Training algae to become more tolerant of rising water temperatures could help save coral reefs, according to a new study from the University of Melbourne. The researchers exposed algae in laboratories to temperatures of 31C for four years, 3C to 4C above what they usually experience. When the algae were reintroduced to coral they were tolerant of higher temperatures. Corals are bleached when rising water temperatures cause them to expel the algae that live in their tissue and supply their nutrition. Mass bleaching caused the Great Barrier Reef to lose around 50% of its corals during heatwaves in 2016 and 2017.
Why does this matter? Aerial surveys of the world’s largest reef system, Australia’s Great Barrier Reef, have shown the most widespread bleaching event ever witnessed occurred this summer, with a quarter of the reef experiencing severe bleaching. Mass bleaching caused the reef to lose around 50% of its corals during heatwaves in 2016 and 2017. This new research could help bolster reefs against warming seas by effectively engineering heat-resistant algae – one critical component of corals. All of the 10 strains of microalgae tested expanded their thermal tolerance in a laboratory environment, and three of these went on to increase bleaching tolerance when reintroduced to coral larvae. The researchers stated these heat-evolved strains could be grown in high quantities in aquaculture facilities for potential future symbiotic use with corals in the ocean. Training microalgae to become heat tolerant is one of a series of approaches to engineer coral to be more resilient, with more advanced genetic engineering techniques investigating the alteration of algae DNA. Efforts to increase coral genetic diversity are also pertinent as it has recently been shown diversity can be reduced by coastal pollution, another factor that can lead to reduced coral resilience. Research is occurring in other areas to save corals. The Australian government’s Reef Restoration and Adaptation Program, for example, is supporting an array of potential solutions to help protect the health of the ecosystem. The scheme has supported a recent cloud brightening trial to test a delivery system for injecting sea salt particles into the atmosphere, where they are hoped to act as cloud condensation nuclei, brightening clouds to reflect solar irradiation and cool the reef. Other methods to attempt to lower local water temperatures include recreating sea fog through a similar method of spraying seawater into the air. Floating water surface shields made of calcium carbonate could also have a similar effect. The physical structure of reefs can also be enhanced using mesh or artificial reef frameworks. Separate research from academics in Cambridge and California has created 3D-printed coral-like structures that can house microscopic algae populations, which the scientists state can be used for research to protect existing reefs, as well as for potential bioenergy production. Unfortunately, engineering methods to sustain reefs are likely to become increasingly necessary as 70–90% of tropical coral is expected to disappear due to climate change, even if temperature rises are kept to 1.5C, according to the Intergovernmental Panel on Climate Change.