The colourful reefs off Scotland, Ireland and Norway, have only just been discovered. They're at least 4,500 years old and are home to thousands of different creatures and plants.
But scientists say if deep-sea fishing isn't more tightly controlled, the reefs could be destroyed.
Scars from nets
Fact File
Coral reefs
Usually found in tropical waters
Indian Ocean has 60% of Earth's reefs
Pacific Ocean has 25%
Caribbean has 15%
Some are almost 6,000 years old
Grow very slowly:12 meters per 1,000 years
Have almost as many species as tropical forests in them
Corals produce natural sunscreen which is being developed for human use
Largest natural structures on the planet
Great Barrier Reef can be seen from the moon
They've found evidence of four kilometres of scarring on the coral.
And it's thought fishing trawlers' nets dragged along the bottom of the sea bed are causing the damage.
When scientists checked the nets, they found big bits of coral and many different reef creatures.
Once scientist said: "The fishermen don't do this intentionally - they're not vandals, but the coral won't last indefinitely with that sort of treatment."
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