Saving the Coral Reefs: 9 Innovations in Coral Reef Restoration

Various species of fish swimming around a colorful coral

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The coral reef, much like the polar bear, has come to symbolize the devastating effects of climate change. The once-colorful ecosystems that support a quarter of all marine species are quickly dwindling due to heat stress, ocean acidification, and water pollution. As of 2021, half of the world's coral coverage had been lost just since the 1950s, and researchers have said that a 2.7-degree temperature rise could increase that number to a catastrophic 70% to 90%.

Scientists are scrambling for ways to save the coral reefs, brainstorming and testing a range of strategies. Some are painstaking, like propagation; others are highly imaginative, like using sound and electricity. Here are some of the most innovative coral reef restoration experiments of the century so far.

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Cloud Brightening

Aerial view of Great Barrier Reef on cloudy day


Australian researchers developed a method called "cloud brightening" that involves creating clouds over coral by spraying microscopic sea particles into the sky using a turbine. The clouds ultimately cast a shadow over the coral and cool the water temperature during heatwaves, ultimately preventing coral bleaching.

The research team tested prototype filtering equipment at Broadhurst Reef in 2020. The experiment was a success, and the team announced plans to trial larger cloud sizes over the coming years. By 2024, the researchers aim to test the technology's impact on rainfall patterns to make sure it's a feasible method.

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Acoustic Enrichment

Healthy reefs are noisy places, but when they're damaged, they go silent. One group of scientists started playing the sounds of a healthy reef over a loud speaker in an unhealthy reef environment to see how the ecosystem would respond.

In 2019, researchers from the University of Exeter, University of Bristol, and Australia’s James Cook University, along with the Australian Institute of Marine Science, conducted a 40-day "acoustic enrichment" experiment on a degraded section of the northern Great Barrier Reef. The number of fish within that reef doubled, and the number of species present increased by 50%.

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Assisted Evolution

Artificial coral in pipe contraption

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Assisted evolution takes an organism's naturally occurring evolutionary processes and expedites them. Scientists internationally are working to apply this concept to coral to prepare it for the stressors of hotter, more acidic water that climate change will bring about.

Assisted evolution for coral takes many forms. One is stress conditioning, in which coral pieces are exposed to sublethal conditions to boost their stress tolerance. Theoretically, they would then pass those evolved traits to offspring. Another method is being explored at the Australian Institute of Marine Science's National Sea Simulator, where scientists are crossbreeding coral species to cultivate a hybrid that can survive future conditions.

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In-Water Propagation

Diver inspects underwater structure designed for coral propagation

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Since 2010, The Nature Conservancy has been working in the Florida Reef Tract to breed new corals from healthy corals using in-water propagation. Coral fragments are trimmed from healthy colonies and set in an underwater "nursery." Here, they grow safely and under the watchful eyes of scientists.

More cuttings are eventually taken from the coral to grow more clones until pieces are eventually replanted at damaged reef sites to hopefully recolonize the reef on their own.

In 2019, there were more than 50,000 corals housed in underwater nurseries and some 10,000 planted on damaged reefs. Now, more than 30-plus countries are using in-water propagation, from Hawaii to Thailand.

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Some corals grow slowly. Brain coral, for example, grows only a few millimeters per year. Targeted specifically toward slow-growing corals, a technique developed by Mote Marine Laboratory called "reskinning" takes micro-fragments of boulder corals and mounts them onto bleached-out, dead coral bases. The baby corals grow and cover the surface of the old coral.

Because coral reproduction depends on size rather than age, the young corals reach maturity in less time and can start reproducing earlier than coral grown from scratch.

Through an organization called the Plant a Million Corals Foundation, 100,000 corals have been planted using the reskinning method.

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Heat-Tolerant Algae

Coral and algae have a symbiotic relationship, but when water temperatures rise, the algae bails and leaves its coral host vulnerable to bleaching.

In 2017, researchers in Saudi Arabia sought to help algae adapt to heat stress, which would encourage them to stay with coral and continue to provide nutrients. This would involve the replication and mutation of genetic sequences called retrotransposons, also known as "jumping genes," to make the algae more tolerant to heat.

The experiment was replicated, with success, in Australia in 2020. Now, researchers are testing the algal strains in adult colonies across a range of coral species.

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Biorock Technology

Diver swimming out of a biorock structure in Indonesia

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"Biorocks" use electricity to restore coral. These steel-framed structures send a low voltage of electricity through seawater, which leads to a chemical reaction that coats the coral with limestone minerals similar to a young coral's natural coating.

The nonprofit Global Coral Reef Alliance says biorock reefs help speed the growth of coral and make them more resistant to temperature spikes and acidity.

The current is safe for humans and animals, and the structures are not limited in size. "They could be grown hundreds of miles long if funding allowed," says the Gili Eco Trust, responsible for setting up more than 150 biorock structures in Indonesia.

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Gene Storage Banks

If (worst-case scenario) the world were to lose many or all its corals in the next 50 to 100 years, a repository of their genetic information would be the only chance of restoration. The Smithsonian Conservation Biology Institute has pioneered this effort using cryopreservation—i.e., freezing coral sperm.

The sperm the institute has frozen so far is kept at about -265 degrees Fahrenheit in banks at the USDA’s National Animal Germplasm Program and at the Taronga Zoo in Australia. As of 2021, 37 species of coral had been cryopreserved worldwide.

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Assisted Gene Migration

By freezing coral sperm, scientists can also migrate coral species that would otherwise remain both geographically and genetically isolated. The same group that pioneered cryopreservation at the Smithsonian Conservation Biology Institute is also leading the charge on migration. Genes from different populations are mixed to make hybrids more resistant to bleaching.

In 2021, the team reported that new coral bred from a Caribbean species had been thriving for two years in Florida under human care.

What Can You Do to Help Coral Reefs?

There's room for everyone in the fight to save coral reefs—not just for scientists with diving certifications. Here how you can help protect these beautiful and immensely important ocean keystones.

  • Wear coral reef-safe sunscreen—always, not just when you're at the beach. The chemicals (namely oxybenzone and octinoxate) that were once commonplace in conventional SPF have been found to exacerbate bleaching. Make sure to use mineral sunscreens made with non-nanotized zinc oxide or titanium dioxide, which are deemed safe by the National Oceanic and Atmospheric Administration.
  • Be diligent about your plastic use and waste. Plastic pollution is rife in the ocean, and it's one of the leading causes of coral reef decline.
  • Tourism can take a toll on coral reefs. If you find yourself near one and fancy a visit, choose a company that does it responsibly and, preferably, gives back to the reef. This means no docking on the reef, requiring reef-safe sunscreens, and teaching tourists not to touch the reefs.
  • Avoid fertilizers and pesticides at home. Yes, even if you live hundreds of miles from the coast, the chemicals you put on your lawn eventually wind up in oceans. Make sure all lawn and garden treatments are natural and safe for the environment.
  • Volunteer or donate to reef conservation and restoration organizations like the Coral Restoration Foundation, Coral Reef Alliance, or the Ocean Conservation Trust.
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