Development of heat-resistant algae could help fight coral reef devastation caused by climate change

MELBOURNE, Aus. — Coral reefs around the world are suffering from the effects of human-caused climate change as ocean temperatures rise, but scientists hope the development of heat-resistant coral could help these fragile ecosystems improve or possibly begin to slowly recover.

The team included researchers from CSIRO, Australia’s national science agency, the Australian Institute of Marine Science (AIMS) and the University of Melbourne. A study published in Science Advances found by developing heat-resistant microalgae from coral, the heat tolerance of the coral improved allowing the coral to adapt and survive in hotter conditions.

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.

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The white skeleton of the coral is visible because it suffered from extensive heat stress and lost their important algal symbiont, which supplies most of the coral’s nutrition through photosynthesis (credit: Chris Jones)

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,” science lead Dr. Patrick Buerger said in an announcement regarding the findings.

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The thermal tolerance of coral larvae and their heat-evolved algal symbionts was tested at higher temperatures in laboratory incubators. The coral larvae with some of the heat-evolved algal strains were more resistant to temperature stress compared to the coral larvae with normal algae types (credit: Patrick Buerger).

Madeleine van Oppen, a professor and ARC Laureate Fellow for the School of BioSciences at the University of Melbourne, lead a research group focusing on the assisted evolution of the microalgae for enhancing coral heat tolerance.

“Some microalgal species—such as the one we used in our study—are ‘generalists’, meaning they can associate with a number of coral species,” van Oppen said in an interview with States of Life. “Others are very specific and can form a symbiosis with only one coral species. Similarly, some corals can associate with several microalga species while others associate with only one.”

Coral reefs form obligate symbiosis with its microalgae, meaning it cannot live without them. The microalgae provide the coral with sugars they fix using carbon dioxide (CO2), water and the sun’s energy.  The team developed microalgal symbionts outside of the coral host in a controlled lab environment before reintroducing  the heat-evolved algae into coral to increase the thermal bleaching tolerance.

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The experiments were conducted at the Australian Institute of Marine Science in the National SeaSimulator, one of the most advanced experimental aquaria facilities. The red light is required to not disturb the corals from spawning (credit: Patrick Buerger).

van Oppen developed the idea together with close colleague Ruth Gates, who passed away in 2018,  because corals and coral reefs are declining fast primarily due to global warming causing more frequent, more severe and longer summer heat waves that cause mass coral bleaching.

“It’s too early to definitively say on what scale heat-resistant coral could be grown, but one possibility is that millions of coral larvae will be reared in large aquaculture facilities or collective from coral spawning slicks, van Oppen said.

van Oppen continued, “A huge challenge is strong action on climate change, which is absolutely critical for the future of coral reefs. Interventions, such as the one in our paper, may be used to buy time for coral reefs until we stabilize the climate. I believe the scientific evidence that climate change is mostly driven by human activities is overwhelming.”

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A healthy coral reef, Hardy Reef in Queensland, Australia. Aerial view. When corals are of good health, they are known for their vibrant colors (credit: CSIRO).

Next the team will examine whether the increased heat tolerance of coral larvae with lab-evolved microalgae is also found in the adult life stage of coral, while also investigating whether other species of micro algae can be lab-evolved and increase the thermal bleaching tolerance.

The research was conducted by CSIRO in partnership with AIMS and the University of Melbourne. It was funded by CSIRO, Paul G. Allen Family Foundation (U.S.A.), AIMS and the University of Melbourne.

Madeleine van Oppen focuses on assisted evolution, where mechanisms of adaptation and acclimatization in corals and genetic manipulations to enhance stress tolerance and fitness of corals in a changing environment are explored. Her research focuses on microbial symbiosis in corals, adaptation/acclimatization to climate change, and connectivity of coral reefs.

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