Acid in seas and mudflats threatens to wipe out local shellfish populations

56 million years ago, a massive release of carbon dioxide into the atmosphere and oceans caused a monumental shift in the climate, increasing the earth’s surface temperature by 11 degrees. Meanwhile, a rapid chemical change in the ocean occurred as the gas and water formed carbonic acid, eventually causing the extinction of all of the carbonate-bearing organisms in the sea, including clams, coral reefs and plankton. But unlike the 170,000-year “Paleocene-Eocene Thermal Maximum,” the climate change event happening in 2015 is almost certainly caused by humans. And the acidification of the oceans may be occurring 100 times faster than at any other time in the last 200,000 years. At that rate, scientists say Maine’s coastal marine ecosystem may not be able to adapt to the changes fast enough.

“People call this a natural process,” said Dr. Mark Green, a marine biologist at St. Joseph’s College in Standish, speaking last month at the Gulf of Maine Research Institute. “There’s really nothing natural about what’s been happening in the past 60 to 70 years. That’s when the bulk of this anthropogenic release of C02 has happened. Over the last 35 million years, C02 has never been this high.”

It’s estimated that humans emit about 11 billion tons of carbon dioxide into the atmosphere every year, with 90 percent of it coming from the combustion of fossil fuels and 10 percent from deforestation. According to Green, who is also an oyster farmer and nationally recognized expert on ocean acidification, ice core from glaciers in Antarctica measuring carbon levels over the past 800,000 years have shown that increased C02 levels correspond with the birth of the Industrial Revolution. Green said that naturally occurring C02 increases take between 6,000 and 7,000 years, but humans have been causing the same effect in less than a century – 75 percent of all of the C02 in the atmosphere has been put there since 1960. Green pointed out that about 25 percent of C02 emissions get absorbed into the ocean, and under normal circumstances it would be able to buffer all of that carbon. However, said Green, because the change is currently happening at a 100-times-faster rate than naturally occurring changes, this time it’s different.

“There’s more than enough buffer in the ocean essentially to buffer all of the C02 that we could ever produce if we dug up all of the coal and all of the tar sands and everything else and put it in the atmosphere,” said Green. “If we did it slowly, the pH in the ocean wouldn’t change or it would change very little…. The problem is that we’re putting it in too fast and so the physical buffer isn’t occurring.”

As Green explained, because carbon dioxide is a very soluble gas, as soon as it goes into the ocean, it creates the corrosive carbonic acid, reducing the pH and the carbonate ion concentration in the sea water. Because many marine organisms – like clams, oysters, sea urchins and corals – use calcium carbonate to build their shells, he said acidic oceans pose a real threat to local fisheries.

“An organism that has a shell has to work harder in terms of physiological stress to build shell,” said Green. “It’s particularly stressful if you couple it with other things like ocean warming.”

Alarming evidence of coastal acidification in Maine

Green said that the Gulf of Maine is more susceptible to ocean acidification than other regions of the U.S. because C02 is more soluble in cold water than at warmer temperatures, which makes local waters acidify at a faster rate. Researchers working with the group Friends of Casco Bay have found several barren mudflats where they believe shellfish can’t live due to increasing levels of ocean acidification. At the forum, FCB Bay Keeper and marine biologist Joe Payne said the group put out tiny clams on one flat to measure the impact of coastal acidification. Within one week, the clam’s shell already showed signs of pitting, which Payne believed was caused by coastal acidification.

On the pH scale, the lower the number, the more acidic the water. At the start of the Industrial Revolution, Green said that the pH in the oceans was at 8.2 globally and now it’s down to 8.1, which is also about the same level as in the Gulf of Maine. According to Green, lab tests have shown some juvenile shellfish completely dissolve in water under 6.8. Payne said his group had found pH levels on Casco Bay mudflats as low as 6.4. He said further tests of local mudflats have found that the pH levels increase at the higher tide points, but drop at lower tide points.

“This correlates to what the clammers are saying,” said Payne. “Clammers generally don’t clam on the whole flat anymore. They only clam up high and they say the clams have all moved up high. Before they would just walk over that zone and clam in the mid and the lower, but they’re not finding clams there anymore.”

Payne pointed to one survey in Brunswick that found 40 percent fewer clams on local flats from one year to the next. Although he noted that the voracious green crabs have contributed to the loss of clams, ocean acidification is likely also a factor.

Local legislators call for action

Last month, a special task force of scientists and policy makers, created through legislation sponsored by Rep. Mick Devin (D-Newcastle), released a report on ocean acidification along with a list of policy recommendations.

“While Maine’s marine environment is a complex ecosystem and there is much we don’t know about ocean acidification, existing scientific data shows that by far, the greatest contributor of open ocean acidification is carbon dioxide and that nutrient and C02 runoff from land-based point and nonpoint sources are additional drivers of acidification of Maine’s estuary and near shore waters,” the report stated.

While reducing fossil fuel consumption is a global challenge, the 16-member state commission stated in its final recommendations that there are also areas where the state and local municipalities can take the lead on mitigating acidification. Task force member Sen. Chris Johnson (D-Lincoln County) said that eliminating potential sources of nutrient run-off and remediating untreated wastewater discharges that lead to acidification would be a start.

“We don’t just have the C02 driver pushing from the air,” said Johnson. “We have it happening locally over our clam flats, and we can take a lot of steps to reduce nitrogen going into the water.”

Johnson has submitted a number of bills addressing nutrient run-off and discharge, such as a bill to fund a program to help low-income people replace their overboard discharge systems with fully engineered septic systems. Another bill would create a farmland restoration program that would help farmers fix drainage issues to avoid nutrient run-off into waterways.

Most importantly, Johnson and Devin want to create an ongoing ocean acidification commission to identify, study and prevent the effects of coastal and ocean acidification on commercially harvested marine species. The commission would have the authority to advise on matters relating to ocean and coastal acidification as well as to respond to advances in research. Payne added that he would like other conservation groups to help gather more data up and down the coast to get a more comprehensive picture of how acidification is impacting the region.

“It would help us focus if we knew where the worst problems were,” said Payne. “If you’re seeding clams on the flats, what use is that if the pH on that flat is 6.4 or 7? It would be good to know the best flats to seed from a pH point of view.”

Nevertheless, Green said that if current trends continue, the ocean could one day become uninhabitable to many different marine organisms and that by 2070 corals could become extinct.

“The ocean has acidified more rapidly than it has in millions of years,” said Green. “The whole issue with that rate of change is that the evolutionary changes of natural selection take time. The big question is can an organism . . . adapt to a rate of change that it has never seen before.”

Andy O’Brien, The Free Press, 22 January 2015. Article.

1 Response to “Acid in seas and mudflats threatens to wipe out local shellfish populations”


  1. 1 olgaanghelici 26 January 2015 at 14:30

    It is unfortunate that the terminology used here is misleading. The definition of “acidic” in the Oxford English dictionary is “having the properties of an acid; having a pH of less than 7″. Despite the process of ocean acidification, the oceans are alkaline (pH higher than 7) and will not become acidic in the foreseeable future. Hence, the “acid” or “acidic” should not be used when referring to seawater. Note that there are few exceptions, seawater can be acidic in the immediate vicinity of CO2 vents or in purposeful perturbation experiments.


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