Dr Julian Barbiere, from Unesco, said there were probably many more of these ecosystems " we just don't know about".
" We should be working to map them and to protect them, " He Said .Twilight zone
Unesco director general Audrey Azoulay said the " remarkable" discovery extended our knowledge of " what lies beneath".
French underwater photographer Alexis Rosenfeld said it had been " magical to witness giant, beautiful rose corals stretching as far as The Eye can see".
" It was like a work of art, " he added.
Coral reefs are among The Ocean 's most threatened ecosystems - Vulnerable to pollution, rising sea temperatures and The Change in chemistry caused by carbon-dioxide emissions dissolving in the water.
" We still associate corals with the shallowest tropical seas but here we find a huge previously unknown Coral Reef system.
" As shallow waters warm faster than the deeper waters we may find these deeper reef systems are refuges for corals in The Future . We need to get Out There to map these special places, understand their ecological role and make sure we protect them for The Future . "
There is currently " no evidence" this reef had been damaged by those pressures and, Dr Barbiere said, its unusual depth was one reason it remained in such a " very good state".
The Discovery provided an important insight into ocean biodiversity, Dr Barbiere said.
" We know that about 25% of marine species can be found in coral reefs, " He Said .
" So The Next stage is to find what species live around this type of reef. "
The Coming months will see further investigation.
Another of The Specialist divers, Dr Laetitia Hedouin, from France's National Centre of Scientific Research, said: " We would expect a reef such as this to take around 25 years to grow and develop like this.
" We think that deeper reefs may be better protected from Global Warming .
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