New treatment could enhance coral heat-tolerance and buy time for threatened reefs

Adult fragments of the coral species Galaxea fascicularsis can better tolerate bleaching and recover faster when treated with heat-evolved cells of algae, called symbionts, new research from the Australian Institute of Marine Science (AIMS) and the University of Melbourne has indicated.

The study, published today in Global Change Biology, used symbionts – the tiny cells of algae that live inside coral tissue and support growth – which had had their heat tolerance bolstered in the lab through exposure to elevated temperatures over a 10 year period. The heat-evolved symbionts were then offered to coral fragments that had been chemically bleached.

Researchers found the symbionts were able to maintain a symbiosis with the adult corals for two years, promoting faster recovery from bleaching and enhancing the coral’s heat tolerance without having a detrimental effect on growth.

Lead author Dr Wing Yan Chan from AIMS and the University of Melbourne said the new findings suggest heat-evolved algal symbionts are a potentially valuable resource for reef restoration, and could be used  across coral species and life stages.

“These symbionts were still detected two years after the corals were first inoculated, suggesting long-term stability of this symbiosis and potential long-term benefits to coral heat tolerance,” Dr Chan said.

“Strategies to enhance coral heat tolerance can buy time for reefs, which are threatened by climate change-driven marine heatwaves causing bleaching and sometimes coral death. The long-term stability of the symbiosis offers hope these heat-evovled cells could provide benefits to their coral hosts for many years.”

Senior author Professor Madeleine van Oppen from AIMS and the University of Melbourne, said earlier work in her group had shown the benefits of exposing coral larvae and juveniles to heat-evolved symbionts.

“These new findings on adult coral close the circle and demonstrate the advantages are not lost in adulthood,” Professor van Oppen said.

“This approach is one of several referred to as ‘assisted evolution’, which involves active interventions to accelerate the rate of naturally occurring evolutionary processes.”

Research Program Director within the Reef Restoration and Adaptation Program (RRAP) at AIMS, Dr Line Bay, said the work was an important step towards enhancing heat tolerance in corals.

“This study is part of the extensive work AIMS, our partners and collaborators are doing to protect corals from climate change,” Dr Bay said.

“To give coral reefs the best chance of survival, we need to reduce emissions, ensure coral reef systems are managed well, and develop interventions like heat-evolved symbionts to help boost climate tolerance and resilience for reefs.”

More about the research:

• The study showed that treatment with heat-evolved symbionts did not compromise the coral’s ability to grow, differing from previous studies of Great Barrier Reef corals which found naturally heat tolerant symbionts could enhance heat resistance in coral, but at a cost to its growth.
• The next stage of this research will be controlled field trials to determine whether the intervention could work outside the laboratory, with more than one coral type and at scale.
• The research was a collaboration between AIMS, the University of Melbourne, Monash Institute of Pharmaceutical Sciences and the Melbourne Centre for Nanofabrication.
• The research was funded by the Australian Research Council, the Paul G. Allen Family Foundation and RRAP, which is funded by a partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.