Two-thirds of cold water corals could disappear by the end of the century, scientists predict

Lewis Brindley/Turin, Italy

The latest studies on ocean acidification indicate that it’s not just tropical corals that are under threat from ocean acidification, but cold water corals too.

Speaking at the 2nd EuCheMS Chemistry Congress in Turin, Italy, James Orr said that his recently completed studies in the arctic pointed at a similar decline for cold water corals as those observed in tropical waters. ’We predict that by the end of this century more than two thirds of cold water corals will be exposed to water that is corrosive to their calcified exoskeletons,’ said Orr, who is based at the IAEA Marine Environmental Laboratory in Monaco.
Cold water corals are not well studied as they usually grow deep underwater - but huge reefs have been found around Norway and the UK that are important habitats for fish and other sea creatures. It’s been estimated that around 25 per cent of fish spend some part of their life around a coral reef, Orr says, so the loss of cold water corals could have a huge impact on the ocean’s biodiversity.

Ocean acidification occurs because atmospheric CO2 is taken up by the sea as carbonic acid. Since the sea is naturally alkaline (around pH 8.1), the acid is quickly neutralised by carbonate ions and trapped as bicarbonate. Over time this results in a decline of the ocean pH, and although it will not be pushed below neutral (pH 7.0) anytime soon, the ocean is already 30 per cent more acidic than it was before the industrial revolution.

The process also means that the availability of free carbonate ions in the ocean is decreasing, which is bad news for organisms that form calcium carbonate shells. Within 50 years, organisms such as corals and clams will struggle to produce their structures faster than they are eroded by natural processes. This will have huge impacts on fish that depend on coral to live or reproduce, as well as creatures further up the food chain, such as the walrus, whose diet is mostly composed of molluscs.

"We have almost reached the point of no return for corals, but we still don’t know exactly what will happen to other organisms" - James Orr

Unfortunately, there is little we can do to prevent this disastrous outcome, Orr says. ’We have almost reached the point of no return for corals, but we still don’t know exactly what will happen to other organisms,’ Orr told Chemistry World.

’Ocean acidification is a serious problem that deserves more emphasis,’ said Gerhard Lammel from the Max Planck Institute for Meteorology in Germany, who attended the Turin lecture. ’Recent concerns have focused on eutrophication, contamination and overfishing, but this is arguably just as important.’