Ocean acidity will dissolve the shells of living shellfish

Researchers in the Laboratoire d'Océanographie at Villefranche (LOV) (CNRS / UPMC) have just demonstrated that key marine organisms, such as deep-water corals and pteropods (shelled pelagic mollusks) will be profoundly affected by the increase of ocean acidity caused by carbon dioxide emissions, whereas they are playing essential roles in their ecosystems.

About a quarter of the carbon dioxide pumped into the atmosphere by factories, power stations and cars now ends up being absorbed by the oceans. That represents more than six million tonnes of carbon a day. This massive absorption has allowed to partly mitigate climate change but it has also caused a major disruption to the chemistry of seawater. Indeed, the carbon dioxide dissolves and is turned into carbonic acid, causing the oceans to become more acidic. Between now and 2100, at the current rate of emissions, it is estimated that the mean ocean acidity will treble, which is unprecedented during the past 20 million years.

The first results published by the LOV team, which studied the he impact of such a reduction in pH on calcifying organisms raise major concerns about the future of pteropods, deep-water corals and the organisms that depend on them for nutrition or habitat.

More carbon dioxide can dissolve in cold water than warm increasing the acidification in the Arctic and Antarctic oceans.

The Limacina helicina, a tiny mollusc which has an important part to play in the food chain and functioning of the Arctic marine ecosystem, mainly as a prey for baleen whales, salmon, herring and various seabirds would will be particularly vulnerable: its calcium carbonate shell which provides vital protection, develops at a rate that is 30% slower when it is kept in seawater with the characteristics anticipated in 2100. An even more marked reduction (50%) has been measured in the cold-water coral Lophelia pertusa. While tropical coral reefs are built by a large number of species, coral communities in cold waters are constructed by one or two species but provide shelter for many others. A reduction in the growth of reef-building corals due to ocean acidification may therefore threaten the very existence of these biological structures.

Ocean acidification can only be controlled by limiting future atmospheric levels of CO2. Negotiations aimed at reducing greenhouse gas emissions that should be finalized in Copenhagen next December must take account not only of increased temperature but also of the acidic nature of CO2 which, once absorbed by the oceans, will have potentially dramatic effects on numerous marine organisms and ecosystems.

More about Ocean acidification >> Visit the European Project on Ocean Acidification website