The world's coral reefs, already enduring multiple threats from bleaching to nutrient run-off from farming, also face another challenge - this time from below.
New research, published in the journal Science on Friday, has found the sediments on which many reefs are built are 10 times more sensitive to the acidifying oceans than the living corals themselves. Some reef bases are already dissolving.
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| Not loving it enough: coral reefs face multiple threats from climate change, including as it turns out, from below. |
As oceans turn more acidic, the corals themselves produce less of the calcium carbonate that forms their base. Instead of growing, the reef bases start to dissolve.
"The public is less aware of the threat of ocean acidification [than warming waters]," said Bradley Eyre, a professor of biogeochemistry at the Southern Cross University and the paper's lead author.
“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,” he said.
At risk will be coral reef ecosystems that support tourism, fisheries and the many other human activities, he said.
The ocean's acidity has increased about 30 per cent since the start of the industrial revolution, as seas absorb about one-third of the build-up of greenhouse gases in the atmosphere.
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| Coral reefs provide important habitats for many species, such this reef at Tufi in Papua New Guinea. |
Rates of dissolving reef sediment will depend on their starting points, including their exposure to organic sediment. The Hawaiian reef studied is already showing signs of its sediment dissolving, with higher organic nutrient levels likely to be contributing, he said.
"Carbonate sediments in Hawaii are already net dissolving and will be strongly net dissolving by the end of the century," the paper said.
Living corals themselves appear to be able to resist the acidification process, with mechanisms and strategies to resist some of the impacts.
Still, the study said the transition of the dissolution of reef sediment "will result in the loss of material for building shallow reef habitats such as reef flats and lagoons, and associated coral cays". It is unknown if the reefs will face "catastrophic destruction" once the erosion begins, the paper said.
Over time, as coral bases begin to dissolve, they are more likely to become more vulnerable to cyclones and other threats, Professor Eyre said.
He said further study was needed to understand how reefs would be affected by temperatures, rising organic and nutrient levels and more acidic waters in combination, he said.
The impact of bleaching - such as the two mass events in the 2015-16 and 2016-17 summers on the Great Barrier Reef - would most likely accelerate the breakdown of reefs by "making more sediment and organic matter available for dissolution", the paper said.
Links
- What is Ocean Acidification?
- Coral reefs will transition to net dissolving before end of century
- 'Rather startling' increase in rate of coral bleaching
- Baby Fish May Get Lost In Silent Oceans As Carbon Dioxide Rises
- Southern Ocean Acidification Increases: Report
- Global Warming’s Toll On Coral Reefs: As If They’re ‘Ravaged By War’
- Can Corals Survive Climate Change?
- Coral Bleaching: Researchers Struggle To Find Anywhere In Pacific Ocean Untouched
- Countries With Coral Reefs Must Do More On Climate Change – UNESCO
- 50 Reefs: World-First Global Plan Says Only 10 Pc Of Coral Reefs Can Be Saved From Extinction
- Enough PR Spin: We Need A Real Plan For The Reef That Includes Ditching Coal
- Great Barrier Reef: Most Coral Now Dead North Of Port Douglas Off Far North Queensland, Scientists Say
- NASA Begins Study Of Australia's Great Barrier Reef
- Great Barrier Reef: Government Must Choose Which Parts To Save, Says Expert
- Global Coral Bleaching Continues For a Record Third Year
- Scientists Call On Australia To Save World’s Reefs
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