Rising acidity in oceans a major threat to coral reefs, says study

Coral reefs could start to dissolve before 2100 as man-made climate change drives acidification of the oceans, scientists said on Thursday.

Many of the world's coral reefs face the threat of erosion over the coming decades as ocean acidity levels continue to rise. This acidification will threaten sediments that are building blocks for reefs, the new study said.

This is in addition to the risks corals already face from rising ocean temperatures, pollution and overfishing.

''Coral reefs will transition to net dissolving before end of century,'' the Australian-led team of scientists wrote in the US journal Science. ''Net dissolving'' means reefs would lose more material than they gain from the growth of corals.

Carbon dioxide, the main man-made greenhouse gas, forms a weak acid in water and threatens to dissolve the reef sediments, made from broken down bits of corals and other carbonate organisms that accumulate over thousands of years, it said.

The sediments are 10 times more vulnerable to acidification than the tiny coral animals that also extract chemicals directly from the sea water to build stony skeletons that form reefs, the study said.

The alarming findings at Heron Island, Hawaii, Bermuda and Tetiaroa showed that the sands which provide material for the building and maintenance of coral reefs began to dissolve at a rate ten times faster than corals can grow.

"Coral reef sediments around the world will trend towards dissolving when seawater reaches a tipping point in acidity which is likely to occur well before the end of the century," lead author Prof Bradley Eyre from Southern Cross University's Centre for Coastal Biogeochemistry told Xinhua.

Coral animals will be able to keep growing and replenish reefs long after sandy sediments start to dissolve, Prof Eyre told Reuters.

''This probably reflects the corals' ability to modify their environment and partially adapt to ocean acidification whereas the dissolution of sands is a geo-chemical process that cannot adapt,'' he said.

The report said it was ''unknown if the whole reef will erode once the sediments become net dissolving'' and whether reefs ''will experience catastrophic destruction'' or merely a slow erosion.

Some reef sediments were already starting to dissolve, such as at Kaneohe Bay in Hawaii, where other pollutants were contributing.

Eyre said it was unclear if the dissolution of sediments could be a long-term threat to entire islands, from the Pacific to the Caribbean. Other studies say that deep cuts in greenhouse gas emissions can limit acidification.

Most studies show that acidification will be overwhelmingly bad for ocean life, also threatening creatures such as oysters, lobsters and crabs.

"It is vital that we put pressure on governments globally to act in concert to lower CO2 emissions as this is the only way we can stop the oceans acidifying and dissolving our reefs," Prof Eyre said.