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Stocking what hobbyists use the catch-all label “corals” together is a process fraught with danger. Simply put, they do not all “play nice together” with their being a few deadly mechanisms in which these tissue-grade organisms wage outright war with each other and other reef life for space and food. Keeping this phylum’s contingent in smaller systems is even more precarious; with danger becoming more-dire with less volume and more mix of species.
To be sure, the chemical and physical warring abilities of
stinging-celled life are formidable, and being haphazard in their
stocking results in failure, loss of life and too often hobbyists
leaving the hobby. However, with some background, a plan and care in
execution thereof, small coral reef systems can be deeply gratifying.
The Issues: Allelopathy in a Word:
This group/branch of life, the Cnidaria (formerly Coelenterata, in
reference to their having only one in/out aperture to a central body
cavity) are easily identified by their possession of Cnidocysts…
stinging and agglutinant (sticky) cell processes. What this means to us
as stocking aquarists is that we need to provide for the fact that all
nine thousand plus species of hard and soft corals, sea fans, Zoanthids,
mushrooms, jellyfishes, anemones and more need to be carefully handled,
selected, acclimated and placed to avoid havoc amongst this life if we
choose to use it. Additional to cnidocysts, many, if not most Cnidarians
produce chemicals that have decidedly detrimental effects on other
sealife… not just other members of their own phylum. Again, the call
here is to be knowledgeable considering what species, groups are more
chemically toxic, place the less noxious ones first, do what you can
(and there is much here that can be done) to reduce altercations, and
possibly eschew the placement of some species.
Workarounds: A Plan, Isolation/Acclimation, Order of Introduction, Exclusion/Species Tanks
The one piece of “killer technology” I hope to have you strictly adopt is to utilize an intermediate “isolation” system for “hardening” new acquisitions AND slowly introducing them to your established display tank. I’m sure you’ve heard and read urgings for hobbyists to quarantine new organisms… to give you time to examine them for good health, perhaps observe whether they or the substrate they’re attached to has undesirable hitchhikers that you’d like to exclude… But here I want to emphasize the two aforementioned advantages and elaborate on the second.
Giving new arrivals (to you) a chance to “rest up” before permanent
placement is a great idea in and of itself. This practice would likely
save more than half of “incidental”, otherwise “mysterious” losses.
Adding the following “water mixing” protocol would probably eliminate
most of the remaining mortality. What this involves, simply put, is
after the new specimen/s have stabilized in your isolation system, and
assuring that you won’t be transferring problems, taking a few cups of
water from this system and blending it in with the water in your
main/display… and vice versa. In essence, giving organisms in both
separate systems chances to “smell” the new soon-to-be neighbours; w/o
being able to react overtly, attempt poisoning or stinging each other.
Over a period of doing this daily for a few weeks you will notice a
lessening of obvious reaction from your livestock. This is important,
can be VERY important to introducing new Cnidarian livestock to each
Cnidarians by Group/Class: Notes on Use, Selection and Placement
Mushrooms, the Corallimorpharians:
Mushroom corals are amongst the most popular Cnidarians for small marine system use; they come in a variety of colors and physical/polyp types, smooth to “hairy”, and due to their being found in not-too sterile natural settings, are quite tolerant of captive water conditions. Discosoma species are superior to less-hardy Ricordeas and more stinging Rhodactis spp. All need to have an eye kept on them lest they encroach on other specimens through asexual/cloning reproduction.
There are more families of soft corals than hobbyists are generally aware of; hence we’ll review the three principal ones folks are familiar with:
Family Alcyoniidae, leather, toadstools… are for the most part hardy, readily available, and easily cultured through asexual fragging. There principal downsides are that they produce copious amounts of allelopathogenic chemicals and can easily overgrow hobbyist sized systems. Starting with small specimens, healed cuttings is a good way to start off a small systems collection, adding other group small specimens once they’re established.
Pulsing corals… small colonies of Xenia, Heteroxenia, Anthelia and Cespitularia are very appropriate for small systems, GIVEN that said system is very well established (let’s say more than half a year going), AND care is taken to isolate these soft coral colonies so that they don’t asexually reproduce/spread out of control. As with all species kept in captive systems, they are best started from cultured specimens.
Dendronephthya, carnation, strawberry soft corals and more… these are generally a hard group of species to keep in large/r, more stable systems; requiring plentiful supply of very small plankton for feeding. I encourage all but the most advanced to leave these in the sea.
Stony Corals, the Scleractinians:
Stony corals, like soft, are capable of outgrowing their small environs and so must be placed to allow for expansion, growth, and ultimately allow for pruning. There are definitely families, genera and species of “stonies” that do better in small/ish systems, but all should be started as “frags” or small specimens to allow for sufficient space and discount chemical and physical warfare.
There still is a convention of (arbitrarily) distinguishing “Large” from “Small” polyped stony corals (LPS, SPS), and it shows some use in stocking considerations for small systems. By and large SPS corals are too difficult to maintain in small systems, the vacillation of water quality, trying to keep up with its re-stabilization and feeding requirements just making their husbandry too difficult. Yes; there are some folks who have (had) success in keeping SPS in Nanos, but these aquarists are in the extreme minority. LPS are not necessarily easy either, with many being so aggressive in maintaining their turf that they require much space about them.
Some Fave LPS Choices: Dendrophylliids:
Mussids: Pineapple, Brain Corals: Of these, the genera Acanthastrea, Blastomussa, Cynarina and Scolymia are my favorites. They don’t require as much light or circulation as many coral groups, can be placed in many areas of tanks, and possess much shorter “stinging tentacles” than other LPS.
About Actinarians, Anemones in Small Systems:
Though I have encountered examples of successful keeping of larger Indo-Pacific Anemone species in small systems, I urge caution in their keeping in anything smaller than 40 gallons. These life forms need space, for expansion and dilution of wastes, and penning them in with fishes particularly, though not exclusive of invertebrates, often results in these being consumed, and/or accidentally stung to death. The better candidates are Condylactis from the tropical West Atlantic, and clones of the Bubble Tip, Entacmaea quadricolor.
Gorgonians; Yes Sea Fans…
Stoloniferans, “Polyps” and such:
Sea Buttons, Button Polyps, Colonial Anemones… This group is a mixed blessing and curse of utility. On the one hand, they’re hardy, and many are gorgeous; on the other they can be extremely, dangerously toxic, to other sea life and the aquarist (do wash your hands thoroughly after handling or being in their tank). Zoanthids should be placed last in established systems, or if this isn’t practical/possible, introduced/acclimated as detailed above.
This brief introduction is by no means all-inclusive; perhaps we’ll have occasion to delve into the stinging-celled animals in greater detail on other occasions. My best advice re-sorting through what’s available and appropriate for your use is to keep apprised via hobby groups, reading, the internet for what others are doing, using, and to stay ever-vigilant in observing your livestock.
Baensch, Hans & Helmut Debelius. 1994. Marine Atlas, v.1. MERGUS, Germany. 1215pp.
Barnes, Robert D. 1974. Invertebrate Zoology. B. Saunders Co.
Borneman, Eric. 2001. Aquarium Corals: Selection, Husbandry and Natural History. TFH/Microcosm, Neptune City, New Jersey. 464 pp.
Fenner, Bob. 1990. The revolution of the mini-reefs. Pets Supplies Marketing. January 1990. http://wetwebmedia.com/AqBizSubWebIndex/minireefbiz.htm
Fenner, Bob. 2001. Good things (including reef systems) can come in small packages. FAMA 6/01. http://wetwebmedia.com/tomwsmreefs.htm
Fenner, Bob. 2007. “Coral” compatibility: On reducing captive negative interactions amongst cnidarians. http://wetwebmedia.com/cnidcompppt.htm
Fenner, Robert, Anthony Calfo. 2003, Reef Invertebrates, An Essential Guide to Selection, Care and Compatibility, Wet Web Media Publications
Michael, Scott. 2010. Cnidarians for
nano-reefs. Some select corals and “polyps” are suitable for smaller
reef aquariums. AFI 11/10