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Drastic Reductions in Global Carbon Emissions is Required to Save Coral Reefs

A new study performed on the growth rates of coral reefs demonstrates that there is still a ray of hope to save the coral reefs of the world—but time is running out.

Saving coral reefs requires immediate and drastic reductions in global carbon emissions. Photo of Bleached reef at Yamacutta Flat by Morgan Pratchett. Image Credit: ARC Centre of Excellence for Coral Reef Studies.

The international study was started at the ARC Centre of Excellence for Coral Reef Studies (Coral CoE), which has been headquartered at James Cook University (JCU).

Morgan Pratchett, a study co-author and professor from Coral CoE at JCU, stated that the findings have demonstrated that without considerable reductions in the emissions of carbon dioxide , the growth of coral reefs will be stunted.

The threat posed by climate change to coral reefs is already very apparent based on recurrent episodes of mass coral bleaching. But changing environmental conditions will have other far-reaching consequences.

Morgan Pratchett, Study Co-Author and Professor, ARC Center of Excellence for Coral Reef Studies, James Cook University

Study co-author Professor Ryan Lowe, from Coral CoE at The University of Western Australia (UWA), stated that the latest coral reef structures reflect a balance between an extensive range of organisms that construct reefs, not just corals. This consists of coralline algae—a rock-hard alga that fastens reefs together.

While the responses of individual reef organisms to climate change are increasingly clear, this study uniquely examines how the complex interactions between diverse communities of organisms responsible for maintaining present day coral reefs will likely change reef structures in the future,” stated Professor Lowe.

The collaborative lead authors of the study, Dr Christopher Cornwall and Dr Steeve Comeau (who are currently working at Victoria University of Wellington and Sorbonne Université CNRS Laboratoire d’Océanographie de Villefranche sur Mer, respectively), estimated how the growth of coral reef will probably respond to ocean acidification and warming under three various climate-change carbon dioxide scenarios: low, medium, and worst-case.

The study results indicate that under an intermediate emissions scenario, few reefs may even keep pace with sea-level increase by growing—but only for a short period of time.

All reefs around the world will be eroding by the end of the century under the intermediate scenario. This will obviously have serious implications for reefs, reef islands, as well as the people and other organisms depending upon coral reefs.

Dr Scott Smithers, Study Co-Author, James Cook University

The study provides wider projections of ocean acidification and warming—and their interaction—on the net carbonate production of coral reefs.

Warming oceans tend to bring more marine heatwaves, which results in mass coral bleaching. Ocean acidification impacts the potential of calcifying corals to develop their calcium carbonate skeletons, a process known as “calcification”. Also, warming waters help decrease calcification.

In the study, the data consist of net bioerosion, calcification, and sediment dissolution rates quantified or compiled from 233 locations throughout 183 distinct reefs. Of the reefs, 49% were present in the Atlantic Ocean, 39% in the Indian Ocean, and 11% in the Pacific Ocean.

Furthermore, these reefs were modeled against three Intergovernmental Panel on Climate Change emissions scenarios for low-, medium-, and high-impact results on ocean acidification and warming for 2050 and 2100.

The projections illustrate that even under the low-impact case; reefs will experience extremely decreased growth, or accretion, rates.

Dr Cornwall stated, “While 63% of reefs are projected to continue to accrete by 2100 under the low-impact pathway, 94% will be eroding by 2050 under the worst-case scenario. And no reef will continue to accrete at rates matching projected sea-level rise under the medium and high-impact scenarios by 2100.”

Our study shows changing environmental conditions challenge the growth of reef-building corals and other calcifying organisms, which are important in maintaining the structure of reef systems. Saving coral reefs requires immediate and drastic reductions in global carbon emissions.

Morgan Pratchett, Study Co-Author and Professor, ARC Center of Excellence for Coral Reef Studies, James Cook University

Journal Reference:

Cornwall, C. E., et al. (2021) Global declines in coral reef calcium carbonate production under ocean acidification and warming. Proceedings of the National Academy of Sciences.


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