First Alaska Explorations | Recent Work

The seas surrounding the Aleutian Island chain may harbor the highest abundance and diversity of coldwater corals in the world. Unlike tropical corals, these high-latitude corals do not form reefs but, rather, assemble into dense gardens, and some are thought to live hundreds of years. Scientists have known something of Alaska's corals for nearly a century; they turned up in trawls in the first expeditions here. But, because of the region's remoteness, they have been little explored by science - until recently.

What is coral?
Coral is made up of small, individual animals, known as polyps.

These polyps are typically joined together in groups, known as "colonies," of hundreds or thousands at a time, by tissue. The connected polyps sit on or surround a skeleton, made by a secretion that hardens into a bone-like structure.

If you've ever found a piece of bleached-out white "coral" on a beach or seen it at a gift shop, this is not a living coral, but a coral "skeleton," stripped of its fleshy polyps. In the ocean on a living specimen, however, the polyps are easy to see. Some people think they look like tiny anemones or jellyfish sitting on their heads and spreading out miniature tentacles into the current to capture food particles.

What makes Alaska's deep-sea corals different?
Unlike many other corals, deep-sea Alaska corals don't need light to grow. They acquire all the nutrients they need directly from the water column. Tropical corals at shallower depths often have a sharing, or "symbiotic," relationship with algae that live within their tissues and help provide them nutrients they need to grow. (The algae get energy from sunlight.)

Alaska corals do not form reefs like tropical corals, in the true sense, but rather form extensive gardens in the Aleutian Islands.

What kinds of corals are in Alaska?
As researchers continue to learn more, the scientific classification of Alaska's corals, like those of all corals, is constantly being revised, which can be confusing -- even to the experts! It is helpful to remember that the scientific groupings of these curious colonial organisms are often based more on the appearance of individual polyps under a microscope than the most obvious characteristics seen at a distance or by the naked eye.

Alaska's corals generally fall into several major groups, including cup corals, octocorals, hydrocorals and black corals:

Cup Corals (Scleractinians):
Also called stony corals, or true corals, scleractinians are the same kind of coral known to flourish in the tropics. Unlike their tropical counterparts, however, Alaska's cup corals are small and solitary, and do not form reefs. They may form cup- or cone-shaped skeletons, each containing a single polyp.

Octocorals (Alcyonarians):
The octocorals include many corals that don't look at all alike. Mushroom-shaped, fleshy "soft corals" (Alcyonaceans) are a type of octocoral. But so are thin, single-stalked "sea whips" and "sea pens" (Pennatulacea). According to the recently drafted Field Guide to Alaskan Corals by Bruce Wing and David Barnard (2003), this group is the most diverse, the least-well-known and the most difficult to identify! Scientists group these many dissimilar-looking corals together in part because they share one feature in common: the polyps of these corals all have eight "pinnate" (or narrow-shaped) tentacles.

The sea fans (Gorgonians), a branching type of octocoral, are so far the most common known in the Aleutian Islands. These include gorgonians such as bamboo corals, whose skeletons are segmented to give the appearance of bamboo, and tree corals, which look more like branches. One type of "red tree coral, has been found growing up to 5 meters high and 7 meters wide. Some are thought to live hundreds of years. The oldest verified was found to be more than 800 years old, making it likely that some may live to be more than a thousand. Other octocorals include stolon corals, an encrusting type of coral (Stoloniferan).

Hydrocorals (Stylasterina):
The polyps that form the hydrocorals are so small they can be difficult to see with the naked eye. The skeletons they form tend to be quite brittle and fragile, and rather than bending, will shatter like ice when knocked into.

Black corals (Antipatharia):
The black corals are named for the color of their skeletons. Black coral skeletons of some (tropical) species, which occur in shallower waters, are used to produce jewelry. Prior to current video and sampling work, they had previously only been collected in Alaska through bycatch surveys in crab and longline fisheries. Sources: Scott France, Bob Stone and Jon Heifetz, as well as Bruce Wing and David Barnard's Field Guide to Alaskan Corals (draft) 2003.

Read about the history of Alaska coral exploration.

Read about recent Alaska coral exploration.

This Alaska coral is commonly called a "bubblegum coral." Scientists know it as a gorgonian coral called a Paragorgia, a branching type of octocoral.

Credit: Bob Stone / NOAA Research.

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