This analysis was done in collaboration with researchers from the University of Milan-Bicocca, the Marine Research and Higher Education Center (Maldives) and the University of Helsinki.
Published in open-access journal Nature Ecology and Evolution, their results show major barriers to effective interventions include the small scale of restoration programs, high costs per hectare, and the tendency to restore already compromised reefs that are highly vulnerable to future heat stresses.
“Most restoration projects only operate over several hundred or a few thousand square metres. Compared to the 14% loss and degradation of coral reefs between 2009 and 2018, equating to nearly 12,000 square kilometres, we come nowhere close to the scale of restoration that is needed to offset the losses from climate change,” says Professor Bradshaw.
“This combination of adverse factors, coupled with the fact conservation efforts can target sites that don’t have the highest chance of success, means over a third of projects fail.
“This reality check should stimulate constructive debate about when and where restoration is most feasible and important. 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.”
Lead author Clelia Mulà says reinforcing complementary strategies could therefore bolster ecosystem resilience, extending the reach and success of coral restoration projects.
The researchers say restoration failures can be for many reasons, including poor planning, unproven technologies, insufficient monitoring and subsequent heatwaves.
“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,” says Professor Bradshaw.
The research shows that coral reefs benefit more than 1 billion people globally by providing tourism dollars, food security and 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%. 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,” says Dr Giovanni Strona.
“One of the problems here is that there are no agreed formats for collecting or reporting data from restoration projects. This makes it difficult or impossible to identify the conditions leading to success and reduces the pace of improvement. Indeed, we found that no measures of human impacts, pre- and post-restoration bleaching risk, coral diversity, remoteness, or type of restoration could explain why a project was successful or not.”
The research – “Restoration cannot be scaled up globally to save reefs from loss and degradation”, by Clelia Mulà, Corey Bradshaw, Mar Cabeza, Federica Manca, Simone Montano and Giovanni Strona – has been published in Nature Ecology and Evolution.
More information has been published in The Conversation.
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