Deep-sea corals were first discovered in 1869, but it took the advent of sonar and deep-sea submersibles to reveal the size and abundance of the reefs that they build. Although less well studied than their tropical counterparts, these cold-water reefs are just as rich in life. The stony corals that form deep-water reefs flourish in water temperatures of 39–55°F (4–13°C). Unlike tropical corals, they can live in total darkness because they do not rely on zooxanthellae living inside them to produce nourishment by photosynthesis in sunlight. Instead, they survive by filtering food from the water.
One of the biggest reefs—covering 38 square miles (100 square km)—was discovered during an oil-related survey of the Atlantic Frontier, norwhest of Scotland, in 1998. Lophelia pertusa is the main reef-forming coral at these reefs, called the Darwin Mounds, which lie at a depth of 3,300 ft (1,000 m). Lophelia reefs occur at similar depths on many seamounts in the Atlantic, and also in shallow cold water such as in Norway’s fjords.
Pictured is Lophelia pertusa.