Gorgonians: Sea Fans, Blades, Rods and Fingers (Feb 2007)

[zanzimog]

Photosynthetic gorgonians



Gorgonians are often known by their more colorful names, such as sea fans, plumes, fingers, blades, whips and so on. At first glance, they can be mistaken for plants, with their flexible branches swaying in the surge, but a quick glance at the polyps on the brances shows that they are really soft corals.

There are both photosynthetic and non-photosynthetic species of gorgonians, and the care of the two groups is rather different. If the coral is bright red, yellow or purple, and has white polyps, there's a really good chance it is non-photosynthetic and will need a lot of food and attention. Photosynthetic gorgonians tend to have brown, light purple or rusty orange branches, and almost always have tan polyps where the photosynthetic zooxanthellae reside.

Phylogeny and Biology
Like all other corals, gorgonians are in the phylum Cnidaria, class Anthozoa. They are grouped with the soft corals, such as the leathers, star polyps, and pipe organ, for example, in the order Alcyonacea. True soft corals (as opposed to corallimorpharians and zoanthids, which are soft but more closely related to the stony corals) can be easily identified by looking at the polyps. All soft coral polyps have eight tentacles, and these tentacles have little branches on them, called pinnules. Even without counting tentacles, if you see pinnules, you know you have a soft coral.


The gorgonians belong to the suborder Holaxonia. One feature that distinguishes gorgonians from all other soft corals is the presence of horn-like axial skeleton in the center of the living tissue. Imagine it as a wire that acts as a frame for the tissues. Like leather corals, most gorgonians also have sclerites, small pieces of stony material, in the tissues for additional support. The base of the colony encrusts rocky substrates, with the site of attachment called a holdfast.

In the Caribbean, the gorgonians occupy the niches that leathers and other soft corals take in the Indo-Pacific. They can dominate the shallows in dense stands, and act as shelter for many species. Even photosynthetic species feed heavily on plankton, and colonies tend to be located in areas of strong flow, where food is constantly being brought by the current. Colony sizes generally range from large to huge, with many species reaching 6-8 feet in height, and may feet across.

Gorgonian colonies provide food and shelter for many commensals (shrimp, barnacles), and they are also subject to predation by fireworms and beautiful ovulid snails like the flamingo tongue below. Note the axial skeleton that has been stripped of flesh by the snail.


Gorgonians are common and fast growing, so the impact of their collection tends to be less than some other corals. However, many species ship poorly, and can adapt slowly to captive life, so the purchase of captive-propagated specimens is a way of getting healthier corals and reducing impact on the reefs.

Care and Feeding
In general, photosynthetic gorgonians do best with strong light and current, and a source of planktonic food. Species vary considerably in their needs, and as with many invertebrates, it can be difficult to know whether you are meeting their needs, because it will take months, or even years, for colonies to show signs of deficiency. The best approach is to get a piece of a colony from someone who has successfully maintain that species, and try to repeat what they are doing.
Lighting: All species benefit from intense light. My experience has been limited to metal halides, but some of the hardier species, like Pseuplexaura, may survive or thrive under high levels of PC lighting, and I expect it will be possible to keep most or all species with high-output T5 lights.
Current: My rule of thumb is that they should have enough current to make the colony gently sway, but not enough to make the polyps close. It is really important to have a lot of flow across the colony, to bring food and to stir up the surface layer, but not a focused stream blasting a small region of the colony. Some species, like the sea blade, Pterogorgia, also need current to clear away the mucus coat that is shed periodically.
Food: This is an area I find frustrating. All species need food, but the form and amount vary a lot, and there is little information out there for guidance. As far as I can tell, all species will accept frozen Cyclopeez and newly hatched brine shrimp. Others seem to do perfectly well with no supplemental feeding at all, prresumably making do with debris from fish feeding or plankton generated by refugia.
Placement: As mentioned above, gorgonians anchor themselves to rocks in the wild. Wild colonies are often collected by pulling the holdfast from the substrate and shipping the whole colony. In this case, clever use of cable ties or nylon screws may be required to hold to coral in its new place until it takes hold. This may take several months. In the case of small frags, I have found a combination of epoxy putty and super glue get to do the trick. First, make a little volcano out of epoxy, and allow it to cure for a few hours until hard. Then glue the end of the frag into the hole with super glue. It's important to clean the flesh off the skeleton of the part being glued, because the flesh will rot, fall off, and the coral will come loose and may become infected as well. In no case should one "plant" a gorgonian in the sand bed, as the buried area will die and decompose, and may take the rest of the colony with it.

Species Identification
There are many species available in the aquarium trade, most clumped into groups based on colony size and color. Unlike most other corals, vendors put little effort into determining the species of a colony, leaving it to the hobbyists to figure things out for themselves. I figure I have succeeded if I can identify the genus, and rarely try to identify species.

Here is how I go about figuring things out. I collect as much information as possible, based on the criteria below, then try to look it up either Humann & Deloach, Borneman or Sprung and Delbeek. In most cases, none of the references has all the views needed to identify a given species, so I often have to look at all three. When all else fails, I take a shot of the colony and the retracted polyps and post it on Eric Borneman's forum.
Colony Shape: Colonies have several branching patterns, shown in crude cartoon form below.
Pinnate: Like a feather, with branches coming off a single axis.
Dichotomous: Each branch can divide into two more branches, and so on. Possibly the most common growth form of common aquarium gorgonians.
Lateral Branching: More sideways than the random pattern of dichotomous forms.
Interconnected, Net-Like: This is most often seen in the sea fans (top photo), in which the small branches run together as a meshwork.

Branch Form: Branches can be fat or skinny (see the photo of Pseudopterogorgia and Eunicea together, below), round or flat-sided (see, e.g., Pterogorgia below).
Polyp Size: Polyps can vary a lot in size. Compare the photos of Pterogorgia to Pseudoplexaura, below.
Calyx Form: What does the area around the polyp look like when the polyps are retracted? This is a key feature, because species can differ greatly as to whether the polyps can retract fully, whether they have spines ay the base, whether the branches have a "warty" appearance, and the shape of the calyx. In the photo below, the polyps of Pseudoplexaura retract fully into circular pores.

Sclerites: Further identification requires microscopic examination of the sclerites. Worthwhile, but I have made no ventures so far at this level of detail.

Meet some of the genera
Gorgonia: This is the classic sea fan, shown at the top of this article. Tightly interconnected meshwork of branches, tiny polyps. I have never seen it in captivity, but it is apparently offered for sale on occasion.
Pterogorgia: The sea blade is easily recognized by its flat-sided branches, with polyps arising from the edges. In my hands, it seems to require more regular feedings of plankton than the other species listed below. This species is subject to fouling by algae, but will periodically shed a mucus coat to clean itself (below, right)

Muricea: Orange sea rod, or spiny sea rod. This is another fairly easy one to recognize. Few other photosynthetic gorgonians are orange. It is also very bristly to the touch. This species appears to do well with strong light and minimal feeding.

Pseudopterogorgia: The sea plume in the photo below (smaller, below the larger Eunicea in the background), is too young to show the pinnate branching pattern clearly. The skinny branches and smallish polyps help in the identification, though. A good aquarium specimen, growing slowly but steadily and easily propagated.

Eunicea: The warty sea rod (dark gorgonian in the above photo) is one of many similar genera of sea rods/fingers available in the trade. The bumpiness of the branches when the polyps are withdrawn (here) are a good indication of the genus. Another hardy gorgonian for the aquarium.
Pseudoplexaura: The corky or porous sea rod is by far my favorite. Identified by the lack of calyces around the polyps, and the round shape (as opposed to slit-like) of the pores into which the the polyps retract. It has beautiful, large polyps, and I have seen this particular coral thrive in many different reef tanks, where it grows rapidly. If it has a disadvantage, it would be the flexibility of its branches, especially in young colonies. In strong currents, the branches can end up becoming permanently curved. Larger colonies are sturdy enough to stay straight.


References and Resources:
Borneman, EH (2001) Aquarium Corals : Selection, Husbandry, and Natural History. TFH Publications
Humann and DeLoach (2001) Reef Coral Identification: Florida, Caribbean, Bahamas. New World Publications.
Sprung and Delbeek (19970 The Reef Aquarium: A Comprehensive Guide to the Identification and Care of Tropical Marine Invertebrates (Vol 2). Two Little Fishies.
Eric Borneman's Coral Forum at Marine Depot
Caribbean Gorgonian article by Julian Sprung, in Advances Aquarist

[OrionGirl]

Fab write up!

[zanzimog]

Originally Posted by OrionGirl

Fab write up!

Thanks! That was a lot of work, and I probably still need to make corrections.

[blackwolfXKAV]

What is the species in the first pic, and how large is it?

Thanks!

[zanzimog]

That's a sea fan, genus Gorgonia. Probably the common sea fan, G ventalina. It's about six feet across, photographed in the shallows in Bonaire. I have not seen this species in a hobbyist's tank, but don't see any reason why they can't be kept.

[blackwolfXKAV]

are they photosynthetic?

what would an ideal seup for them be?

where can one purchase them?

[zanzimog]

Originally Posted by blackwolfXKAV

are they photosynthetic?

The title of this article may give some hints about that.

what would an ideal seup for them be?

From the article above "I have never seen it in captivity, but it is apparently offered for sale on occasion." They live in the shallows, with strong currents, so I would expect they would do best with strong light and strong surgy motion, with fflow perpendicular to the face of the fan. Based on the structure, I would also expect them to be sensitive to fouling by filamentous algae, so keep nutrients low.

where can one purchase them?

Dunno. You might try frags.org.