A team of scientists exploring a possible deep-sea coral reef off the coast of Benin that 1960s researchers had deemed likely dead found a living, thriving reef supporting a complex underwater ecosystem, including several coral and fish species.
Led by scientists from the Institut de Recherches Halieutiques et Océanologiques du Bénin, the discovery is the first known mesophotic coral reef in the region and offers scientists a tantalizing target for future deep-sea marine-life expeditions.
Deep-Sea Coral Reef Spotted in the 1960s was Considered Dead
According to a statement announcing the unexpected discovery, previous historical surveys of the area had indicated a possible reef more than 50 meters below the water’s surface. When a 1960s survey detected the unusual feature, they suspected it was a coral reef that was likely dead.
When team leader Gérard Zinzindohoué and colleagues studied the features, they suspected that the team from the 60s may have provided them with a golden scientific opportunity. Although the feature’s depth ruled out a typical shallow-water coral reef, the researchers note that it could be an entirely different kind of reef structure, known as a mesophotic coral ecosystem, that can inhabit such depths.
“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.”
Instead of using mid-twentieth-century technology to settle the debate, the team turned to the National Geographic Exploration Technology Lab, which provided access to its Deep-Sea Camera System.
“We Could Actually See the Sea Floor”
Following the path set out by the 1960s survey, the team used the underwater camera to map the seafloor with sonar. After several passes, the team covered a total of 11.5 kilometers. Zinzindohoué highlighted the difficulty of the effort, noting that it was “not an easy field campaign.”
“It was a mix of long days at sea, technical problems, and a lot of uncertainty,” the researcher explained. “But then we saw structures on the sonar that looked like they could be reef signatures, which gave us hope that we were close.”
The closer the team drove the Deep-Sea Explorer’s cameras, the more the shockingly unexpected scene began to unfold.
“That was a big moment for us, because suddenly we could actually see the seafloor,” Zinzindohoué said.
Instead of the dark, lifeless structure anticipated by the original survey team, the new team found a healthy reef containing eight distinct types of coral. The system was also actively supporting eight fish species, with the camera capturing them feeding and sheltering among the corals. The species identified by the team include golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish, and two distinct species of damselfish.
“I still remember seeing those first images,” Zinzindohoué recalled of the vibrant ecosystem lying directly in front of the cameras. “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.”
More Research Needed to Determine if the Coral Reef Was Ever Dead
When discussing the discovery’s significance, Zinzindohoué said that to the team’s knowledge, “this is the first confirmed record of a living mesophotic coral ecosystem on the Gulf of Guinea continental shelf.”
Although the cameras captured a complex ecosystem, the researchers said that the reef does not appear to be a continuous barrier. Instead, the deep-sea environment consists of several patches of coral that occupy rocky seabed areas most suitable for their survival. Still, they add that further surveys may identify more reefs in the same area.
“I think what we found is probably not an exception,” Zinzindohoué said. “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?”
Since the team was unable to sample the corals directly, they were unable to confirm the species identification with genetic analysis. The team was also hesitant to condemn the original 1960s survey, noting that it is impossible to tell, without more data, whether the corals were dead at the time and have since rebounded.
“This is still an initial exploration,” Zinzindohoué said. “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.”
Although there are no immediate plans for a return expedition, the research leader said the only thing holding them back from learning more about these ecosystems, which are “still poorly known in this part of the world,” is adequate financial support.
“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,” he said, before adding that “every additional piece of information matters.”
“I do believe there are more coral systems out there that we have not yet documented,” he said. “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.”
On a personal note, the team leader said the most exciting part is understanding the reef’s history and the lessons that can be gleaned from this underexplored region.
“It feels like we have only just started to read an archive that has been there for a very long time.”
The study “First evidence of live mesophotic coral reefs on the Benin continental shelf” was published in Frontiers in Marine Science.
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org