Coral reefs worldwide are in major trouble. Their numbers have dwindled dramatically over time and today, they’re facing yet another mass bleaching event. But research has offered hope that human intervention can help restore these crucial ecosystems.
Once-decimated swaths of coral reef off Indonesia’s coast are now bouncing back after years of efforts by the Mars coral reef restoration program. That’s according to a recent study from an international group of researchers who analyzed the project.
READ MORE: Coral reefs across the globe once again endure mass bleaching amid warming oceans, scientists say
Coral reefs offer crucial habitat for marine creatures and protect coasts from strong waves and storms. Many nearby coastal communities also rely on them for economic, cultural and recreational benefits.
Today, the planet is enduring its fourth global coral bleaching event of the past three decades due to blisteringly hot ocean water temperatures, according to the National Oceanic and Atmospheric Administration.
A healthy coral reef that didn’t require restoration is pictured in Sulawesi, Indonesia. Photo provided by Ines Lange
Bleaching isn’t always fatal for corals, and the process can be reversed if its root cause is remedied. But in the meantime, widespread bleaching can have major implications for food security, economies and people’s livelihoods, the agency said.
In addition to climate change, these ecosystems grapple with other human-driven threats like pollution and the fishing industry. The Mars program’s restoration efforts focused on a reef system near Pulau Bontosua, an island in South Sulawesi, Indonesia, that suffered major damage several decades ago from dynamite fishing, a practice that uses explosives to stun or kill fish.
“These explosives destroy the solid reef structure, and ecosystems do not recover naturally as loose dead coral fragments rolling around on the seafloor crush any new life that tries to settle,” Ines Lange, a senior research fellow in coral reef ecology at the University of Exeter and lead author of the paper, told the PBS NewsHour.
Animation by Megan McGrew/PBS NewsHour
The group that oversaw the restoration process took fast-growing branching coral fragments from donor colonies and transplanted them onto sand-coated, hexagonal steel frames dubbed “Reef Stars.”
Lange’s research team assessed the health of reefs that were restored between 2018 and 2023 by looking at how much limestone (calcium carbonate) is produced within the coral reef versus what was lost to erosion. They found that the net carbonate budget at sites that have marked four years since their initial restoration was identical to nearby healthy ones. Images taken at these reefs in 2023 show what the recovery process looks like at different points in time, Lange said.
The Mars program worked closely with local community members to carry out their project, a collaboration that Lange said is crucial to the long-term success of restoration efforts.
“Local stewardship ensures that restoration goals align with the needs of local communities, increases understanding of threats and importance of protection and provides manpower for the laborious restoration work,” she said.
Communities in Indonesia worked with Mars Sustainable Solutions to restore coral reefs using Reef Stars. Photo provided by The Ocean Agency
Corals are a foundation species akin to trees in a forest, University of Miami marine research associate Joe Unsworth told the NewsHour. He said that the goal of bringing them back to barren reefs is to restore an entire ecosystem that will allow other organisms to thrive, too.
Unsworth, who was not involved in the study, noted that corals grow very slowly and that it can take decades for restored reefs to fully resemble healthy ones. Carbonate budgets don’t capture the full picture of reef health, he said, but they do offer an important snapshot.
“Over time (decades), as corals on nearby reefs spawn and their larvae settle on the restored reef, the coral population on the restored reef will become more diverse,” Unsworth said. “We don’t really know how long it will take for a restored reef to become identical to an unrestored, healthy reef, but it’s certainly longer than five years.”
That’s why although the results of the Mars program mark significant progress, the formerly damaged sites are not considered fully recovered. Lange noted that after four years, the restored reefs do not yet have a full diversity of coral types, and that tracking natural coral settlement over the next five to 10 years would offer clues as to whether they’ll grow to more closely resemble healthy reefs.
But so far, the program and study mark one notable example of a promising effort to revive once-decimated reef systems.
“As far as I know, it is the closest anyone has come to demonstrating coral restoration as a tool to recover ecosystem function in a short timeframe,” Unsworth said.
