Several species of deep-sea corals form an underwater garden 165 m (540 ft) below the ocean’s surface off the coast of Alaska’s Aleutian Islands. Photo credit: Alberto Lindner/NOAA
Spectacular coral ecosystems also thrive in deep, cold waters around the world, sometimes thousands of meters below the ocean’s surface. Also referred to as “cold-water corals,” these corals are architects of the deep, forming three-dimensional structures upon which vibrant communities are built. They are distributed across a wide range of depths and latitudes, in both temperate and tropical oceans. Deep-sea corals are a diverse collection of organisms that occur in deeper or colder oceanic waters and lack symbiotic algae (zooxanthellae) characteristic of most reef-building shallow water tropical corals. Unlike their shallow water relatives, which rely heavily on photosynthesis to produce food, deep-sea corals take in plankton and organic matter for much of their energy needs. Deep-sea corals are also often extremely long-lived, slow growing animals, characteristics that make them particularly vulnerable to physical disturbance.
Structure-forming deep-sea coral
: Any colonial, azooxanthellate (does not contain symbiotic algae
called zooxanthellae) corals—generally occurring at depths below 50 m—that provide vertical structure above the seafloor which can be utilized by other species. These include both deep reef-building stony corals (e.g., Lophelia pertusa
), as well as individual branching colonies of corals (e.g., gorgonians, black corals, and gold corals). These are often referred to as habitat-forming deep-sea, deepwater, or cold-water corals.[a]
There are probably as many species of deep-sea corals as there are shallow-water corals. While some species are small and inconspicuous, the calcified skeletons of certain branching stony coral species form large reef-like structures in deep water. Other kinds of corals often have branching tree-like forms and either occur singly or form thickets of many colonies. The three-dimensional features formed by these "structure-forming deep sea corals" provide habitat for rich and diverse fish and invertebrate communities in deeper waters on continental shelves, slopes, canyons, ocean ridges and seamounts around the world, generally in waters ranging from 50 m to over 2,000 m (160 ft-6,500 ft) in depth. Deep-sea coral habitats have been documented in many areas in the U.S. exclusive economic zone, except the Arctic Ocean, but their full extent is unknown, since most areas have been incompletely surveyed.
Despite scientific advances in the understanding of deep-sea corals, there is still very little known about their growth rates, reproductive cycles, their functional role as habitat for marine species, and their effects on biodiversity. However, what we do know is changing our view of the undersea world and the importance of these ecosystems.
The State of Deep Coral Ecosystems of the United States
- Roberts, JM, A Wheeler, A Freiwald, S Cairns. (2009) Cold-water Corals: the biology and geology of deep-sea coral habitats. Cambridge, UK: Cambridge University Press. 352 pp.