Most people envision coral reefs as colorful places in shallow tropical waters. However, corals can be found throughout the world from the coast of tropical Thailand to the cold Alaskan and Norwegian waters. These latter deep water corals and Arctic corals are also important ecosystems and should not be dismissed or forgotten.
What Are Cold Water Corals?
The NOAA’s Coral Research Information System (CoRIS) explains the difference between tropical and cold water corals on their “Deep Water Corals” page. As the ocean gets deeper, temperature also falls which means deep water corals must withstand frigid temperatures as low as 4 °C (39.2 °F). Cold water corals can be found in the shallows of Arctic waters or as far down as the cold depths of 2,000 meters. Deep water corals can be ancient with some still living corals aged at 10,000 years old.
How Do Deep Water Corals Live?
Tropical corals generally live in a symbiotic relationship with algae that use photosynthesis to provide corals with nutrients. Cold water corals do not get enough sunlight and cannot make use of this relationship. Instead, cold deep water corals are suspension feeders. The coral polyps use tentacles to capture and eat plankton or other small organic detritus floating by. Deep cold water corals are often found on ridges and pinnacles that enable them to better catch what is floating in the water column.
Arctic Corals Found off Alaskan and Norwegian Coasts
GRID-Arendal, the Key Polar Center of the United Nations Environmental Program, describes where Arctic corals can be found in the article “Rapid Response Assesments Coral Reefs”. Cold water corals have been found in the waters of 41 countries worldwide. Some cold water corals form reefs while others span out into gardens. The largest cold water reef so far discovered is the Rost reef off the Norwegian coast. Discovered in 2002 it is twice the size of New York’s Manhattan. The main species in this reef is Lophelia pertusa. The cold water corals off of Alaska’s Aleutian Islands do not form reefs but rather gardens. These gardens are made up predominantly of soft corals.
Threats to Cold Deep Water Corals
GRID-Arendal goes on to explain how humans are negatively impacting cold water reefs, killing off huge swaths with fishing equipment. Bottom fishing which uses trawls and dredges drags along the bottom of the ocean destroying what is in its path. Submarine observations show that most reefs in the North Atlantic have been impacted by trawling. Lost fishing gear such as nets and lines also get tangled in the corals, thus damaging them. Reefs can take thousands of years to grow and then be destroyed in a matter of hours. Cold water corals are an important part of the ecosystem, providing for fisheries that humans dine out of. It is vital to learn about cold water corals and protect them.
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