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May 28, 2013

Are 'mega-crabs' coming to Maine?

Carbon-rich waters could spawn new threat

by Craig Idlebrook

This summer, the movie Pacific Rim will show the perils of giant, plated monsters rising up from the depths of the ocean to attack humanity. A team of researchers at the University of North Carolina believes oyster beds might face a similar threat if current trends in climate change continue.

In a study published in Geology, researchers found in laboratory conditions that blue crabs and American lobster grow bigger if exposed to sea water with higher levels of carbon, like the levels predicted in the future if climate change continues. In the tanks, these mega-crabs were able to cut through oyster shells with ease, which would seem to suggest that oyster beds could become a giant buffet line for crabs.

And this phenomenon would happen at the same time that ocean acidification would be thinning oyster shells. While the shift would be a short-term gain for crabs, it might cause populations of oyster and crab to crash in the long-term, said Justin Baker Ries, a marine geologist at UNC.

"The shells would get so thin that it would throw off that balance," Ries said. "Oysters co-evolved with crustaceans for hundreds of millions of years. They've both been in this evolutionary arms race."

While the study focused on blue crab and American lobster, the findings suggest that similar results would occur across the board among other crustaceans. It's somewhat puzzling that some shell-bearing creatures would suffer from ocean acidification while others get bigger and stronger. Researchers speculate this may occur because lobster and crab are able to utilize the extra carbon in the water because of their quick molting process, and this adaptation may offset the negative effects of acidification. 

In the Gulf of Maine, the prospect of mega-crabs is still decades away. Right now, Maine's oyster growers have enough on their plates dealing with crabs at the size they are. Many take preventative measures to curb crab loss by keeping oysters off the sea bottom until they grow to around an inch and three-quarters, said Dana Morse, a University of Maine and Maine Sea Grant extension associate.

"A small oyster below that size is kind of like a potato chip and everybody loves potato chips, especially crabs," Morse said.

But if crabs grow bigger, the size of safe oyster shells could change. Climate change's effect on oysters is something the industry discusses, but it's more of an immediate problem on the West Coast than in Maine, said Chris Davis of Pemaquid Oyster Company. Davis wouldnt speculate about the possibility of mega-crabs.

One finding in the UNC study may offer a silver lining to oyster lovers. In the study, larger crabs exposed to the higher levels of carbon at times acted confused and were less focused on eating oysters. Researchers speculate that's because carbon dioxide may be displacing oxygen in the bloodstream of the crabs, creating disorientation, but more research would be needed to confirm those findings.  

The study predicted these larger crabs can be expected to wander the ocean floor sometime by the end of the century, if the current growth of carbon in the atmosphere continues.             




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