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Scientists develop ‘heat resistant’ coral to fight bleaching

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By Milthon Lujan

Australia – Scientists from the University of Melbourne, CSIRO and the Australian Institute of Marine Science (AIMS) have successfully produced in a laboratory setting a coral that is more resistant to increased seawater temperatures.

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The coral was made more tolerant to temperature-induced bleaching by bolstering the heat tolerance of its microalgal symbionts – tiny cells of algae that live inside the coral tissue.

The team isolated the microalgae from coral and cultured them in the specialist symbiont lab at AIMS. Using a technique called “directed evolution”, they then exposed the cultured microalgae to increasingly warmer temperatures over a period of four years, helping them to adapt and survive hotter conditions.

“The microalgae were then reintroduced into coral larvae, leading to increased heat tolerance of the larvae,” Professor Madeleine van Oppen, of AIMS and the University of Melbourne, said.

“These exciting findings show that the microalgae and the coral are in direct communication with each other.”

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Corals with increased heat tolerance have the potential to reduce the impact of reef bleaching from marine heat waves, which are becoming more common under climate change.

The microalgae were exposed to temperatures that are comparable to the ocean temperatures during current summer marine heat waves causing coral bleaching on the Great Barrier Reef.

The researchers then unveiled some of the mechanisms responsible for the enhanced coral bleaching tolerance.

“We found that the heat tolerant microalgae showed reduced activity of photosynthesis genes which they compensate for by increasing the activity of genes used for fixing carbon and making sugars,” Professor van Oppen said.

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“The algae also induced higher activity of known coral heat stress genes. We believed that these mechanisms combined improved the heat tolerance of coral larvae that were inoculated with the heat-evolved microalgae.”

CSIRO Synthetic Biology Future Science Platform (SynBio FSP) science lead, Dr Patrick Buerger, said climate change has reduced coral cover, and surviving corals are under increasing pressure as water temperatures rise and the frequency and severity of coral bleaching events increase.

“Our novel approach strengthens the heat resistance of coral by manipulating its microalgae, which is a key factor in the coral’s heat tolerance,” Dr Buerger said. “Once the microalgae were reintroduced into coral larvae, the newly established coral-algal symbiosis was more heat tolerant compared to the original one.”

The scientists now plan to further test the algal strains in adult colonies across a range of coral species.

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“This breakthrough provides a promising and novel tool to increase the heat tolerance of corals and is a great win for Australian science,” SynBio FSP Director Associate Professor Claudia Vickers said.

Reference (open access):
BY P. BUERGER, C. ALVAREZ-ROA, C. W. COPPIN, S. L. PEARCE, L. J. CHAKRAVARTI, J. G. OAKESHOTT, O. R. EDWARDS, M. J. H. VAN OPPEN. Heat-evolved microalgal symbionts increase coral bleaching tolerance. Science Advances 13 May 2020: Vol. 6, no. 20, eaba2498 DOI: 10.1126/sciadv.aba2498 

Source: The University of Melbourne

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