Australian scientists have made corals in the lab that are more resistant to high water temperatures, making it easier for the corals to survive in the warming waters of the Great Barrier Reef. To do this, the team crossed corals from different parts of the reef and combined the offspring with different types of algae. For example, they were able to make coral-algae combinations that survive better in water at 32°C. That is the temperature at which in the Great Barrier Reef the cooperation between coral and algae, which is vital for both, usually breaks. The biologists described their experiments on Tuesday in Nature Communications

    The work offers hope that the Great Barrier Reef can be better protected from rising water temperatures due to climate change than previously thought. Coral scientist Erik Meesters of Wageningen University, who was not involved in the research, calls the publication “extremely high quality”. It shows that the resistance of corals to climate change is “underestimated and can be influenced”.

    Since 2020 there has been a major program in Australia (the Reef restoration and adaptation program) to restore the ravaged east coast reef and adapt to climate change.

    Globally, warm water corals are threatened by the warming of the oceans. There are also sea heat waves, which cause a lot of stress. Normally, corals live in symbiosis with certain types of algae, as some fungi do with trees. “They can’t exist without each other,” says Kate Marie Quigley of the University of Melbourne and lead author of the now published article. The algae make sugars through photosynthesis, part of which they donate to the coral.

    Serious damage

    The coral in turn filters trace elements from the water and transports them to the alga. If there is too much stress, this cooperation breaks down and the alga disappears. The coral fades. bleaching) than. “In the Great Barrier Reef, that happens around 31.32 degrees Celsius,” Quigley says. At the moment in the Great Barrier Reef is the sixth mass bleaching event – large-scale bleaching – ongoing since the late 1990s. According to the report published in September last year According to the IPCC climate panel, 90 percent of warm water corals worldwide are seriously damaged by an average warming of 1.5°C. At the current rate, that limit could be reached within a few decades.

    For the crossing of corals, the Australian researchers assumed one species, Acropora tenuis† “An important species for the reef here,” Quigley says. They made offspring with the eggs or sperm of different individuals, originating from the northern or central part of the reef. “You could call it marine farming,” Quigley says. In some cases, this produced offspring that were more heat tolerant than the parents. According to Quigley, such crossings can also occur in the wild in the Great Barrier Reef, but “on very long time scales.”

    Based on model calculations, the biologists determined which of the more than 3,000 reefs in the Great Barrier Reef could possibly be found in heat-tolerant parent corals. They identified 251 reefs as “potential sites” for such corals, which should produce offspring that survive temperatures between 32 and 35.5°C. Quigley has since visited many of those locations, she says. “We conducted these lab experiments in 2018. A year later I visited many of those 251 locations and collected coral.

    Last week, three other scientists, and participants in the reef’s recovery program, expressed all their hopes for the survival of the Great Barrier Reef, based on previous research. As it turns out an article published in February that after bleaching, corals can start a symbiosis with other, more heat-tolerant algae.

    big discussions

    But there are limits to the heat tolerance of corals, Quigley emphasizes. “We shouldn’t think, oh, the warming can continue for a while. Above all, greenhouse gas emissions must stop.”

    Meesters says the research was done on one coral species. But the reef has many types of corals, plants and animals. “You can make a few coral species more heat-resistant, but countless species will still become extinct, and the ecosystem threatens to impoverish dramatically.”

    Quigley adds that a huge increase in scale is needed to introduce more heat-tolerant corals in the Great Barrier Reef. “The area is slightly larger than Italy.” If that were even possible, the question still remains whether the large-scale release of lab-grown corals is desirable? “That will require major discussions.”