Coral reefs: cold-water corals

Gorgon's head Gorgonocephalus caputmedusae in the Selligrunnen, a protected cold-water coral reef ... / ©: WWF-Canon / Erling SVENSEN
Gorgon's head (Gorgonocephalus caputmedusae) in the "Selligrunnen", a protected cold-water coral reef in the Trondheimsfjorden, Norway.
© WWF-Canon / Erling SVENSEN
Corals are not just warm-water creatures. They also live at depths of 40m down to 2,000m, in water temperatures as low as 4ºC.
Although fishermen and a few scientists have known about cold-water corals for nearly 250 years, it’s only in the past few years that we’ve had the combination of advanced technology and political will to begin to explore them.

Unlike tropical corals, cold-water corals don't have symbiotic algae living in their polyps so they don’t need sunlight to survive. They feed solely by capturing food particles from the surrounding water. Their polyps tend to be much bigger than tropical corals.

Cold-water coral reefs are commonly found where current flow is accelerated. They are found on the continental shelf, and also in deep-sea areas with topographic highs, such as seamounts, mounds, ridges, and pinnacles.

Deep-sea corals grow slowly (5-25mm a year), but over time they form extensive reefs. The largest reef yet discovered, off the coast of Norway's Røst Island, is 40km long and 2-3 km wide. Another Norwegian reef has grown to a height of 165m above the surrounding seabed. Radiocarbon dating of coral from the Sula Ridge off Norway suggests that the reef complex, the second largest in the Northeast Atlantic Ocean, has been growing for around 8,000 years.

Deep-sea coral reefs are made up of only a few coral species but they provide a home for many other animals, including sea fans, sponges, worms, starfish, brittle stars, sea urchins, crustaceans, and fish.

The number of invertebrate species on reefs in the Northeast Atlantic Ocean can be as high as that found in shallow-water tropical reefs. Although the number of fish species is relatively low (20-40 species compared to 3,000 species on some tropical reefs), cold-water coral reefs do attract large masses of fish and, like their tropical cousins, serve as important spawning and nursery grounds.

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