Coral can, however, come back from the brink. During the climate fluctuations of the last 30,000 years, Australia’s Great Barrier Reef has died and grown back five times. There is a growing acceptance that if coral reefs are going to weather the intensifying present-day survival parameters, human intervention will be needed. “The coral biology world has undergone a radical transformation over the last five years,” Steve Palumbi, marine biologist at California’s Stanford University, recently told ScienceMag.org.

Transplanting warm-water corals to other regions is one method of helping existing reefs survive hotter conditions. Scientists from the Red Sea Transnational Research Center are working to establish the factors that make coral in the Red Sea and the Gulf of Aqaba more resistant to rising temperatures – with the possibility of establishing these species elsewhere.

On the Great Barrier Reef, the University of Technology Sydney’s Future Reefs Program has been selectively breeding coral polyps that survived recent bleaching events in a separate lagoon “nursery”. The researchers hope to retransplant this hopefully hardier coral back into the wild with the aim of speeding up reef recovery.

Others have suggested introducing heat-resistant algae from warm waters to coral in other regions, but this approach could have its limitations. Research shows that such algae can reduce bleaching mortality by 30%, but it also reduces coral growth rate by over 50%.

The National Sea Simulator, in Townsville, Queensland, Australia, also experiment with breeding coral and algae under heat-stressed conditions – but are delving deeper into the coral genome for other possibilities. In the seawater tanks at the $25 million facility, scientists are crossbreeding coral species that would otherwise spawn at different times in the hope of producing more resilient varieties.

A recent study shows that a hybrid of Acropora tenuis and A. loripes – both commonly found on the Great Barrier Reef – tolerated hotter, more acidic water better than the purebred varieties. Acidification is another challenge corals face as the oceans’ absorption of carbon dioxide lowers the pH of seawater; this corrodes corals’ calcium carbonate exoskeleton.

Healthy coral reefs attract a huge range of marine life. Image by 舰 周 / Pixabay

The National Sea Simulator’s “assisted evolution” approach is also looking at the potential of CRISPR gene-editing for identifying specific genes in both coral and algae relating to heat and stress. Researchers elsewhere have proposed going further to genetically engineer entirely new coral species – though it is likely introducing such “super-corals” into natural ecosystems they may quickly overwhelm will face opposition.

With the world’s largest reef under its supervision, Australia is fast becoming the frontline for innovative coral-preservation strategies. Other proposed methods include employing a biodegradable polymer “sun shield” sitting on the ocean surface to protect coral from the sun-rays, and pumping cold deep-sea over in-shore reefs through large-diameter, polymer-reinforced pipes.