Researchers Find a Pristine Coral Reef Off the Coast of Tahiti

With rose-shaped corals as far as the eye can see, it is one of the largest healthy reefs on record

Scuba divers swim above the reef
Last November, a team of scientists and photographers spent 200 hours studying the vast reef during a dive expedition supported by UNESCO. Alexis Rosenfeld/1 Ocean/UNESCO

Scientists have discovered a coral reef off the coast of Tahiti that stretches almost two miles long and appears untouched by climate change or human activities. With rose-shaped coral as far as the eye can see, the newfound reef is one of the largest healthy reefs on record, per UNESCO.

“When I went there for the first time, I thought, ‘Wow — we need to study that reef. There’s something special about that reef,’” Laetitia Hédouin, a researcher at the French National Center for Scientific Research in Moorea, French Polynesia, tells the Associated Press’ Victoria Milko.

Last November, a team of scientists and photographers spent 200 hours studying the vast reef during a dive expedition supported by UNESCO. They measured corals over six feet in diameters and also witnessed coral spawning.

Most coral reefs known to researchers lie at depths down to about 82 feet. But the reef off the French Polynesian coast sits deeper, at about 100 to 210 feet, between shallow, well-lit waters and the deep ocean. This area is called the mesophotic zone, the deepest place sunlight can penetrate in the ocean.

Scientists think its depth may protect this reef from the effects of human activities.

Corals in reefs across the world are vulnerable to coral bleaching, which makes them susceptible to disease and mortality. Corals are marine invertebrates that rely on microscopic algae living in their tissues called zooxanthellae for food. But the algae dissipates and the coral turns white under stress due to changes in water temperatures, pollution, too much sunlight or low tides. The primary cause of coral bleaching is climate change.

“French Polynesia suffered a significant bleaching event back in 2019, however this reef does not appear to have been significantly affected,” Hedouin says in a statement. “The discovery of this reef in such a pristine condition is good news and can inspire future conservation. We think that deeper reefs may be better protected from global warming.”

While the coral’s depth may protect it, it also made it difficult for the scientists to study, measure and take samples. Researchers have just recently, with advancements in technology, been able to study mesophotic coral ecosystems, per NOAA.

“We’ll be seeing more of these discoveries as the technology is applied to these locations,” former NOAA oceanographer Mark Eakin tells the AP. “We may find some bigger ones somewhere, but I think this is always going to be an unusual reef.”

Scientists have only mapped 20 percent of the ocean’s floor, per UNESCO, which supports sea mapping projects and is planning future dives to continue studying the reef off the Tahitian coast.

"As shallow waters warm faster than the deeper waters we may find these deeper reef systems are refuges for corals in the future,” Murray Roberts, a marine scientist at the University of Edinburgh, tells BBC News’ Victoria Gill. “We need to get out there to map these special places, understand their ecological role and make sure we protect them for the future."