In the 1960s, government-requested fish surveys detected a coral reef barrier off the coast of Benin in West Africa, but it was presumed to be dead.
Now, however, researchers have taken a second look and found a flourishing coral ecosystem, they report in a study published on July 19 in the journal Frontiers in Marine Science. Their observations provide the first documented evidence of living low-light coral communities on the Gulf of Guinea's continental shelf. The reefs' rediscovery also sheds light on an understudied marine region.
"I was guided by the hope that sometimes nature can surprise us, and what you don't intend to see is what can actually happen — it surprised me as well," says study co-author Gérard Zinzindohoué, an oceanographer at the Benin Fisheries and Oceanological Research Institute.
The project began in January 2025, thanks to an exploration grant. Since Benin doesn't own a permanent research vessel, the scientists had to make do with small fishing boats to travel roughly 14 miles offshore. "The fishermen's boats are not used to going that far offshore, so it was risky for everyone," Zinzindohoué says.
Between April and December 2025, the team used sonar mapping, underwater drone surveys and stationary video recorders to examine a 4.3-mile stretch of the suspected 24-mile-long barrier mapped in the 60s.
The data revealed a patchwork of corals about 177 feet below the surface at a depth called the mesophotic zone, where little sunlight reaches. Additionally, the video surveys captured eight fish species, including golden African snappers and Guinean angelfish, using the corals for shelter and feeding. The team did not estimate how many individual fish lived there, but the observations hint that the habitat supports a diverse assemblage of animals.
It was a "really undisturbed environment," Zinzindohoué says. "Everything was alive. And it was a really big moment for us."
The team was looking at a mesophotic coral garden, an ecosystem that differs from shallow coral reefs by living in deeper, darker waters and sometimes forming separate patches instead of a continuous reef. It's the first verified documentation of such an ecosystem on the Gulf of Guinea continental shelf, Zinzindohoué says.
"However, I think what we found is probably not an exception," he adds. "It is more likely a reflection of how little we still know about coastal regions in West Africa and elsewhere."
Luiz Rocha, curator of fishes at the California Academy of Sciences, agrees. "I think the most significant aspect of the study is that it confirms that living mesophotic coral communities occur in a region where we knew almost nothing about [them]," says Rocha, who did not participate in the research, in an email. "The Gulf of Guinea remains a major gap in our knowledge of deeper (and shallow) coral ecosystems."
Still, many questions remain, including about the corals' extent and their communities' diversity, Rocha adds. The researchers have yet to directly sample the corals, so the species still need to be verified. Further data could also reveal whether the corals detected in the surveys were indeed dead in the 1960s and rebounded or whether the initial assumption was simply wrong.
Regardless, the new work offers a helpful starting point, Zinzindohoué says. "We hope that, through this result, people will start to look at the ocean differently, and that it might inspire others to do more ocean research and focus on the protection and conservation of marine ecosystems."