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.
-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 propagationâ€).(BELOW)
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.
(CONT)
-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.
-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 propagationâ€).(BELOW)
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.
(CONT)
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