Crabs Are Getting Bigger - Is Carbon Dioxide to Blame?

A recent study of blue crabs from the Chesapeake Bay and other areas shows that crabs and other crustaceans are growing at up to four times their normal rate. But the same conditions are causing oysters and scallops to grow at a rate of one–fourth of their normal speed. So what’s causing this ecological chaos? It looks like it’s carbon dioxide that is gradually falling from the air into the world’s oceans. And that’s bad news for the oysters.

A research team from the University of North Carolina’s Aquarium Research Center, led by marine geologist Justin Baker Ries conducted a study in 2009 in which they raised crabs in high- carbon tanks. They found that the creatures grew bigger and bigger, but that they actually ate fewer oysters. They also found that while the animals grew bigger and faster, which helped make them less vulnerable to predators, they spent much of their energy producing new shells rather than gaining flesh.

Oysters and scallops, on the other hand, are growing much more slowly than normal because of the same carbon dioxide levels. Smaller oysters are easier prey, so the number of survivors living to adulthood is almost certain to be lower than it was in the past despite the crabs’ loss of appetite.

Maryland and Virginia have worked hard to improve oyster populations in Chesapeake Bay.  One of the reasons is that oysters filter pollutants from the bay’s waters. Over the last hundred years, however, drops in oyster populations have reduced the filtering cycle in the bay from once every three weeks to approximately once every three years. Some experts predict the current trend will continue so long as atmospheric carbon dioxide levels continue to rise.

It is hoped that a way will be found to stabilize the Chesapeake Bay ecosystem. Oysters help to increase biodiversity in the bay’s environment and are credited with helping to reduce erosion on shorelines.

Seafood lovers are also losing out. Even though the crustaceous are growing faster, they are no meatier than their ancestors. Fewer, smaller scallops and oysters also will negatively impact the fishing industry.

Can the denizens of Chesapeake Bay and other affected areas adjust to the new levels of carbon dioxide in time? We can only hope that “life finds a way.”

There’s more discussion about the crabs and their potential effect on Chesapeake Bay here