Oysters and Mussels

Rising CO2 levels 'put shellfish in danger'

Oysters and mussels, two pearls of France's gastronomic heritage, are in danger of dying out because of rising greenhouse gas levels in seawater, say scientists.

French and Dutch researchers found that rapidly rising concentrations of carbon dioxide in seawater is having potentially devastating effects on the lifecycles of both types of shellfish, slowing down their growth and weakening their shells, leaving them vulnerable to predators.

This is the first time this effect has been shown on shellfish, the researchers say.

The study, conducted by France's CNRS research centre with the Netherlands Institute of Ecology, shows that higher carbonic acid levels in the ocean increase acidity, which makes it harder for the molluscs to calcify their shells. All sea life needing calcium carbonate for its shell, including coral, is at risk.

Oceans absorb a third of the atmosphere's carbon dioxide. Levels have risen by 30 per cent since the beginning of the industrial revolution, but could increase by up to four times by the end of the century.

If the amount absorbed only doubles, mussel growth will drop by a quarter and oysters by 10 per cent by 2100. But at higher carbone dioxide concentrations, mussel shells may dissolve completely, the researchers found. Oysters are less affected, as they use another crystalline form of calcium carbonate for their shells.

France produces 200,000 tons of shellfish annually, amounting to £450 million in revenue. The industry employs around 20,000 people.

The image of French oysters suffered last year when authorities banned the sale of them in Arcachon, south-west France, after two suspect deaths. It was later established that there was no link with oyster consumption.