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Acidification takes growing toll on ocean life

November 25, 2009

Marine scientists in Maine and elsewhere say it threatens to do more harm than global warming.
By JOHN RICHARDSON, Staff Writer November 24, 2009 

Saint Joseph's College professor Mark Green has seen it dissolve clamshells in Casco Bay.

University of Maine professor Robert Steneck has seen coral reefs weakened by it in the Pacific Ocean.

And William Balch, a researcher at Bigelow Laboratory in Boothbay Harbor, is studying its effects on plankton from the Patagonian Shelf to the Gulf of Maine.

The world's oceans are getting more acidic, scientists say, as they absorb excess carbon dioxide, put into the atmosphere by the burning of oil, coal and gas.

Ocean acidification, known as "the other carbon problem," has not attracted the same level of attention as global warming. In fact, the oceans' absorption of carbon dioxide has widely been considered a good thing, because it takes the heat-trapping gas out of the atmosphere and slows the rate of climate change.

Now, however, marine scientists in Maine and around the world are warning that the effects of acidification are potentially more disastrous.

"In my opinion, acidification is a bigger problem than warming," said Steneck. "You're talking about complete collapse of our biosphere. You're talking about things that play these little supporting roles, like making oxygen for the planet."

About 25 percent of the carbon dioxide that goes into the atmosphere is absorbed by the oceans. That has increased acidity in the oceans by about 30 percent in the past 20 years, the scientists say. The high levels of carbon dioxide remaining in the atmosphere, and the current rates of fossil fuel use, mean the trend is sure to continue, they say.

"These are not academic kinds of things. These are real," said Steneck.

The rising acidity is changing the chemistry of the water and reducing the oceans' supply of calcium carbonate, so it's harder for marine organisms to produce and maintain shells and skeletons.

The organisms most clearly at risk include commercially valuable ones such as clams and lobsters, and ecologically vital ones such as some types of plankton that drift at the oceans' surface, feeding marine life and making oxygen.

Green, at Saint Joseph's, was one of the first researchers to show acidification's effects in coastal waters, where pollution, fresh water and other factors help increase acidity faster than it increases in the open ocean.

He started studying problems with clams and clam flats in the 1990s, "way back before anybody knew we were acidifying the ocean," said Green, who lives on Peaks Island.

At the time, predators were typically blamed whenever clams disappeared from the mud in a particular cove. Green showed that the culprit was acidity.

"A huge amount of these juvenile clams are dissolving when they hit the sediment," Green said.

At certain times of year, tiny baby clams, which are called spat, settle into mud flats by the hundreds of thousands per square yard. A week later, in some cases, nearly all of them are gone because the mud is acidic, he said.

Green and his students have been studying acidification's effects in Mill Cove, a mud flat in South Portland. They have found that small, juvenile clams clams don't even burrow in mud that is too acidic, basically leaving themselves exposed and taking their chances with crabs and other predators.

Green has shown that he can make acidic mud flats habitable again by mixing old shells – calcium carbonate – into the sediment. "It's like adding Tums or antacids into the mud," he said.

While that won't halt acidification of the oceans, it can help keep clam flats alive and productive, he said.

Also showing the effects of the chemical changes are corals, according to Steneck at UMaine. "They're definitely showing signs of loss in density in their skeletons," he said.

Steneck, who studies coral reefs around the world and marine life in the Gulf of Maine, said he believes the acidity is already affecting organisms off the New 

England coast, including lobsters. The more energy it takes to calcify – make shells and skeletons – the less energy an organism has to avoid predators or fight off pathogens.

"It's not going to be all of a sudden we're going to wake up and corals are going to be history. It's more that we'll continually be surprised by things like diseases that you can't predict because the organisms are more stressed," he said. "I'm quite sure it's already happening."

Perhaps the biggest concern about acidification is how it may affect plankton, the tiny plants and animals that drift at the surface of the ocean. Many types, including planktonic plants that produce much of the planet's oxygen, need calcium carbonate.

"That's the bottom of the marine food web, on which all life in the ocean depends," said Balch, the researcher at Bigelow Laboratory.

"Every other breath you take is produced by phytoplankton," he said.

Balch has been tracking such plankton in the Gulf of Maine, and in oceans as far away as the Patagonian Shelf off Argentina. He has seen some drops in the abundance of calcifying plankton, but can't yet say that it's due to acidity changes.

"What we're providing is really a baseline," he said. "We have seen some decreases (in the Gulf of Maine). But, in fairness, what makes them bloom in the particular year they bloom is still up for grabs."

Balch and the other scientists said there is still much to learn about acidification, but the issue has attracted more scientific attention in the past five to 10 years. "It's been creeping up on us," Balch said.

For a long time, it was assumed that the ocean could absorb limitless amounts of carbon dioxide without changing its chemistry or harming plankton and other organisms, Green said.

"But it turns out, if you produce the quantities of carbon dioxide that we've been producing, the buffering effect is not there," he said. "When all is said and done, I think it might be the more significant problem." 

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