Coral Reef 101: Gorgonians

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.

On a clear, calm day, Gorgonians can be seen from the bow of the boat as you travel across the Bahama’s Banks.  Gorgonians grow on any hard surface.  Seeing them like this is an indication that the bottom is hard with little sand for good anchoring.
Sea Rods and Sea Fans on a small coral head near Staniel Cay, as seen from the surface.
Sea Plumes (Antillogorgia sp.)–front and top left.  Black Sea Rod (Plexaura homomalla)–center and top-center and probably two other species near a reef at Highbourne Cay.  Those having fuzzy branches are so because the polyps are expanded.
A forest of Sea Fans at Conception Island, Bahamas.

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.

Closeup of the branches on a Swollen-Knob Candelabrum (Eunicea mammosa).  The polyps on the left are expanded showing the characteristic eight feathery tentacles that all Octocorals have.  Some of the polyps on the right are retracted into the protective rind.  The protruding compartments for each polyp is characteristic of this species.

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.

You may have found Gorgonians that have been cast up on shore. If they are fresh they will still have the colorful rind. The rind will eventually disintegrate leaving the dark core as it has in these sea fans.

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.

A Black Sea Rod (Plexaura homomalla) colony on a reef at Highbourne Cay. The branches are long and upright with few branchlets. This colony is probably about 2 1/2 ft tall. Compare with the Bent Sea Rod colony, part of which can be seen to the left, which has many short branchlets.
Expanded polyps of the Black Sea Rod. A couple of of polyps have a tentacle bringing food to the mouth.
Black Sea Rod polyps in various stages or retraction showing the dark rind holding the polyps.



The Sea Fan on the left is a Common Sea Fan (Gorgonia ventalina).  The one just under it to the right may be a Venus Sea Fan (Gorgonia flabellum) because of the small clusters of branches sticking out from the main plane of the colony.  Certain identification would require examination of the alignment of the polyps on the branches.  Other Gorgonians and hard corals can also be seen.
It is common to see Sea Plumes (Antillogorgia sp.) well over 5 ft. tall.
The Encrusting Gorgonian (Erythropodium caribaeorum) grows in a sheet over the substrate instead of upright and bushy.  The fuzzy brown polyps are expanded on the left and retracted into the grey, leathery-textured rind.
Closeup of the polyps of the Encrusting Gorgonian.


The polyps of this Deep Water Sea Fan (Iciligorgia schrammi), photographed at Long Island at a depth of about 35 ft., are characteristically arranged on the edges of the flattened branches.

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.

Gorgonian Associates

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.

Bearded Fire Worm (Hermodice carunculata) preying on a Sea Plume.
One of the species of predatory snails on Gorgonians is the Spotted Cyphoma (Cyphoma mcgintyi).  You can see the damage done by the snail to this Slit-Pore Sea Rod (Plexaurella sp.)
The most common species of Cyphoma is the Flamingo Tongue (Cyphoma gibbosum).  The snail’s colorful mantle covers the white shell.
A Fingerprint Cyphoma (Cyphoma signatum)
A sponge (large blue mass) and an Atlantic Winged Oyster (to the right) attached to a damaged part of this Sea Plume as larvae.
An Atlantic Winged Oyster (Pteria colymbus) attached to a Sea Plume.  Attached to the oyster is a Florida Wormsnail (Vermicularia knorrii).  The head of the snail is on the top-right of the oyster.  The outline of the snail’s coiled shell is below the head, hidden by algae and hydrozoans.
This Gorgonian has been completely encrusted by Branching Fire Coral (Millepora alcicornis)


Close up of Branching Fire Coral encrusting a Gorgonian.  The Fire Coral is a Hydrozoan, a Cnidarian like the Gorgonians.  The orange/brown/tan/ color with white tips is characterisitic.  The Fire Coral’s tentacles are expanded in this photo giving the coral a fuzzy appearance.  Hydrozoan polyps are not arranged like those of Gorgonians or hard corals and they sting like crazy.
The arrow points to a branches of a Gorgonian matted together by a Giant Basket Star (Astrophyton muricatum).  Basket Stars do not appear to harm the Gorgonian.
The Giant Basket Star has a central body with large multi-branching arms radiating from it.  At night, it unfolds the arms creating a web, that can be nearly two feet in diameter, with which it captures small organisms drifting in the current.




2 thoughts on “Coral Reef 101: Gorgonians”

  1. Excellent explanations and descriptions. Gorgonians are rather confusing because they take so many different forms. This is very helpful. Inspired to examine them more closely in future.

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