Carbon the culprit in predator crabs

Bigger blue crabs sound like exactly what evolution should produce if the human palate were the driver: A crustacean that rewards easier picking with more meat. Unfortunately for the hungry, the results of ocean acidification appear to be precisely the opposite, according to a report in The Washington Post.

The oceans are slowly getting more laden with the carbon produced when humans burn oil, gas and coal. Carbon not only makes ocean water more acidic, but it proves a fine building block for crabs and other crustaceans. Or at least their shells, which are largely composed of calcium carbonate.

The result is bigger crabs with tougher exoskeletons. And since so much of the crab’s energy goes into the intense process of building a shell, molting and building another shell, relatively little meat results.

It gets even worse for diners.

Because the crabs are bigger and stronger, they are also better predators. And they like to eat oysters.

Disease, habitat destruction and overharvesting have already decimated the oyster population in the Chesapeake Bay. Hungry supercrabs are not going to help.

Ocean acidification is one of the worrisome results of burning fossil fuels, a process that helps warm the planet, which raises sea levels.

Much of the carbon dioxide produced by burning fuel is absorbed in the oceans, where it is turned into carbonic acid. While that helps slow the progression of global warming, more acidic oceans have been shown to do serious damage to corals and other marine species.

Even so, scientists are only beginning to understand the ramifications for the food chain. So far, acidification appears to be a double-whammy for the Chesapeake’s signature ingredients.

The Washington Post reported recently on a 2009 study that showed blue crabs grow four times faster in high-carbon tanks. Shrimp and lobsters also got bigger faster. Shellfish didn’t. They were also more susceptible to attack.

Scientists worry that the experiment shows the future of the two species. Millions of dollars have been spent over the years in an effort to understand and reverse the decline of both oysters and crabs, under the belief that the creatures represent both the bay’s heritage and its future.

Thanks to harvest restrictions, the crab population has rebounded in the past few years. Aquaculture and careful habitat management have shown at least some promise in helping oysters. Mankind should begin taking the necessary steps to protect the seas before all that good and delicious work is undone.

The Virginian-Pilot, 10 April 2013. Article.

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