Time's running out to save coral reefs

New research shows there is still a window of opportunity to save the world’s coral reefs – but time is running out according to a team of researchers including from The University of Western Australia.

An international study, published today in PNAS, calculates how coral reefs are likely to react to ocean acidification and warming under three different climate-change carbon dioxide scenarios: low, medium and worst-case.

The study, initiated at the ARC Centre of Excellence for Coral Reef Studies, gives broader projections of ocean warming and acidification – and their interaction – on the net carbonate production of coral reefs.

Warming oceans bring more marine heatwaves that cause mass coral bleaching and also reduce calcification, affecting the ability of calcifying corals to form their calcium carbonate skeletons.

The study examined net calcification, bioerosion and sediment dissolution rates measured or collated from 233 locations across 183 distinct reefs.

Nearly half (49 per cent) of the reefs were in the Atlantic Ocean, 39 per cent in the Indian Ocean and 11 per cent in the Pacific Ocean.

These were then modelled against three Intergovernmental Panel on Climate Change emissions scenarios for low, medium and high-impact outcomes on ocean warming and acidification for 2050 and 2100.

The projections showed even under the low-impact case, reefs would suffer severely reduced growth, or accretion, rates.

Co-author Professor Ryan Lowe, from the ARC Centre of Excellence for Coral Reef Studies at UWA, said that modern coral reef structures reflected a balance between a wide range of organisms that help build reefs, such as corals, as well as the actions of other organisms that erode reef structures.

“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.”

Professor Ryan Lowe

Co-author Professor Morgan Pratchett, from the ARC Centre of Excellence for Coral Reef Studies at James Cook University, said the results showed unless carbon dioxide emissions were drastically reduced the growth of coral reefs would be stunted.

“The threat posed by climate change to coral reefs is already very apparent based on recurrent episodes of mass coral bleaching,” Professor Pratchett said.

“Saving coral reefs requires immediate and drastic reductions in global carbon emissions.”