XI. Introduction to Soft Coral and Colonial Polyps
This article discusses “Soft Coral” including Leather Coral, Xenia & Zoanthids
Coral providers often offer "Beginners Packages", an assortment of coral suitable for the early stages of a tanks maturity due to their durability. There are several species of coral that are capable of thriving in lower light conditions, some that have adapted to survive higher nutrient levels due to natural environmental factors, while others are so pervasive and low maintenance they are deemed durable simply due to limited needs to flourish. Most coral that possesses these traits to fall into the category of soft corals. In this article we will discuss the unique considerations of the most common examples soft coral, however, this is by no means a comprehensive list of all the varieties available.
Leather Coral
The moniker refers to the texture of these corals flesh. Lacking any rigid skeletal system, their bodies contain microscopic structural elements called spicule that interlocks creating a flexible, woven support system. Like many coral leather coral host symbiotic algae capable of converting sunlight into energy that is transferred to the host colony. Secondly, the polyps of most leather coral are capable of capturing prey as large as brine shrimp eggs.
Existing at deeper depths than many reef-building corals and often along the reef shelf, these coral have adapted to lower light intensity and higher currents due to the crashing waves on the reef above. As such, most leather corals are happiest when provided strong, multi-direction flow patterns. If an inadequate amount of current is provided the polyps of the leather coral will not open fully and the coral will not achieve optimum growth or appearance. Additionally leather coral as a whole will appreciate subdued lighting. When high-intensity lighting is used care should be taken to position Leather corals towards the bottom and sides of the tank as too not over stimulate them with light.
Throughout some leather corals life, it will go through periods of dormancy. Its polyps will not appear to expand and you will notice a sheen across the surface of the coral. The sheen you are seeing is a thing mucus coating secreted by the leather coral. Within a day or two, with the adequate flow, this mucus coating will lift away and be carried through the water column to your filter. You should not attempt to remove this mucus coating as it is part of the natural sloughing of the corals' flesh. Similar to when a snake sheds its outer layer of skin as it grows, coral purges their surfaces of debris and bacteria as they age.
Xenia
One of the most commonly suggested soft coral is included in this list due only to its existence on every other list. Xenia is a fascinating coral that displays a rhythmic pulsing motion with its polyps. Capable of surviving in lower light due to its advanced filter feeding capabilities. Beyond filtering plankton from the water with its pulsing polyps, Xenia can also absorb nutrients from the surrounding water directly. Its ability to absorb nutrients from the water also makes it a great candidate for nutrient export in the same fashion macroalgae do.
In the wild Xenia inhabits large swaths of the shoreline. Found in exceptionally dense populations where sewage from nearby hotels and municipalities are expelled into the oceans. As far as a low fuss coral is concerned Xenia takes the cake. But it is in these many benefits that Xenia is a double-edged sword of a coral and why I hesitate to recommend it. Xenia not only survives but has no problem thriving in less than ideal conditions, when provided optimum conditions its growth is exponential and a small colony can quickly reproduce until every square inch of rock is covered in pulsing polyps. As time goes on the tank may become overpopulated with Xenia and other coral may begin to suffer from contact with the mucus produced by this coral.
While certainly a great candidate for many reef tanks, Xenia will spread uncontrollably in most tanks and as a result, I hesitate to nominate it for an early addition as it will take up valuable real estate as we move forward with other coral additions. I hesitate nominating for later additions as its invasive nature may negatively impact existing coral. As a closing note on Xenia I will mention that unlike much soft coral, Xenia does not appear to produce a copious volume of noxious chemicals when it is manually removed from the glass and equipment of your aquarium. Xenia will grow up the walls and on the equipment in your aquarium.
Zoanthids
Comprising dense mats of polyps about the size of a pencil eraser, Zoanthids are an amazing coral that is coveted equally by equally and veteran reef keepers. Having by far the largest variety of color combinations of any single species, entire aquariums can be filled with this single species and you would still achieve the full spectrum of color possible with a reef tank. Highly marketed with brand names referencing sports teams or pop culture this coral can appear expensive however their rapid growth means that a small fragment of only a few polyps is enough to populate a large portion of rockwork. There are sisters to Zoanthids, mainly Palythoa but they are so similar in care in the description I do not feel a need to split the two when discussing them on an introductory level.
Both Palythoa and Zoanthid even share the same precautions when considering. Any tank containing Zoanthids must run activated carbon filtration. Any time you handle Zoanthids or water Zoanthids have resided in for any period of time you must wash all affected areas thoroughly. Within the beautiful exterior lurks a powerful neurotoxin called "Palytoxin". Palytoxin is lethal to mice and has serious side effects in humans with symptoms persisting for days. Even the South Australian Government has a health page dedicated to the dangers of palytoxin exposure and while it is a serious risk, in my opinion, proper consideration and handling are supremely effective at avoiding all consequence. My opinions aside, however, if after handling coral or aquarium water you feel unwell, please seek medical attention.
Although I have only addressed three families of coral above, within these families are forty-four classified genus containing hundreds of options to consider. Soft coral makes amazing additions to a mixed reef tank with proper consideration, however, when given an environment more tailored to their needs soft coral really shine. Diffused lighting, alternating strong currents, routine feedings with zooplankton and pristine water quality will lead to phenomenal growth rates and vibrant coloration for a majority of soft coral.