Crabs supersized by carbon pollution

Changes could upset marine balance

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WASHINGTON -- It is the dawn of the supercrab.

Crabs are bulking up on carbon pollution that pours out of power plants, factories and vehicles and settles in the oceans, turning the tough crustaceans into even more fearsome predators.

That presents a major problem for the Chesapeake Bay, where crabs eat oysters. In a life-isn't-fair twist, the same carbon that crabs absorb to grow bigger stymies the development of oysters.

"Higher levels of carbon in the ocean are causing oysters to grow slower, and their predators -- such as blue crabs -- to grow faster," Justin Baker Ries, a marine geologist at the University of North Carolina's Aquarium Research Center, said in an recent interview.

Over the next 75 to 100 years, ocean acidification could supersize blue crabs, which may then eat more oysters and other organisms and possibly throw the food chain of the nation's largest estuary out of whack.

That would undermine an effort to rebuild the stocks of both creatures. Virginia and Maryland are pouring hundreds of millions of dollars into rebuilding the populations of blue crabs and oysters to some semblance of their historic numbers.

The problem extends beyond crabs and the Chesapeake Bay. Lobsters and shrimp are also bulking up on carbon dioxide along the Atlantic coast. Like oysters, coral that helps protect small organisms from big predators is being adversely affected by higher acidity in the waters.

Crabs put away carbon like nobody's business. The more they eat, the faster they molt, a growth spurt during which their shells go soft. Carbon helps speed the process so that they emerge bigger and perhaps stronger, less vulnerable to predators and more formidable predators themselves.

At UNC, marine geologists are analyzing video of the slaughter that took place when they put mud crabs and oysters in tanks they intentionally polluted with carbon over three months for a 2011 study.

It was like watching lions tear apart lambs. The crabs scurried from their side of the tanks, banged on the shells of the traumatized oysters, pried them open with a claw in a way similar to what humans do with a knife at restaurants and gobbled them down.

For crab lovers, bigger doesn't necessarily mean better. Carbon-absorbing crabs put all their energy into upgrading shells, not flesh -- like a mansion without much furniture. So diners might be disappointed years from now when they crack open huge crabs and find little meat.

The research showing the effects of carbon on marine organisms was published in the journal Geology in 2009. The study, led by Mr. Ries and co-authored with Anne Cohen and Daniel McCorkle, found that crabs, lobsters and shrimp grew bigger more rapidly as carbon pollution increased. Chesapeake blue crabs grew nearly four times faster in high-carbon tanks than in low-carbon tanks.

But under the same conditions, oysters, scallops and other organisms struggle to grow, making them more vulnerable to carnivores. Oysters in high-carbon tanks grew at only one-quarter the speed they did in low-carbon conditions, according to the study.

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