• The island nation of Mauritius is home to nearly 250 kinds of corals, but saw 80% of its corals bleached in the latest mass bleaching caused in part by climate change.
• Faced with lackluster results from an audit of restoration efforts earlier this year, the Mauritian government moved to reevaluate its coral restoration policy.
• The predicament of the island nation highlights concerns raised by some scientists who question whether coral restoration works in the face of mounting threats: from heat stress, ocean acidification and marine pollution.
• For now, Mauritius is not abandoning restoration but advocating a different path: promoting sexual propagation rather than the asexual means currently used in most coral restoration projects worldwide.

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PORT LOUIS, Mauritius — Seeing coral reefs can color one’s monochrome view of the ocean forever. In the pink of health — and red, blue, green and purple — corals resemble underwater fireworks, forming glorious landscapes pulsating with marine life.

But the latest episode of mass coral bleaching, starting in 2023 and stretching into 2025, has left much of the coral world gasping for life. Mass bleaching occurs when an oceanic heat wave sweeps across the planet, leaving dead and damaged corals in its wake. Such events are amplified by the climate crisis.

The island nation of Mauritius, off the east coast of Africa, is home to nearly 250 kinds of corals, and it wasn’t spared. This March, ocean heat waves bleached 80% of corals in Mauritian waters, according to Pierre Edgard Daniel Marie, director of the Mauritius Oceanography Institute (MOI).

Coral reef systems may have already reached a point of no return. Scientists estimate that warm-water corals, like those found in Mauritius, reach their tipping point when the temperature rises by 1.2° Celsius (nearly 2.2° Fahrenheit). The planet has seen an average increase of 1.4°C (2.5°F), according to the 2025 Global Tipping Points report.

Scientists say humans could be one generation away, by the year 2050, from losing nearly all healthy coral reefs due to climate change. With them, entire ecosystems would disappear; coral reefs shelter a quarter of all marine species.

To save them, conservationists have often turned to restoration, painstakingly helping decimated coral colonies recover. But the latest spell of coral bleaching has brought a reckoning: Does restoration really work?

A view of the southeastern shore of Mauritius. Image by Malavika Vyawahare/Mongabay.

An island nation contends with the realities of restoration

For small island nations like Mauritius, this is a growing concern. Corals are central to Mauritius’s appeal for tourists seeking salubrious sea and sun-soaked vacations. Tourism makes up a fifth of the nation’s GDP, while thousands of Mauritian families rely on reef-based fisheries. Seafood is a mainstay of the island’s cuisine.

Given the enormity of the threats facing corals, scientists like Clelia Mulà argue that human-aided restoration simply isn’t enough to save them. In a paper published in the journal Nature Ecology & Evolution, Mulà, who was then at the University of Helsinki in Finland, and her colleagues described current restoration efforts as an “expensive distraction to addressing the root causes of reef loss.”

Others, like Nadeem Nazurally, a leading proponent of restoration in Mauritius, and David Suggett, a marine biologist at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, caution against dismissing restoration in the face of mounting threats.

Faced with disappointing results from an audit of coral restoration efforts earlier this year, the Mauritian government has adopted a middle-of-the-road approach. It’s not abandoning restoration, but it is advocating a different path: promoting sexual propagation of coral rather than asexual propagation. The latter is the most common approach to coral restoration the world over, but sexual propagation is being touted by some as a more cost-effective and scalable way to revive reefs.

The Mauritius fisheries ministry didn’t respond to Mongabay’s request to share the findings of the coral restoration audit. However, it told local news outlet L’Express that the decision to change tack was prompted by “a series of scientific surveys conducted by the ministry revealing troubling facts.” Those facts: the survival rate for corals being grown in nurseries was mostly 0-10%, and only in some cases up to 30%, according to the ministry.

Record-breaking heat comes for corals, again and again

The assessment was carried out in the shadow of the most recent bleaching episode. Sea surface temperatures in Mauritius hit 31° Celsius (88° Fahrenheit) this year, according to MOI data, significantly above normal.

Every few years, the ocean’s surface waters warm, part of a natural phenomenon called El Niño. But in recent decades, human-induced climate change has fueled extreme heating. Marine heat waves are now erupting with alarming regularity. The first large-scale bleaching event occurred in 1998; since then, three have been three more. In a few decades, scientists warn, they could turn into an annual occurrence.

Heat stress can be deadly to corals, inducing them to expel their symbiotic (and colorful) zooxanthellae. If this happens, they turn ghostly white and may starve.

Bouncing back involves reproducing. In nature, corals reproduce both sexually and asexually. The first involves spawning; corals release eggs and sperm that combine to form embryos. These embryos become larvae that settle on existing reefs or the seafloor and grow into new coral colonies.

In asexual propagation, a fragment from the mother colony grows into a genetically identical copy of the parent coral. For restoration, conservationists gather or remove these fragments, then farm them in nurseries, either on land or at sea. When the young corals are deemed ready, they’re transplanted to existing reefs or human-made structures that mimic reefs.

Nadeem Nazurally at his office at the University of Mauritius. Image by Malavika Vyawahare/Mongabay.

A hasty move to regulate restoration meets resistance

The fisheries ministry’s comments suggest growing concerns about damage to parent corals when fragments are harvested by restorers, and dangers from the structures placed at sea to host them. In its statement to L’Express, the government also cited “misuse of permits” granted by the ministry to the operators of restoration projects, including NGOs, researchers and private companies. It also pointed to illegal structures cropping up along the coast and some abandoned coral nurseries that pose a danger to the public.

The Mauritian government’s policy directive, which became public in May, caught Nazurally and others involved in restoration efforts off guard, and drew sharp criticism from them.

“It’s incredible that they made this move without any consultation, no consultation even with partners … no consultation with big financers like the UNDP,” said Sébastien Sauvage, who heads Eco-Sud, a Mauritian NGO implementing coral restoration under a United Nations Development Programme (UNDP) project.

The U.N agency’s “Restoring Marine Ecosystem Services by Rehabilitating Coral Reefs to Meet a Changing Climate Future” initiative is one of the biggest on the island. The $10 million project was launched in 2020 to promote coral restoration in Mauritius and Seychelles, another Indian ocean island state, financed by the U.N. adaptation fund, which was set up to help nations cope with the impacts of climate change.

The UNDP initiative aims to restore at least 3.2 hectares (7.9 acres) of degraded sites in Mauritius using nursery-grown corals, working with local partners and the Mauritian government. The initiative relies on asexual coral propagation.

Jean Lindsay Azie, who leads the environment unit at UNDP Mauritius, told Mongabay by email that an area of 1.2 hectares (3 acres) has already been planted in Mauritius. He said some species are showing “good recovery in both nurseries and out-planting sites.”

However, Azie didn’t share details about how the restored corals fared during the recent bleaching episode.

The six-year project ends in November 2026.

The Mauritius Oceanography Institute is one the partnering organizations for the UNDP project. Daniel Marie, the MOI director, told Mongabay they’ve identified heat-resistant species of corals. But he too didn’t provide details about the survival rates of the restored corals.

A screengrab from the camera feed of a coral restoration site supervised by Nadeem Nazurally. Image by Malavika Vyawahare/Mongabay.

What makes restoration stick?

Nazurally, who heads the agriculture and food science department at the University of Mauritius, has worked for decades on coral restoration using asexual reproduction.

He heads the NGO EcoMode Society and leads multiple coral restoration projects. These initiatives have benefited from funding from international organizations like the UNDP and the IUCN, the global nature conservation authority, as well as private sector actors such as Chinese technology giant Huawei and Japanese shipping company MOL. The latter chartered the MV Wakashio, a cargo ship that crashed into reefs on Mauritius’s east coast in 2020.

Nazurally said corals in nurseries he supervises didn’t suffer too badly from the latest bleaching event.

“With all the research that we are doing, we managed to have very less bleaching in our nurseries compared [to] in the wild,” he told Mongabay. “I’ve not yet fully [assessed] it, but it is only around 10% bleached.”

These findings are not published yet.

Nazurally and his team did publish results from coral monitoring at two restoration sites in Mauritius between 2019 and 2021. Survival rate in those cases were 88%, the study said. The research was conducted after the last major bleaching event, which took place from 2014-2017, and ended before the latest episode.

Mulà, the scientist who has expressed skepticism of restoration effectiveness, pointed to the lack of uniformity in the approach and design of coral restoration efforts across the world. Most initiatives also don’t build in long-term monitoring, making them hard to evaluate, she noted.

Mulà’s paper said that even if coral survivability rates were the only parameter being measured, 30-40% of coral restoration projects would fail. Almost all projects rely on asexual breeding, with only a tiny fraction relying on sexual reproduction.

However, experts like Suggett say the benefits from restoring coral systems aren’t always easy to capture and may not be limited to coral survival rates. Nazurally echoed Suggett’s argument that a cost-to benefit calculation that focuses only on coral survival is narrow. He highlighted the case of the dusky farmerfish (Stegastes nigricans), named as such because it “plants” algae on reef structures. “[They] are making their homes on some of the structures we put in place [for coral restoration],” Nazurally said.

Through his projects, Nazurally said he also helps inspire a new generation of scientists who care about corals, and train community members in coral farming.

Coral restoration sites often require intensive stewardship by humans, so logistically it makes sense to install them in easily accessible locations. But this also increases their exposure to destructive human activities, including farm runoff, pollutants, urban settlements and disturbances, that can undermine their success.

This has left some experts questioning whether continuing to pour money into coral restoration even makes sense. Mulà’s paper noted that restoring even 10% of the coral reefs would need more than $1 billion, more than four times the money invested in such efforts in the past decade ($258 million). The authors concluded that “restoration alone is not a practical or affordable solution to counteract the global decline of coral reefs.”

Considering the range of the threats facing corals, some experts like Suggett say it’s important not to abandon restoration. “Many efforts are now growing in maturity and scale — it is not a question of if we need, but rather how do we do it well,” he wrote.

A coral farming site supervised by Nadeem Nazurally. Image by Malavika Vyawahare/Mongabay.

A pivot promoting sexual coral reproduction

The Mauritian government, at least for now, is not giving up on restoration, but is steering it in a different direction.

The fisheries ministry said in it statement to L’Express that it “will now prioritize and encourage other innovative coral restoration methods that have demonstrated acceptable survival rates, without the removal of live corals.”

The innovative technique involves humans helping corals breed sexually.

The NGO Eco-Sud is partnering with Mauritius-based Odysseo, an aquarium (or in its words, an “oceanarium”) showcasing marine species, on a project that uses sexual reproduction methods. It’s the first facility in Mauritius dedicated to large-scale coral restoration through sexual methods. The Odysseo team is working with Secore International (short for Sexual Coral Reproduction), a U.S.-based nonprofit, and the University of Mauritius for the three-year project launched in 2024.

The Odysseo team collects eggs and sperm, released during coral spawning events (which occur once or twice a year depending on the species), and brings them together in a floating nursery. Here, they fertilize naturally, producing millions of larvae. The nursery includes seeding units where the coral larvae can settle and grow, before they’re transplanted onto reefs.

Prashant Mohesh, a marine conservationist and National Geographic Explorer who collaborates with Odysseo, said he believes investing in sexual propagation is the future. “It is more cost-effective and scalable than traditional methods,” he said, referring to asexual propagation.

It promises more genetically diverse colonies because they’re not just clones of the parent coral colony, but genetically unique corals, he added.

Gaëlle Quéré, a marine scientist and project lead at Secore International, told Mongabay that the NGO is “a strong advocate that both methods are complementary. It doesn’t make sense to ban one method, or to say that one method is better than the other.”

Facing backlash over its decision, the Mauritian government is now in consultation with scientists and coral restoration project managers, including Nazurally.

“I agree with the need for a policy but you cannot just ban asexual reproduction,” Nazurally said, “If sexual reproduction alone was working, there would have been no asexual reproduction in the world.”

Schools of fish at a coral nursery site supervised by Nadeem Nazurally. Image courtesy of Nadeem Nazurally.

Can humans keep shielding corals from the surging climate threat?

Asked about the Mauritian government’s new push, Azie at the UNDP said their existing work continues as planned. “We recognize that this line of work is dynamic and continues to evolve,” he said, adding that “we remain actively engaged.”

He called the endeavor an “existential question for Small Island Developing States like Mauritius.”

Still, scientists like Mulà, now at the University of Western Australia, warn that given the rate at which the planet and its oceans are warming, even sites hosting corals today (both naturally occurring and restored) could succumb to the ravages of climate change in time.

“Heat stress will likely wipe out gains even in areas where we see some success now,” she said.

2024 was the hottest year on record, with temperatures 1.47°C (2.6°F) warmer than the preindustrial baseline. A widely cited analysis warned that coral reefs in the Western Indian Ocean (which includes Mauritius) could collapse as soon as 2070. The prediction is based on a high-emissions scenario in which global average temperatures rise by 3-4°C (5.4-7.2°F) by 2100 compared to preindustrial levels.

“We are doing some projects to restore, but then we are still being impacted by climate change,” said Daniel Marie at the MOI. “But do we say this won’t change, and then stop? No. We keep on trying.”

Banner image: Schools of fish at a coral restoration site managed by Nadeem Nazurally’s team. Image courtesy of Nadeem Nazurally.

Citations:

Mulà, C., Bradshaw, C. J., Cabeza, M., Manca, F., Montano, S., & Strona, G. (2025). Restoration cannot be scaled up globally to save reefs from loss and degradation. Nature Ecology & Evolution, 9(5), 822-832. doi:10.1038/s41559-025-02667-x

Suggett, D. J., Guest, J., Camp, E. F., Edwards, A., Goergen, L., Hein, M., … Moore, T. (2024). Restoration as a meaningful aid to ecological recovery of coral reefs. npj Ocean Sustainability, 3(1). doi:10.1038/s44183-024-00056-8

Obura, D., Gudka, M., Samoilys, M., Osuka, K., Mbugua, J., Keith, D. A., … Zivane, F. (2021). Vulnerability to collapse of coral reef ecosystems in the western Indian Ocean. Nature Sustainability, 5(2), 104-113. doi:10.1038/s41893-021-00817-0

Boström-Einarsson, L., Babcock, R. C., Bayraktarov, E., Ceccarelli, D., Cook, N., Ferse, S. C., … McLeod, I. M. (2020). Coral restoration — A systematic review of current methods, successes, failures and future directions. PLOS ONE, 15(1), e0226631. doi:10.1371/journal.pone.0226631

Nazurally, N., Pomeroy, A. W., Lowe, R. J., Narayanan, I., & Rinkevich, B. (2025). Evaluating coral farming strategies in Mauritius: A comparative study of nursery types, biodiversity and environmental conditions at Pointe aux Feuilles and Flic-en-flac. Journal of Marine Science and Engineering, 13(7), 1268. doi:10.3390/jmse13071268