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 Ries and co-authored with Anne Cohen and Daniel McCorkle, and 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.
"It's taking them longer to go from oyster spat to oyster adult," said Luke Dodd, a doctoral candidate at UNC who put the crabs in a tank with oysters. "When you're a baby, there's tons of predators that want to eat you up."
But when they put mud crabs and oysters together in the tanks polluted with carbon, Dodd, Michael Piehler of UNC and Jonathan Grabowski of Northeastern University observed something they didn't expect, a response that gave oysters a prayer.
Under conditions with lower levels of carbon, two mud crabs polished off 20 oysters in six hours. But in the aquariums with higher levels of carbon, the mud crabs seemed confused.