Without tackling climate change, coral restoration efforts are insufficient

As oceans continue to warm and coral bleaching events increase across the globe, scientists are taking a close look at the effectiveness of restoration projects aimed at saving some of the planet’s most vibrant and valuable ecosystems. 

While restoration has become a common strategy for helping damaged reefs recover, a new international study suggests that many of these efforts may fall short – not because they’re misguided, but because they can’t keep up with the pace of destruction.

Bleaching occurs when corals, stressed by unusually high sea temperatures, expel the algae that live in their tissues. These symbiotic algae not only give corals their brilliant colors but also help provide nutrients. 

Without them, corals turn white – and if the stress continues, they can die. Marine heatwaves, mostly driven by climate change, are the leading cause of these events, although other factors like pollution and overfishing make reefs more vulnerable.

Coral restoration on a small scale

The most widely used method of reef restoration is known as coral gardening. It involves growing coral fragments in underwater nurseries and then transplanting them to damaged reef areas.

Other approaches include removing coral-eating species such as parrotfish, distributing coral spawn to new locations, or even tweaking the microbiomes surrounding the coral in hopes of boosting their survival.

But according to the new study, the scope and scale of these interventions don’t come close to matching the problem.

The study was led by Giovanni Strona from the European Union Joint Research Center, Clelia Mulà of the University of Western Australia, and Professor Corey Bradshaw from Flinders University in Australia. The researchers investigated why many reef restoration projects fail to deliver long-term benefits.

“Most restoration projects only operate over several hundred or a few thousand square meters,” said Professor Bradshaw.

“Compared to the 14% loss and degradation of coral reefs between 2009 and 2018, equating to nearly 12,000 square kilometers, we come nowhere close to the scale of restoration that is needed to offset the losses from climate change.”

Why many restoration projects fail

The analysis revealed several reasons for the high failure rate of coral restoration efforts – which is about one-third of all projects. Among the most common were high costs per hectare, reliance on unproven or poorly monitored methods, and efforts focused on reefs already severely degraded and highly vulnerable to future bleaching events.

According to the experts, there’s also the issue of poor planning. And without consistent methods for collecting and reporting data from these projects, it’s nearly impossible to figure out what works and what doesn’t.

The review encompassed a wide range of factors – including human impact, risk of bleaching before and after intervention, coral diversity, and remoteness – but no consistent correlation between these conditions and the success of restoration efforts was found. In other words, it’s not yet clear what makes a reef restoration project succeed or fail.

Coral restoration and climate change

The stakes couldn’t be higher. Coral reefs support an estimated one billion people worldwide, offering everything from food security to income from tourism, and even natural protection from storms and coastal erosion.

“Some estimate that over the past 40 years, the coverage of coral reefs has declined by at least 50%,” said Strona. “As climate change continues, bleaching events and coral deaths will only become more common, with projected losses of total coral cover of more than 90% by the end of the century.”

And while many coral restoration efforts are well-meaning, the researchers argue that relying too heavily on them could create a false sense of hope.

“Although coral restoration has the potential to be a valuable tool in certain circumstances, our research makes it clear it is not yet – and might never be – feasible to scale up sufficiently to have meaningful, long-term, and positive effects on coral reef ecosystems,” explained Professor Bradshaw.

Looking beyond restoration

The authors emphasize that this shouldn’t be a reason to give up on coral conservation altogether. Rather, it’s a call to think bigger, and to be more strategic about how and where restoration is attempted.

For example, focusing on less degraded reefs, or those that are more resilient to heat stress, may yield better long-term results.

Lead author Clelia Mulà suggests that part of the answer lies in complementing restoration with broader conservation strategies.

“Reinforcing complementary strategies could therefore bolster ecosystem resilience, extending the reach and success of coral restoration projects,” she said.

Ultimately, the researchers agree that no amount of coral restoration work will be enough without a serious global effort to slow climate change.

“This reality check should stimulate constructive debate about when and where restoration is most feasible and important,” said Professor Bradshaw.

“But the truth is that without stemming the pace and magnitude of climate change, we have little power to save coral reefs from massive losses over the coming century and beyond.”

The study is published in the journal Nature Ecology and Evolution.

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