A deep-water coral reef that vanished from the scientific record more than half a century ago has resurfaced and – in a dramatic twist of fate, has been found thriving. 

Surveys conducted in the 1960s – aimed at charting productive fishing grounds off Benin – picked up hints of a possible reef structure but concluded it was almost certainly dead. Now, armed with modern sonar and the Deep Sea Camera System supplied by the National Geographic Exploration Technology Lab, researchers have confirmed the reef not only survived, but appears to be flourishing.

“It was not an easy field campaign,” said Gérard Zinzindohoué of the Institut de Recherches Halieutiques et Océanologiques du Bénin, lead author of the study published 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, the team 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,” continued Zinzindohoué. “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.”

The original 1960s surveys had located a possible reef more than 50 metres (164 feet) below the surface, yet had written it off as dead. Decades later, Zinzindohoué and his colleagues suspected that rather than dead, this might be a mesophotic coral ecosystem – a type of reef system that behaves nothing like its shallow-water cousins.

“A mesophotic coral ecosystem lives deeper than the usual shallow coral reefs, in zones where light is much more limited,” Zinzindohoué explained. “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.”

Guided by the historical survey data, the team mapped 11.5 kilometres (7.1 miles) of seabed using sonar, turning up two signals consistent with reef structures. The most promising sites were then investigated with an underwater drone and the Deep Sea Camera System – effectively underwater trail cameras positioned to capture life on the reef undisturbed. 

What came back was a picture of a reef in good health: eight coral types, and eight fish species moving through the structure to feed and shelter, among them golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish, and two species of damselfish.

The team has not yet been able to sample the corals directly, so species identifications remain provisional. Nor is it yet possible to say whether the corals were genuinely dead in the 1960s and have since recovered, or whether the earlier assessment simply missed what was really there. Answering either question will take considerably more research – both on this reef, and on others that may lie nearby.

“This is still an initial exploration,” said Zinzindohoué. “Historical reports suggest that this could be a continuous coral reef barrier extending roughly 40 kilometers (25 miles) 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 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.”

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