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How a new super-coral could save reefs from climate catastrophe

BY Ashley Balzer

8th Sep 2022 Environment

How a new super-coral could save reefs from climate catastrophe

With climate change on track to devastate the world's coral reefs, scientists race to create a new super-coral that can survive extreme temperatures

More than half of Earth's coral reefs have been lost since the 1950s, primarily due to rising ocean temperatures. But coral has a built-in way of responding to overheating that works a bit like how humans sweat to cool down.

Many scientists think this could be the key to saving coral reefs.

Coral bleaching: Why algae holds the key

Bleached coral on sandy ocean bedWithout algae, coral is deprived of nutrients and its vibrant colour, and will over time starve to death

A type of microscopic algae called Symbiodiniaceae lives within most coral’s tissues. The two organisms have been working symbiotically for hundreds of millions of years in a way that resembles the relationship between humans and trees.

The algae consume coral’s waste products, and coral consumes nutrients that the algae photosynthesise. Coral also provides shelter for algae.

But when exposed to excessive heat or light, the algae release harmful chemicals, so the coral casts them out.

Since the algae give coral its color, the algal exodus leaves its former home looking skeletal—a phenomenon called coral bleaching. Left without their main energy source for too long, the coral will starve to death.

This is also bad news for the algae. But evolution has provided a biological feedback loop that can help the two reunite.

"The two organisms have been working symbiotically for hundreds of millions of years"

One of the compounds that algae release when under thermal stress, called dimethyl sulfide (DMS), bubbles up to the surface of the water and forms a thin, low-hanging cloud layer.

The clouds shield the reef like a natural, on-demand layer of sunscreen. With this protection, the water cools down and algae can return to the coral and reestablish their partnership—unless the stress is too severe.

Climate change is putting a strain on this self-regulation. Research suggests there may be a tipping point; if the water is too hot for too long, the coral may consume the components that make up DMS before it can form.

Summer heatwaves are becoming too common and intense for coral and algae to naturally adapt fast enough.

Evolving heat-tolerant coral and algae

Red coral grows out of reef in deep blue oceanSelectively breeding heat-tolerant coral could help to regrow coral reefs while ocean temperatures are still hot

Scientists are testing out different ways to hasten that adaptation through various methods of assisted evolution.

Some teams are currently conducting small field trials of selective breeding, where they identify the most heat-tolerant members of a sample of corals. Then they breed them together to create hardy offspring that can be used to help restore coral reefs.

Others are focusing their efforts on speeding up the algae’s adaptation, attempting to increase its thermal tolerance in labs. Recent laboratory studies show that some heat-evolved algae can make coral more resistant to bleaching once they have been reintroduced into reefs.

Another potential solution involves probiotics, and it relies on some of the reef’s tiniest members.

“Corals have a very diverse bacterial community, like our gut microbiome, that’s important for their health,” says Madeleine van Oppen, a professor at the University of Melbourne and senior principal research scientist at the Australian Institute of Marine Science, who co-authored a paper discussing how bacteria could help preserve coral reefs.

“We’re exploring the possibility of developing a bacterial probiotic to make corals more resilient to summer heatwaves.”

"Some heat-evolved algae can make coral more resistant to bleaching"

This method is still in its infancy, but scientists know it requires a few specific things.

Probiotic bacteria need to be culturable, form a stable association with corals (instead of washing away to other parts of the ocean), and have the right traits that will benefit coral under heat stress.

Experimental evolution can help certain bacteria mitigate coral bleaching even better than they naturally do. If bacteria can combat the overproduction of toxic chemicals that algae release when it gets too hot, it could prevent the algae from being cast out from the coral in the first place.

“We are accelerating nature’s own processes by keeping a culture of bacteria through hundreds of generations in conditions that will lead them to adapt to increased heat, similar to what they would be subjected to during coral bleaching,” says Justin Maire, a postdoctoral fellow at the University of Melbourne in Australia, and the lead author of the paper.

The team will focus on bacteria that occur naturally in many species of coral all over the world, so that they could be safely and stably introduced into reef environments.

Once they demonstrate the concept in the lab, they’ll begin trying it out in the real world in small areas to monitor the effects.

Giving coral reefs time to cool down

Sunlight shines from surface of water down underwater to coral reefEven if we halted climate change now, coral reefs would need to endure while the oceans take time to cool down

Ultimately, scientists may implement a cocktail of solutions to save coral reefs.

“We could, for example, selectively breed heat-tolerant corals and combine that with enhanced algae and a bacterial probiotic,” says van Oppen.

“Even if we stopped all greenhouse gas emissions today, it would still take time for warming to decrease and coral reefs to recover. We have a relatively narrow window now to act by helping coral become more resilient while the world transitions to green energy.”

"We have a relatively narrow window now to act by helping coral become more resilient while the world transitions to green energy"

“Our goal is to get corals over the line until they can survive by themselves, once climate change isn’t such a dire threat,” Maire adds.

“This kind of solutions-based research holds the power to solve problems we humans created in the first place, simply by accelerating mechanisms that already happen naturally.”

Paired with strong action on climate warming, assisted evolution could save our coral reefs.

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