Scientists Are Learning How to Help Coral Reefs Save Themselves

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CRISPR for Corals

Before Phillip Cleves turned his attention to corals, his focus was biomedicine.

"It was always kind of the plan," he said. "When I was an undergrad, my 'aha' moment was when I learned that corals have algae that live inside their cells, undergo photosynthesis, and feed the corals. To me, as a young scientist, I was completely blown away by that."

Today, Cleves runs a lab at the department of embryology at the Carnegie Institution for Science in Baltimore, Maryland, where, like Howells, he works to understand the basis of resilience to heat stress in corals.

"What we're doing in my lab now is trying to apply biomedical techniques to corals, to better understand their genetics and molecular biology in order to better prevent and ameliorate the effects of climate on these ecosystems," said Cleves. "Just like it's important to understand the molecular basis of human diseases, we think that if we understand the molecular basis of coral biology we can better predict and make therapeutics to help preserve corals, just like we do for human diseases."

Cleves pointed out that even though coral reefs are being wiped out an unnerving rate — 30% of the Great Barrier Reef was destroyed during a 2016 heat wave — scientists actually don't know much about how corals work at the genetic level.

"The reason we know so little is because corals are really hard to study in the lab and we didn't have genetic tools like we have in other systems to really understand the genes involved," he said.

In recent years, Cleves has helped to overcome this barrier by developing and applying CRISPR/Cas9 genome-editing technology to coral specimens from the Great Barrier Reef. "In the short term, what we're really excited about using CRISPR for is to be able to ask, really for the first time ever, 'what do genes do in coral?'" said Cleves. "We've been able to characterize some genes as master regulators of the coral heat stress response. So we have some clues as to the types of genes that protect corals from heat stress, and we're interested in developing these tools to better understand how corals work at the genetic level."

"I think it's mostly us in collaboration with great people around the world using genetic engineering to study corals right now," he added. "I hope there's going to be more attention to it and that the [coral gene editing] method will expand so that we'll really understand what's happening."

Cleves hopes that scientists might eventually be able to find genetic determinants for corals that can withstand future climate scenarios, helping to focus limited conservation efforts on those most likely to withstand the coming changes.

"My dream would be that with a deeper understanding of what genes make corals resilient to climate change, we could go out into the field and use that genetic information," said Cleves. "Wouldn't it be cool to have like a 23andMe for corals? Or you go out and you say, okay, this animal, this animal, this animal — these ones have genotypes that make them the corals of the future."

But Cleves' dream does not involve manipulating the genomes of corals in the wild. He limits his genetic engineering efforts to the lab, where he and his team try to make mutations that confer extra resilience on corals. The end game is to find resilient corals that already exist in nature and to propagate these evolutionary winners.

"The idea of making genetically modified coral and releasing it is not really something that we are thinking about because our understanding of genetic information and the genetic basis of coral biology is really in its infancy," said Cleves. "We don't know the genes that could enhance tolerance even if we wanted to do that. Also, there would be a lot of regulatory and ethical considerations about releasing genetically modified corals."

Not all of Cleves' coral research involves gene editing. In a Science Advances paper published in January 2021, Cleves, first author Amanda Williams, and colleagues extracted and analyzed metabolites involved in growth and development from bits of Hawaiian corals that they bleached in a lab to investigate their physiological responses to bleaching. The researchers identified several metabolites that may offer diagnostic markers for heat stress in wild corals."

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By understanding corals' strengths, scientists can guide conservation efforts.