Silver lining to coral reef climate cloud

Photo by Bayden Russell
Photo by Bayden Russell

Researchers have found parts of our coral reefs are more resistant to ocean acidification than first thought, casting a ray of hope on the future of our reefs.

The study, published today, details their analyses of the mineral structure of coralline algae, which form a hard ridge around the reef, protecting delicate corals from harsh waves and holding the structure together.

They discovered an extra mineral, dolomite, in coralline algae, which made the organism less susceptible to being dissolved in increasingly acidic oceans.

"A coral reef is like a house – the coral are the bricks, but the coralline algae are the cement that holds it all together," explains lead author and PhD candidate with the ANU Research School of Physics & Engineering, Merinda Nash.

"Researchers are concerned that when atmospheric carbon levels rise and ocean acidity increases, the magnesium calcite which makes up the coralline algae will dissolve first, threatening the very foundations of the reef.

"However, in a rare piece of good news, we found when we analysed algal samples from Heron Island on the Great Barrier Reef that the cell spaces in the algae were filled with dolomite, the same strong mineral that makes up the Dolomite Alps in Italy.

"Dolomite is about half magnesium and half calcium and is less susceptible to acidity than the magnesium calcite, meaning the structure of the coral reefs is stronger than previously thought."

Brad Opdyke from the ANU Research School of Earth Sciences, who collaborated with Nash on the paper, together with other researchers from Australia, Japan and America, said:

"Coralline algae play a really important role in the architecture of the reef. Without it, the reef would just be a big pile of rubble.

"The clouds of climate change are very dark, but now there is this thin silver lining. The dolomite may just make some of the coralline stable enough to keep holding things together."

Past research has shown that the structure of a coral reef consists mainly of forms of calcium carbonate, a mineral formed in the skeletons of coral and algae and laid down in sedimentary layers over thousands of years.

The algal skeletons are made of a type of calcium carbonate called magnesium calcite which contains about 10 to 20 per cent magnesium instead of calcium.

"It’s a much weaker structure than the version used by other organisms and is quite vulnerable to rising acidity levels.

"But the dolomite-rich coralline algae are better able to resist rising acidity levels. There is less space for sea water to circulate and less surface area for the acidic water to act," said Nash.