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Supersized crabs could upset Chesapeake ecosystem

Posted By GABRIELLE LEVY, UPI.com   |   April 9, 2013 at 2:29 PM   |   Comments

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April 9 (UPI) -- No, it's not your imagination.

Those blue crabs on your dinner plate are getting bigger, or at least they will over the next century.

Increasing carbon in the atmosphere eventually settles in the oceans, causing crabs, lobsters and shrimp to grow to bigger and bigger sizes.

Conversely, higher carbon levels slow down the growth of crabs' food source -- oysters -- which could undermine the delicate balance of the seabed and undermine efforts to rebuild populations in waters like the Chesapeake Bay.

Researchers at the University of North Carolina's Aquarium Research Center found crabs living in carbon-polluted waters turned into supersized monsters with insatiable appetites.

Justin Baker Ries, the UNC marine geologist leading the research, found in a 2009 study that crustaceans such as the Chesapeake blue crab grew at a clip of four times the normal rate in high-carbon environments, while oysters and scallops grew at one-quarter their normal speed.

“It’s taking them longer to go from oyster spat to oyster adult,” Luke Dodd, a doctoral candidate at UNC told the Washington Post. “When you’re a baby, there’s tons of predators that want to eat you up.”

But the acidification that made the crabs grow bigger in high-carbon tanks could actually be making them loopy -- Dodd said they found the crabs eating fewer oysters -- but they could adjust over time.

"Acidification may be confusing the crab,” he said, but "you can’t discount evolution taking over."

To make things worse, the bigger crabs aren't necessarily better for eating. The increased carbon and resulting speedy growth means they molt more often, growing faster and emerging stronger and less vulnerable to other predators. And the crabs put more energy into growing the new shells, rather than more flesh.

Virginia and Maryland have poured resources into improving the oyster populations in the Chesapeake, and it's beginning to show results, because oysters filter polluted water.

“One hundred years ago, the bay was crystal-clear because they filtered it every three weeks, as opposed to every three years today,” Ries explained.

But efforts to protect the crabs, including a ban on dredging during the crab's prime reproduction season, means that its pouplation is growing too, at a clip of 66 percent up from 2003.

At that rate, the oysters simply won't be able to keep up. And that's bad, not just because of their pollution cleaning abilities, but because they are considered "ecosystem engineers," helping to increase biodiversity, provide habitats to other species and even protect shorelines from eroding.

Follow @gabbilevy and @UPI on Twitter.
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