Underwater drones discover coral reefs off Benin, long presumed dead, teeming with life Swati Mestri Scientific Editor Andrew Zinin Chief Editor A coral reef, missing and presumed dead, has been found alive and well off the coast of Benin. Surveys in the 1960s, focused on identifying promising fishing areas, flagged a possible deep-water coral reef but assumed it must be dead. Now, using a modern sonar survey and the Deep Sea Camera System provided by the National Geographic Exploration Technology Lab, scientists have found an apparently healthy reef.

"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." The unexpected survivor The historical surveys had identified a possible reef more than 50 meters (164 feet) beneath the surface and declared that it was probably dead. Zinzindohoué and his colleagues reasoned that it could have been a mesophotic coral ecosystem. "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." Using the historical surveys as a guide, the scientists surveyed 11.5 kilometers (7.1 miles) of seabed with sonar. This revealed two signals that could represent reefs.

To investigate the most promising areas, the team used an underwater drone and the Deep Sea Camera System, like underwater trail cameras. The footage showed a seemingly healthy reef, with eight different types of coral and eight species of fish sheltering and feeding around the corals: golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish and two species of damselfish. This reef does not appear to be a continuous coral barrier, but rather patches of coral occupying rocky areas suitable for their growth.

However, it is possible that further surveys will identify more reefs. "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?