Discovery of a huge “pristine” reef of giant rose-shaped corals hidden at an unusual depth off Tahiti

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A UNESCO diver studies the rose-shaped corals on the newly discovered reef in Tahiti. (Image credit: UNESCO/Alexis Rosenfeld/1 Ocean)

Divers from the United Nations Educational, Scientific and Cultural Organization (UNESCO) have discovered and mapped a huge giant rose-shaped coral reef hidden off the coast of Tahiti, the largest island in French Polynesia in the South Pacific. The structure is in pristine condition and has remained surprisingly sound despite recent coral bleaching events in the region.

The newly discovered coral reef, which remains unnamed, is about 1.9 miles (3 kilometers) long and between 98 and 213 feet (30 to 65 meters) in diameter. It lies between 100 and 180 feet (31–55 m) below the surface, which is unusually deep for a tropical coral reef and may have protected it from effects of climate change. The reef is composed mainly of Pachyseris speciosaa plate-like encrusting coral that forms rose-shaped colonies up to 6.5 feet (2 m) wide, depending on the World Register of Marine Species.

Divers from the Ocean 1 seabed exploration project first discovered the reef in November 2021. “It was magical to see beautiful giant pink corals stretching as far as the eye can see,” said Alexis Rosenfeld , underwater photographer and founder of the Ocean. project, which is jointly managed by UNESCO, said in a press release. “It was like a work of art.”

Related: 10 signs that the Earth’s climate is out of whack

Exceptionally deep

The majority of coral reefs in tropical regions like Tahiti are found in shallow water above 82 feet (25 m) deep. The newly discovered reef is located toward the upper limit of the mesophotic zone, which extends from 100 feet (30.5 m) below the surface to more than 490 feet (149 m) below the surface, according to the National Oceanic and Atmospheric Administration (NOAA).

Corals in the mesophotic zone receive less light than their shallow coral reef counterparts. To compensate for this lack of light, corals like P. speciosa are wide and flat to maximize their light-gathering surface.

The location of the new reef at the upper limit of the mesophotic zone has always been very difficult for scientists to study because it is too deep for traditional scuba diving and too shallow to use remotely operated vehicles (ROVs), according to the NOAA. However, divers have developed new technologies, such as the use of air containing heliumwhich reverses the hallucinations caused by oxygen and nitrogen depth and avoids turns or decompression sickness which makes it easier to explore these deep regions for longer periods of time. Combined with better underwater camera equipment, this new technology has made the mesophotic zone fully explorable for the first time, according to the release.

Advances in diving and camera technology have made mesophotic reefs more accessible to researchers. (Image credit: UNESCO/Alexis Rosenfeld/1 Ocean)

The 1 Ocean team took advantage of these technological advances and completed dives on the reef totaling approximately 200 hours, allowing them to map it in great detail and even witness coral spawning, according to the statement. .

Protected from harm

Coral reefs are one of the most threatened ecosystems Earth. A total of 237 coral species are currently listed as endangered on the International Union for Conservation of Nature (IUCN) Red List, according to Our world in data.

The corals are threatened by plastic and chemical pollution, overfishing, sediment runoff, ecotourism and explosive dynamite fishing. However, the main problem facing coral reefs is the increase in greenhouse gas, which increases sea surface temperatures and acidifies the ocean. This combo can cause coral bleaching, where corals expel photosynthesis algae that live inside their tissues and provide them with energy. This bleaching process not only drains corals of their color, but is often fatal to coral colonies.

The newly discovered reef has not been affected by climate change related issues like coral bleaching. (Image credit: Shutterstock)

Between 2014 and 2017, more than 75% of the world’s coral reefs experienced some degree of coral bleaching due to an El Niño event, a natural phenomenon that increases sea surface temperatures in the Pacific and has been exacerbated by climate change, according to NOAA. However, the mesophotic reefs may have escaped relatively unscathed due to their cooler temperatures.

“We believe that deeper reefs can be better protected against global warming“, said Laetitia Hedouin, a coral expert at the French National Center for Scientific Research, who participated in the project, in the press release. For example, the new reef was spared a major bleaching event that hit French Polynesia in 2019.

Thus, mesophotic reefs could become vital backups for decimated shallow-water reefs and provide a new home for displaced species such as fish and shellfish, according to NOAA. “The discovery of this reef in such pristine condition is welcome news and may inspire future conservation,” Hedouin said in the statement.

Originally posted on Live Science.

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