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Coral Propagation… It’s not just for Coral Farmers! Part 2

“Coral propagation for many soft corals, like this green-polyped Sarcophyton, is as simple as a bilateral cut with a sharp razor blade.” photo by Anthony Calfo

In part one of this article, I offered a simple introduction to endeavors of coral propagation. As marine aquarium hobbyists and reefkeepers, we are reminded of the need to understand how and when to propagate our corals, almost every month or week, as we watch them grow. At minimum, we propagate corals to prune growth and keep the peace between encroaching neighbors. Indeed, they may not look aggressive, but corals and their cnidarian kin (anemones, zoanthids, etc.) are in constant, silent warfare with each other – amplified by the inevitable realities of closed aquarium systems. For this reason, in large part, it is so very important that we all realize the importance of good husbandry to relieve or control the chemical and physical aggression of our beloved reef creatures, starting with the fundamentals of light and water quality.

You may be wondering how light can help control aggression between corals? You might also be surprised at the answer. In some ways – more light is better. To be specific, we need to start our aquariums with an appropriate amount of light for the species we intend to keep (about 5-10 watts per gallon for average reef keepers). Then we need to support the delivery of that light optimally to and through the water as time passes. This is an obligation that many aquarists fail to appreciate. Light bulbs and lenses need to be cleaned of dust, salt creep and debris faithfully on a weekly basis. And some lamps age much faster than others. For optimal performance, most fluorescent light bulbs need to be changed every 6-10 months. And how does this all relate to coral aggression, now? Very simple – as the quality of light reaching corals degrades over time from lamps obscured by dust, debris or age, then corals begin to expand their polyps and tentacles (swelling with water) in an effort to spread out their zooxanthellae to catch more of the weakly available light. And so, the worse the lights get, the more some corals pan for light and the closer they get to each other. The increased sensation of competitive species stimulates coral to produce more allelopathic compounds (chemical aggression) and turns a closed system into an increasingly more noxious environment! They are also wasting precious energies for defense that could otherwise be used for reproduction, growth, etc. Some aquarists, in fact, misinterpret the increased “mass” of a swollen coral that is panning for light as growth. This is not growth, of course, and it is also not an excuse for delaying the servicing of outdated or dirty reef lights.

“With good husbandry, many common and hardy soft corals like this Alcyoniid “finger leather” can grow double or triple in just one year’s time. They will require very large spaces to grow into or that you prune them regularly.” photo by Anthony Calfo

With the same reasoning you can now infer, perhaps, how water quality has an effect on coral aggression and the need to prune and propagate. There are several angles from which to approach this. The least obvious one for too many aquarists is the parameter of “water clarity.” We hear about discolorants in the water or yellowing agents, but how many of us truly measure or track this quality? It’s not really something we can readily test for (although the old-fashioned rule was to hold a glass of aquarium water against a stark, white sheet of paper), and for those of us without superb vision, a slight tinge to the water may not be apparent even with aquarium water siphoned into a white bucket during a water change. But rest assured that after just a couple of weeks, natural discolorants produced (as well as imported to the system with food/feedings via dyes and the degradation of the very matter) accumulate to the extent that they can measurably reduce the penetration of light into the aquarium. Thus, for aquarists not using adequate carbon and/or chemical media and/or doing regular partial water changes, water clarity is usually significantly handicapped in just a couple months. Discolored water is obviously a waste of electricity (a dear expense to most people!) when the light produced cannot penetrate the water optimally at depth. Indeed, the increasing levels of discoloration to the water, however clean or new the bulbs may be, has the same effect on your corals as if the lights were simply inferior from the start as if aged or dirty! And as if that wasn’t all bad enough, there is the risk of shocking your corals and other light sensitive creatures with a sudden correction of water clarity (overdue water change or sudden use of heavy chemical media). The solution to these water clarity/quality concerns is simply good basic husbandry and due diligence. Changing small amounts of water weekly is better than larger amounts monthly. In kind, changing small amounts of chemical media frequently is extremely helpful for water quality. Please do consider using a high quality grade of activated carbon, exchange resin and or adsorptive media (like Poly-Bio Marine “polyfilters”) in small, consistent portions changed frequently (in weeks rather than months).

“A conservative method for propagating corallimorphs is to make a single radial cut from the mouth outward to encourage a continued, natural fissionary process.” photo by Anthony Calfo

Whew! With that out of the way, let’s get back to talking about propagating corals. Soft corals are usually the first variety that new reef aquarists start with, and for good reason. They may not necessarily be more hardy with regard for water quality than some of the best scleractinian (“stony” or hard coral) species, but they are categorically more durable with regard for handling. Truth be told, though, most really are hardier overall and it is both conservative and appropriate for new reef aquarists to keep only “softies” for the early months to more than a year until a reasonable level of comfort, familiarity and proficiency with reef creatures is achieved. This is very helpful and at times a matter of life and death as new aquarists tend to be unsure of new coral placement at first. They often handle their new corals excessively in the ensuing days to weeks. And they may not securely situate new colonies well enough or even have a stable rock structure from the start, simply from their inexperience (no worries, though… we all learn fast with enthusiasm here :). The bottom line is that new corals in the hands of new aquarists are at somewhat greater risk. As such, soft corals (octocorals and other cnidarians “sans skeleton”) really are better choices early on.

“Soft corals and corallimorphs will naturally divide on their own in due time with good care and handling as we can see here with this “mushroom anemone” that first developed two fully formed mouths, then began a fairly equal fissionary split.” photo by Anthony Calfo

Some of the best corals for this purpose are common “mushroom anemone” corallimorphs and Alcyoniid “leather corals.” These two groups comprise some of the most popular and commonly imported reef creatures. They run the gamut of color and price with features to satisfy the preferences of most any kind of aquarist. And while they are both very hardy and easy to handle, they favor different techniques of propagation and settling for best success.

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Corallimorphs (AKA “mushrooms,” “false anemones,” or “mushroom anemones”) are simply fabulous creatures. Possessing great variety of color, texture and even behavior… species in this group thrill even the most tenured reef aquarist. Some rare specimens even command prices in the range of hundreds of dollars. A few fascinating types in the family even grow a couple of feet across and have evolved strategies of “funneling” their bodies to allow detritus to settle in the bottom of their “vase-shape” as bait to trap fishes to eat! The majority of corallimorphs, however, are simply coin sized as adults, reproduce easily on their own and will tolerate a wide range of light – favoring the lower end of the spectrum. Coupled with low price and great color, these creatures are winners!

“Sharp culinary scissors work very nicely for making fast, clean cuts through soft coral tissue – notice the strategic taking of a forked branch that is at least several inches long here for improved chances of success.” photo by Anthony Calfo

Natural and imposed modes of corallimorph propagation can occur by fission. In the latter case, individual polyps, if fed well and in good health, will form a second mouth and then split in half fairly equally to form two like-sized and well-developed clones. Both are imparted with zooxanthellae, defensive mechanisms and digestive systems to feed themselves; the strategy is highly successful. It can be spurred or instigated to occur faster by taking a sharp, single-edged blade like a razor and nicking or notching the “base” (pedal disc) of the polyp. More assertive coral farmers can confidently take the action to its logical conclusion and simply make a complete bilateral (equally halved) cut right through the animal from top to bottom. This is actually a very safe and successful strategy. It is possible to extend the “logic” further and try to quarter the polyp or make even greater numbers of divisions, but the rates of success drop as the number of cuts increase. The tinier portions for settlement combined with the increased contact time and increases stimulation of the animal encourage greater amounts of mucus production, which is partly to blame for the increase in morbidity or mortality as mucus attracts bacteria. The bacteria initially may not be pathogenic, but a stressed animal secreting excess mucus (like in shipping bags) can attract growing numbers of bacteria, which are opportunistic and may become pathogenic. A single bilateral cut is all that is recommended to begin with for corallimorphs.

“Sewing soft corals with a needle and plastic thread is perhaps the single fastest and best way of insuring a sure settlement of cut divisions. Just a stitch or two through the base will allow you to tie the division off to a piece of rubble or rock.” photo by Anthony Calfo

Alcyoniid “leather corals” include the genera Sarcophyton, Sinularia and Lobophytum. Simple pruning and propagating techniques are really as simple as a fast cut with sharp scissors, or better – a clean cut with a sharp single-edged blade like a razor or scalpel. The reason that razors are better than scissors is that scissors have a crushing action to their blades, which incurs slightly more collateral damage to both the parent and the division. To improve rates of success with cuttings from leather corals, take at least 3″branches off of “finger” digitate forms. Forked branches are also usually a bit stronger or at least easier to secure and settle. For lobes of Alcyoniid tissue trimmed away, as with toadstool or like-crowned specimens, rates of success are improved with divisions taken from the “crown” (capitulum), which have fully formed polyps.

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Settling naturally pinched (fissionary splits) or imposed (cut and taken) divisions of propagated corallimorphs or leather corals can be done several different ways. If a tray, refugium or another dedicated space can be reserved for coral cuttings with a waiting rubble base, then natural settlement by placing the fragments on the substrate is safe, easy and successful. This is not quite convenient for most aquarists though, without a deliberate attempt to harvest and rear divisions of coral systematically. Most aquarists simply have a display aquarium and no extra space (yet!) for a formal attempt at farming greater numbers of corals. In such cases, divisions of coral will need to be kept in the main display. If so, it is important that the small divisions of coral are placed securely the first time and not allowed to blow around the aquarium or become dislodged and carried with the water flow into peril like an overflow, inaccessible recess of the rockscape or the stinging tentacles of a completive coral. For leather corals, the single best and easiest way to insure solid attachment is to simply sew the base of the cutting to a piece of rubble or rock. Take some plastic sewing thread or fine fishing line and throw a stitch or two through the base of the coral. After a week or two, you can snip the thread and pull it out assuming the coral has attached by then, as they most always do in mere days.


Anthony Calfo is the author of Book of Coral Propagation and co-author of Reef Invertebrates and Conscientious Marine Aquarist.

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