Enormous ‘twilight zone’ coral reef discovered off the coast of Tahiti

That a coral reef so large and so beautiful had yet to be discovered emphasizes how little we still know about the world’s oceans, scientists say. And its impeccable condition — with no evidence that the reef has yet been harmed by the climate crisis — suggests the need for urgent action to protect the ocean’s remaining healthy reefs.

Alexis Rosenfeld, the photojournalist who led the team of international divers, said the reef, which stretched “as far as the eye can see,” was “magical to witness.”

“It was like a work of art,” he said.

The research mission, led by UNESCO, found the reef stretches for nearly two miles and exists at depths down to 70 meters, or 230 feet. This is around the ocean’s “twilight zone,” where there’s just enough light to sustain life, and below which the ocean transitions into a dark abyss.

“For once, it’s a positive story about coral reefs in the news, which is quite rare these days,” Julian Barbiere, head of marine policy at UNESCO, told CNN.

Warming oceans and acidification caused by the climate crisis has led to widespread coral bleaching. Last year, scientists found the global extent of living coral has declined by half since 1950 due to climate change, overfishing and pollution.

The outlook is similarly grim, with scientists predicting about 70% to 90% of all living coral will disappear in the next 20 years.

Only around 20% of the ocean floor has so far been mapped, according to UNESCO. And until its latest discovery, the vast majority of the planet’s known coral ecosystems were believed to extend to a depth of just 25 meters, illustrating how much of the ocean — which covers more than 70% of Earth’s surface — still needs to be explored.

“The discovery suggests that there are, in fact, many more large reefs out in our ocean at depths of more than 30 meters, which have not been mapped,” Barbiere said. “It’s quite a puzzling finding.”

The dive team was able to spend about 200 hours studying the reef using specialized scuba equipment called rebreathers.

Coral reefs are an important food source and habitat for a wide array of marine organisms, such as the fish seen here.

“While we are witnessing major investment in space exploration, there’s not enough on studying our own home and the ocean in particular,” Barbiere said. “And I think this is really where we want to put our emphasis in the next 10 years — to create the knowledge we need to put the planet on the sustainable path through marine protected areas.”

Despite its depth, researchers say the newly discovered reef still receives enough sunlight for the corals to grow and reproduce. Some of the divers even witnessed the corals spawning.

Researchers went into the mission in November last year with little knowledge of the reefs existing in the region, and came out with an incredible understanding of how widespread, unique and pristine the coral there is.

Depsite its depth, the reef still receives enough sunlight for the corals to grow and reproduce.

A researcher swims above the reef, which stretches for nearly two miles.

Using scuba rebreathers, which filter carbon dioxide out of exhaled air and recycle much of the unused oxygen, the dive team was able to spend about 200 hours studying the reef. Rebreathers allow divers to go deeper into the ocean floor and stay for longer periods of time. The rebreathers contain a special helium-based gas mixture that guards against narcosis or a state of drowsiness.

Barbiere said researchers were surprised to learn that the coral was fully intact and healthy, a sign they’ve survived for decades, given large reefs take roughly 25…