Soft corals, typified by their internal fleshy skeletons, are the most appropriate varieties of stinging animals for the marine aquarist graduating from fish to invertebrate to full-blown-reef enthusiast. Many of these are tolerant toward aquarium conditions, relatively inexpensive, and more easily cared for than the small or large polyped true or stony corals.
Beyond the above considerations is one that should be important to every conscientious aquarist; the removal of soft corals from the worlds reefs is less destructive to the environment than chipping away, otherwise removing calcareous corals. Their recruitment (growth and replacement) rates are far greater, they're not principal prey species, and little used as habitat by other reef creatures.
Classification: Taxonomy, Relation With Other Groups
Here I'll present some of the higher taxonomy of the group and their kin, as I've found an understanding of the same to be a tremendously helpful tool in identification and keeping straight the husbandry of related forms.
The soft corals are members of the stinging-celled animals, Phylum Cnidaria ("Nigh-dare-ee-ya"), formerly Coelenterata; a group that includes the anemones, jellyfishes, hydroids, sea-pens, the true corals and other coral-named groups.
Cnidarians are tissue-grade life characterized by having just two germ layers (ecto- and endoderm), stinging-cells, and principal radial symmetry. Other salient characteristics; they have a single body cavity (the coelenteron) that is sac-like, with one opening that serves as both an mouth and an anus; lack a central nervous system (have simple nerve nets), no head or gas exchange, excretory or circulatory systems.
The phylum Cnidaria is separated into three Classes roughly by the principal form (bell-shaped free-living medusoid, or attached polypoid) they take as life stages.
And finally, the Order Alcyonacea ("Al-see-oh-nay-see-ah"), the soft corals. Made up of either encrusting or erect colonies, mostly fleshy and flexible with a bizarre assortment of internal structural elements called sclerites, rendering shape and structure.
Briefly, you can see that it is not only the lack of external hard, stony, calcareous skeletons that distinguish the "true" corals (Order Scleractinia, Subclass Hexacorallia) from the soft fleshy or leathery corals, the Alcyonacea and their relatives; but major elements of body plan and symmetry (tentacular and body segmentation number, mouth-anus openings).
Soft corals are found worldwide, more in tropical than temperate reefs, mainly in mid-depths of 5-30 meters. Abundance on reefs in the Indo-Pacific and Red Sea is often conspicuous compared with stands of colonies in the Caribbean, Hawaii and elsewhere.
Principal Forms in the Hobby
First the general disclaimer regarding classifying difficult-to-discern life forms. The alcyonaceans that we call soft corals are really told apart only by microscopic examination of the aforementioned calcareous particles (sclerites). Therefore we will detail them more generically, as in by family and most commonly available genera.
Family Nephtheidae; Carnation, Tree, Colt Soft Corals, the genera Capnella, Dendronephthya, Nephthea, Scleronephthya, Cladiella, Lemnalia and more are known to all divers and other appreciators of tropical marine environments. They are the gorgeous warm colored (red, pink, yellow) and purplish cotton-candy looking creatures attached to reefs. Know that these colorful, branched-tree animals inflate and shrink regularly in rhythm with feeding and metabolite flushing, and that many species are difficult to care for; read-up and ask your dealer.
Family Alcyoniidae, the mushroom, ridged and lobed leather or toadstool corals, Lobophytum, Alcyonium, Cladiella, Sarcophyton, Sinularia With their almost unreal rubbery appearance with tentacles retracted, hardly recognizable as living, yet alone as stinging-celled animals. Mainly yellow, brown to grayish in overall uniform color. Amongst all the animals called corals, the leathers are the toughest for aquarium use; getting by on higher nutrient levels/lower water quality, and less stringent turbulence and lighting conditions.
Family Xeniidae, the pulsing and not Xenia, Stereosoma, Anthelia, Efflatournaria with their very fine wafting colonies of long feathery tentacled polyps pulsing and waving rhythmically. White, brown to bluish in coloration.
Family Nidaliidae, some of these soft corals are superficially very similar to gorgonians (sea fans). Though quite common in the wild (Indo-Pacific) the gorgonian-like ones (genera Chironephthya, Siphonogorgia) are almost impossible to keep in captivity. Lacking zooxanthellae Nidaliids must be fed on suspensions of small zooplankton. Other genera that more resemble Nephtheids (Agaricoidea, Nidalla, Pieterfaurea) are of use to aquarists, though not as easily kept as the more hardy members of that family.
Selection: General to Specific Criteria
Turgidity; though these animals can easily and without apparent cause shrink their spongy tissue down to looking wrinkled or downright limp, healthy specimens for purchase should occasionally be erect and full and show open polyps (or a promise made that they will become so if buying a large wholesale order).
Tears & Rips; may be obvious from where the animal was removed from the substrate; check over the rest of the body. The same as the Anthozoans called anemones, bad tears can lead to infection or outright death from trauma. Wait to ensure the animal can return to turgidity.
Obvious Infection Sites: disqualify any purchase. Look for white to grayish sores and receding tissue areas. disqualify any purchase. Look for white to grayish sores and receding tissue areas.
Time On Hand; that is, how long the specimen(s) have been at your source. Excepting the leather corals of the family Alcyoniidae, soft corals rarely ship well. If possible, practical, I'd leave them at the dealers for a good week before picking them up.
A note to collectors, and their packers: these organisms need to be placed in organism-width bags with very little water and each bag arranged such that the piece does not slosh end to end with the movement of boxes. Some preeminent shippers wedge a flaccid smaller bag of water in with soft corals to dampen motion. Also, pure oxygen is not needed when bagging them; they are best about half-oxygenated by not squeezing out all the air.
Difficult Species; you're dealing with life, investing real money here, so do the due diligence and invest your time in seeking out what species you're potentially dealing with. Some Dendronephthya and Nephthea have poor survival rates at present, and all living things can be killed by neglect and ignorance. Soft corals are the best beginner, and starter forms; yet you must choose the types that are suitable for your knowledge and ability level. As always, you are encouraged to seek out "cultured" soft coral stocks; these have proven extremely hardy and fast growing (some records of more than an inch in a month).
Soft corals rely on currents to bring them food and oxygen, and carry away their wastes. The best circulation arrangements involve strategies for periodically varying the direction and intensity of water movements in addition to filtration.
Despite claims that some species tolerate less than ideal water quality, all soft corals should be maintained in clear, metabolite free environments. Pre-mixed seawater should be made up to a matching high specific gravity (1.025), and efforts made to sustain a high pH (8.2-8.4). Remember that most of these species are found in parts of the reef with the greatest current, facing the open ocean.
Practically speaking, reef or invertebrate systems with soft corals cannot be over-filtered. Take note that the actual biomass of alcyonaceans is easily ten times that of hard corals; as the octocorallians bodies are composed almost entirely of live tissue, whereas the scleractinians are mainly non-living matrix.
An oversized protein skimmer, source of calcium replenishment, and use of activated carbon are requisite.
In my opinion even the non-photosynthetic species of Nephtheids appreciate a good 2-4 watts of full-spectrum illumination for 12-14 hours per day. The other two families showcased here are definitely positive light-responsive. My long-standing favorite lighting mode is boosted fluorescents, though other writers have recorded success with metal halides and mercury vapor.
Soft corals for the most part are more flexible in their use and placement than stonies. They may be placed in lower lighted areas as long as they receive adequate food and circulation. A reminder here regarding granting them adequate space to avoid touching other benthic, attached animal life. Remember to leave a clear circumference for full expansion and growth; some Sarcophytons can reach a large size (up a meter in diameter)
One of the obvious strange attributes of soft corals is the lack of "fouling organisms" that bedevil them. Take a look; do you see algae, worms, barnacles, anything growing on or in them? Apparently not. Alcyonaceans have been investigated for chemical reasons for such cleanliness for bio-pharmacological and anti-fouling properties. Yes, they have allelopathic (toxic to other species) chemical effects; terpenoids and other molecules that poison would-be settlers and neighboring life forms. For practical purposes this means you must be aware of how close you situate other valuable livestock, particularly other stinging-celled organisms. Leave a good 8" or more space between soft corals and your other animal stock.
Further, as these chemical materials are released and carried in the water, you'll want to pay attention to stocking, filtration methods and maintenance that will reduce concentration and toxic effects (protein skimming, chemical filtrants)
Following up on the above chemical concerns, newly received specimens should be put through successive rinses of system water, that is vented to waste, to dilute materials released during transit. Personally, I hold that there is more damage done in quarantining the soft corals and re-moving them to the main/display units... hence I just place them there.
Few organisms are known to be really deleterious to soft corals in the wild; some mollusks and butterflyfishes will chew on them, but rarely to their destruction. You might want to check new arrivals for the presence (and eradication) of commensal crabs; these may prove destructive.
Reproduction, Sexual Differentiation:
Soft corals reproduce asexually by budding and fragmentation, and sexually via egg and sperm production. They can be artificially propagated by way of cutting and grafting. A typical simple pro forma involves slicing off a reasonable size piece, dipping it into sterilizing solution and attaching it with epoxy or "super" glue to a hard substrate.
Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes
Though various authors have stated that the various soft coral groups can "get by" with chemical supplement feedings and "correct" lighting (though many are non-photosynthetic). Be aware that all species investigated are known planktivores, some consuming more zoo- others more phyto-plankton in the wild. All soft corals should therefore be periodically offered such small foodstuffs.
Whether you culture a mix or buy it bottled, tubed, frozen or dried, directing ground up nutritious matter onto the tentacular surfaces when opened, with your particulate filtration temporarily suspended (leaving the complementary recirculation-only pump(s) running) ensures growth and health. A few times per week to daily regimens are practical per species, sizes and system.
Chemical feedings do directly and indirectly benefit these animals. Iodine in particular should be fed into the water; in concert with water changes and feedings.
Often for no discernible cause leather and other soft corals will go through shrinking phases. You should take this in stride and as a signal to check your water and mechanicals, and not necessarily panic if other livestock seems unaffected. Do however watch for slimy and waxy exudates that may accompany a return to rigidity. Such matter is toxic and should be removed when observed.
Folks who know that I've written and given pitches for the diving interest the last few decades often ask me if I have a conflict with espousing the virtues of appreciating living reefs up close, but not touching, and some aspects of "reef-aquarium keeping" that regularly involve breaking off parts or colonies of true or stony corals (Order Scleractinia). Well, yes I do.
As much as I'd like only advanced aquarists (whatever that is) to delve into such involved endeavors, leaving out government intervention to protect natural resources, it dawns on me that only by allowing such experimentation with scleractinian "cuttings" (of course from wild-collected specimens) and whole small animals can the hobby and human awareness progress.
As a stop-gap measure, I ask that on your way to trying scleractinians that you practice with their octocorallian kin, especially the soft corals presented here. These stinging-celled animals have much higher growth and replacement rates, and their removal represents a far less traumatic loss of habitat than that of hard coral loss. Besides that, the Alcyonacea are just as beautiful and utilitarian.
When and if you're ready to graduate to SPS or LPS (Small and Large polyp Stonies or Scleractinians) I urge you to pursue the cultured cuttings that are more and more available. Start with an Alcyoniid leather coral, feed it sparingly, keeping an eye on circulation and water quality.
Allen, Gerald R. & Roger Steene. 1994. Indo-Pacific Coral Reef Field Guide. Tropical Reef Research, Singapore. 378 pp.
Barnes, Robert D. 1987. Invertebrate Zoology, 5th ed.. Saunders, USA. 893 pp.
Bayer, F.M. 1981. Key to the genera of Octocorallia exclusive of Pennatulacea (Coelenterata: Anthozoa) with diagnoses of new taxa. Proc. Biol. Soc. Wash. 94:902-947.
Benahayu, Y. 1991. Reproduction and developmental pathways of Red Sea Xeniidae (Octocorallia, Alcyonacea). Hydrobiologia, v 216-217:125-130.
Debelius, Helmut & Hans A. Baensch. 1994. Marine Atlas, v. 1. MERGUS, Germany. 1216 pp.
Delbeek, J. Charles. 1989. Soft corals spawn in the aquarium. FAMA 3/89.
Fabricius, K.E. Slow population turnover in the soft coral genera Sinualria & Sarcophyton on mid and outer-shelf reefs of the Great Barrier Reef. Mar. Eco. Progress Series, v. 126, n. 1-3:145-152.
Fenner, Bob. 1996. Gorgonians: sea fans for marine aquaria. FAMA 3/96.
Fenner, Robert M. 1998. The Conscientious Marine Aquarist. Microcosm, VT. 432 pp.
Frank, U.; Rabinowitz, C.; Rinkevich, B. 1994. In vitro establishment of continuous cell cultures and cell lines from ten colonial cnidarians. Mar. Biol. (Berlin) v. 120, n.3:491-499.
Gosliner, Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific. Sea Challengers, CA. 314 pp.
Griffith, J.K. 1994. Predation of soft corals (Octocorallia: Alcyonacea) on the Great Barrier Reef, Australia. Aust. J.
of Mar. and Freshwater Research, v. 45, n. 7:1281-1284. Hunt, Philip. 1994. Soft is beautiful. TFH 10/94.
Maida, M.; Sammarco, P.W.; Coll, J.C. 1995. Preliminary evidence for directional allelopathic effects of the soft coral Sinularia flexibilis (Alcyonacea, Octocorallia) on scleractinian coral recruitment. Bull of Mar. Science v. 56, n. 1:303-311.
Malyutin, A.N. 1990. Two new species of Sinularia (Octocorallia, Alcyonacea) from South Vietnam. Asian Mar. Bio. v. 7:9-14.
Puterbaugh, Ed & Eric Borneman. 1996. A Practical Guide to Corals For The Reef Aquarium. Crystal Graphics, KY. 110 pp.
Quenga Kerr, J.N.; Paul, V.J. 1995. Animal-plant defense associations: the soft coral, Sinularia sp. (Cnidaria, Alcyonacea)
protects Halimeda spp. from herbivory. J. of Experimental Mar. Bio. and Eco. v 186 n.2:183-205.
Tullock, John H. 1997. Natural Reef Aquariums. Microcosm, VT. 312 pp.
Verloop, Ria and Ron Ates. 1992. Nephthea. FAMA 7/92.
Verseveldt, J. 1983. Sinularia molokaiensis, a new species of Alcyoniidae (Octocorallia: Alcyonacea) from Hawaiian water. Occasional Papers Bernice P. Bishop Museum, 25(8):1-4.
Wilkens, Peter. 1989. Fireworks in the deep: Observations of soft corals. TFH 6/89.
Williams, G.C. 1988. Four new species of South African octocorals (Cnidaria, Alcyonacea) with a further diagnostic revision of the genus Alcyonium Linnaeus 1758. Zool. J. of the Linnaean Society v. 92, n. 1:1-26.