Researchers exploring the Gulf of Guinea off the coast of Benin have rediscovered a living mesophotic coral reef that was presumed dead for six decades. The finding, documented in a new study published in Frontiers in Marine Science by the Institut de Recherches Halieutiques et Océanologiques du Bénin, reveals thriving marine biodiversity in dimly lit waters.
For sixty years, historical records and early marine surveys had consigned a deep-water coral formation off the West African coast to the history books. Early fishing surveys conducted in the 1960s, which were primarily designed to locate productive fishing grounds, had detected unusual seafloor formations at depths exceeding 50 meters (more than 164 feet, or approximately 54 meters). Relying on rudimentary sonar and destructive dredging techniques that involved removing sediment rather than capturing direct imagery, early scientists concluded that the formations were dead. No researchers returned to inspect the site for six decades.
That long absence ended when a modern research expedition revisited the area. Led by oceanographer Gérard Zinzindohoué of the Institut de Recherches Halieutiques et Océanologiques du Bénin, lead author of the article in Frontiers in Marine Science (alternatively referenced as Gérard Zanzandoue of the Benin Marine Fisheries Institute), scientists set out to map the seabed between April and December 2025 using advanced side-scan sonar. The team scanned 11.5 kilometers (7.1 miles) of seafloor, identifying promising signals that pointed toward hard-bottom habitats.
Modern Side-Scan Sonar and Underwater Drones Reveal Living Coral
The breakthrough came when researchers deployed high-tech visual equipment to inspect the acoustic targets. Using an underwater drone and the Deep Sea Camera System provided by the National Geographic Exploration Technology Lab, the team captured the first clear images of the seafloor more than 50 meters below the surface.
“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.”
Gérard Zinzindohoué, Institut de Recherches Halieutiques et Océanologiques du Bénin
Zinzindohoué described the expedition as involving technical challenges before the team spotted promising structures on their sonar monitors. When the camera feeds finally reached the surface, the initial reaction among the crew was astonishment. The footage exposed a vibrant mesophotic coral ecosystem thriving in the dim twilight zone (in dimly lit waters at depths of 30 to 150 meters) of the continental shelf.
“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.”
Gérard Zinzindohoué, Institut de Recherches Halieutiques et Océanologiques du Bénin
Biodiversity on the Gulf of Guinea Continental Shelf
Unlike shallow-water reefs that form continuous barriers bathed in bright sunlight, mesophotic reefs exist in patchy communities adapted to lower light levels. The Benin discovery consists of separate coral patches growing on rocky sections of the seabed where conditions are suitable rather than a single uninterrupted wall. Researchers identified at least eight different types of coral, including six different morphological types of soft octocorals and two morphological types of black coral.
The habitat also supports a diverse array of marine life. Cameras recorded eight different fish species sheltering and feeding among the coral branches. The documented fauna includes golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, Monrovia doctorfish, three-banded butterflyfish, and two distinct damselfish species.
Scientific Implications for West African Marine Conservation
The discovery represents the first confirmed record of a living mesophotic coral ecosystem on the Gulf of Guinea continental shelf. Because West Africa’s underwater environments remain largely understudied and under-documented compared to regions like the Caribbean, Australia, or Brazil, scientists suspect this ecosystem is far from unique.
Historical reports from the 1960s suggested that a reef system might stretch approximately 25 miles (40 kilometers) parallel to the coast. While the recent expedition surveyed only a small fraction of that potential expanse, the findings suggest that many similar habitats may exist undocumented across coastal West Africa. Unmapped reefs create blind spots for regional governments and conservation planners when making decisions regarding commercial fishing, development, marine spatial planning, and habitat protection.
Next Steps and Future Field Research in Benin
Despite the excitement surrounding the rediscovery, researchers emphasize that this expedition marks only the beginning. Because the team collected no physical samples during the initial survey due to budgetary and logistical constraints—meaning only one of the two sonar-identified areas could be visually surveyed—all species identifications derived from the camera footage remain provisional. Furthermore, scientists cannot yet determine whether the corals were dead in the 1960s and later recovered, or if the original surveys simply misinterpreted the seafloor features.
The research team plans to pursue expanded acoustic mapping, systematic video transects, diving, and a comprehensive scientific diving and coral sampling program to clarify the spatial extent, structure, and history of the Benin reef system.
