Study finds a third of coral restoration projects fail, with scaling up unlikely
Coral restoration is falling far short of the scale required to counter mass bleaching and reef decline, with more than a third of projects failing and many unlikely to be expanded effectively, according to a study published in Nature Ecology and Evolution.
The research, led by Giovanni Strona of the European Union Joint Research Center, Clelia Mulà of the University of Western Australia, and Corey Bradshaw of Flinders University in Australia, examined why restoration efforts often underperform.
Working with collaborators from the University of Milan-Bicocca, the Marine Research and Higher Education Center in the Maldives, and the University of Helsinki, the team identified major barriers: projects are typically small, costs per hectare are high, and interventions frequently target already compromised reefs that remain highly vulnerable to future heat stress.
“Most restoration projects only operate over several hundred or a few thousand square meters,” Bradshaw said, noting the mismatch with the scale of losses.
Between 2009 and 2018, coral reefs suffered a 14% decline and degradation—nearly 12,000 square kilometers—he said, adding that “over a third of projects fail.” He argued the findings should prompt debate about when and where restoration is most feasible, but warned 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.” Coral restoration commonly involves “coral gardening,” where fragments grown in nurseries are transplanted to damaged reefs.
Other interventions include removing species that eat corals (such as parrot fish), transferring coral spawn, or manipulating the local microbiome to boost survival. The study found projects falter for multiple reasons, including poor planning, unproven technologies, insufficient monitoring and the impact of subsequent marine heat waves.
Scientists say warming seas and climate-driven marine heat waves are the primary drivers of mass bleaching—when corals expel the symbiotic algae they rely on—often leading to coral death. Overfishing and pollution compound the damage, with bleaching recorded in iconic locations such as Australia’s Great Barrier Reef.
While restoration can be valuable in specific circumstances, Bradshaw cautioned that 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.” The stakes are high: the study notes that coral reefs provide benefits to more than 1 billion people through tourism, food security and coastal protection.
Strona added that some estimates suggest coral coverage has declined by at least 50% over the past 40 years and projected losses could exceed 90% of total coral cover by the end of the century as climate change progresses. The researchers also highlighted the absence of agreed formats for collecting or reporting data from restoration projects, complicating efforts to compare outcomes and refine best practices.
Overall, the authors say their results should sharpen focus on targeted, well-planned interventions where they are most likely to succeed, while emphasizing that curbing climate change remains essential to limit further reef losses.