pH level of 6.8 or 6.9, you won’t find it 24 hours later — it’ll totally dissolve,” Green said. “It’s well documented now that we see pH levels that are causing larval shellfish to die, and in relatively large numbers. And the pH projections in the future are [much more acidic than] what’s been seen in laboratories to cause massive die-offs.”

Dean Doyle is a longtime shellfish harvester based out of Phippsburg. He said clammers are quick to promote practices that sustain their industry, such as seeding clams in the mud flats to cultivate future populations for digging. But Doyle, who said he has turned to foresting for additional income in the absence of reliable shellfish harvests, said muds like those described by Green are hopeless. And they’re growing.

“We’ve lost huge amounts of area,” Doyle said. “We can’t even keep areas that we seed. They just disappear. They just dissolve away. Areas where I used to dig 2 or 3 bushels, I can’t find a single clam now. [Clamming] is not even a full-time job anymore in my town. It’s not like it was 10 or 12 years ago.”

Denis-Marc Nault, a biologist with the Department of Marine Resources, said he’s aware of the concern over high acidity in clam flats, but with a staff of just two people to watch over nearly 150,000 acres of intertidal flats, the state hasn’t been able to map out acidic trouble areas or conduct enough studies to be sure acidity is causing the die-offs in places where clammers are seeing them.

“We are looking at it,” Nault told the Bangor Daily News. “We’re interested in it. I do have areas where I can set clams and they grow just fine, but I have other areas where the clams struggle with shell erosion or a loss of larva. Is it acidification? Is it a drop in the pH in the mud itself? I don’t know.”

Nault said changes in salinity can be deadly for young shellfish as well, and said he and the one other department biologist assigned to monitor Maine’s flats are stretched too thin to do the comprehensive research necessary to determine how pervasive the dead muds are.

“It’s something we think about,” he said. “It’s definitely a concern.”
Acid oceans

Conversationally, the notion that Earth’s oceans are becoming more acidic is often lumped into a larger discussion about climate change, said Joseph Salisbury, a researcher in the University of New Hampshire‘s marine program and a South Portland resident. But unlike the politically volatile subject of global warming and its potential causes, Salisbury said, there’s no such debate about ocean acidification.

“We’ve seen carbon dioxide in the atmosphere go from 200 parts per million up to 392,” Salisbury said. “It’s almost doubled. Some people may argue that this does not affect global warming, but there’s no question there’s an increase in carbon dioxide in the atmosphere — and it has caused an increase in the ocean’s acidity.”

Adding carbon dioxide to the ocean adds to the water’s concentration of hydrogen ions, increasing its acidity. Green said the Earth’s oceans absorb more than 21 million metric tons of carbon dioxide each day.

“There may be controversy surrounding global warming, but there’s no debate about the fact that the ocean is becoming more acidic,” said Paul Dobbins, former oyster farmer and co-founder of the Portland-based kelp grower Ocean Approved LLC. “It doesn’t receive all that much coverage, because it’s not controversial, but [the ocean’s acidity is] what has all of us who are working with ocean organisms and shellfish worried.”

Casco Baykeeper Joe Payne said the pH of coastal ocean waters has decreased by 0.02 over the past few decades.

“I’ve had people say to me, ‘Well, that’s just .02, that’s tiny,’” Payne said. “Your blood and seawater are 98 percent the same. If your blood pH changed by .02, you’d be comatose. That’s what it does to the ocean.”

What Payne described as a “major problem” in the form of worldwide ocean acidification, though, isn’t the only problem for Maine’s shellfish flats.

Seth Koenig, Bangor Daily, 7 October 2011. Full article.


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