Shellfish Weakened by Greenhouse Gas

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March 6, 2007 — Oysters and mussels could have a harder time making their shells if projections of thickening carbon dioxide by the year 2100 pan out.

A preliminary laboratory study of the two shellfish living in water tanks under a carbon dioxide-enhanced atmosphere showed the increased acidity caused by the greenhouse gas stemmed the shellfishes' abilities to calcify shells by 10 to 25 percent.

The ecologic and economic effect of this could be huge in coastal areas where shellfish play vital roles, reports Frederic Gazeau and his colleagues at the Netherlands Institute of Ecology, the French Centre National de la Recherche Scientifique and Universite Pierre et Marie Curie.

"There hasn't been any data before on this," affirmed coral researcher Chris Langdon of the University of Miami.

It matches the sort of troubles seen in laboratory experiments with corals, which also excrete hard skeletons which form reefs. The chemistry behind the problem is basically just a matter of supply and demand, Langdon explains.

As higher carbon dioxide in the atmosphere dissolves in ocean waters, it is turned into bicarbonate instead of hanging around as a more useful carbonate ion. It's the carbonate that shellfish and coral need to make their calcium carbonate shells and skeletons.

"This study was really preliminary," cautioned Gazeau, the lead author of a paper on the short experiment in the latest issue of Geophysical Research Letters.

It established that a measurable effect exists, but leaves unanswered whether or not the shellfish can adjust to more acidic waters.

"Now we are going to start a three, four, five-month experiment," said Gazeau, "to see if they can acclimatize."

If it turns out the shellfish can adjust their metabolisms to somehow generate just as much shell with less carbonate available, the future looks bright for shellfish eaters — human, avian and otherwise.

Humans alone consumed 11.7 million tons of shellfish in 2002, the latest year with data available, Gazeau and his team report, citing figures from the Federal Accounting Office. That translates into a $10.5 billion business that's been growing almost 8 percent each year for 30 years. The Pacific oyster and mussels accounted for more than 14 percent of that business in 2002.

Precisely how a reduction in shell-building could hurt shellfish, corals and the species that depend on corals is difficult to predict. Most likely it would make reefs weaker and more vulnerable to storm damage, and make shellfish more vulnerable to predators.

"All we can do is observe that the rate at which they build their skeletons is less," said Langdon. It's not currently possible to make a high carbon dioxide sea habitat to test the real world effects.

In addition to a longer tank study of oysters and mussels, Gazeau says there are also plans to look into the effects of a higher carbon dioxide atmosphere on the larvae of shellfish and other marine organisms. The larvae are the immature, microscopic forms of marine organisms that might be more vulnerable to increased carbon dioxide.

Gazeau's research is part of a proposed, larger, coordinated research program involving about 30 institutions, which is being called the European Project on Ocean Acidification (EPOCA).