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By Bob Goemans
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Q&A - Gorgonian

Authored by: Rob Toonen

Rob,

I saw a beautiful orange gorgonian with red “warts” all over the branches. The polyps emerge from the warts, and a quite large and almost feather-like. The people at the pet shop told me that they lack symbiotic zooxanthellae, and that they would therefore require feeding. Is this true? If so, how do you go about it? I think strong current is a must otherwise hair algae might build up, right? What about lighting -- what are their requirements?

Thanks in advance,

Mia

Mia,

Just to bring everyone to same starting point, let me explain what is a gorgonian. Gorgonians are in the Phylum Cnidaria, Class Anthozoa and along with sea pens, soft corals, and stoloniferans (like the pipe-organ coral, Tubipora) form the subclass Octocorallia. The other subclass of anthozoans is the Hexacorallia, which includes all the stony corals, the anemones, the zoanthids and the corallimorphs (commonly called mushroom polyps). The Gorgonacea is an order of corals that includes all the sea fans, sea whips, sea rods and the like that have a firm interior axial skeleton (the hard rod inside the animal that keeps it upright). This axial skeleton is usually composed of a tough proteinaceous compound called gorgonin (although some may be calcareous), and the colony forms a thin, rough layer of living tissue over that skeleton. You can tell than a gorgonian is not doing well if there are extensive portions of the skeleton showing, because you know that the live tissue has died and rotted (or been washed) away from that area. Although many animals make a complete recovery from losing some tissue, and the animals are often propagated by simply cuttings off a healthy branch, the problem with selecting a gorgonian with exposed skeleton is that: 1) you know that something has caused some of the colony to die recently, but you don’t know whether that was mistreatment during collecting or a systemic problem, such as a disease; and 2) the exposed skeleton provides substrate upon which algae can grow, and that makes it more difficult for you to keep the animal healthy. If the animal looks to be in great health otherwise, and you are determined to buy an animal with exposed skeleton, it is a good idea to simply cut off the dead portions of the colony before securing it in your tank. Use a sharp pair of scissors (I like to use kitchen scissors with a scalloped blade for this) and cut as close to the live tissue as possible without cutting any of the living tissue away.

Although you don’t mention from which Ocean this animal was originally collected (along with the most detailed description possible, the original location is an important detail when asking for an identification), the colorful sea rod you describe is most likely Diodogorgia nodulifera. These lovely gorgonians are very common throughout the Caribbean, and are both hardy and adaptable to a wide variety of habitats in deeper waters. They are found only in deeper waters, and first appear at about 40 or 50 feet and are common to as deep as about 600 ft. They are typically found in shaded areas on shallower patch reefs, under ledge overhangs on walls, in caves and out in the open on deep reefs, sandy and rocky bottom areas. Because these animals lack symbiotic algae from which to gain some nutrition, there is no specific lighting requirement for these animals, but if their natural distribution is any indication, they should certainly be kept out of strong lighting. I have spoken to people who have successfully kept them in full lighting, but in general, there is much more success with animals kept in shaded regions of the aquarium.

You are correct about a good current, and that these animals also need to be securely attached to the substrate in order to provide that current. Concerns about the growth of algae aside (that is an entirely different subject), these animals need the strong currents to feed effectively. Because they need a secure attachment, to avoid being blown over in a strong current, they should either be purchased on a rock large enough to support the colony in heavy flow, or you should also buy a stick of underwater epoxy (there are several of these two-part putty mixtures that form an underwater bonding agent) from the pet shop, and use that to securely attach the gorgonian to a rock in an area of high, and preferably variable flow. Studies on feeding in natural populations suggest that variable current speeds on the order of 5-20 cm/s with an average of about 10cm/s is best for the successful feeding of gorgonians. OK, great, but what does 10cm/s mean to you? Well, although it sounds silly, the best way to determine current speed in your tank is to simply measure it. Locate a bubble, a piece of food or some other marker you can follow, and place one finger on the aquarium where that marker is first seen (this should ideally be upstream of where you want to locate your gorgonian). Watch that marker for 2 seconds and place another finger on the tank where ever the item you were following has ended up. Simply divide that distance by 2 and you have a very rough estimate of the mean current speed in your aquarium, and that will help you to decide whether there is sufficient flow in the area in which you hope to keep the gorgonian.

In general, asymbiotic (lacking symbiotic zooxanthellae, and therefore non-photosynthetic) gorgonians do not do well in most aquaria, and unless you are prepared to feed it regularly, you shouldn't consider getting one, because in even the best stocked tanks, it is unlikely to get enough food without directly feeding it. Like most asymbiotic gorgonians, D. nodulifera likely feeds on a variety of small plankton, detritus, marine snow and possibly even phytoplankton. Your local shop is absolutely correct that these animals need to be fed, or they are not going to do well in your aquarium. Of course, if you're willing to care for it properly, these corals can be very attractive additions to a reef tank, and I actually have a couple of these wonderful animals growing in my tanks.

The reason that I say “likely feeds” in the section above is that I do not know of any studies specifically on the natural feeding of this species. However, the few studies on the natural feeding of other gorgonians in the wild suggest that most probably feed in a similar manner. In fact, based on that research, I would go so far as to say gorgonians need to be fed, regardless of whether they contain symbiotic algae or not. Even photosynthetic species with large polyps (such as the commonly imported Plexaura, or Eunicea) are capable of capturing a range of medium-sized zooplankton (in the approximate range of 100-700 microns), as well as taking up nutrients from symbiotic zooxanthellae. One recent study on this "photosynthetic gorgonian" found that Plexaura needs to eat roughly 7.2 +/- 1.9 microorganisms per polyp per day (primarily ciliates, dinoflagellates, and diatoms) in addition to their photosynthetic uptake to make their annual energy budget for growth and reproduction. That is a lot of food for an animal that isn’t supposed to require feeding, and like all cnidarians, you should be feeding your corals whether they contain photosynthetic symbionts or not.

Another study on the small-polyped asymbiotic gorgonian Paramuricea clavata found that nauplii, copepod eggs, other invertebrate eggs, and other small (100-200 micron size range) prey items accounted for 78% of the diet, though adult calanoid copepods (roughly the size of a newly hatched brine shrimp) were also captured and likely important to the diet. Despite the fact that this species has relatively small polyps, there was no indication of phytoplankton capture, but that is hard to determine conclusively from gut analyses. I suspect that like the large polyped photosynthetic gorgonians discussed above, they would gladly capture ciliates, dinoflagellates, and diatoms if present. The number of prey per polyp was much lower in this species (although there are more polyps per gorgonian, so it sorta evens out), averaging between 1.2 and 3.3 items per polyp per day.

In any case, these gorgonians are not generally recommended for beginners, and not recommended for anyone who is not dedicated to feeding them at least a couple of times a week. If you are still interested in buying the animal, and are willing to feed it, then I guess I ought to answer the most important part of your question and explain how to do that. Most gorgonians will gladly capture rotifers, and if you happen to have a tank with a live sandbed or refugium of some sort, other live foods (such as ciliates and invertebrate larvae) are likely generated in your tank to provide some treats for you animal from time-to-time. If the polyps of the species you are trying to keep (such as D. nodulifera) are large enough, they will also eat newly hatched brine shrimp. They will also likely capture some of the larger diatom and dinoflagellate phytoplankton (which are now available from some larger pet shops and a variety of mail order companies) if you feed phytoplankton to the other critters in your tank. If you don’t have access to these foods, there are a variety of artificial plankton foods, frozen Daphnia, commercial invertebrate foods, and even finely ground fish foods will probably help to keep the animal alive. The problem with using these latter choices is that they don’t tend to stay in suspension very long, and it is easy to overfeed your aquarium if you’re not careful with artificial and frozen foods.

If you chose a healthy gorgonian, place it in a suitable environment, and make sure that it gets enough food, there should be absolutely no problem keeping one of these beautiful animals. Of course, the same can be said of almost any animal we hope to add to our aquaria, and knowing what constitutes a “suitable environment” and “enough food” is one of the keys to success with any of the animals we try to maintain in an aquarium.

Good luck!

Rob

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