Silver Lining to Coral Reef Climate Cloud

Researchers from The Australian National University (ANU) have found parts of our coral reefs are more resistant to ocean acidification than first thought, casting a ray of hope for the future of our reefs.

The study, published in Nature Climate Change and coauthored by a researcher at Scripps Institution of Oceanography at UC San Diego, 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 Merinda Nash, lead author and Ph.D. candidate with the ANU Research School of Physics & Engineering.

Scripps' Davey Kline worked with an international team to test the impact of ocean acidification on coral reefs in as natural a reef setting as possible.

"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 analyzed 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."

"This newly found mechanism of ocean acidification resistance means corals of the future with healthy coralline algae can fight damage from high wave energy, tsunamis and other threats," said Davey Kline, a Scripps marine biologist and coauthor of the new paper. "This information will help the management and preservation of coral reefs, with the data applied to protect the most vulnerable parts of the reefs."

The study's results were partly derived from a field experiment led by Kline and others called the Coral Proto - Free Ocean Carbon Enrichment system, or CP-FOCE, and based at Heron Island, Great Barrier Reef, Australia.

Kline said the new study's findings are especially encouraging since dolomite is found in reefs around the world.

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 percent 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," said Nash. "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."

Text provided by The Australian National University.

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