A decade ago, the world experienced its third global coral bleaching event — and the vibrant, colorful corals along the western coast of Hawai‘i’s big island began to fade. Rising sea temperatures drove these famed corals to “bleach,” a process that strips them of color following the expulsion of a nutrient-producing algae called zooxanthellae. Without this vital algae, corals essentially starve.

In 2015, researchers surveyed 14,000 coral colonies across the South Kohala and North Kona regions of West Hawai‘i and found that 38-92% of the reefs had been partially or fully bleached. Many ended up dying.

“These aren’t little corals dying; these are really big, the size of Volkswagens, that have died,” ecologist Greg Asner, director of Arizona University’s Center for Global Discovery and Conservation Science and a longtime Hawai‘i resident, told Mongabay in an interview. “It’s brutal to see, it’s visually arresting.”

For Asner, this bleaching event in Hawai‘i was a turning point, not only for the health of the reefs, but for his work.

“It changed my career,” he said. “I had been doing a lot more with tropical forests … but with that 2015 event, I said, ‘We got to do way more on reefs.’”

Asner stayed true to his intention. In 2018, he and his team began using the Global Airborne Observatory, an airborne laboratory that Asner help equip with advanced mapping technologies such as lasers and infrared imaging technologies to survey coral colonies in the Caribbean and Hawai‘i to assess their health and understand what led to their demise. Asner, who is the managing director of the Allen Coral Atlas, a tool that provides data on the world’s corals, helped generate the first global, high-resolution map of the world’s shallow tropical coral reefs.

But now, as the world experiences its fourth global bleaching event, Asner said he believes it’s time to move away from “research for the purpose of research,” and move forward with action. His latest project, which launched this year, will be the restoration of a 193-kilometer (120-mile) stretch of reef along the west coast of Hawai‘i Island, the largest contiguous coral reef in the Hawaiian archipelago.

The project, called ʻĀkoʻakoʻa, which means “bringing people and coral together” in the Hawaiian language, could be one of the first to conduct coral restoration at a large scale. To achieve this goal, funders have pledged to invest $25 million over five years. Some of the funding comes from the Dorrance family (heirs to the Campbell’s Soup Company) and the Dorrance Family Foundation; other funding comes from grants from the National Oceanic and Atmospheric Administration, the state of Hawaiʻi, and a mix of other government and private sources. If successful, the project could provide knowledge for how to restore ailing reefs around the world suffering from an onslaught of human-driven thermal stress.

Can coral restoration save the world’s reefs?

Corals are foundational animals, providing habitat for about 25% of all marine species. It’s estimated that coral reefs support 6 million fishers in more than 100 countries, and that reef fish and other animals comprise 20-25% of total catches in developing nations. Yet the world’s coral reefs are under threat from numerous stressors: pollution, destructive fishing practices, and human-driven changes to the ocean, including ocean acidification and rising sea temperatures, which can lead to coral bleaching.

Many of these stressors can be controlled through targeted conservation measures, such as restricting fishing activities or preventing pollution from running into the ocean and harming coral colonies. But dealing with thermal stress is trickier. The most effective solution would be to lower global greenhouse gas emissions, thereby slowing global warming and decreasing the amount of anthropogenic heat the ocean absorbs. Yet this solution is looking increasingly difficult to execute within a short time frame; at present, emissions only continue to rise, even as countries make increasingly ambitious commitments to decrease them. Additionally, even if humankind stopped emissions today, experts say global temperatures would continue to rise, likely for a few decades.

Some scientists are zooming in on another way to save coral reefs: coral restoration, which typically involves growing and then “outplanting” healthy coral onto sickly reefs, or even helping to breed genetically strong corals to place back on reefs. There are hundreds of coral restoration projects around the world, including locations in the Red Sea, the Caribbean and the South China Sea. Funders have invested hundreds of millions of dollars in coral restoration efforts and other protective measures to try and save the world’s corals. But there’s a catch.

While many of these projects have successfully restored coral colonies, most have only done so on a small scale. According to a 2019 study in Restoration Ecology, the majority of research-based coral restoration projects only take place over a year or two, and only restore a small area — the median size was found to be about 108 square meters (1,163 square feet), an area less than half the size of a tennis court. On top of that, the median cost was about $400,000 per hectare ($162,000 per acre), according to the study. While there are bigger projects that take place over longer periods of time, manage to restore larger areas and cost far less, experts are still divided as to whether coral restoration is a feasible solution to save the world’s corals in this era of accelerating climate change.

Terry Hughes, a professor of marine biology at James Cook University in Australia, who has been surveying the coral bleaching on the Great Barrier Reef, has called that idea “delusional,” and even said it detracts from the urgent need to curtail burning of fossil fuels. In a recent interview with Cosmos Magazine, Hughes illustrated the difficulties of performing effective restoration in a place like the Great Barrier Reef: “You would need to raise and out-plant roughly 250 million adult corals, each the size of a large dinner plate, to increase coral cover on the Great Barrier Reef by 1%.” In April of this year, Hughes wrote a dismal note on the social media platform X, formerly known as Twitter, noting that “[e]very tiny-scale coral ‘restoration’ project on the Great Barrier Reef has been destroyed or severely damaged this [austral] summer due to anthropogenic heating.” This recent bout of heating triggered the Great Barrier Reef Marine Park’s seventh mass bleaching event since 1998.

Emma Camp, a marine biologist at the University of Technology Sydney, Australia, has a different view. She said smaller-scale, research-based restoration projects have been necessary to figure out what can be done in terms of coral restoration and how such projects can be scaled up.

“I think that there’s a real risk if we brand restoration as being a failure because it’s costly or it’s not working based on small-scale science experiments needed to actually get us to a point of being scalable,” Camp told Mongabay. “Then we’re comparing apples and oranges. It’s not the same thing.”

Camp added that while the most important task is addressing climate change, coral restoration can buy us time. “And we absolutely need to buy time because all of the models, all of the predictions that are out there, are saying that if we get to two degrees of warming, that less than 1% of reefs are likely to survive,” she said.

Turning up the heat

As sea temperatures continue to rise, one thing is certain: To survive into the future, coral reefs need to be thermally tolerant. With this fact as a guiding principle, Asner and his team are using data collected from Asner’s Global Airborne Observatory to identify which coral colonies are persisting in the face of rising sea temperatures. Then the team is taking samples of these corals and testing their resilience in the lab. If the corals are confirmed to be thermally resilient, they enter a breeding program.

When asked which corals are proving to be the most resilient, Asner set the record straight: many different types of coral can cope with heat. The difference lies with individual corals, not with species, he said.

“You and I are in the same species, Homo sapiens,” Asner told this reporter. “I don’t know which of us has more heat tolerance — you’d have to put us in a room, turn up the heat, but one of us is going to croak before the other one, right? That is literally what happens with corals. There’s a range of thermal tolerance.”

However, Asner said about 10 species of coral dominate the reefs in West Hawai‘i, and his team is prioritizing these since they constitute the foundation of the reef habitat.

Thermal resistance isn’t the only trait the team is searching for. Grace Klinges, a molecular and microbial ecologist working with the ʻĀkoʻakoʻa project, said they may also look for corals that are fast growers, or corals that can deal more easily with pollution.

“There’s all sorts of things that a coral can be strong against [and] high-performance traits that we can select for,” Klinges told Mongabay in an interview. “The principles that we use to select for resilience are really similar to the principles used in agriculture — not genetic modification, but selective breeding. So just like we would select for a strain of corn that has higher oil content, that’s going to have juicier kernels, if we can … identify a coral that has high heat tolerance, and then we identify another coral that is a fast grower. We breed those two corals together and we’ve demonstrated that we can have an improved progeny.”

‘Turbocharging Mother Nature’

One method of breeding corals is simply placing corals of the same species with advantageous characteristics into a tank and synchronizing their spawning. Corals spawn about once a year, taking cues from the lunar cycle and water temperature to release tiny eggs and sperm, but this process can be manipulated in the laboratory. By spawning together, the corals may “naturally mix and make new genetically diverse combinations,” Klinges said.

Another method involves collecting eggs and sperm of different corals of the same species and mixing them to create two-parent crosses.

The researchers may raise some larvae on land, growing them into fragments that can be outplanted. However, Asner said the team will really only do outplanting at reefs of high cultural importance in Hawai‘i or for educational purposes. Their main aim is to release the larvae into the water at times when corals are naturally spawning.

“We’re going to inject hundreds of millions of these tic-tac-size larvae into the water at night when corals spawn so that we’re not going against Mother Nature,” Asner said. “We’re just turbocharging Mother Nature. We’re saying, ‘Hey, we know you’re spawning on May 6, two, three days after the last full moon, Pocillopora meandrina … so we’re going to come out and join you.”

Corals may also naturally select thermally tolerant traits when spawning, but Asner said more frequent and intense marine heat waves are making this natural process more difficult for corals, so the ʻĀkoʻakoʻa program is giving nature a helping hand by accelerating this selection process.

While the ʻĀkoʻakoʻa program has not yet attempted this full-scale larval injection, the team anticipates starting in 2025, and will be trialing the technique in some locations in 2024. The program has multiple facilities along the western coast of Hawai‘i Island, housing 72 specialized coral-rearing tanks — known as raceways in the coral restoration world — and two colossal seawater filtration systems, each worth about $1 million.

“Each one of these [raceways] can hold 1,000 coral colonies,” Asner said. “But then our system is designed to produce millions of babies from each of these coral colonies.” Once the program is running at full capacity, Asner said, they’re pushing to produce “one million coral offspring per tank per year.”

But corals need more than reproduction to survive. With this in mind, ʻĀkoʻakoʻa is working with a number of partners to reduce other stressors to the reefs, which can help corals be more resilient to rising sea temperatures. For instance, the team is working with an NGO called Terraformation to reforest parts of the island with the view of restabilizing sediment that is running into the coral reefs. It’s also working with Hawai‘i’s Division of Aquatic Resources (DAR) to regulate the ornamental fishing industry in an effort to increase fish biomass on delicate reef systems.

The ʻĀkoʻakoʻa project is also steeped in traditional Hawaiian values of environmental stewardship.

Cindi Punihaole, one of ʻĀkoʻakoʻa’s advisers and the project director at Kahalu‘u Bay Education Center on the Big Island of Hawai‘i, said she believes the ʻĀkoʻakoʻa project is built on a “strong, solid pa‘a foundation.” In the Hawaiian language, pa‘a means “solid.”

“ʻĀkoʻakoʻa is “bringing a community together and understanding the importance of taking care of place not only for generations now, but for future generations for your children’s children,” Punihaole told Mongabay in an interview. “One hundred years from now, we want a child to say, ‘Mahalo, kupuna [thank you, ancestors], wherever you are, for thinking of us,’ because they will see that our oceans are still there for them. And they’re still healthy and they can survive.”

‘This has to work’

Klinges, who used to work on coral restoration in the Florida Keys, has seen her fair share of devastation as a result of coral bleaching. In 2023, for instance, marine heat wiped out decades’ worth of restoration work in this area. Yet Klinges said she feels optimistic about the goals of the ʻĀkoʻakoʻa program.

“In Florida, we started miles behind … in terms of coral health,” Klinges said. “In Hawai‘i, we have a fairly healthy, robust reef. We’re not coming into a scorched earth reef where we have to start from ground zero and rebuild the entire ecosystem. As long as we can augment the populations a little bit by introducing more genetic diversity through reproduction, identifying more resilient genotypes through the experimental testing that we’ll do, we’re going to improve the overall population sustainability.”

Asner said he expects a range of restoration outcomes along the 193-km stretch of reef on the west coast of Hawai‘i, with some “hotspots of success and cold spots of success.” He added that the team will measure success by the level of improvement they can make in terms of reef condition over a 10-year period, as well as their ability to work with communities and government programs “to improve human behavior and land-based pollution sources.” Moreover, Asner said he believes the program will proffer knowledge of how to approach scaling up coral restoration in other parts of Hawai‘i — and other parts of the world.

“We’re going to broadcast everything we learn,” Asner said. “Nothing is held privately. It’s all shared. That way we know we haven’t lost.”

For Asner, failure doesn’t feel like an option.

“If we can’t make this work here, over the next five to 10 years, I don’t know what other answers there are,” he said. “I don’t really believe in some technological answer, like some super coral … so this has to work.”

Disclosure: One of Mongabay’s board members, Robin Martin, works with ʻĀkoʻakoʻa and is married to its founder, Greg Asner. Mongabay editorial staff retain full editorial control of this and all published articles.

Banner image: Coral reefs seen along the coast in an aerial photo. Image © Andrew Richard Hara.

Elizabeth Claire Alberts is a senior staff writer for Mongabay’s Ocean Desk. Follow her on Twitter @ECAlberts.

Science and culture join forces to restore 120 miles of Hawaiian reefs

Citation:

Bayraktarov, E., Stewart‐Sinclair, P. J., Brisbane, S., Boström‐Einarsson, L., Saunders, M. I., Lovelock, C. E., … Wilson, K. A. (2019). Motivations, success, and cost of coral reef restoration. Restoration Ecology, 27(5), 981-991. doi:10.1111/rec.12977

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Rebecca Kessler Editor

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Climate Change And Coral ReefsCoral BleachingCoral ReefsEcological RestorationEcosystem RestorationMarineMarine BiodiversityMarine ConservationMarine CrisisMarine EcosystemsOcean CrisisOceansOceans And Climate ChangeResearchRestorationHawaiiPacific IslandsUnited States

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