News / Species Spotlight / The (Not-So) Hard to Keep Gorgonian (09/03/13)

The (Not-So) Hard to Keep Gorgonian

by Charles J. Hanley III

Scientific Name: Numerous
Common Name(s): Gorgonians, Sea Fans, Sea Whips, Sea Sprays, Sea Rods, Knobby Sea Rods, Hydrocorals, Sea Plumes, Red Polyp Octocoral, Corky Sea Fingers, Corkscrew, Whip Coral, Horny Coral, plus many others

Taxonomy:

Domain: Eukarya
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Order: Gorgonacea
Family: Numerous
Genera: Numerous

Description:

Todays species spotlight installment covers one of the more unique and beautiful invertebrate aquarium animalsGorgonians! These guys are not for the faint of heart, as many varieties are exceedingly difficult to care for. Fortunately, not all gorgonians are so difficult, and one reason I chose to write this article is to point out which species make suitable tank inhabitants. As certain types of gorgonians have been subjected to overharvest for the jewelry trade, using a very selective criteria is a must when choosing a specimen. You want to be sure to buy a species which is not overharvested, and which has a good chance of long-term survival in the home aquarium. In fact, nowadays we are seeing aquacultured gorgonians with much higher survivability than their wild-harvested analogs, so it may be advisable just to seek out captive-bred animals.

Like hard corals, soft corals, and sea anemones, gorgonians are from Class Anthozoa. They also belong to the same subclass, Alcyonaria (= Octocorallia), as anemones and soft corals, though they are distinct from both. Gorgonians secrete skeletons to support their colonial polyps. The skeleton is comprised of either the protein gorgonin, or of sharp calcareous spicules, and can be hard or flexible. The colonies form a variety of shapes, including encrusting morphs, but most create an array of branches. Branching can occur in a single, intermeshed plane, as in the sea fans, but may also happen dichotomously and in bush-like clusters. The variability in structure and skeletal composition is mostly a function of habitat. Typically, deep-water, non-photosynthetic gorgonians form bush-like shapes. Their calcareous branches are hard, thin, and long. Conversely, shallow water species often have flexible protein skeletons which form fan-like planes, columns, or encrust hard substrates. Though all gorgonians are filter-feeders, many shallow species are zooxanthellate photosythesizers as well.

The amazing coloration of gorgonians is quite special, and has made them highly desirable for the jewelry, curio, and livestock trades. They come in just about every color of the rainbow, but are often brilliant hues of blue, purple, and red. Fascinatingly, in some species the color you see is the color of the skeleton. In others, the predominant color originates in the thin layer of connective tissue surrounding the skeleton. Their polyps, when extended, are usually a brightly contrasting color of white, blue, or yellow. Some animals have the appearance of shaggy carpet when their polyps are out, while others look like they have a halo of wispy peach-fuzz.

Natural Habitat and Ecology:

As is so often the case, gorgonians are nearly ubiquitous in the worlds oceans. That is, there are species found in all the worlds seas, and in depths ranging from extremely shallow to thousands of feet deep. Nonetheless, the majority of them are tropical or subtropical. Though they are not considered to be reef-builders, tropical shallow-water species are often found attached to coral reefs. In fact, most species need to secure themselves to hard substrate to begin growing at all.

The interesting and extensive branching patterns of these animals make them important habitat areas for a number of fish and invertebrates. One famous inhabitant, the pygmy seahorse (Hippocampus bargibanti), lives on either of two Muricella species gorgonians. The seahorse is so well-camouflaged that it can be virtually impossible spot it while it sits on the correct species. The body of the seahorse exhibits precisely the same coloration as the gorgonian, and even has small projections that mimic the invertebrates tubercules. In general, a single sea fan may be several meters in diameter, and so dramatically increases the habitat available for other animals. The gorgonians weaved and/or pinnate branches present excellent spaces for animals to secure themselves against strong water currents. At the same time, shallow-water gorgonians usually have flexible skeletons that allow them to sway dramatically when the current increases.

Many gorgonians are photosynthetic, using symbiotic zooxanthellae in a way similar to corals. Others are exclusively filter feeders, but all filter-feed to some degree. Though most are nocturnal, healthy animals also extend some polyps during the day. Their eight-tentacled polyps are capable of catching tiny planktonic meals, and the entire colony gets to share in the nutrition. Most reproduce sexually, but there are examples of gorgonians which propagate through fragmentation.

From an evolutionary perspective, gorgonians are quite interesting. They are believed to be the first animal group to develop a gastrovascular cavity. The cavity, which allows for larger foods to be digested, is a step in the direction of possessing true organs; therefore it is also a step in the direction of becoming a more biologically advanced animal.

In spite of the wonderful qualities of gorgonians, humans have found them to be most valuable for making jewelry. Deep water Precious Corals like pink, red, and gold gorgonians, as well as black corals (which are neither corals, nor gorgonians), have been overharvested for decades. They are killed, and their skeletons are polished to be put into high end jewelry. Unfortunately, such deep-water gorgonians live a long time but grow very slowly, so overharvesting is quite detrimental to their populations.

Aquarium Care:

For the intrepid aquarist, or rather, the very attentive aquarist, gorgonians can be quite rewarding. They are truly unusual looking animals, with great coloration and strange morphology. However, what I find most attractive is the challenge, or at least the perception of challenge. As an aquarist, I think it is beneficial to step out of your comfort zone and try to ramp it up a notch. What I like even better is that there are a number of suitable aquarium species which will not stretch your abilities to the breaking point. In fact, there is reason to believe that past difficulties caring for these animals is due, in large part, to poor collection and holding practices. When seeking out a gorgonian for purchase, look for the following good choices:

  • Aquacultured Corkscrew Gorgonian
  • Caribbean Encrusting Gorgonian
  • Corky Sea Fingers
  • Knobby Sea Rods
  • Purple Feather Gorgonian
  • Purple Frilly Gorgonian
  • Spiny Sea Fans


AVOID Precious Corals, including Red Gorgonians (Lophogorgia chilensis).

There are a few good recommendations which will carry you a long ways toward successful gorgonian care. Before anything else, you must learn as much as possible about the species you intend to purchase. For example, photosynthetic and non-photosythetic species will require substantially different tanks set-ups. Those that photosynthesize usually like brightly lit tanks, using a standard reef-tank lighting cycle. Non-zooxanthellate species, on the other hand, can easily succumb to algal overgrowth when exposed to too much light. These animals typically need much more moderate illumination, if any at all, and it is often best to limit daylight cycles to less than six hours a day. Some gorgonians also grow very large (e.g. several meters tall!), and the colonies can also expand laterally very quickly. When gorgonians are not provided ample space, they may grow into contact with other sessile tankmates. While some gorgonians can extend sweeper tentacles to defend themselves, others cannot. It is thus advisable, for the safety of all your livestock, to create a substantial buffer zone between gorgonians and other anthozoans.

Another reason to create a buffer zone is that it allows you to direct water flow right at the gorgonian, making it sway and keeping it clean of waste and detritus. The current will help to bring food particles, as well as slough away the waxy secretion these animals sometimes create. The secretion, if not removed, will trap waste and provide a medium that cultivates the growth of algae, bacteria, and cyanobacteria. Good flow also removes the potent allelopathic toxins secreted by other polyps, especially soft corals. Gorgonians can exhibit varying degrees of sensitivity to such chemicals, and some species may not do well at all in mixed reef tanks. At the same time, certain encrusting varieties may kill and overgrow soft and hard corals with impunity, making it all the more important to do your homework before the final purchase.

Feeding can be quite tricky, as non-photosynthetic gorgonians will need substantial amounts of food. Good choices include Artemia nauplii, rotifers, Cyclop-eeze, and any foods which dissolve into fine particulate matter in the water column. While feeding, it is helpful to turn off powerheads and pumps, so that the gorgonian has the opportunity to catch food before it is blown away. It also works well to induce polyp extension with a small amount of food, before providing the full meal.

Due to the excessive feeding, allelopathic chemicals, and need for clean water, gorgonian tanks will need strong filtration with a substantial amount of protein skimming. Other water parameter needs are not unusual, and typical reef-tank conditions are suitable (e.g. 72-78 degrees Fahrenheit, 1.023 to 1.025 S.G., and 8.1 to 8.4 pH).


Quick Notes:

  • Give your Gorgonian plenty of buffer space and water flow.
  • Check for parasites, and do a 1-minute freshwater dip if necessary, along with manual pest removal.
  • Daily feeding of small foods like Artemia nauplii, rotifers, and Cyclop-eeze
  • Husbandry needs vary dramatically according to species, so be familiar with your animal.
  • AVOID Red Gorgonians (Lophogorgia chilensis).


Works Cited

Anonymous. Gorgonians. Aquaticcommunity.com website. 2008. URL: < http://www.aquaticcommunity.com/Gorgonians/>

Castro, Peter and Michael E. Huber. Marine Biology 5th Ed. Boston: McGraw Hill, 2005.

ITIS report. Gorgonacea. URL: < http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=52079>

Perun, Blane. Blueberry Gorgonian. thesea.org website. URL: < http://www.thesea.org/gorgonian/blueberry_gorgonian.htm>

Perun, Blane. Encrusting Gorgonian. thesea.org website. URL: < http://www.thesea.org/gorgonian/encrusting_gorgonian.htm>

Perun, Blane. Purple Gorgonian. thesea.org website. URL: < http://www.thesea.org/gorgonian/purple_gorgonian.htm>

Perun, Blane. Red Gorgonian. thesea.org website. URL: < http://www.thesea.org/gorgonian/red_gorgonian.htm>

Shimek, Ronald L. Marine Invertebrates. Neptune City: T.F.H Publications, 2004.