Living Coral Reef Discovered off the Coast of Benin

For decades, a coral reef off Benin’s coast was regarded as little more than a long-standing enigma.

Surveys conducted in the 1960s indicated that a possible reef lay beneath the sea at depths exceeding 50 metres. Yet the researchers then concluded that it was most likely lifeless.

That accepted view has now been challenged by fresh evidence. A new investigation found living coral at depths where many would expect to find only the remains of an ancient reef.

The discovery offers a different picture of Benin’s coastline and suggests that other features may still be waiting to be found below the surface.

A forgotten clue reveals a surprise

The initial surveys had been undertaken to locate potentially productive fishing areas. Although the deep reef attracted little attention at the time, scientists later considered it worth revisiting.

The researchers thought the location could contain a mesophotic coral ecosystem. Such reefs develop deeper than the colourful coral reefs familiar to most people. They persist where sunlight is far weaker, often below 50 metres beneath the surface.

Rather than creating a single, unbroken coral wall, these ecosystems generally occur as separate patches spread over the seabed.

Searching the seabed off Benin

Guided by the historic survey data, the team used modern sonar to scan 11 kilometres of seafloor. The results highlighted two sites that appeared sufficiently promising for detailed examination.

“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.

“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,” he explained.

Zinzindohoué said the team examined these structures using an underwater drone and a Deep Sea Camera System.

“That was a big moment for us, because suddenly we could actually see the seafloor,” he said. “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.”

A healthy coral reef supporting marine life

The underwater images indicated a healthy coral ecosystem, rather than an empty stretch of seabed. Across the rocky patches, the researchers documented eight distinct coral types.

The reef also hosted a range of fish species. Camera footage recorded golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish and two damselfish species feeding and taking shelter among the corals.

Although it does not form one continuous barrier, the reef extends across several rocky areas offering suitable conditions for coral development. Scientists think further surveys may identify additional patches in the surrounding area.

Why Benin’s coral reef is important

Deep-water coral ecosystems have received much less study than shallow reefs. With less available sunlight, they frequently grow at a slower rate. Nevertheless, they can provide important habitats for fish and other marine organisms.

They may also retain valuable evidence of previous ocean conditions, helping scientists assess how marine environments have altered over extended periods.

“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,” he commented. Further fieldwork will be needed to determine whether deep reefs of this kind are more widespread.

Questions about the deep reef remain

Scientists describe the finding as exciting, but stress that it is only an early step. No coral samples have yet been gathered, meaning the identities of the coral species still require confirmation.

Nor can researchers establish whether the reef was genuinely dead in the 1960s before recovering, or whether the earlier surveys simply drew the wrong conclusion.

“This is still an initial exploration,” said Zinzindohoué. “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.”

These ecosystems remain very poorly understood in this region of the world, and every new piece of evidence is significant.

“For me, the most exciting part is about 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,” concluded Zinzindohoué.

The complete study appeared in the journal Frontiers in Marine Science.