The ocean acidification caused by rising levels of carbon dioxide in the atmosphere will disrupt marine ecosystems
Scientific American (28 SEP 2012), by Lauren Morello and ClimateWire
MONTEREY, Calif. -- Move over, polar bear.
The white prowler of Arctic ice fields may now be an icon of climate change, but when it comes to ocean acidification -- the shift in ocean chemistry caused by rising carbon dioxide emissions -- it's the tiny Pacific Northwest oyster that dominates the discussion.
The little mollusk brings in an estimated $110 million for West Coast shellfish growers, an economic shot in the arm for many struggling communities in Washington and Oregon.
But today, the ongoing process of ocean acidification, fueled by man-made CO2 emissions, threatens that bounty. Scientists working with oyster hatcheries have linked recent widespread deaths of oyster larvae to periodic influxes of more acidic ocean water.
Oyster growers have developed temporary fixes for the problem, like cutting off the flow of ocean water into hatchery tanks when sensors show a pulse of acidified water is about to hit. But with a grim long-term prognosis, some hatcheries are taking more drastic steps. Washington-based Goose Point Oysters and Taylor Shellfish Farms have shifted some of their oyster operations to Hawaii.
The problem is so severe that Washington Gov. Chris Gregoire (D) commissioned a blue-ribbon panel on the topic, which is expected to release its findings next month.
A SAD STORY
"The science around our industry has already told us a sad story," said Taylor spokesman Bill Dewey. "Our fate is sealed for the next several decades. Even if we change our CO2 emission policies today and stop the assault, [scientists] have told us it's probably going to get worse for the next 50 years before it gets better."
He and other experts who gathered in Monterey this week say they fear the fate of the Pacific Northwest's oysters is the first hint of widespread disruption of marine ecosystems and commercial fisheries that is likely to result as CO2 sours the world's seas.
Oceans have absorbed roughly two-thirds of the carbon dioxide emitted by human activities since the Industrial Revolution began, leaving seawater 30 percent more acidic now than it was then. That corresponds to a drop of 0.1 unit on the 14-point pH scale scientists use to gauge a substance's relative acidity or alkalinity.
By one recent estimate, the chemistry of the ocean is shifting faster now than it has for at least 300 million years.
Scientists began studying the problem less than a decade ago, and the field has exploded. But much of the existing research looks at the fate of single species in isolation. Researchers are just now beginning more ambitious experiments to examine the fate of whole ecosystems.
"We started out with a pretty simple view, but like everything else with biology, it gets complicated very quickly," said Joanie Kleypas, a marine ecologist at the National Center for Atmospheric Research. "There's a lot of ways ocean acidification affects organisms that we didn't predict, and there's a lot of variation in those organisms."
And that makes predicting the fate of the world's fisheries in a more acidic ocean a difficult task.
"What the science needs to do is move from single organisms, to move from the lab to the field to examine the food web," said Jean-Pierre Gattuso, a biogeochemist at the French National Center for Scientific Research. "We don't know how the impacts on the base of the food web will propagate up to the top predators."
In the Pacific Northwest, scientists have discovered that oysters are most vulnerable to today's acidified water as fast-growing young larvae.
SEVERE CHEMICAL SHIFT
Some studies suggest that some strains of oysters and mussels may be better able to adapt to that chemical shift. Dewey says Taylor Shellfish Farms is already investigating the possibility of identifying ocean acidification-resistant strains as part of its ongoing selective breeding program.
But even species that appear undaunted by acidification in limited laboratory tests may not be home free.
Walleye pollock, a species that supports one of the largest and most valuable commercial fisheries in the world, appear able to cope with the level of ocean acidification scientists expect over the next century, said Thomas Hurst, a fisheries ecologist at Oregon State University.
But it's not clear whether their prey are as sturdy. Some research suggests that more acidic water shifts the balance of fatty acids in the plankton that pollock consume -- a change that could throw the fish off balance.
"There's still a lot of work to do," Hurst said. "This being one of the nation's fisheries, we can't close the book yet."
Beth Fulton, an expert in marine ecosystem modeling at Australia's Commonwealth Science and Industrial Research Organization, said it is also important to note that the world's fisheries were struggling before ocean acidification was on the horizon.
In many parts of the world, fisheries catches have declined even as demand for fish has ratcheted up.
"We're starting at a baseline where the stocks of the world are already under pressure," Fulton said. "About two-thirds of the world's commercially fished stocks are recovering from past overfishing or are still overfished."
Her work modeling the effect of ocean acidification in southeastern Australia suggests that, if humans continue producing CO2 emissions at the current rate, the region could see a reduction of up to 40 percent of its biodiversity and the average size of many marine species could be cut in half by the end of the century.
"We will still have fisheries -- if we are willing to eat different fish," she said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC.
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