Ocean acidification – the twin of global warming – threatens sea life

The West Coast’s famously abundant fisheries are at risk as the region’s waters become more acidic, a group of scientists have warned.

The researchers, with the West Coast Ocean Acidification and Hypoxia Science Panel, this month released a report that projects dire changes to ocean chemistry and marine life, and recommends ways to avert it, including restoring kelp forests and eelgrass beds, and combating local marine pollution.

The panel, including Andrew Dickson, a professor of marine chemistry at Scripps Institution of Oceanography, convened in 2013 to study how global carbon emissions are lowering pH and reducing oxygen levels in the ocean off the West Coast.

“Although ocean acidification is a global phenomenon, emerging research indicates that the U.S.-Canadian West Coast will face some of the earliest, most severe changes in ocean carbon chemistry,” the report states.

Because of the way the Pacific Ocean circulates, the West Coast is exposed to more acidic water than other areas of the globe. Oyster production in the Pacific Northwest has already declined, as changes in ocean chemistry tamper with shell formation, and scientists warn that popular game fish and other species are also at risk.

“For some organisms, and perhaps ultimately for some ecosystems, high carbon dioxide levels where they had not previously been expected could be a problem,” Dickson said.

Disturbance of ocean chemistry is the lesser known twin to the atmospheric warming and weather changes wrought by climate change. About a third of the carbon released by humans is absorbed by the ocean, according to the report. That keeps some of the excess carbon out of the air, but creates its own problems when carbon dioxide reacts with water. Together, they form a weak acid that sours the sea.

Overall, ocean water has dropped by about 0.1 pH units, from about 8.2 to 8.1 pH, the report states. It seems like a small change, but because pH values are logarithmic, it represents a 30 percent increase in acidity.

Oyster production in the Pacific Northwest dropped 22 percent between 2005 and 2009, the report states, and major oyster hatcheries saw production crash.

The increased acidity damages small, floating snails called pterapods — or sea butterflies — that are a key food source for fish including herring, mackerel and salmon.

“Scientists on the West Coast, when they collected these sea butterflies in the wild, they could actually see that their shells are starting to corrode,” said ecologist Francis Chan, the panel’s co-chair and a professor of integrative biology of Oregon State University.

The increased acidity can also disrupt reproduction, neurology and behavior of other sea life.

As carbon dioxide levels in the ocean rise, dissolved oxygen decreases, researchers said, posing a separate but related problem for marine life.

“There are episodes where we’re seeing low oxygen closer to shore than we think is normal,” Chan said. “Quite simply, things can’t breathe and they suffocate.”

Starting in 2006, “dead zones” of low oxygen in shallow waters off the Pacific Northwest led to mass die-offs of Dungeness crabs and other animals.

Gretchen Hofmann, a panel member and biology professor at UC Santa Barbara, is studying whether combined effects of ocean acidification and low oxygen could disrupt egg production of popular sport fish such as rockfish and cabezon.

The impacts on fisheries could cripple the region’s seafood supply. A 2005 report to the California State Resources Agency by the The National Ocean Economics Program ranked the top five most valuable fisheries in the state as market squid, sea urchin, chinook salmon, rockfish and Dungeness crab — all species threatened by changes to ocean chemistry.

The disturbance is particularly troublesome for California and other parts of the West Coast because of upwelling currents that heave deep, cold, biologically rich waters toward shore.

Deborah Sullivan Brennan, The Sun Diego Union-Tribune, 15 April 2015. Article.


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