Scientists put a dying coral next to a healthy one — and watched it heal before their eyes

The best medicine for a dying coral may be the power of touch. 

Scientists at Stanford University in California stumbled on a promising discovery when two coral fragments in the lab — one bleached and one healthy — tipped over in a tank and touched. 

“We watched the healthy coral send over these colourful beneficial algae over to the bleached corals, and we watched its colour restore basically in front of our eyes,” ocean scientist Danny Collins told As It Happens guest host Dave Seglins.

Within a couple weeks, he says, the dying coral had recovered “to the point where it was indistinguishable from the healthy coral.”

“We were blown away,” Collins said. “It does seem like this could open a door to possible reef restoration.”

The findings, published this month in the journal Science Advances, brings new hope at a time when the world’s coral reefs are facing imminent collapse. But researchers caution the findings are limited to lab settings for now and that any efforts to restore coral must be paired with efforts to protect them.

Healthy coral reef ecosystems are explosions of bright colour.

But that colour doesn’t come from the corals themselves, Collins said. Instead, it comes from beneficial algae, which are absorbed into the coral’s tissues through photosynthesis and provide nutrition.

“The coral provides the housing and these algae provide the food. And this relationship really is the bedrock for why coral reefs ecosystems can be so productive,” Collins said.

“But as the water gets warmer, they both get stressed out. And as a result, these beneficial algae start to produce toxins that the coral doesn’t really like. And in a kind of fascinating response, it kicks … the algae out of its tissues.”

That leaves corals whitened, starving and on the brink of death, a phenomenon known as coral bleaching.

“We’ve demonstrated that, you know, they aren’t dead. And not only are they not dead, they’ve got a remarkable capacity and potential to rapidly recover,” Collins said.

Only works with genetically related corals

But this doesn’t mean the problem of coral bleaching is solved, says Collins. The experiments have limitations.

For one, there has to be direct contact. When the team put the coral fragments a few millimetres apart, there was no effect.

“It kind of sounds science fiction-esque, but the healthy coral and the bleach coral, their tissues actually fuse together,” he said. “They create a tissue bridge that kind of acts as a nutrient highway that allows for the healthy coral to then send over nutrients and this colourful algae over to the bleached coral.”

Scientists have found that when a bleached coral touches a healthy genetic clone, it recovers ‘to the point where it was indistinguishable from the healthy coral,’ says Stanford University’s Danny Collins. (Dannny Collins)

What’s more, it only works with genetically identical corals.

“When we put them with different genetic backgrounds, what we found was actually a fascinating immune and antagonistic response, where the corals actually rejected each other, similar to an organ donor or an organ transplant might be rejected in someone’s body,” Collins said.

He says that’s because it’s a “colonial animal” — a living organism made of thousands to millions of polyps. 

“When corals of the same genetic background come in contact with each other, they recognize each other and actually can infuse,” he said. 

“It’s actually beneficial on a reef that you can have fusion, because if you’re in a big wave and part of you gets knocked off, you can then kind of reconnect with yourself.”

Stanford University ocean scientist Danny Collins says his new research provides a possible pathway to coral restoration. (Submitted by Danny Collins)

About 96 per cent of the world’s shallow-water reef systems are critically endangered and could disappear by 2075, the International Union for Conservation of Nature announced on the sidelines of a UN biodiversity conference in Albania on Thursday. 

This will have ripple effects for biodiversity, tourism and fisheries, the report notes, as coral reefs are ecosystems that support between a quarter and a third of all marine species.

‘Glimmer of light’

The Stanford research is a “glimmer of light” in a wave of bad news, says coral scientist Julia Cole, who was not involved in the study.

“I think it’s super exciting,” said Cole, chair of the Department of Earth and Environmental Sciences at the University of Michigan. “The natural world can just surprise us sometimes.”

But she cautions there are hurdles to overcome.

“If you think about the scale of reefs as kilometres, or in the case of the biggest reefs, thousands of kilometres … something that requires coral-to-coral contact, it would be a very meticulous and kind of overwhelming project.”

Collins says his team is working on ways to extract algae from healthy reefs, culture it in labs, and use it to protect at-risk reefs from expected bleaching events. 

“We hope in the near future we can have some interventions that actually could be field deployable and possibly scalable,” he said.

Even if we can heal the bleached coral, Cole says warming oceans remain a threat.

“We know how to solve the warming climate that’s causing these problems,” she said. “It comes back to getting serious about reducing greenhouse gas emissions, getting off of fossil fuels and transitioning to a clean-energy economy.”