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Climate Solutions

Scientists are weighing radical steps to save coral

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The world’s coral reefs are in dire shape because of climate change. Severe bleaching in 2016 and 2017 killed off nearly 50 percent of the Great Barrier Reef, and similar damage has struck around the globe. If the Earth warms by 2 degrees Celsius or 3.6 degrees Fahrenheit – and we’re already halfway there – then 99 percent of coral could be gone, scientists say.

Some corals are still doing fine, like this healthy coral reef off the coast of Isla Mujeres, Mexico.

Bleaching occurs when warm waters stress corals and cause them to eject the symbiotic algae that live within them, as seen in the Society Islands of French Polynesia.

Scientists and conservationists are wondering what, if anything, they can do to keep corals going, even as the climate continues to warm, which increases the risk of bleaching as well as coral diseases, since weakened corals have a harder time fighting them off.

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Some corals are more resistant to temperature changes. After they bleach, they can still recover if the water is not too hot for too long.

But if the heat stress lasts long enough, as in this reef off Japan, the corals die. Corals can’t go too long without their symbiotic algae for nutrition and basic metabolism.

One approach to helping corals fight climate change is well underway. In Florida, divers with the Coral Restoration Foundation are actively reimplanting corals on degraded reefs, an approach that is also being adopted in the Caribbean and other spots around the world. The groups grow the new corals on underwater metal structures, called “trees,” within larger nurseries. The Coral Restoration Foundation has planted more than 100,000 corals on the Florida Reef Tract, the third largest barrier reef structure on Earth.

A coral nursery in Jamaica.

They’re not in the business of picking winners, these coral “gardeners” say. Rather, they simply try to grow a genetically rich crop of corals – even going so far as to collect coral sperm and eggs from the sea when the organisms spawn once a year, and then blend them in the laboratory to foster many different genetic combinations. Diversity, says the Coral Restoration Foundation’s Alice Grainger, gives corals the best chance of surviving the coming threats.

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In Hawaii, something more dramatic is in the experimental stage. It’s called “assisted evolution.” Here, scientists study which corals are the most resilient to warming, and even bring them into the lab to condition them by exposing them to even more heat – almost like exercise. They also breed corals that are more heat-resistant to produce stronger offspring. “We have these little coral babies that survive three times as long as your average coral under temperature stress,” says Crawford Drury, a lead researcher on assisted evolution at the University of Hawaii at Mānoa.

A scientist studies coral larvae at the Hawaii Institute of Marine Biology on Coconut Island, Hawaii.

Coral growing under ultraviolet light at the Hawaii Institute of Marine Biology on Coconut Island, Hawaii.

Some ethicists are struggling with the implications. Assisted evolution “raises challenging ethical questions because the intention is not to revert to a previous status quo, but to modify a community so that it survives better in the conditions that we created,” two scholars wrote recently. Drury says that for now, the researchers are not reimplanting selectively bred corals in the wild – they are simply learning more about what’s possible, so better choices can be made. “I always want that information and that knowledge,” he said.

The seas off Hawaii have also seen a recent coral bleaching event, which researchers used to study coral resilience.

Even with all these strategies, though, it’s not clear reefs can be saved in their current form. The largest corals, which provide reefs with their structure, tend to be pretty slow growing. So programs to actively reintroduce them would face a big hurdle – time – as climate-driven ocean heat waves are forecast to become even more frequent and intense. Still, Drury says we have to at least study the options for intervening. “We’ve got this impending situation that will lead to drastically different looking reefs in the next several decades if nothing happens,” he says.

A close-up of polyps on an Orbicella faveolata (Mountainous Star Coral) at the Mote Marine Laboratory in Florida.

While scientists test these strategies, bleaching continues to kill corals around the world.

Videos by Chris Mooney, Whitney Shefte, and Associated Press. Photos by Donald Miralle/Getty Images for Lumix; Alexis Rosenfeld/Getty Images; Kyodo; David J. Phillip/Associated Press; Caleb Jones/Associated Press; Stefan Irvine/LightRocket via Getty Images; Lucas Jackson/Reuters. Photo editing by Karly Domb Sadof