Sex in the lab can save coral reefs. But at what cost ?

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Crawford Drury, coral ecologist and principal investigator of the Coral Resilience Lab at the Hawai’i Institute of Marine Biology, works in selective coral breeding. This involves selecting wild corals that have desirable genetic traits – such as the ability to survive high ocean temperatures – and then crossing them to produce offspring with a better chance of resisting the effects of climate change on their habitat.

Over the past decades, more than half of the world’s coral reefs have died. And, according to a UN climate assessment, they are expected to decline by 70 to 90 percent over the century, even if global warming is kept at the 1.5 degree Celsius target set in the 2016 Paris Agreement. Mass bleaching events – a stress reaction in corals that weakens and sometimes kills them – are increasingly common. Ocean acidification, pollution, storms, disease and overfishing endanger these ecosystems.

Although they cover less than one percent of the world’s oceans, coral reefs – dubbed the tropical rainforests of the sea – are home to nearly a quarter of marine species. Millions of people depend on it for income from tourism and fishing, as a source of food and new medicines, and to protect themselves against coastal erosion. They also have significant cultural value for indigenous peoples.

Drury’s laboratory is a continuation of the work of its founder, Ruth Gates, who died in 2018. About seven years ago, Gates joined forces with Madeleine Van Oppen, a coral geneticist at the Australian Institute of Marine Science (AIMS), and together they pioneered a concept known as assisted evolution, at a time when this concept was still widely regarded as a fringe concept. “Most of our work is trying to understand and exploit the natural processes that are already happening, and to take advantage of some of the real mechanisms that nature already has to deal with change,” Drury explains. His team collects eggs and sperm from colonies of corals they know are heat tolerant, puts them in small tubes, and fertilizes them with other species of coral, which in turn produce coral larvae with these. characteristics. The hope is to use these corals to restore damaged reefs.

Van Oppen’s group, meanwhile, is focused on selecting more heat-resistant algae that could be introduced into the coral. In a 2020 study, his team showed that corals created this way were up to 26 times more likely to survive extreme heat than others. His lab is also exploring the use of probiotics on coral reefs to help them withstand rising temperatures. “I hope that we will eventually produce tools and knowledge that will help us avoid the impending disaster,” she said.

Not everyone is sure this will work. One criticism is that we don’t know what consequences might have on species diversity from playing with coral genetics. Another is its scalability. But those worries get ahead, Drury says: The problem is so serious that if we don’t act now, coral reefs will die. “If you’re dealing with this climate change freight train and all of these stressors, you might not have much to deal with or manage at the end anyway. “

Drury and Van Oppen both point out that assisted evolution is only a temporary solution to save time for reefs. To truly save them, the root cause – climate change – must be addressed. “It’s like a bandage,” Van Oppen explains. “You can hopefully manage the symptoms for a while. But then, if you don’t actually remove the cause, in the long run, that won’t be enough. “


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