The Soft Corals are the softer, more flexible animals that provide an attractive visual compliment to reef landscapes all around the world!
Soft corals are some of the most attractive corals found in the world’s oceans. They are quite fascinating, taking many exotic forms and often have a very rich and colorful palette. Soft corals have all the colors of the rainbow, but their predominant hues are rust, red, orange, yellow, olive and purple.
Like the stony corals, Soft Corals are Cnidarians, meaning stinging celled animals. The familiar aquarium soft corals belong in the Family Alcyoniidae under the Alcyonacea Order. These are considered to be the “true” soft corals, yet they are just a part of this very large group. The Alcyonacea Order itself is part of the Subclass Octocorallia, known as Octocorals, and this entire subclass is also often loosely referred to as “soft corals”.
The Alcyonacea order consists of hundreds of animals. It is divided into several families and suborders that include not only the Soft Corals, which encompass the Leather Corals as well, but also the Gorgonians. Many other unique Octocorals include the Sea Pens, Blue Coral, and Mat Polyps like the Organ Pipe Coral.
There are approximately 800 species of Soft Corals and more than 1200 known species of Gorgonians. With so many different species, it is easy to see why not all are considered to be easy keepers. So be sure to learn about the type of soft coral you wish to keep to have a successful experience.
For Information on keeping Corals see:
Reef Tanks – Mini-Reef Aquarium Basics
Soft Coral Facts
Soft Corals are quite numerous throughout the waters of the world, primarily in tropical waters. They are principally found in intertidal zones though a few live at depths of 650 feet (200 m) or more.
Soft corals are found on inner reefs, at depths just below the stony corals. They inhabit mostly dim areas, like underneath rocky outcrops or in caverns. They are not usually the dominant coral on many areas of the reef, but can be in areas where there is a lot of sediment.
Small cuttings of soft corals are easily collected from the wild. They are less prone to damage or ailments from collecting and shipping than the stony corals. Many species thrive and will grow quickly in captivity. Many of the popular soft corals are successfully propagated in captivity.
What Are Soft Corals?
Soft corals are Cnidarians, which means stinging celled animals. They are also members of the Subclass Octocorallia, known as the Octocorals. These are corals that generally have eight-fold symmetry or eight-branched tentacles in their polyp structure.
The soft corals are primarily colonial sessile animals, with the exception of members from the Xeniidae family. Sessile meaning they are anchored firmly to the substrate, and from there they can be either erect or encrusting. They can have either a fleshy or leather-like texture and include some of the most vibrantly colored corals. Soft corals have all the colors of the rainbow, but predominant hues are rust, red, orange, yellow, olive and purple.
There is a broad spectrum of shapes, but all soft corals have the same morphology. The hermatypic, or reef building corals, are the stony corals. Soft Corals are not reef building corals. They are called “soft” because unlike the stony corals, they do not have a rigid calcium carbonate skeleton. They are composed mostly of living tissue, though they do have tiny calcareous components called sclerites.
The sclerites are spiny skeletal elements embedded within the tissue. They help to give soft corals some support and add a grainy texture, and they are also used to help identify them. Though soft corals don’t add large calcareous masses to the reef like stony corals do, their sclerites do add large amounts of sediment to the reef.
Their entire surface, known as the coenenchyme, is covered with small polyps. There are two types of polyps, the autozooids and the siphonozooids.
- Autozooid Polyps The polyps known as autozooids have eight pinnate tentacles and eight septae. Their role is to acquire food for the colony. The tentacles capture the prey, primarily planktonic foods from the water column, and move it to the mouth in the center. The eight septae are equal sized compartments with interconnecting channels that distribute the food throughout the colony.
- Siphonozooid Polyps The second type of polyp is known as siphonozooids. It has reduced tentacles and cilia, along with an oral cavity. Its job is to pump water into the body of the colony, which supplies oxygen and also helps so keep the soft coral erect.
Types of Soft Coral
There are many types of soft coral. They are all members of the Order:Alcyonacea. The Order Alcyonacea is part of the Subclass Octocorallia, known as the Octocorals. These are corals with eight-branched tentacles in their polyp structure. Alcyonacea order is further divided into several families and suborders, which include not only the Soft Corals, but also the Gorgonians.
The systematic classification of the Octocorals involves a huge, highly complex, and diverse group which at present is considered poorly understood and understudied. Current taxonomy is under constant flux. For example, the Gorgonians have been moved between the Order Gorgonaria, to more recently being placed as a Suborder under Alcyonacea order. So it is to be expected that classifications will continue to change. In fact many experts are in favor of a complete revision.
Subclass: Octocorallia – Corals with eight-branched tentacles and eight septae in their polyp structure
Order: Alcyonacea – Includes the Soft Corals, Leather Corals, and Gorgonians (sea fans and sea whips)
- Family: Astrospiculariidae
This family consists of only one genus from the Pacific Ocean. They are bushy looking, low growing corals that are usually green. They are not yet known in the aquarium trade.
- Family Clavulariidae (Hickson, 1894)
This family consist of a quite a few diverse corals, contained in four subfamilies. Those most familiar in the aquarium belong in the Subfamily Clavulariinae, though this is a very ‘loosely’ defined group. Their polyps can have long tall stalks, topped with either feathery tentacles are stark tentacles, but giving them the look similar to the feather duster worm.
They have a poor record of survivability in the aquarium. Common names include Clove Polyps, Glove Polyps, Palm Tree Polyps, and Fern Polyps.
- Family: Nephtheidae These are some of the most colorful and ‘fluffy’ of the soft corals. They can be bushy or tree-like and come in beautiful hues of red, pink, yellow, and purple. Being branched and tree-like, they are known by such names as Carnation Coral, Tree Coral, and Colt Soft Coral
- Family Siphonogorgiidae These are commonly known as the China Corals. They form large tall colonies with many thin, brittle branches. Their colors are typically red with contrasting white or yellow polyps. They can look like beautifully colored fans, superficially resembling Gorgonians from the Pacific. They are very rarely available.
- Family Xeniidae (Ehrenberg, 1828)
This family has both pulsing and non-pulsing varieties. Their colors can be white, brown, or a blue hue. Many varieties have long feather-like tentacles and their polyps will pump water into the colony, creating a rhythmic pulsing motion. They are known by such names as Pulsing Xenia, Waving Hand Coral, Glove Coral, Pulse Coral, and Pom-Pom Xenia.
Suborders under the Alcyonacea – Includes the Leather Corals and Gorgonians
- Suborder: Alcyoniina
Family: Alcyoniidae – Leather Corals
These are soft corals that are mostly referred to as the Leather Corals. This family includes some of the hardiest aquarium coral species. They are often found in areas of high nutrients and lower water quality than others, which lends to being excellent beginners soft corals. They are known for being thick and encrusting and for their leathery skin. They can grow very large and take on many forms.
This genus is extremely variable and can have many forms including branched, fingered, ridged, and lobed. Their colors are usually yellow, brown or grayish, but can be other hues as well, and very vibrant. Common names often reflect their shapes and colors including such things as Finger Leather Coral, Encrusting Leather Coral, Dead Man’s Fingers, Hand Coral, and Seaman’s Hand Coral.
See the Leather Corals for more information.
- Suborder: Calcaxonia – Gorgonians
- Suborder: Holaxonia – Gorgonians
- Suborder: Scleraxonia – Gorgonians
See the Gorgonians for more information.
Soft Corals for Beginners
Soft corals include many of the easy to care for coral favorites. Many types of soft corals are quite hardy, especially the Leather Corals in the Sarcophyton, Lobophytum, Sinularia, and Cladiella genera. The Leather Corals are some of the best beginner aquarium soft corals. They are generally very hardy though they do need a typical reef aquarium environment. Most leather corals need a moderate to strong water flow and tend to do well under various types of reef tank fluorescent lighting. Metal halides are not needed.
Some of the Leather Corals are commonly Finger Leather Coral, Toadstool Leather Coral, Mushroom Leather Coral, Cup Leather Coral, Cabbage Leather Coral, Flexible Leather Coral, Knobby Finger Coral, and the Ridged and Lobed Leather Corals. They tend to have a more leathery feel, while other Soft Corals tend to be sticky or slimy to the touch.
Some of the most popular Leather Corals include:
- Colt Coral – Cladiella Sp.
- Common Toadstool Coral – Sarcophyton glaucum
- Yellow Leather Coral – Sarcophyton elegans
- Yellow Toadstool Leather Coral – Sarcophyton tenuispiculatum
- Elephant Ear Coral – Sarcophyton trocheliophorum
- Cabbage Leather Coral – Lobophytum crassum
- Devil’s Hand Coral – Lobophytum Sp.
- Cabbage Leather Coral – Sinularia dura
- Finger Leather Coral – Sinularia notanda
- Flexible Leather Coral – Sinularia flexibilis
Other popular, but slightly more difficult to keep soft coral varieties include
- The pretty Carnation Corals
- Kenya Tree Coral
- Tree Coral
- Colt Soft Coral, also known as the Finger Leather Coral
- Palm Tree Polyps or Glove Polyps
- Green Star Polyps
- The Xenia species are also sought after, especially the fascinating Pulsing Xenia.
Besides the best-known varieties, there are hundreds of other types of soft corals. Each of these beautiful animals will have care requirements that are just as diverse as they are. Consequently not all soft corals are easy keepers. It is very important to learn about the soft coral species you keep for a successful reef aquarium.
Soft Coral Care
Many of the soft corals are quite hardy and some of the easiest corals to keep. A beginner aquarium soft coral will grow into a beautiful, impressive specimen in the reef tank. They are very commonly available and considered to be some of the best beginner corals.
A typical reef environment is what is needed for soft corals. Provide moderate to strong lighting and a good water flow. They need good water quality maintained, so a protein skimmer and frequent water changes are very helpful. Follow this up with the particular care parameters for the species you are keeping.
Despite their great track record in the aquarium, be aware that all Octocorals produce toxins. Like other corals, these toxins can be released to ward off competition for space. Some are highly toxic while the toxins other produce is very minimal. The impact of these toxins is often reported as aquarists find their stony corals receding when kept with too many, or in some cases, any soft corals.
Excellent filtration with a protein skimmer, along with activated carbon, can help to remove and control some of the toxin. But soft corals can do best when kept in a tank dedicated to softies, or with a very minimal mix with other corals, depending on the type and space available.
Feeding Soft Corals
Like the stony corals, the majority of the soft corals obtain their nutrition from multiple sources. Most species receive nutrients through a symbiotic relationship with marine algae, known as zooxanthellae. They also capture planktonic organisms and microscopic food particles from the water column and can absorb dissolved organic matter.
Most species live in symbiosis with the marine algae, zooxanthellae, and will derive the majority of their nutrition from it. But in captivity they usually will eagerly accept small foods like brine shrimp and plankton as well. They will benefit from occasionally soaking food in vitamins as well.
It is common for soft corals to change forms, even within a single species, to adjust to different water flows and types of prey. The polyps can completely retract into the surface. Extending and retracting to capture prey can create an interesting pulsing type action. This is especially notable in the Xeniidae family, as is commonly seen in the popular “Pulsing Xenias”.
- Animal-World References: Marine and Reef
- Harry Erhardt and Horst Moosleitner, Marine Atlas Volume 2, Invertebrates (Baensch Marine Atlas), Mergus Verlag GmbH, Revised edition, 2005
- Eric Borneman, Aquarium Corals : Selection, Husbandry, and Natural History , TFH Publications, 2001
- Bob Fenner, The Soft Corals, Order Alcyonacea; Use In Marine Aquariums,WetWebMedia.com
Featured Image Credit: scubaluna, Shutterstock