Long-lost coral reef found thriving off West Africa – Earth.com
<img src="https://www.earth.com/assets/_next/image/?url=https%3A%2F%2Fcff2.earth.com%2Fuploads%2F2026%2F07%2F22091704%2FLong-lost-coral-reef-found-thriving-off-West-Africa–1400×850.png&w=1200&q=75" alt="Living coral reef off the coast of Benin with sea fans and soft corals growing on the deep seafloor at mesophotic depth.”>
Long-lost coral reef found thriving off West Africa
ByRaquel Brandao
Earth.com staff writer
A new study has found living coral reefs off the coast of Benin on a stretch of West African seafloor that scientists wrote off as dead more than 60 years ago. Soft corals and sea fans are growing there about 177 feet (54 meters) down, with reef fish moving among them.
No one had confirmed a living coral community at that depth anywhere along this part of the West African shelf. Trawlers actively work the water where the corals sit, and they carry no formal protection.
Chasing a footnote
In 1963 and 1964, French researchers surveyed the seabed off Dahomey, now Benin, and neighboring Togo at the request of both governments. They were hunting for ground a trawler could work, and for a record of the fish living on it.
The report noted a coral barrier at 171 to 184 feet (52 to 56 meters) – an easy detail to miss. Working only from dredge hauls and sound readings, with no cameras, the surveyors concluded the coral was dead.
That call went unchallenged for six decades. No coral research followed on Benin’s shelf. The reef’s extent and condition remained unknown.
Gérard Zinzindohoué, an oceanographer and National Geographic Explorer at the Benin Fisheries and Oceanological Research Institute (IRHOB) in Cotonou, decided to go back and look.
He led the project, launched in 2025, that set out to relocate the corals described in the old report.
Asked by Earth.com what the search says about the ocean beyond this one reef, Zinzindohoué said, “This project shows the value of combining historical scientific observations with modern exploration technologies to rediscover ecosystems that were previously overlooked.”
Finding the corals
Between April and May 2025, the team ran 35 survey lines from small motorboats, covering 7.1 miles (11.4 km) of seabed with side-scan sonar.
The technique drags a torpedo-shaped sensor behind the boat that listens to sound bouncing off the bottom. “It was not an easy field campaign,” said Zinzindohoué.
Rock throws back a strong echo, while sand throws back a weak one. Across roughly 4.3 miles (6.9 km) of otherwise sandy shelf, two bright patches stood out, about 3.4 miles (5.5 km) apart.
One held structures up to 680 feet (207 meters) long and 24 feet (7 meters) high. The other was a ridge 900 feet (274 meters) long and 34 feet (10 meters) high. Both sat between 171 and 184 feet (52 to 56 meters) down, matching the depths logged in the 1960s.
Cameras confirm the find
Confirming what lived on those structures took two camera systems. A tethered drone carrying a 4K camera and 5,000-lumen lights made two dives at the first target.
Alongside it, a baited camera built by the National Geographic Society’s Exploration Technology Lab was lowered five times that August.
That unit films from inside a glass sphere, then burns through a wire to release a 22-pound (10 kg) weight and floats back up on its own.
A 2021 paper describing the design put its cost far below that of a crewed submersible.
That price difference is much of the reason a small national institute could run this survey at all. Money and logistics remained major challenges. Close-up work reached only the first of the two areas.
A garden of soft corals
The footage showed coral at 177 feet (54 meters), growing on large angular blocks of rock. Almost all of it was octocorals – soft corals with bendable internal skeletons rather than stony ones.
Speaking with Earth.com, Zinzindohoué said, “When we observed living corals and associated fish communities on the footage, we realized that these formations were not simply old structures, but living ecosystems.”
The team counted at least six distinct growth forms, including fan-shaped and sheet-like colonies, plus two kinds of black coral. Sea fans were thick enough in places to fill the frame.
Reef-building stony corals barely featured. The few that appeared were small and pale. There was no trace of the piled-up limestone that shallow tropical reefs lay down over centuries.
Life in the coral garden
That absence is why the researchers describe the site as a coral garden – a community of corals that are tenants on rock, not architects of it. The distinction matters: a garden can be scraped off, and nothing underneath rebuilds it.
Living at that depth places them among the world’s mesophotic corals, the communities that hang on below easy diving range using whatever light still reaches them.
The cameras filmed eight species of reef fish feeding and sheltering in the colonies, among them snapper, angelfish, soldierfish and damselfish.
Some soft corals were dead and already overgrown by tube worms and other small colonial animals, which suggests the garden turns over rather than sitting still.
Water that never sits still
Sensors on the seafloor camera recorded bottom temperatures swinging between 66°F and 79°F (19°C and 26°C) across the five drops. That is a wide range for one patch of seabed.
The corals sit right at the boundary where warm surface water meets the colder water underneath, and that boundary rides up and down. Oxygen levels swung just as widely, from a little under half of what the water could hold to nearly the maximum.
The 1960s survey logged temperatures of 61°F to 64°F (16°C to 18°C) at comparable depths off Cotonou in August. The new numbers run warmer.
A few days of readings cannot separate a seasonal swing from a lasting change, though, and the researchers make no claim that the water has warmed.
Until now, the only confirmed mesophotic community in the Gulf of Guinea came from São Tomé, several hundred miles to the south, where a 2017 survey described black coral forests between 100 and 165 feet (30 and 50 meters).
Both sites sit on hard rock in a region where nearly everything else is sediment. That hints the limit on where these communities turn up may simply be the availability of rock to grow on, rather than anything unusual about Benin.
Protecting the reef
Benin now has a documented living coral community on its continental shelf. The survey provided coordinates, video, and the first temperature and oxygen readings ever taken at the site. There was no baseline before this.
The sonar also settles an old claim. Historical reports described a continuous barrier running about 25 miles (40 km) along the coast.
The sound data instead show separate patches on hard ground, not a wall – though the survey covered only a small slice of the described area.
What is still unknown
Two questions stay open. No coral was collected, so every identification rests on video alone.
Whether these colonies died in the 1960s and recovered, or were alive the whole time and simply never seen, cannot be settled from imagery either.
Answering those questions means going back to the reef. The team intends to bring up pieces of coral and read their chemistry for the age of the structures and for traces of past ocean conditions.
In an email to Earth.com, Zinzindohoué said, “Our next steps are to return to these reefs to collect coral samples for radiocarbon dating and palaeoclimate analyses.”
From discovery to protection
The practical consequences may arrive sooner than the science. Trawl gear works Benin’s shelf along the bottom. Until this survey, nothing on any chart steered that gear away from the coral.
The sites can now be written into fishing regulations and into the maps that decide what happens on the seabed.
The wider implication reaches past one country. Other reefs dismissed in mid-century fishing surveys along the West African coast may still be down there, intact and unrecorded.
The study is published in Frontiers in Marine Science.
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