Propagation of Small-Polyped Stony Corals

As most people are aware, "small-polyped stony" corals is a rather imprecise term because the size of the polyps in stony (hard or solid skeleton forming) corals is a continuum rather than a discrete division of small versus large. Nevertheless, the term generally describes many of the fast-growing, branching, encrusting, whorl-forming and plating corals that are commonly grown in captive reef systems.

Fortunately, small-polyped stony (SPS) corals are quite forgiving of the way they are propagated. Given time and good conditions, the end product of almost any ham-handed attempt at propagation will eventually regain a natural-looking colony formation when provided with the proper conditions. Some of the techniques described here should help you to minimize the damage to and unnatural look of your mother colony, and to do the same for the fragments that you take.

Why Do It?

SPS corals can grow very quickly in a reef tank with strong lighting and water motion. When colonies touch, they begin to compete for space and attempt to sting each other. Sometimes the colonies reach some type of stalemate, with neither colony gaining an advantage over the other. In some cases, however, extremely aggressive corals (Hydnophora, in particular) can burn or digest large patches of adjacent colonies. Some extremely fast-growing corals simply shade out their neighbors. After a few years, most successful SPS-dominated tanks need some colony trimming. It's a great opportunity to take some fragments and trade with friends. Your buddy's tank can then serve as a reservoir for your most prized corals, should some disaster befall your tank. The continued propagation of captive-raised corals may also reduce the demand for corals collected from the natural reef and the energy needed for their collection and long-distance transport.

What Should I Cut Up?

The greatest success always comes from taking fragments from the actively growing portions of a colony. Other areas can also be fragmented, but the length of time these take to begin growing again after fragmentation may be longer. Fragmenting from a dying coral is least likely to succeed. If a colony has an infection, cutting a fragment as far away from the affected section as possible, and possibly moving the fragment to a different tank, might be the best way to ensure that the entire coral is not lost.

Assemble Your Tools

It is possible to propagate some SPS corals with nothing but your bare hands. Some species have branches that are easily broken off with the flick of a finger. If a suitable hole can be found to tuck the branch into, and it is kept immobilized and in contact with the substrate, many times the branch will begin to encrust onto the substrate, sprout new branches and form a completely new colony over time. Some species even tolerate being dropped onto the sand, and can also form new colonies right where they fall. To go beyond this simplest method of propagation a number of other tools are useful.

Counter-clockwise starting from top left - commercially available fragging shears, special cable cutting pliers, one of my pairs of trusty (rusty) wire cutting pliers, a high-speed rotary cutoff tool with two sizes of diamond cutoff blades and a miniature hacksaw blade holder.

Counter-clockwise starting from top center - commercially available high viscosity cyanoacrylate glue, part of a plastic egg carton useful for dispensing the glue, bottle holder made from a small tube and a sheet of acrylic, and a large bottle of liquid cyanoacrylate accelerant.

Counter-clockwise starting from top left - coarse wet-dry sanding pad glued to wood board (used for sanding base of fragments flat), needle-nosed pliers (useful for breaking or removing small coral branches from easily broken branching corals), chisel (for breaking off outer whorls of whorl forming corals, or for breaking branching corals by prying), small concrete squares (substrate for mounting fragments), and latex gloves (used when mixing commercially available putty-type underwater epoxies pictured above).

Probably the most important tool for fragmenting SPS corals is a pair of cutting pliers. I've been using the same two or three pairs of rusted out wire cutting pliers for many years now. I'm very lazy when it comes to my tools; I almost never remember to rinse them off with freshwater and I do not lubricate them. This is partly because I use them on a very regular basis. I just leave them hanging about, here or there, to be grabbed quickly for the next project. I don't lubricate the tools because I don't want any toxins from synthetic lubricants polluting my tanks, and I don't want to have to wash any lubricants off the tools before each use. I've found that the quality of the cutting pliers doesn't really matter much; in fact, high quality cutting pliers with precise action and fine tolerances between their moving parts can be problematic with the abuse that I subject them to. After each use in saltwater, rust will form between the moving parts. The pliers may freeze up and have to be forcibly worked back and forth until they free up again (a little water helps here). Each time this occurs, more and more of the steel between the moving surfaces wears away, making the joint looser and easier to use. After enough abuse, so much steel will have worn away that the pliers will never freeze up again, and are then the perfect tool for fragging.

High grade specialized stainless steel fragging shears with sharp cutting edges are available now for the hobby. These shears are more resistant to oxidation than cheaper standard shears, but if not rinsed carefully after use in saltwater, over time they will rust, as well. For certain applications these shears might have some benefit over my rusted-out cutting pliers but, in most cases when propagating SPS corals, the branches are not so much cut as they are crushed or snapped by the tool's action. Therefore, the tool's sharp cutting edge adds little benefit and, in the case of thicker branched SPS corals, may actually be more of a problem. Because the tips of such a tool are tapered, when extreme force is required to break the branch the tool flexes too much, and makes the cut more difficult to achieve.

When I give coral propagation demonstrations at my house, I always warn the newbies never to use any metal objects in their aquariums, as the toxins can kill invertebrates and fish. Then I show them my 10-year-old cutting pliers with large flakes of rust falling off, plunge the tool into my 400-gallon SPS-packed tank and say, "Don't believe everything you hear." In all seriousness, many people frequently dose their tank with iron and various trace elements. While I understand that steel is composed of many elements, including toxic chromium and nickel, I've never found a few bits of rust getting into a functioning reef tank to cause any problems at all.

In the first tools photo above is pictured a special cable cutting pliers. This pliers, while large and hard to maneuver, can be useful for cutting particularly thick or solid branching corals. I've often thought it would be nice to find a similar pair of pliers, or modify another pair, but with a larger hole so that the cutting force would be increased when cutting thick branches. With such a modified pliers, the cutting force would be applied when the pliers' grips are more fully closed, a position in which the human hand can naturally apply more force in a controlled fashion. Being able to cut branches off corals in a controlled fashion can mean the difference between neatly cleaving off a single branch, leaving the colony aesthetically pleasing, or ending up with a dozen fragments and a mangled mother colony. Whenever possible, it's usually easier to make a more controlled cut if the colony can be removed from the tank, or at least brought near the water's surface.

Other tools that can be useful include a high speed rotary tool with a diamond encrusted cutoff wheel (mine is permanently rusted to my Dremel tool). These wheels are surprisingly affordable and amazingly durable. I've been using the same one for many years, and have sliced directly through some very hard rocks and corals. While harder to find, larger diameter diamond encrusted cutoff wheels may also be useful in some cases.

Hack Up Your Coral

Propagation of an SPS coral with long branches is really quite straightforward. In an attempt to maintain the colony's aesthetics, look for branches in the rear of the colony, or in an inconspicuous area near the base. It is okay to use branches that might be shaded and that are no longer growing well. Clip the branches off with your cutting pliers, break them off using your fingers, or pry and snap them off with a screwdriver or chisel. When removing branches, try to minimize the damage to the coral's surface, as this is the living tissue. Try to keep cut branches out of the sand, or shake off any debris if they do fall onto the sand. Whorl-forming Montipora species can be tricky to fragment. Sometimes their large outer whorls can be removed by hand, or pried free with a small, flat chisel if the base is not too thick. All too often, though, the outer whorls end up breaking into a dozen small, and perhaps less valuable, fragments. If the colony can be removed from the tank, the diamond encrusted rotary cutoff tools are particularly useful for harvesting large fragments. If the colony is too big, or encrusted to large rocks, I've found that a simple hacksaw blade is useful. This blade can be handheld or wrapped with a piece of duct tape. If more force, or a large amount of cutting, is required, a small hacksaw blade holder can sometimes be used (see first tools photo).

I generally place my fragments in a small plastic bucket (photo above), gently dropping them in as I move about my tank pruning. Though other authors warn not to mix multiple species in a single bucket, I've never seen a problem if the corals are not kept together for more than a few hours. One exception to this, however, are SPS corals of the genus Hydnophora. After just a few minutes in a stagnant bucket, these corals will start to digest any corals that they contact.

Fragmentation and Mounting Branching SPS Using Cyanoacrylate Glue

Once the coral fragments are out of the tank, they can be cut up the rest of the way into the desired shape and size. I've found that for optimal survival rates, it's best not to try to cut fragments smaller than about one inch. This is a good time to remove any sections of dead coral skeleton that might otherwise serve as an attachment point for undesirable algae.

I like to grind the fragment's base flat with a high-speed rotary tool with a diamond cutoff wheel (photo above left). If the fragment is particularly large, it may be advantageous to find its balance point, and grind the base in such a way that the coral can nearly balance on a flat surface. Ideally, live coral tissue on all sections of the fragment should be in close contact with the attachment substrate. Having the base perfectly flat is not a requirement for mounting, but it does make for a stronger attachment initially, and allows the coral to encrust faster along its base.

A piece of coarse grit wet-dry sandpaper glued to a small wooden board can also be used to grind the base flat (shown above). If it's brushed and rinsed clean in a sink after each use, the same piece of sandpaper can be used for many years. The sandpaper is glued to the board so that when it dries, it remains flat. While it might be difficult to sand a thick Acropora using this technique, most branching Montipora are quite porous and can be sanded to a flat base very quickly. If working with a large number of fragments, this may be much faster than drying your hand repeatedly before picking up the high-speed rotary cutoff tool.

After grinding the base flat, the exposed skeleton is gently rinsed clean to remove any proteinaceous slime by gently rubbing it with your fingers in a bowl of tank water (photo below left).

The base is then dried with a cloth or paper towel (photo above right). Sometimes, with porous branching corals such as Montipora digitata, it may be difficult to completely dry the base. Leaving the coral out of the water for a few minutes may help here. Also, keeping the fragment inverted will help the water in the skeleton to flow away from the attachment point you are trying to dry.

Quickly apply the cyanoacrylate glue after drying the coral's base. With some porous skeleton branching corals, water will begin to reappear on the coral's base within just a few seconds of being dried. Only a drop of glue is necessary. Excess glue will not, in most cases, strengthen the bond, and it will take much longer for the coral to encrust over the glue and actually bond to the surface of the substrate. In the photo, note the "fraggers' nail polish," - cured glue from a previous propagation session.

At this time I keep the fragment inverted with one hand, and use a cotton swab to apply a tiny dab of cyanoacrylate glue accelerator to the substrate with the other hand. Only a fraction of a drop of accelerator is required. As shown in the second tools photo, I use a special homemade holder for the cyanoacrylate glue accelerator to reduce the chance of an accidental spill of this toxic organic solvent.

Once the accelerator has been applied to the substrate's surface, immediately place the fragment onto the substrate because the accelerator evaporates very quickly. When positioning the fragment, make sure that no water flows over the surface of the glue or the contact point on the substrate before the contact is made. Once the fragment is positioned, water flowing onto the bond's surface makes no difference. You will have only a few seconds to orient the fragment once contact is made. Usually within 10 seconds the bond is strong enough that you can lift the fragment without the base falling off while gently lowering it into a bowl of tank water. If something goes wrong, and the attachment is not strong after a short period of time, you can re-dry the fragment and the substrate and try again.

Multiple fragments from the same colony can be mounted to the same substrate, if desired. Branches that touch often anastomose (fuse) as they grow. This, combined with the increased surface area and multi-point attachment to the substrate, can result in a very structurally durable fragment that can withstand the average drop kick from the FedEx guy during shipping. Branches can also be attached flat against a substrate, which, in some cases, might force the fragment to create more numerous, smaller branches than a vertical orientation. Mounting in a horizontal orientation requires additional sanding or grinding to remove the outer, growing layer of tissue so that a good bond can be formed between the fragment and the substrate using cyanoacrylate glue.

After 10 minutes or so, glued-down fragments can be moved back into a tank to start the grow-out process. If the fragment was taken from the underside of a colony, care should be taken to slowly acclimate it to stronger light. Here I've shown the use of small squares of concrete that I make myself. Flat fragment attachment disks also are commercially available, as are disks with small shaped pegs on the bottom (, which can fit into the plastic eggcrate material that many reefkeepers use as shelves in grow-out tanks. Fragments can also be glued to just about any hard surface. Some hobbyists use plastic flower stem holders, or small pieces of acrylic, ceramic tiles or live or base rock, for this purpose.

While I've described the use of cyanoacrylate accelerant here, there is no need to use the chemical. Its only purpose is to speed the curing process. When you are done with your fragmentation work, and all your fragments are back in a tank, be certain to throw out the water that was used in the propagation work.

Fragmentation and Mounting of Whorl-Forming SPS Using Cyanoacrylate Glue

Diamond encrusted cutoff wheels greatly simplify fragmentation of whorl-forming SPS corals. The desired shape and size can easily be cut out of the main colony. It's usually easiest to cut from the rear of the coral when making the cuts.

I like to bevel the coral's edge, to make its position on the substrate more naturally "inclined" (photo above).

As with branching corals, the base is washed clean of proteinaceous slime and any debris, and the base is dried.

The glue is applied quickly before water can recover the surface (photo above left). I try to get a thin layer of glue over the majority of the contact surface, if possible. Next, the accelerator is applied over the substrate's contact surface (photo above right).

The fragment is positioned and held for 10 seconds or so. If the fragments were taken from an area of the colony that was not receiving much light, they should be positioned at an angle to receive indirect light in the fragment grow-out tank. This will give them time to adjust to increasing light levels.

Mounting SPS Using Underwater Putty Epoxy

I've previously described the methods of use and hazards of underwater two-part epoxy, which is particularly useful for SPS corals such as Anacropora or Hydnophora, or any other SPS coral that does not effectively encrust.

For SPS coral mounting, the epoxy is pressed onto the surface and shaped around the edges to form a small crater. At this point it's best to wait several minutes for the epoxy to start to set up.

The fragment is positioned and the putty epoxy is formed up around its base (photo above right). Putty epoxy has no significant adhesive properties, so it's necessary to cover enough of the coral so that when the epoxy hardens, the coral is effectively anchored to the substrate. Corals with particularly smooth branches can be notched near their base to provide a place for the epoxy to flow into.

When using putty epoxy on SPS corals, it's important to recognize that all covered coral tissue will die, and also that while curing, the putty will heat up and kill any tissue very close to the edge of the epoxy. In some rare instances the dying tissue can form a front of diseased tissue that will travel up the fragment, killing the entire fragment. The probability of this can be minimized by keeping the coral fragments' base cool by placing them in a bath of tank water that has good circulation from an airstone or a small powerhead.

Under good conditions, in a few weeks the corals will encrust down onto the surface of the substrate, or encrust over the putty epoxy's surface. The concrete substrates and the epoxy surfaces will quickly become covered in coralline algae, taking on a more natural appearance.

Other Hints

People often ask, "How long can the corals be out of water?" Well, it depends. I've found that most SPS corals are fine for two to three minutes out of water. Those that tend to slime a lot tend to be okay for longer periods of time than those that seem to be dry in a short period of time. If your fragments look like they have a dry surface, you need to get them back into water ASAP.

Lugol's dips: I've heard some say that a 10-15 minute dip in 10-15 drops per liter of Lugol's strong iodine solution can increase the success rate of fragments. When fragmenting healthy corals, I've found the success rates to be so high that I see no need for the expense and extra time required for a Lugol's dip.

To minimize the risk of introducing coral parasites into my main tank, I carefully quarantine any corals I obtain from sources other than my own tanks. If, after the quarantine period, I decide I want to keep a coral long-term in my display tank, I mount it on a large rock using the methods described in this article. I often use rocks with holes bored in their base. Because my tank's rock structure also has holes drilled in its top surface, this allows me to position the colonies wherever I like using acrylic rods poked though the holes. This methodology allows the entire colony to be moved about the tank if I need to "remodel," and also allows easy removal of the colony if I need to do significant pruning.

There are many other ways to attach SPS corals to substrates. Hot melt glue, fishing line, many other forms of epoxies and any other things you can think of can be used to keep healthy coral tissue immobilized and in contact with a suitable substrate.

Happy fragging!

If you have any questions about this article, please visit my author forum on Reef Central.

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"Frag" of the Month - January 2007 - Propagation of Small-Polyped Stony Corals -