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New folks to the marine and reef aquariums are often amazed to find out how "young" these hobbies are. In all actuality, only since the mid-eighties of last century have we been able to keep "reef life" alive with any success. A few advents have led us to this captive "evolution"; better filtration, lighting and improved livestock collecting, handling and shipping techniques principally'¦ maybe along with the popularization of live rock and protein skimmers.
When people talk about going from the relatively sterile set-ups that only contain fish, or fish with hardy invertebrates, versus full-blown reef set-ups, they've almost always got the Stinging-Celled Animals in mind'¦ Zoologists classify them as the phylum Cnidaria. These are the True Corals, Soft Corals, Sea Fans, Colonial Anemones (zoanthids), Mushrooms (corallimorphs), and more. This tissue-grade life is defined more by what it lacks to distinguish it from other forms of invertebrates than what it has. Besides the aforementioned sticky, to stinging specialized cellular components, the cnidarians ("nigh-dare-ee-ans") have only one body opening for both sex and excretory products'¦ and the ones we have in mind have a body plan termed polypoid, a cone-shape, stuck to the substrates where they live.
This is a vast assemblage of non-vertebrate animals that span the entire gamut of suitability for captive use. Happily, many species are now captive-bred, asexually fragmented in captivity to make new specimens. Unfortunately, there are many others that rarely live for any real time. Here we'll point on of the hardiest varieties per popular group, giving notes on their practical husbandry.
Order Scleractinia: The True or Stony Corals: In the sciences only the one group of cnidarians are actually correctly called "Corals", the order Scleractinia are the true or stony Corals. The term stony hints up their salient characteristic, a hard limestone home for their soft living tissue that they secrete beneath them. True corals are found in the tropics, roughly 20 degrees North and South of the Equator in shallow seas where they receive sufficient light and warmth.
Artificially divided by hobbyists into Large Polyp, and Small Polyp Stonies (LPS, SPS), this artificial designation does serve as a convenient separation of smaller, versus bigger polyp size'¦ the LPS are typically much more resilient in captivity, requiring less stringent water quality, less light intensity and water current.
But not all LPS Corals are easy to keep. Amongst the poorest in survivability is the second most popular genus, Goniopora, the Flowerpot Corals. Most don't live more than days in captivity.
Alternatively, the current number-one genus of Stony Corals, Euphyllia ("You-feel-ee-ah") are real winners, my best choice for first time corals for new reefers. These are the popular Frogspawn, Torch, Grape, Anchor and Hammer Corals. The related (same family, Caryophyllidae) Bubble Corals (genus Plerogyra) are also excellent.
Acroporid in Fiji Goniopora in an aquarium Euphyllias
A Bubble (Plerogyra) Coral at right
Soft Corals, Order Alcyonacea: As you might surmise, do not have stony skeletons'¦ though they do have a varying amount of small internal skeletal elements.
The Leather or Toadstool Soft Corals (genera Sarcophyton, Lobophytum), Tree and Finger (genera Nephthea and Sinularia) come in a mix of green, brown, yellow, even purple colors. They're tough, tough, tough, requiring little in the way of special circumstances or feeding.
Similarly the Soft Corals called Pulsing types (family Xeniidae) are generally excellent'¦ as long as you can secure initially healthy specimens. They take a beating in transit due to their soft bodies. Though these gently wafting animals don't require direct feeding, they greatly benefit from weekly supplementing with iodine.
Such cannot be said for the fabulously beautiful, but nearly impossible to keep Carnation Soft Corals (Dendronephthya species). These animals rarely live for any length of time in captivity.
Toadstool/Sarcophyton Soft Corals in a Tank Sinularia in captivity
Nephthea in an aquarium A Pulsing (Xeniid) Coral A beautiful Dendronephthya
Mushrooms and Zoanthids: Two groups of almost-always hardy stinging-celled animals (also called corals in the hobby) are the Mushrooms or False Anemones (Order Corallimorpharia), and Colonial Anemones (Order Zoanthidea). These button-like animals don't require much in the way of intense lighting or dedicated feeding, but do have one dark-side: territoriality. The Mushrooms are too susceptible to dangerously stinging other attached livestock (hence the need to place them far away from others). The Zoanthids have about the same problem, in reverse. They are "easy losers" to being too close to more aggressive stinging-celled animals.
The smaller Mushrooms (genus Discosoma) come in a plethora of colors and textures, and are all about the same couple of inches across maximum. There are some giants in this group though. Elephant Ear (Rhodactis and Amplexidiscus) grow to several inches across. If you're fortunate you may find some of the very hardy Ricordea for sale. There are hobby culturists of the tropical West Atlantic R. florida, and some very nice new South Pacific Ricordea coming into the market.
Some Discosoma Images:
A Rhodactis and Amplexidiscus and Ricordea
Parazoanthus gracilis Zoanthid in aquarium
Aye, they be Sea Fans: Though most folks have seen their black skeletons in shell shops to fancy seafood restaurants, living Sea Fans (Order Gorgonacea) are far more gorgeous'¦ and a few species have become standards in the trade. In particular, the two Pseudopterygorgia and Sea Rods (genus Eunicea) out of the Caribbean are being enjoyed in reef aquariums worldwide. Some Sea Fans are photosynthetic and require bright-lighted conditions like the Stony Corals to power their endosymbiotic algae (zooxanthellae). Others do fine without intense lighting, but require periodic feeding. A few times a week, squirting a melange of meaty based puree their way while your mechanical filtration is cycled off (best with timers) suits them fine.
Pseudopterygorgia bipinnata and Eunicea mammosa in aquariums
The Polyp Corals, Order Stolonifera, are the last group we have room to mention. Linked with Pipe Organ "Coral", these are low lying inter-connected colonies of mats of individual polyps. Very hardy, in fact so much that they should be physically separated on their rocks to prevent over-growing other attached livestock.
The many "Polyps" of the genus Clavularia are highly recommended.
A Clove Polyp (clavulariid)
Some general care notes: For True Corals and their relatives, it is best to wait until your system is thoroughly cured to add them'¦ a good three months from setting up the tank. Healthy live rock, high water quality from sufficient filtration, aeration and circulation, and intense, full-spectrum are requisite. A last comment regarding a common misunderstanding with these biomineralizing animals, they need both high alkalinity (3 or more milliequivalents per liter, or 9 dKH) AND calcium (350ppm plus), often failing to thrive from a lack of one or both.
All the "corals" true or not require high quality water and near-tropical sunlight conditions to thrive. More difficult than fish only systems, there are many stinging-celled animals worthy of your keeping. One view of someone's reef set-up and you'll be hooked.