Surveys have revealed thriving mesophotic coral gardens where historical studies had reported what were thought to be dead reef structures.
Rediscovered Benin coral reef.
More than 60 years after surveys reported apparently dead coral structures off Benin, scientists have returned to the area and discovered living coral communities flourishing at depths of around 54m.
Using side-scan sonar, underwater cameras and a remotely operated underwater drone, researchers found dense gardens dominated by octocorals, together with black corals and reef-associated fishes. The discovery provides the first confirmed visual evidence of living mesophotic coral communities on Benin’s continental shelf—and, according to the researchers, the first documented on the continental shelf of the Gulf of Guinea.
Returning to a 1960s discovery
The story began in 1963–64, when surveys conducted off what was then Dahomey, now Benin, and neighbouring Togo reported a coral reef barrier at depths of approximately 52–56m.
Those surveys were primarily intended to map seabed suitable for trawling and document fish diversity. Without modern underwater imaging, researchers could not directly assess the ecological condition of the coral structures, and they were subsequently regarded as dead. No dedicated coral surveys followed for more than six decades.
Researchers returned in 2025 through the Coral Reefs Rediscovering and Exploration project in Benin (COREB), using the historical maps to guide their search.
Side-scan sonar surveys across approximately 7km revealed two areas of hard substrate standing out from the predominantly sandy continental shelf. Cameras sent down to investigate showed that some of these structures supported abundant living corals.
Coral gardens rather than a barrier reef
The new observations also revise the earlier interpretation of what lies beneath the Gulf of Guinea. Rather than finding a continuous coral barrier, researchers documented separate patches of hard seabed supporting mesophotic coral gardens. The communities were dominated by octocorals, including at least six different morphotypes, along with at least two types of black coral. Reef-building stony corals were comparatively scarce.
Eight reef-associated fish species were identified from the video, including the African angelfish (Holacanthus africanus), Monrovia doctorfish (Acanthurus monroviae) and robust butterflyfish (Chaetodon robustus). The researchers caution that species identifications remain provisional because the exploratory survey relied on imagery rather than physical specimens. They also cannot yet determine whether the coral communities have persisted there throughout the intervening 60 years or whether ecological conditions have changed.
An unexplored part of the ocean
The significance of the discovery extends beyond Benin. Mesophotic ecosystems—coral communities occurring in the deeper, lower-light portion of tropical seas—remain poorly studied, particularly along the West African coast. The findings therefore reveal as much about a gap in scientific exploration as about coral resilience.
The apparent absence of such ecosystems elsewhere in the Gulf of Guinea may partly reflect how little of the region’s deeper continental shelf has actually been surveyed. The researchers are now calling for wider acoustic mapping, quantitative surveys and physical sampling to determine how extensive the newly documented habitats are and what ecological role they play.
For now, a habitat effectively absent from the scientific record for six decades has re-emerged as a biologically active coral ecosystem—and raised the possibility that other overlooked communities remain to be found along West Africa’s largely unexplored continental shelf.
