New research on coral reef growth rates shows that there is still a window of opportunity to save the world’s coral reefs – but time is running out.
The international study was initiated at the ARC Center of Excellence for Coral Reef Studies (Coral CoE), headquartered at James Cook University (JCU).
Co-author Professor Morgan Pratchett of Coral CoE at JCU said the results show that if carbon dioxide emissions are not drastically reduced, coral reef growth will be slowed.
“The threat posed by climate change to coral reefs is already very apparent based on recurrent episodes of massive coral bleaching,” said Professor Pratchett. “But the changing environmental conditions will have other far-reaching consequences.”
Co-author Professor Ryan Lowe, of the University of Western Australia’s (UWA) Coral CoE, said modern coral reef structures reflect a balance between a wide range of organisms that build reefs, not just corals. This includes coralline algae – a rock hard algae that binds reefs together.
“As the responses of different reef organisms to climate change become increasingly clear, this study uniquely examines how the complex interactions between diverse communities of organisms responsible for maintaining current coral reefs are likely to change reef structures at the time. future, “said Professor Lowe.
Co-lead authors Dr Christopher Cornwall and Dr Steeve Comeau (who are now at Victoria University of Wellington and Sorbonne University CNRS Laboratoire d’Océanographie de Villefranche sur Mer, respectively) calculated how coral reef growth is likely to react to ocean acidification and warming. according to three carbon dioxide scenarios related to climate change: low, medium and worst.
The results suggest that in an intermediate emissions scenario, some reefs may even keep pace with sea level rise as they expand – but only for a short time.
“All of the world’s reefs will erode by the turn of the century under the intermediate scenario,” said co-author Dr. Scott Smithers of JCU. “This will obviously have serious implications for reefs, reef islands, as well as people and other organisms dependent on coral reefs.”
The study gives broader projections of ocean warming and acidification – and their interaction – on the net carbonate production of coral reefs.
Warming oceans lead to more marine heat waves, which cause massive coral bleaching. Ocean acidification affects the ability of calcifying corals to form their calcium carbonate skeletons, a process called “calcification.” Warming water also reduces calcification.
The study data includes the net calcification, bioerosion, and dissolution rates of sediment measured or aggregated from 233 sites across 183 separate reefs. 49% of the reefs were in the Atlantic Ocean, 39% in the Indian Ocean and 11% in the Pacific Ocean.
These were then modeled against three emission scenarios from the Intergovernmental Panel on Climate Change for low, medium and high impact results on ocean warming and acidification for 2050 and 2100. .
Projections show that even in the low impact case, reefs will experience severely reduced growth or accretion rates.
“While 63% of reefs are expected to continue growing by 2100 as part of the low impact path, 94% will erode by 2050 in the worst case,” Dr Cornwall said. “And no reef will continue to grow at rates corresponding to the projected sea level rise in the medium and high impact scenarios by 2100.”
“Our study shows that changing environmental conditions challenge the growth of reef-building corals and other calcifying organisms, which are important for maintaining the structure of reef systems,” said Professor Pratchett.
“Saving coral reefs requires immediate and drastic reductions in global carbon emissions.”