A coral reef off the coast of Benin that was thought to be dead for decades has been found alive and apparently healthy.
Surveys conducted in the 1960s, which were primarily designed to locate productive fishing grounds, identified what appeared to be a deep-water coral reef. At the time, researchers concluded that the reef was probably dead. More than 60 years later, scientists returned to the area armed with modern sonar and the Deep Sea Camera System provided by the National Geographic Exploration Technology Lab.
What they found was very different from what the historical records had suggested.
“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.”
A Deep Coral Ecosystem Thought To Be Dead
The older surveys had placed the possible reef more than 50 meters below the ocean surface and described it as probably dead. Zinzindohoué and his colleagues suspected that the site might instead contain 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.”
Guided by the decades-old survey records, the researchers scanned 11.5 kilometers of seafloor using sonar. They detected two areas with signals that looked potentially reef-like.
The team then examined the most promising locations with an underwater drone and the Deep Sea Camera System, which functions somewhat like a set of trail cameras placed beneath the ocean.
The images revealed what appeared to be a healthy coral community.
Cameras Reveal Coral and Fish Life
Researchers observed eight different types of coral, along with eight fish species using the reef for shelter and feeding. The fish included golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish, and two species of damselfish.
Rather than forming one solid coral wall, the reef appears to consist of separate coral patches growing on rocky sections of the seabed where conditions are suitable. Scientists say additional surveys may reveal more reefs elsewhere in the surrounding area.
“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? So yes, I do believe there are likely more coral systems out there that we have not documented yet. 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.”
How Many More Reefs Could Be Hidden?
The discovery raises the possibility that other coral ecosystems along West Africa may have been overlooked, forgotten, or never documented in the first place.
Still, the researchers caution that this is only an early look at the site. They have not yet collected physical samples of the corals, so the identifications made from the camera footage still need to be confirmed.
There is also no way yet to determine whether the corals seen in the 1960s really were dead and later recovered, or whether the original survey simply misinterpreted what was there.
Answering those questions will require much more detailed research at the site and in nearby waters.
A Possible 40 Kilometer Coral System
“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. 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. These are ecosystems that are still poorly known in this part of the world, and every additional piece of information matters.
“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.”
