Gorgonians and hard corals belong to the same group, the Cnidaria, which also includes the jellyfish, hydrozoans, sea anemones, and the Portuguese Man of War. These animals are similar in that they all contain a special type of stinging cell (cnidoblast). The cnidoblasts are microscopic capsules which, when triggered by touch, chemicals or changes in salinity, eject a barbed filament with venom used for prey capture and defense. Depending on the species, the venom ranges from deadly, to mildly irritating, to undetectable to humans. Luckily, none of the deadly species of jellyfish live in the Atlantic Ocean.
Gorgonians are easy to pick out whether you are snorkeling on the surface or SCUBA diving. They are generally bushy or tree-like, waving in the current, often mistaken for some kind of plant. Their common names include sea whip, sea plume, sea rod, and sea fan. Although it is tempting to refer to them as Soft Corals, this term has common use for a specific family of these animals that are rarely found in the Atlantic Ocean and will not be discussed here.
The basic unit of all corals is the polyp. This is the living animal that makes the supporting structure. The polyp looks like a sea anemone or an upside down jellyfish, a watery sack of flesh embedded in the structure with a ring of tentacles around a central mouth. They feed by capturing planktonic organisms using the cnidoblasts in the tentacles. Food is manipulated into the mouth which is also used to eject waste. Many corals have algae living within their tissues. These algae, called Zooxanthellae, produce some of the Gorgonian’s supporting structure and also provide sugars to the corals.
Gorgonians are sometimes called Octocorals because their polyps have eight tentacles that are feathery in appearance.
The colony has a flexible core made of a substance similar to cow hoofs and horns that makes a firm attachment to the substrate. Around the core the polyps create a colored matrix, the rind, within which they can retract for protection.
Each species of Gorgonian creates an opening for each polyp in a characteristic shape; additionally each species branches out in a characteristic way, although sometimes this can be modified by locality or environmental conditions.
All polyps of a particular coral colony are derived from a single individual by asexual budding. Corals can also reproduce sexually, launching their spawn to drift with the plankton. The resulting larvae, if lucky, find substrate to settle on and form their own colonies.
On the reef, no bare space is left bare for long. When a small part of a Gorgonian dies by damage or predation that space is often grabbed up by a larva of a different organism. The rest of the Gorgonian goes on living as long as it can keep the intruder localized by stinging it with its cnidoblasts. In some cases, though, the coral colony will be completely covered by fire coral or algae.