Check out breathtaking images of 'pristine' coral reef discovered near Tahiti

This reef is located at depths between 30 and 65 meters. It is about 3 km long and between 30 and 60/65 m wide, making it one of the largest healthy coral reefs ever recorded. These giant rose-shaped corals measure up to 2 meters in diameter.

This is an extraordinary discovery because, until now, the vast majority of known coral reefs in the world are found at depths of up to 25 meters. This discovery, therefore, seems to indicate that there are many other large reefs, located at depths of more than 30 meters, in the so-called "twilight zone" of the ocean, which we simply do not know exist.

This expedition is part of UNESCO's action plan to map the ocean. Coral reefs are an important food source for other organisms. Their location can therefore facilitate research on biodiversity. Organisms that live on reefs can play an important role in medicinal research, and reefs can also provide protection against coastal erosion and tsunamis.

The newly discovered coral reef, which remains unnamed, is around 1.9 miles (3 kilometers) long and between 98 and 213 feet (30 to 65 meters) across. It lies between 100 and  180 feet (31 to 55 m) below the surface, which is unusually deep for a tropical coral reef and may have shielded it from climate change effects.

The reef is made up predominantly of Pachyseris speciosa, an encrusting plate-like coral that forms rose-shaped colonies that can grow to be 6.5 feet (2 m) wide, according to the World Register of Marine Species.

Divers from the seafloor exploration project Ocean 1 first discovered the reef in November 2021. "It was magical to witness giant, beautiful rose corals which stretch for as far as the eye can see," Alexis Rosenfeld, an underwater photographer and founder of the Ocean project, which is jointly run by UNESCO, said in a statement. "It was like a work of art."

The location of the new reef at the upper limit of the mesophotic zone has historically been very hard for scientists to study because it is too deep for traditional scuba diving and too shallow to use remotely operated vehicles (ROVs), according to NOAA.

However, divers have developed new technology, such as the use of air containing helium, which negates hallucinations caused by oxygen and nitrogen at depth and helps prevent the bends, or decompression sickness that make it easier to explore these deep regions for longer periods.

Combined with better underwater camera equipment, this new technology has made the mesophotic zone fully explorable for the first time, according to the statement