The world’s coral reefs could start to disappear by the middle of the century as stress induced by climate change erodes their skeletons faster than they can regenerate.
Corals build their skeletons using calcium and carbonate ions in seawater, a process known as calcification. Climate change is making calcification harder by driving ocean acidification, which reduces the concentration of carbonate ions in the water. It is also causing more severe weather events like heatwaves and cyclones, which stress corals and deplete their energy for growth.
To see how this is affecting global reef health, Kay Davis at Southern Cross University in Lismore, Australia, and her colleagues analysed data from 36 coral reef sites in 11 countries, including the Great Barrier Reef in Australia and Shiraho Reef in Japan.
They found that the rate at which coral reefs are depositing new calcium carbonate has been dropping by around 4 per cent per year since 1970.
If this trend continues, a tipping point will be reached in the year 2054 whereby corals stop growing altogether and their calcium carbonate structures start to dissolve away into the ocean.
“It’s not going to be every single reef at exactly 2054, but our analysis indicates that will be the average,” says Davis.
The trend has already begun – some corals in the northern part of the Florida Reef Tract have hit this tipping point.
As coral reefs struggle to rebuild, they are at risk of being taken over by algae, says Davis. “As stress events impact corals, it gives marine algae a chance to establish themselves and start growing,” she says. “We found that marine algae are increasing concurrently with declining calcification, which indicates a shift in ecosystem functionality towards algal domination.”
To slow or stop this trend, we must urgently address climate change, says Davis. “Coral reefs globally have already been severely impacted, but the only hope to preserving them really lies in global reduction in greenhouse gas emissions and local changes to improve water quality.”
Journal reference: Communications Earth & Environment, DOI: 10.1038/s43247-021-00168-w
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