SerpApi.Org
Coral reefs might make you think of beautiful tropical islands and shallow seas teaming with fish, but there exist other kinds of reefs that occur at deeper depths.
These are known as mesophotic coral ecosystems, and one off the coast of Benin was thought to be long dead. Now, new surveys have revealed that the area is full of life, with potentially more waiting to be discovered.
Mesophotic coral ecosystems occur at the limit of where the light can penetrate through the waves and where the ocean temperature starts to cool. This means they're deeper in the ocean than most typical coral reefs, at a transition zone between shallower waters and the deep ocean.
Despite their ecological importance, these areas have been historically understudied. This is particularly true in the waters of the Gulf of Guinea off the coast of western Africa.
One such deep-water reef off the coast of Benin was first identified in the 1960s. While studying fish diversity in the region to identify trawlable areas, the survey found a thriving coral ecosystem at depths of 52 to 56 meters (170-183 feet). Since then, these reefs were assumed to have died, and nobody thought to take a closer look.
“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, in a statement.
“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."
The team used side-scan sonar mapping to discover more about the area, and undertook underwater drone surveys. The results show a healthy coral ecosystem composed mostly of octocorals, which form a coral garden.
Fish species recognized from video footage included the Guinean angelfish (Holacanthus africanus), blackbar soldierfish (Myripristis jacobus) and golden African snapper (Lutjanus fulgens).
"We surveyed the structures with an underwater drone and the Deep Sea Camera System," said Zinzindohoué. "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.”
"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."
These results represent the first evidence of a living mesophotic coral community off the coast of Benin more than 60 years after it was first discovered.
The team has not been able to sample the corals, so there is more work to be done to fully identify the species present. But they think there could be many more regions out in the Gulf of Guinea and off the Benin coast with reefs that have been forgotten, or are waiting to be discovered.
Earlier this year, a staggeringly large porites coral colony was discovered off the Mariana Islands in the Pacific Ocean. Thought to be over 2,000 years old and more than 31 meters (100 feet) across at the top, the jury is still out on whether this enormous coral colony is the world's largest.
“The historical reports suggested that this could be a continuous coral reef barrier extending roughly 40 kilometers [24.8 miles] parallel to the coast," said Zinzindohoué. "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."
The paper is published in Frontiers in Marine Science.
