When you think of coral reefs, you most likely picture a tropical underwater landscape with clownfish and blacktip reef sharks swimming gracefully. But, did you know that coral reefs are also found in the cold, dark waters of the deep, deep ocean? It’s true! Cold-water corals, known as deep-sea corals, have been living in frigid, deep waters for thousands and thousands of years.

Deep-sea corals belong to a group of animals called the Cnidaria. They are closely related to sea anemones—living fixed in one place and catching prey with their stinging tentacles in order to eat. Corals are composed of polyps, each having a ring of tractable tentacles surrounding a mouth.

Excited to learn more? Dive in and explore these five facts about cold water corals.

No sunlight? No problem!

Deep-sea corals don’t need sunlight to survive and thrive. Corals have been found up to 20,000 feet below the ocean’s surface, where the water is icy cold and the light is dim or completely absent. In order to eat, deep-sea corals obtain the energy and nutrients they need to survive by trapping tiny organisms (like plankton) in passing currents. Believe it or not, scientists have discovered about as many species of deep-sea corals as shallow-water species. So far, more than 3,300 species of deep-sea corals have been identified, but new species are being discovered continually.

Living in every corner of the ocean

Deep-sea corals are able to live in a wide range of ocean habitats because they don’t need warmth or sunlight to survive. They have been found living in waters as cold as 30.2ºF.

The range is vast! Deep-sea corals occur in the waters of the United Kingdom, Australia, New Zealand, Canada, Ecuador, Japan, Norway and the United States. Scientists have even found deep-sea corals off the coast of Antarctica. They grow in all the world’s ocean basins, where they form deep-water havens on continental shelves and slopes, in ocean canyons and on tall seamounts.

Coral reefs have been discovered in the North Atlantic, and several species of deep-sea corals form an underwater garden 540 feet below the ocean’s surface off the coast of Alaska’s Aleutian Islands.

Growing old (really, really old)

Cold water coral reefs grow and mature over long periods of time. The deep sea is a low energy environment, and the corals there grow very slowly. Some reefs on the Sula Ridge in Norway, for example, developed at the end of the last ice age, about 10,000 years ago!

Deep-sea corals are OLD. One colony of gold coral (Gerardia sp.) found off Hawaii was estimated to be about 2,742 years old. The estimated lifespan of a black coral colony is 70 years. However, in March 2009, a deep-water species of black coral was discovered, and scientists estimate it was around 4,265 years old. These coral colonies are the oldest marine organisms on record. There may be even older deep-sea corals out there still to be discovered.

Hot-spot for habitat

Although some species of coral live as solo individuals forming a single polyp, most corals form colonies of many hundreds or thousands of polyps. These colonial corals are comprised of large, complex skeletons, usually made from calcium carbonate (limestone). Some species can eventually produce elaborate branching frameworks which, over time, can grow to become the basis of cold-water coral reefs.

Colonial corals are crucial to the deep-sea environment since they establish habitat and alter the surroundings—making more places for ocean animals to live, thrive and hide. As a result, deep-sea reefs can have greater abundance and diversity of marine life than surrounding areas. Cold-water coral reefs are biodiversity hot-spots in the deep-ocean.

Coral reefs need our help

Stressors such as climate change, ocean acidification, disease, overfishing, sedimentation and pollution have degraded coral reefs around the world. The ocean is acidifying due to increased carbon dioxide, making it harder and harder for corals to build the physical structure of the reef. Thankfully, people are hard at work trying to replenish coral populations with coral reef nurseries to ensure they survive for generations to come. However, the best way we can help corals—and the animals that depend on them—is by cutting carbon emissions and limiting the effects of climate change.

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