A deep-sea coral reef once written off as lifeless has been found alive and flourishing off the coast of West Africa.
Using advanced sonar mapping and underwater drone technology, researchers located the vibrant marine habitat far beneath the Gulf of Guinea’s surface.
The reef’s existence was first hinted at during 1960s surveys that were originally carried out to pinpoint productive fishing grounds.
At the time, however, scientists believed the deep-water coral formation was no longer living.
Decades later, a modern sonar expedition paired with the Deep Sea Camera System from the National Geographic Exploration Technology Lab has revealed what appears to be a healthy, active coral ecosystem.
Details of the remarkable rediscovery were published in the scientific journal Frontiers in Marine Science.
Lead author Gérard Zinzindohoué reflected on the challenges of the mission, saying: “It was not an easy field campaign.”
“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.”
The historical surveys had identified a possible reef more than 50 meters (164 feet) beneath the surface and declared that it was probably dead.
Zinzindohoué and his colleagues at the Institute of Halieutic and Oceanographic Research in Cotonou, Benin, reasoned that it could have been a mesophotic coral ecosystem.
He said: “A mesophotic coral ecosystem lives deeper than the usual shallow coral reefs, in zones where light is much more limited.
“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.”
Using the historical surveys as a guide, the research team surveyed seven miles of seabed with sonar.
It revealed two signals which could represent reefs.
To investigate the most promising areas, the team used an underwater drone and the Deep Sea Camera System, like underwater trail cameras.
The footage showed a seemingly healthy reef, with eight different types of coral and eight species of fish sheltering and feeding around the corals.
The fish included golden African snappers, blackbar soldierfish, Guinean angelfish, West African goatfish, the Monrovia doctorfish, three-banded butterflyfish, and two species of damselfish.
The reef doesn’t seem to be a continuous coral barrier, but patches of coral occupying rocky areas suitable for their growth.
But the researchers say it’s possible that further surveys will identify more reefs.
Zinzindohoué said: “To our knowledge, this is the first confirmed record of a living mesophotic coral ecosystem on the Gulf of Guinea continental shelf.
“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.”
The research team hasn’t been able to sample the corals directly yet, which means that the species identifications still need to be confirmed.
It’s also impossible to know, without more data, if the corals were really dead in the 1960s and have since recovered.
The team say further research is needed to learn about the reef and other possible reefs nearby.
Zinzindohoué said: “This is still an initial exploration.
“The historical reports suggested that this could be a continuous coral reef barrier extending roughly 40 kilometers (25 miles) 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.”
He added: “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.”
