Scientists studying Australia’s Great Barrier Reef may have detected the first signs of impact of ocean acidification after finding a sharp cut in growth rates in some corals.

Oceans become acidic when carbon dioxide (CO2) emitted by humanity dissolves in sea water. This increase in acidity makes it harder for marine organisms to grow and maintain their shells.

The researchers studied a common coral species called porites, growing along the northern end of the Great Barrier Reef off Queensland. The species grows into massive reefs and is a key species for reef eco-systems around the world.

The scientists found that calcification - the process by which corals extract calcium carbonate from seawater to build their protective shells - had slowed by 21% over the past 16 years.

Timothy Cooper, a scientist at the Australian Institute of Marine Sciences, said the findings were “consistent” with the impact of raised CO2 levels and raised temperatures, both of which are linked to global climate change.

However, the study, just published in Global Change Biology, also warns that further research was needed to confirm the link.

The process of ocean acidification is attracting increasing attention from scientists, many of whom fear it could prove far more destructive in the short term than climate change.

Humanity currently emits about 49 billion tons of CO2 a year of which 40-50% is absorbed by the oceans. This slows climate change but causes a surge of hydrogen ions in seawater, which in turn raises acidity

A recent Royal Society report warned that hydrogen ion concentrations in surface seawater had already risen by 30% since 1800. It added that by 2100 hydrogen ion levels would rise threefold compared with 1800, with potentially catastrophic results.

Dr Carol Turley, a senior researcher in ocean acidity at Plymouth Marine Laboratory in Britain, said the same changes would affect waters around this country “profoundly”.

She said: “Many organisms ranging from plankton to shellfish and corals might be unable to build their shells. Many others which have already grown might start dissolving.”

View the Royal Society Ocean acidification report

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