Story at a glance

  • There are more species on coral reefs than any other place in the ocean.
  • More than a fifth of the world’s coral reefs are damaged or lost and another 35 percent could be lost in the next 10 to 40 years.
  • Scientists are fighting back with a growing arsenal of weapons.
  • Scientists hope they can help increase resilience among corals, though some of the techniques are also controversial.

The United Nations released a dire warning for the world’s coral reefs last month: Even if global warming is limited to 2 degrees Celsius, almost all reefs will “degrade,” according to the Intergovernmental Panel on Climate Change’s (IPCC) latest oceans report.

As reef health declines, everything from biodiversity of millions of species to tourism will be impacted. Heatwaves over the past 20 years have killed or bleached corals across nearly all reefs listed as World Heritage sites in places such as Hawaii, the Galapagos Islands and Australia. In 2016 and 2017, half of all corals died in the Great Barrier Reef in one of the most harrowing back-to-back bleaching events ever seen.

It’s not just warmer oceans though that puts corals at risk. As seas absorb more carbon dioxide they become more acidic. This, in turn, corrodes calcium carbonate, the core ingredient of corals. Industrial chemical runoff from farms, lawns and golf courses also hurts reefs.

This summer, some scientists gained hope that a giant “raft” of floating pumice rock spotted near Australia could help replenish the Great Barrier Reef. Scientists think the Manhattan-sized mass of volcanic rocks could help transport new colonies of barnacles, corals and other organisms to help replenish the reef.

But given moments like these only happen about once every five years, researchers are also working on a whole host of other initiatives to save our world’s reefs.

1. Replanting

As Jessica Levy, restoration program manager at the Coral Restoration Foundation, explained, the conservation community recently came to a consensus: “If we do nothing, we will lose everything.”

So, four years ago there was a call for “active restoration as a necessity for any chance of these corals persisting into the future,” Levy says. And indeed, replanting nursery-grown corals is perhaps one of the most successful methods for restoring reefs.

Coral can be grown in both land-based and ocean-based nurseries. One example is the coral tree, which allows conservationists to suspend small corals like ornaments in the ocean to grow.

One of the most typical methods for cultivating coral involves pruning and propagating, much like you would for a plant. You snip a little piece of wild coral off and bring it back to the nursery to continue growing. Once it’s big enough you head back out to the reef and replant it.

“You can make more biomass by doing that in a controlled environment,” says Iliana Brigitta Baums, a biology professor at Penn State.

And while it’s “not rocket science,” says Levy, it is pretty labor intensive.

Another challenge, adds Baums, is that by pruning and replanting “you’re basically making more of the same.” This means less genetic diversity — which comes from sexual reproduction rather than propagation. The more genetically diverse the reef, the better chance it has of adapting to new environmental conditions.

2. Boosting diversity

Coral reproduce once a year, usually around a full moon. Sperm and eggs are released like a blizzard, swirling around and fertilizing in the water.

Each summer in the Caribbean, people use what Baums described as handmade “coral condoms” to collect eggs and sperm to make larvae.

To help guide conservationists on how to best produce thousands of “coral recruits,” as Baums calls the resulting baby coral, she and several colleagues released a scientific guideline in July.

It takes about three days for the larvae to be strong enough to swim, and one more day before it’s able to find a solid surface onto which it can metamorphose into adult coral; kind of like a tadpole becoming a frog.

This can be done either in the lab or in floating hatcheries, where the larvae are able to attach to small chunks of reef and then be transported by divers down onto the reef to continue growing.

The challenge is how to scale this up and make it go more quickly, says Baums. “We need tens of millions of coral recruits if we want to keep our coral populations healthy.”

One attempt to do this is the LarvalBot. Developed by scientists in Australia, the robot is able to spread larvae more efficiently than divers.

3. Cryobanking

Scientists are also exploring how they might preserve today’s coral species for the future. Namely, through cryobanking.

Coral banks in the U.S. and Australia currently hold genetic material from more than 30 coral species. And recently, some researchers made a breakthrough with this technique. In 2018, a Hawaii-based team was able to use an antifreeze solution mixed with gold particles and “quick-thaw lasers” to cryogenically freeze, and unfreeze, coral larvae for the first time.

Shortly after, another team of scientists was able to use cryogenically frozen coral sperm to fertilize live eggs, which successfully grew into larvae.

Meanwhile, some scientists are going one step farther. 

4. Genetic Engineering

Once considered a radical idea, millions of dollars are now being invested in efforts to genetically engineer coral. The goal is to create new breeds that can better survive extreme heat.

Raising larvae in the lab, scientists are crossbreeding species to become more heat tolerant. This can also be done by raising coral in hotter water.

Another technique is to focus on algae, which coral rely on for oxygen and other nutrients. By creating new types of heat-tolerant algae and bacteria, scientists hope they can help corals fend off bleaching events. And last year, scientists in the U.K. and Saudi Arabia were able to successfully tweak one algae’s genome.

A postdoctoral scientist at Stanford in 2018 also became the first to successfully use gene-editing CRISPR technology to genetically modify coral.

There are, however, some risks. Some researchers worry that by editing a species to become stronger in one specific way, it could mean weakening it in other unforeseen ways. There’s also the chance that the new coral becomes an invasive species, potentially wreaking havoc on marine ecosystems.

5. Artificial cooling

The scale of the problem is so big, though, that it has led some researchers to consider what Baums calls “pie in the sky” options to cool the water down. This includes ideas like using underwater fans, creating artificial upwellings of colder water or using localized shading structures.

The aim with all of this is to fend off bleaching events by reducing heat and light stress on the corals. But as a recent report by the National Academy of Sciences points out, “these interventions have not been implemented beyond experimental scales in the field, which makes their efficacy and impacts uncertain at this time.”

6. Reef Insurance

Yet, as scientists explore all of these innovations, storms are becoming more intense and more devastating as the world warms. To help reduce the impact on corals, there is now an insurance policy for reefs.

Last year the Coastal Zone Management Trust, a partnership between the Mexican state government of Quintana Roo, hotel owners, the Nature Conservancy and the National Parks Commission, bought the world’s first coral insurance policy.

Storm-force winds will trigger a rapid payout. Damage assessments can then be conducted, debris removed and repairs carried out. “Post-storm brigades” of divers conduct rapid repairs, often involving drilling metal rods into the reef or using cement to reattach coral.

They have to work fast though; damaged parts of the reef can die in just 45 days.

7. Fight climate change

Ultimately, one of the biggest things that can be done to keep coral reefs healthy is to tackle climate change.

“It is crystal clear to the scientific community,” says Baums, “that the only way we will maintain healthy and thriving coral reefs is if we limit carbon emissions.”

This sentiment is echoed by Levy. Replanting corals, she says, should not be viewed as the “scapegoat” for thinking it’s okay to “screw everything up and restoration will come behind and fix it.”

And while some activists and scientists might say there’s no point spending time on anything other than finding ways to reduce emissions, others like Baums see their work protecting corals as preparing “for the hopeful day when we’ve figured out how to reduce carbon emissions and temperatures aren’t rising anymore.”

Want to do your part? Here’s how you can help:


NOAA’s guide: “What can I do to protect reefs?”

[Similar guide available from the EPA here]

The Nature Conservancy: “8 easy ways you can help coral reefs”

Some guides to reef-friendly sunscreens here, here and here [important caveat: ‘reef friendly’ is not regulated]


Social contacts:

Coral Restoration Foundation

the Nature Conservancy

the Coastal Zone Management Trust

Published on Nov 04, 2019