Researchers used sonar and underwater imaging systems to locate a mesophotic coral garden that scientists in the 1960s had assumed was dead.
More than 50 meters beneath the waters off Benin, cameras revealed a coral community that scientists had once presumed dead. Fishing surveys conducted in the 1960s had identified what appeared to be a deep-water reef, but concluded that it was probably no longer alive. Decades later, modern sonar and the Deep Sea Camera System from the National Geographic Exploration Technology Lab have shown an apparently healthy ecosystem.
“It was not an easy field campaign,” said Gérard Zinzindohoué of the Institut de Recherches Halieutiques et Océanologiques du Bénin, lead author of the article in Frontiers in Marine Science. “It was a mix of long days at sea, technical problems, and a lot of uncertainty. But then we saw structures on the sonar that looked like they could be reef signatures, which gave us hope that we were close.
“Next, we surveyed the structures with an underwater drone and the Deep Sea Camera System. That was a big moment for us, because suddenly we could actually see the seafloor. I still remember seeing those first images. It was a mix of excitement and disbelief, because after all this time thinking about this reef, suddenly there was something real in front of us.”
Old records guide a new search
The earlier surveys had recorded a possible reef at a depth greater than 50 meters and judged it likely to be dead. Zinzindohoué and his colleagues suspected instead that the site might contain a mesophotic coral ecosystem, a community that survives in deeper water where far less sunlight reaches the seafloor.
“A mesophotic coral ecosystem lives deeper than the usual shallow coral reefs, in zones where light is much more limited,” explained Zinzindohoué. “Unlike typical shallow reefs, it does not always form a single continuous reef structure. Instead, it can appear as patchy or scattered coral communities spread across the seafloor.”
https://youtu.be/8OU5oVyVEDc
A video of the reef. Credit: Gérard Zinzindohoué
Cameras confirm a living coral community
Using the historic survey records to narrow their search, the scientists mapped 11.5 kilometers of seabed with sonar. They detected two signals that might represent reefs, then examined the most promising locations with an underwater drone and the Deep Sea Camera System, which functioned much like trail cameras beneath the ocean.
The footage revealed what appeared to be a healthy reef community. Researchers observed eight types of coral and eight fish species feeding or sheltering among them. The fish included golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish, and two species of damselfish.
Rather than forming one continuous coral barrier, the reef appears to consist of separate coral patches growing across suitable rocky areas. Additional exploration could reveal more reefs beyond the limited area surveyed.
More reefs may remain undocumented
“To our knowledge, this is the first confirmed record of a living mesophotic coral ecosystem on the Gulf of Guinea continental shelf,” said Zinzindohoué.
“However, I think what we found is probably not an exception. It is more likely a reflection of how little we still know about coastal regions in West Africa and elsewhere. If we were able to find this reef again after 60 years, how many others are still undocumented or simply forgotten? So yes, I do believe there are likely more coral systems out there that we have not documented yet. But we should not assume they are everywhere. Each discovery needs to be confirmed. Without going back into the field, we are really just guessing.”
Major questions still require fieldwork
The scientists have not yet collected physical samples from the corals, so their species identifications remain unconfirmed. The available evidence also cannot determine whether the reef was truly dead during the 1960s and later recovered, or whether the original surveys misjudged its condition. Additional research will be needed to reconstruct its history and search for other nearby coral communities.
“This is still an initial exploration,” said Zinzindohoué. “The historical reports suggested that this could be a continuous coral reef barrier extending roughly 40 kilometers parallel to the coast. We only surveyed a small section of this area, and we had a limited number of visual transects. If I had all the grant money in the world, the first thing I would do is return to the site with a proper scientific diving and sampling program. These are ecosystems that are still poorly known in this part of the world, and every additional piece of information matters.
For me, the most exciting part is about understanding the reef’s history, and what it can tell us about how the ocean in this region has changed over time. It feels like we have only just started to read an archive that has been there for a very long time.”
Reference: “First evidence of live mesophotic coral reefs on the Benin continental shelf” by Coffi Gérard Franck Zinzindohoué, Houangninan Midinoudéwa, Bôla-Nlé Christelle Akondé, Zacharie Sohou, Ursula Schauer, Björn Fiedler, Kanna Rajan and Jonatha Giddens, 10 June 2026, Frontiers in Marine Science.
DOI: 10.3389/fmars.2026.1848226
This research was funded by the National Geographic Society (Grant No. EC-115084R-24). National Geographic Exploration Technology Lab supported this research by providing access to specialized equipment.
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