TEXT AND PHOTOS BY DANIEL KNOP

Artificial Propagation of Corals —
The Soft Corals

Soft corals are generally considered to be more hardy than most hard coral species. While aquarium husbandry of hard corals, especially the small-polyped scleractinians (SPS), is considered to be a challenge for the experienced reefkeeper, keeping soft corals in the aquarium presents something of a challenge for the newcomer. Despite this, there are many aquarists who love the beauty of the soft corals and their gently moving branches and polyps. A little “forest” of beautiful tree-shaped Nephthea corals makes many aquarists raise their eyebrows, and a colony of pumping Xenia that looks like waving hands immediately makes them smile.

Soft corals are quite adaptable to different environmental conditions because they are used to strong variations in conditions in their natural environment. As a result, much more is known about their requirements than about the needs of many of the hard coral species, and they are the first corals to have been successfully propagated in modern reef aquaria.

The natural habitat of soft corals is mainly the shallow water, strongly illuminated portion of the reef. Here, during the tropical rainy season, they are subjected to large changes in pH, water temperature and salinity as heavy rains mix freshwater with saltwater, significantly reducing the salinity. The corals also come in contact with the rain during low tide, and this is when some corals are exposed to the air, which can also cause severe damage to a vast field of soft corals. In this case, a huge portion of the colony may dissolve and the small surviving parts are carried away by the water current. What remains in place is sometimes no more than a small portion of the formerly beautiful corals. However, quite soon the ugly clumps of damaged soft coral tissue will sprout beautiful polyps and start regrowing, so that after a year nothing remains of the little “catastrophe” that occurred.

Nephthea sp. fragment prepared for “toothpick” method of attachment.

Tissue Regeneration

Soft corals have a great ability to regenerate tissue, which enables us to propagate many of them artificially. What we are actually doing is imitating some type of natural catastrophe — sudden changes in environmental conditions or the results of a predator feeding on the colonies by severing fragments from the mother colony. Unfortunately, although aquarium care of soft corals is easier than the care of hard corals, artificial propagation seems to be more difficult. The reason is very simple: when fragmenting a hard coral, we mainly fragment calcareous skeleton that is not vital to the hard coral’s well-being. Only a small portion of an Acropora branch is living polyp tissue that can be damaged and has to be healed.

When cutting a soft coral, the situation is totally different because everything we cut is living tissue. So, we leave behind a huge wound that is prone to infection by various microorganisms if the environmental conditions in the tank are not ideal. As long as the coral is healthy and is not cut, many of these microorganisms might actually be beneficial by consuming dead tissue cells. But, because they are able to find a lot of nourishment in cut tissues, they sometimes propagate en masse, which leads to serious tissue damage and can be lethal to the soft coral fragment. Additionally, the mother colony is also sometimes prone to this type of infection — for example, colonies of the soft, fast-growing Alcyonium spp. that are commonly misidentified as Cladiella sp. This makes it advisable to take precautions and observe some simple rules for soft coral fragmentation (see sidebar entitled “Ten rules for successful soft coral propagation”).

In some experiments we did on soft corals in 1986, we found that corals will usually heal cut tissue quite rapidly, as long as infections are avoided. In these experiments we cut a leather coral of the genus Sarcophyton into 30 10-millimeter squares so that the fragments were cut on all four sides. Given that the thickness of the lobe was 5 millimeters, the cut surfaces matched the size of the intact coral surface (2 square centimeters). Substrate attachment was done using the toothpick method, which I will describe in detail later in this article. All of the fragments were exposed to the same environmental conditions as the mother colony, and 26 of them grew out to a marketable size within one year. The other four fragments (about 13 percent) dissolved and died.

Only the toothpick should touch the substrate.
Another experiment was done with branching soft corals of the genus Alcyonium. Again, 30 fragments were cut and attached to the substrate using the toothpick method. Only three fragments survived and could be raised up to a larger size. Also, the mother colonies sometimes reacted very negatively. A colony that was 60 centimeters in diameter normally tolerated 10 to 15 cuts when severing some fragments. But, when we cut 30 fragments from another colony of the same size, we observed a progressive dissolving of tissue and lost the whole colony.

Choosing the right substrate

It is important to choose an appropriate substrate for each individual coral fragment. This sounds simple, but sometimes it is quite difficult. Soft corals need some type of indentation in the substrate they are going to be attached to using the toothpick method, and, depending on the species and growth form, this depression must have a certain shape to be ideal. For your first two or three fragments you might easily find the perfect rock in your reef tank to act as a substrate, but as time passes you will run out of available rock space and will have to start looking for new substrates.

Making a substrate from cement is a lot of work, but if you are going to need a lot of substrate it’s well worth the effort. It also has the advantage that you won’t have to search for rocks with perfect indentations that fit the coral fragments because you can form the substrate with the desired shape. When producing larger numbers of fragments for the trade, it can be helpful to produce substrates shaped like a stick or a sheet with indentations, so the substrate can be broken at a later time when the corals have grown too large or are about to be sold.

After four weeks the coral is firmly attached.
We use iron-free cement mixed with a double volume of fine sand for our substrates. Once the substrates have hardened, we cure them in saltwater for about two weeks (you can use aquarium water from a partial water change). After two weeks we add some hydrochloric acid (HCl) to the water (33 percent or 20 milliliters per 100 liters of water) to neutralize alkaline substances. After thoroughly cleaning the substrates with freshwater, they are ready to use.

Fragmentation

Propagating new colonies is simple for those genera that exhibit a mat-like growth form. Corals of the suborder Stolonifera belong to this group, as well as the genus Anthelia from the family Xeniidae. It even works with the disk anemones of the order Corallimorpharia and with zoanthid polyps. Just place some coral rubble near or even on top of a colony. As soon as the polyps have overgrown the new substrate, this rock will be transferred to a different place in the aquarium, where the polyps will begin to spread. But be careful — this is so successful that it can lead to a rapid and large increase in population, fast becoming a pest that is hard to control.

Loebbecke Aquazoo in Düsseldorf, Germany, successfully propagated a Zoanthus sp. in a large reef tank using this method. The zoanthid polyps started to propagate rapidly and soon covered all available substrates, causing massive disturbance to other invertebrates. Because the zoanthids contain toxic substances that they release when they are injured, it is difficult to reduce their population by mechanical means. Thus, when propagating zoanthids in this manner it is better to use a substrate that consists of separate rocks that can be removed individually.

Other genera, like this Sinularia sp., can be attached with the toothpick method.
It is much easier to fragment corals that exhibit a tree-shaped growth form. With these types of corals the aquarist does not have to wait for the polyps to do all the work. He or she can speed things up by using a scalpel. Xenia sp. and Heteroxenia sp. belong to this group, as well as many tree-shaped soft corals of the family Nephtheidae and the leather corals of the family Alcyoniidae. They can, of course, also be propagated by just putting a rock near the mother colony and waiting for them to attach spontaneously. Once the coral has grown onto the new rock, the tissue can be separated with a cut and a new coral is born. It is also possible to cut several pieces of tissue and attach them to a substrate using the toothpick method that I developed for the tree-shaped Nephtheidae in 1986.

The best success is achieved in tanks that are dominated by the coral species you intend to propagate. In a tank dominated by Xenia, it is usually not necessary to attach the coral to a substrate because the cut coral will attach itself to the gravel or rock decoration within a few days. In tanks that contain a variety of different genera this can be much more difficult. Many coral genera or even species inhibit each other indirectly by secreting substances into the water.

By far the most difficult of the soft corals to attach to a substrate are members of the genus Sinularia. While species such as S. flexibilis or S. mollis don’t normally cause problems, the more difficult species, like the one known as Sinularia asterolobata, tend to dissolve their tissue before they have readily attached themselves to the substrate. The reason might be that their tissues contain many more sclerites, so the percentage of vital tissue is relatively small compared to other Sinularia sp. This is especially true for the base of the coral, in which the percentage of soft tissue is very small and the thin layer of tissue surrounding all the sclerites dissolves rapidly. A few days after cutting the coral (which can be difficult as it is hard for the scalpel to cut through the sclerites) a small heap of tiny white sclerites is visible under the coral. In many cases this dissolving of tissue continues until the coral disappears or turns into a slimy mass because of the activities of microorganisms.

Artificial substrates made from cement can help in producing many small corals. Note resemblance to oversize chocolate bar, as mentioned in the text.
For these species it seems to be much better to place a lime rock near the base or a branch of the coral and wait until it has attached, so the fragment will at least be attached to a substrate. Furthermore, it might make sense to practice the method that Johannes Birkholz developed several years ago. He tied a thin nylon wire around the part of the coral that he wanted to severe and pulled it until it almost started to cut the tissue. Each day he pulled it a little tighter, but without really cutting it. After several weeks the fragment was fully severed from the mother coral and no tissue was hurt. If this is done after the fragment has attached itself to a new substrate, nothing is likely to go wrong.

Also, after it has been cut from the mother colony, the very soft tissue of the Alcyonium spp. (often misidentified as Cladiella spp.) tends to dissolve before it has completely attached to the substrate. Even the toothpick methods fails because the tissue starts to dissolve around the toothpick. In this case it is much better to proceed in the way described above for the harder corals of the genus Sinularia. If the mother colony is placed on the gravel, some of the branches can be bent down and fixed between small rocks, so they will spontaneously attach. Later they can be separated using a scalpel or the nylon wire method.

The umbrella-shaped Sarcophyton spp., which are normally considered suitable for the beginner because they are quite tolerant of a wide range of environmental changes, generally do well when fragmented. Interestingly, these Sarcophyton fragments quickly develop the natural growth form of the species. If a small fragment is cut out of the umbrella (the capitulum), in a matter of a few weeks a new stem will start to grow at the bottom of the fragment and will develop the typical umbrella shape.

When fragmenting Sarcophyton and closely related species like Lobophytum sp., it is important to give the fragment time to heal the cut edges of the tissue in order to avoid infections. This is the main cause of failures in propagating Sarcophyton spp. corals, as well as tissue necrosis caused by the pressure on the fragments when affixing the fragments to the substrate using a rubber band or a thin thread. Either the rubber band is loose enough not to cause pressure to the tissue and the fragment will very likely be blown away by the water current or the rubber band is tight enough to hold the fragment in place, but it causes tissue necrosis from the pressure, which will lead to dissolving tissue. Often the entire fragment is lost this way.

For Sarcophyton species I strongly suggest the toothpick method. Even the healing of the cut tissues can be achieved in a simple way before separating the fragments from the mother coral. The method is very simple. The umbrella of the coral is cut into segments from the periphery to the center, but without separating the fragments totally. Imagine the capitulum of the corals as a clock and cut from the periphery to the center at 1:00, 3:00, 5:00 and so on, all around the clock. Then provide good water circulation and allow about two to three weeks for the cuts to heal. The coral will probably not open fully during this period, but that is normal. After the cut tissue is totally healed, you can fully separate the fragments. Just place these loose fragments on the gravel and allow the wounds to heal before attaching them to the substrate. Alternatively, you could attach them to the substrate sideways, so the cut tissue is in good water current.

Substrate attachment methods

As mentioned above, many aquarists try to fix the coral to a substrate by simply tying it with a nylon wire or a rubber band. This works quite well for some of the fast-growing hard corals like Acropora sp., provided the wire lasts long enough in saltwater to hold the coral in place. Rubber bands normally dissolve quickly (and release undesirable substances into the water). With soft corals, however, this method seldom works. The soft tissue quickly suffers and dissolves when under pressure. Once necrosis caused by a pressing wire develops, the tissue often continues to dissolve until the fragment is divided or even dissolved completely. In this case it is best to release the pressure and place the coral fragment in good water circulation to ensure adequate oxygen supply and prevent accumulation of dissolved tissue particles. Once a day the necrotic tissue should be cleaned well using the pump outflow.

In 1986, problems caused by dissolving coral tissue lead us to experiment with cyanoacrylate glue — better known as superglue — as a means of attaching coral fragments. We tried to simply glue the coral tissue to the substrate, and even succeeded, but in almost all cases the corals were able to free themselves within a few minutes by producing mucus secretions. Since then different cyanoacrylate glues have become commercially available, and gel-type glues seem to produce better results.

Take the coral fragment out of the water and touch it lightly with a dry towel on the underside to remove excess water. The surface does not necessarily have to be dry, as the glue also hardens underwater. Apply some of the gel-type superglue to the coral tissue you want to connect to the substrate and let it harden in the air. Once it has set, the fragment is ready to be attached. Apply some more glue to the same area on the coral, attach the fragment to the substrate and hold it in place for a few seconds. Corals, especially species that develop plenty of calcareous sclerites in the basal part of the colony, such as Sinularia sp. and also Sarcophyton sp. and others, can successfully be attached using this method.

A simple and cost-effective soft coral culture tank system.
After failing using the cyanoacrylate substrate settlement of Nephtheidae corals in 1986, we developed the toothpick method for attaching branching soft corals. Here are the easy-to-follow steps.

1) Cut the coral at the stem — use a scalpel or razor blade, never scissors!
2) Insert a thin stick of plastic or wood (toothpick) through the stem of the coral fragment, about 10 to 15 millimeters above the cut, so that it protrudes on both sides of the coral tissue.
3) Allow the wounded tissue time to heal. Place the coral fragments on the gravel in the same aquarium in good illumination and water current.
4) As soon as the tissue is healed, the fragments are ready to be attached on the substrate. This method requires a substrate with an indentation big enough to encompass the lower portion of the fragment that is below the toothpick. This tissue should fit completely into the indentation in the substrate without any pressure (even when the coral tissue is fully expanded). It is better to use a larger indentation, and it’s sufficient if the coral tissue has contact to the substrate on one side. When the coral is in its position on the substrate, the two ends of the toothpick should be touching the surface of this substrate. Use a nylon wire to tie the toothpick. In rapidly growing corals, such as Nephtheidae or xeniids, you can also use a rubber band to tie the toothpick. Normally, the coral tissue attaches to the substrate within a few days, long before the rubber band begins to rot (but don’t re-use the same rubber band in the aquarium later).

When attaching Sarcophyton sp. tissue, you will very likely use tissue from the umbrella-shaped capitulum, and this will probably not be round like the stem of a branching or tree-shaped coral. It will be flat and lobe shaped. In this case, instead of a round indention you might need a longer groove. You can find a few of these types of substrates among the coral rubble in most reef tanks, but when producing larger numbers it is better to create a sheet-like substrate from cement in the shape of a stick or an oversized chocolate bar that has blocks of chocolate meant to be broken off into small square pieces.

Fragmentation and substrate settlement in gorgonians is relatively simple, especially species from the Carribean Sea that contain zooxanthellae and have proven to be very hardy in the reef aquarium. The inner skeleton that consists of gorgonin stabilizes the coral and allows the aquarist to simply cut a fragment and glue it onto a new substrate, such as a stony coral fragment, using underwater epoxy or hot glue (to be described in a future article on stony corals).

A soft coral culture tank system

During the past 10 years, my experience with coral fragmentation has demonstrated that most fragments that do well in a mixed-community reef tank fare much better in a tank inhabited by only one species. Therefore, a small culturing tank devoted to just Xenia species coral will probably provide better results, if you are attempting to propagate lots of Xenia for the trade, than a tank that contains a mixed community of invertebrates. The same holds true for many other soft coral species, such as members of the families Nephtheidae, Alcyoniidae, Zoanthidae and Corallimorphidae, among others. They all develop and grow far better when they are not competing with invertebrates of other genera. Even among members of the same genus strong competition may develop that will inhibit growth.

In 1992 we designed a soft coral culture tank system that allows us to operate several shallow tanks with simple equipment and minimal consumption of electricity. It consists of six tanks, one on top of the other, with no additional stand. Illumination consists of just one fluorescent tube per tank. The bottom tank serves as a biological filter (live rock), and a pump distributes the water from the bottom tank to all tanks above, producing water current in these tanks and feeding an overflow that keeps the water surface clean and returns the water down to the bottom tank.

Water evaporation just affects the water level in the bottom tank, and is relatively small because the setup is totally sealed on the sides and at the back. Filtration (granular activated carbon and, if necessary, mechanical filtration) takes place only in the bottom tank. If the water turnover for each tank is not too great (the entire tank volume once per hour) and granular activated carbon is used in the bottom tank, it is our experience that the species in one tank will not affect the growth of species in the neighboring tanks. And, due to the low consumption of electricity, the system can be operated on a cost-effective basis.

TEN RULES FOR SUCCESSFUL PROPAGATION OF SOFT CORALS

1. Never cut a coral if you believe it is not doing well, even if it is fully expanded and shows the species-specific growth form and growth rate. A suffering coral that has bacterial infections or is being held under bad conditions, such as the wrong lighting, high nitrate/phosphate values or unnatural pH/salinity values, should not be cut because it will very likely not be able to fight off attacking microorganisms.

2. Soft corals should only be cut using a scalpel or razor blade. Never use scissors because the shearing effect may “squeeze” the tissue and cause it to bruise, which can quickly become infested with microorganisms.

3. If you produce more than a few fragments, limit yourself to only one species, because the mother corals and the fragments of many species tend to set free large amounts of secretions when their tissue is being cut. Those secretions will partly be distributed in the tank system and can affect the condition of other corals.

4. If you stock the coral fragments in a bowl or bucket for a while before doing the substrate attachment (because you are still busy creating fragments), make sure the amount of water given to the fragments is sufficient and the temperature remains stable.

5. If the coral fragments belong to a species that produces plenty of mucus secretions when the tissue is cut, you might have to change the water in the bowl or bucket where you store the fragments. If the concentration of the secretions gets too high, the coral fragments might suffer.

6. Never keep fragments of different species or genera in the same bowl or bucket. Even though it is just for a short period of time, the secretions released to the water can severely damage each other.

7. When fragments have been set on the substrate, as much as possible they should not be placed in different environmental conditions with different water values. Though all the corals have a certain ability to adapt to different environmental conditions, the cut coral fragments are severely injured and might be unable to survive under different conditions.

8. Place the coral fragments under the same spectral light composition and light intensity as the mother coral has been living under. Up to a certain limit the corals can adapt to changes in illumination, but the separation from the main coral has a drastic impact on the coral and the healing process of the tissue, as well as its ability to defend against attacks of microorganisms. It could be fatal if at the same time it has to adjust to different lighting conditions.

9. If possible, place the fragments with only the same species in a separate tank. This provides the best conditions and the highest survival rates, especially if the mother coral has also been held under those conditions.

10. Many soft corals tend to develop tissue damage if the newly cut tissue is placed on a substrate without having healed first. It is advisable to keep the fragments unattached in the aquarium for about one or two weeks until the cut tissue has been regenerated and the wound is healed. Provide good lighting and a current that is strong enough to supply oxygen, but does not blow away and relocate the fragments. Some coral species (e.g. Nephthea species) will even try to lift up the cut tissue into the water current, probably to improve the healing process by enhancing the oxygen supply.

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