Corals are not just warm-water animals. They also live at depths of 40 m, up to an incredible 2,000 m, at water temperatures as low as -1oC. While fishermen and several scientists have known about cold water coral for almost 250 years, it is only within the last few years that we have had the combination of advanced technologies and government willpower pursue investigating them.

How Are Cold Water Coral Reefs Different?

Unlike tropical corals, cold-water corals do not have symbiotic algae in their polyps, so they do not require sunlight to live. As a result, cold-water corals will thrive in dark, deep, cold water, and consume food for energy. They eat only by capturing food particles from the surrounding water. Their polyps appear to be very much larger than the tropical corals. Cold-water coral reefs are usually found when the current flow is accelerated. They are present on the continental shelf, as well as in deep-sea regions with high topographical regions, such as seamounts, mounds, ridges and pinnacles.

Since they don’t rely on warm water or light, deep-sea corals can survive in many different parts of the world. They are much more extensively spread than scientists had historically imagined—living even in waters as cold as -1oC. The biggest exposed reef off the coast of Norway’s Røst Island is 40 km long by 2-3 km wide. Another Norwegian reef has grown to 165 meters, well above the nearby seabed. Radiocarbon dating from the Sula Ridge off Norway indicates that the reef, the second largest in the Northeast Atlantic Ocean, has been expanding for some 8,000 years.

Cold Water Coral Reef Species

Credits : Monterey Bay Aquarium Research Institute

For a number of years, when deep-sea corals were all so inaccessible, no one had any understanding how many species there really were. Today, by analyzing specimens gathered on scientific expeditions, scientists are just beginning to get a more accurate count on the number of species. They research the shape and structure of corals (morphology) to classify species that are known to be present in other regions and species that are new to science. Since too many deep-sea coral species appear to be the same, marine researchers also have to conduct DNA tests to validate the findings.

So, just how many deep-sea coral species are out there? It is far too early to say because new species are constantly being discovered and identified. Currently, over 3,300 deep-sea coral species have been described. And the numbers are still rising.

Other Creatures Found In Deep-Sea Corals

Surprisingly, the number of invertebrate species found on cold water deep-sea reefs may be as large as those present in shallow-water tropical reefs. While the number of fish species is comparatively low (20-40 species compared to 3,000 species in some tropical reefs), cold-water coral reefs do accommodate significant numbers of fish and, like their tropical counterparts, serve as valuable breeding grounds and nurseries. 

How Old Are These Corals?

Deep-sea corals more complex than marine researchers have ever thought, they’re also remarkably old. Deep-sea corals grow steadily (5-25 mm per year), but over many years they develop into expansive reef networks. According to scientific reports, one unique colony of gold coral (Gerardia sp.) discovered off the coast of Hawaii was about 2,742 years old. Marine explorers have also estimated that another deep-sea coral colony in Hawaii, this one a black coral (Leiopathes sp.), is approximately 4,265 years old. These coral ecosystems are the oldest marine species ever recorded.

Thanks to the ongoing regeneration of new polyps, some deep-sea coral reefs have been developing for over 40,000 years. There could be many older deep-sea coral reefs or communities out there, they just need to be discovered!

Help For Humans

A few species living in deep-sea coral environments have been found to generate compounds with tremendous potential for use as new medicines. For example, researchers have discovered that two sponges emerging in deep-sea coral habitats have compounds with anti-inflammatory and anti-viral capabilities. A substance from another deep-water sponge, Discodermia dissoluta, shows potent anti-tumor resistance against human lung and breast cancer cells. And who knows what other possible life-saving chemicals lie in coral reefs far below the surface of the ocean?

Exploring The Ocean’s Deep Realms

A modern wave of exploration vessels and underwater vehicles has allowed ocean researchers to collect knowledge on even the most isolated deep-sea reef ecosystems. Some underwater vessels, such as the Pisces V submersible, carry scientists directly to the bottom of the ocean, where they can study deep-sea corals directly. The Remotely Operated Vehicles (ROVs) and the Autonomous Underwater Vehicles (AUVs) help scientists see and research the areas they usually cannot access. Specialized underwater cameras take close-up photographs of deep-sea coral habitats, and precisely calibrated robotic arms gather samples that are closely inspected and stored for further research.

Climate Change

Since deep-sea corals have been discovered globally and have been alive for so long, their skeletons offer valuable hints to the history of the Earth’s atmosphere. As deep-sea corals grow, layers or bands (similar to tree rings) are produced. The chemical makeup of the bands reflects the shifting ocean environment under which the corals were formed. Through examining and analyzing the thickness of each band, marine scientists can measure how much corals have grown over a given period of time. This knowledge sheds light on the conditions of the ocean during that period. Through performing more complex analyses of deep-sea corals, ocean scientists can collect information on changes in water temperature, nutrients and circulation over long periods of time.

Threats to Cold Water Coral Reefs

Deep-sea corals typically grow in remote areas, due to being found in the deep seas. Yet they are not within the reach of human activity, mainly fishing. Commercial fisheries have increasingly targeted deeper waters, increasing the pressure on deep-sea corals. The destruction caused by fishing equipment, in particular machinery trawling the bottom of the water, presents a significant threat to deep-sea corals. Decades of bottom trawling can totally alter the underwater landscape as these machines smooth out the seafloor, and destroy deep-sea coral in their wake.

Exploration and production of oil and gas also contribute to the loss of coral reefs, particularly if accidents occur such as oil-spills. Deep-sea coral habitat was devastated by the Deep Water Horizon oil leak in the Gulf of Mexico. Climate change and, in particular, ocean acidification, are additional threats. Water acidification happens as the ocean absorbs harmful carbon dioxide in the air, altering the water chemistry of the oceans to become more acidic, resulting in coral skeletons growing slower and weaker.

Deep-sea corals grow exceptionally slowly, so it can take decades or even centuries to recover from these threats and disturbances, if they recover at all.