Aquascaping is more than simply placing the live rock and corals in a tank in a random fashion. Careful planning is crucial in that not only is it necessary to provide for an aesthetically pleasing tank, but it also determines in many instances the long-term health of the corals. One of the most frustrating aspects of keeping a reef tank is to lose a coral unnecessarily. One of the biggest reasons for this loss is improper placement of the coral. Improper placement can result in one coral falling into another if it is not positioned properly. In addition, if inadequate space is provided when the corals are introduced, they will eventually grow into each other; which can result in aggression between them and the eventual demise of one or both. For these and several other reasons outlined below, placing corals in the proper spot in a reef tank is crucial to the long-term success of the inhabitants.
With the dramatic improvement and widespread use of metal halide lighting and the increasing availability of new coral species, extra consideration needs to be taken as to where corals should be placed. In addition, coral placement to reduce aggression needs to be taken into consideration because many of the corals that we are now keeping are much more aggressive than species we used to keep. This aggression has also become more of a problem as a result of our being more successful at keeping corals in general because now corals grow to much greater sizes than they did in the past. As the size of these corals increases, so too does their proximity to each other and as a result more of their aggressive nature manifests itself. While their aggressiveness was hardly observable and not a problem when many of these corals were small, their effect on neighboring corals becomes dramatically noticeable when they grow to their normal size.
Before describing the placement of corals, a brief description of coral aggression will illustrate the need for adequate spacing between corals. This spacing of corals is important as corals will grow to their full potential only when sufficient room is provided. When looking at pictures of a reef, the first thing noticed is the diversity of life. All spaces on the reef are filled with different organisms suited to fill every niche. This diversity is the result of the organisms evolving through competition. The factor underlying this competition is aggression; both subtle and overt.
This subtle aggression takes the form of gradual conflicts that occur slowly on a continuous basis. Subtle aggression is particularly prevalent among corals as a result of their constant battle for survival. Corals have to cope with currents, predation by fish and other invertebrates, as well as competition from neighboring corals for light, nutrients and food. Consequently, corals have developed several specialized mechanisms for protection and competition with other corals. These include sweeper tentacles, mesenteric filaments, and terpenoid compounds (Ates, 1989).
Sweeper tentacles are the most common of these defense mechanisms in hard corals. These mouthless elongated tentacles form the outermost portion of the coral colony and act as a "patrol" along the periphery. When these tentacles encounter a competing coral, it may attack the competing coral and literally "burn" the offending coral to the point of either killing it or severely damaging it. This "burning" is the result of specialized stinging cells called nematocysts being present in these tentacles. The chemical present in these nematocysts is an alkali toxin similar to bee venom. This may be why corals are said to "sting one another". The relative toxicity of these tentacles differs among various species of corals, as does the length to which these tentacles can elongate (Sheppard, 1982). This degree of toxicity is important in that if two corals fall into each other the relative toxicity of their nematocysts will determine how long they can be in contact before serious injury results. Some corals will be killed after falling into another coral after just fifteen minutes of contact. When two corals have relatively equal toxicity in their nematocysts it is possible for them to kill each other when they fall together. This is why it is important to take precautions to prevent corals from falling into one another.
The length of these sweeper tentacles is not correlated to the length of the normal coral polyp and may in fact be many times longer. One of the most dramatic illustrations of this is in the sweeper tentacles present the coral Pavona cactus, a small-polyped stony coral who's branches are thick and resemble potato chips. Despite the fact that the branches of this coral are only several millimeters thick, the sweeper tentacles that come out may be four or five centimeters long. Another example of dramatic elongation of sweeper tentacles is seen in the sweeper tentacles of the Crystal Coral (Galaxea fascicularis). In this coral, normal polyps are only one to two centimeters long while sweeper tentacles have been seen that are 30cm. long. These sweeper tentacles are especially toxic and often clear the area completely of any other invertebrates within the colony's proximity. Therefore, when selecting this coral, care should be taken to provide abnormally wide spacing between it and other corals.
These sweeper tentacles not only appear when a coral is placed in close proximity to another, but they also seem to result when a coral senses the presence of another aggressive coral. I have observed this phenomenon first hand with my Crystal coral. When first placed in my tank no sweeper tentacles appeared during the first three months. However, a Hammer coral (Euphyllia species) was placed in this same tank, the sweeper tentacles appeared within three days. These tentacles also appear to be able to sense where the competitor is located in that regardless of where a Crystal coral is placed relative to the Hammer coral, the sweeper tentacles always develop toward the Hammer coral. Interestingly, the Euphyllia also developed sweeper tentacles, but they were present only on the side nearest the Crystal coral.
In addition to these tentacles, several hard coral species can produce mesenteric filaments from their stomachs. Corals of the genera Favia, Favites, Scolymia, Pavona, and Cynarina all have this capacity (Chadwich, 1987). These filaments can also kill or devour other coral polyps through a process similar to digestion. Some corals even have the capacity to produce both of these defensive structures, enabling them to fight a battle on several fronts (Wallace, 1984).
These two defense mechanisms are utilized predominantly by hard corals. It is only until recently that sweeper tentacles have been observed in the soft corals. I had never read or heard about soft corals producing these tentacles, but in my friend Dr. Michael Fontana's 1000 gallon reef aquarium I observed a Leather coral (Sarcophyton sp.) producing very fine sweeper tentacles that were irritating a nearby zooanthid colony. This tentacle did not appear to be as well defined as the sweeper tentacles produced by the stony corals, but they appeared to produce the same result.
The soft corals generally compete with the hard corals by releasing terpenoid or sarcophine compounds into the water to injure or impede the growth or neighboring corals and then overgrow these impeded individuals in a process called allelopathy (Delbeek and Sprung, 1994). Like their name implies, these compounds are similar to turpentine in chemical structure and in most instances are just as toxic. By releasing these compounds, the soft coral injures neighboring stony corals and can thus grow above them and eventually block out the light that they are both dependent upon and thus kill the underlying hard coral.
In a reef aquarium, this aggressiveness can have severe and dire consequences. If it is allowed to progress to its conclusion, a large and expensive coral head could die. If these sweeper tentacles or mesenteric filaments are observed, the reef keeper should make sure to move all invertebrates in their proximity out of the way. However, if these tentacles have reached their target they should immediately be removed from the injured animal. If a portion of tentacle remains attached it should be physically removed, otherwise the toxic substances these tentacles secrete will continue to work and will kill the colony to which they have become attached. Fortunately, if the reef tank is well maintained and no microalgae are allowed to grow on the skeleton, the coral colony may recover and grow back over the damaged area.
(CONT)
With the dramatic improvement and widespread use of metal halide lighting and the increasing availability of new coral species, extra consideration needs to be taken as to where corals should be placed. In addition, coral placement to reduce aggression needs to be taken into consideration because many of the corals that we are now keeping are much more aggressive than species we used to keep. This aggression has also become more of a problem as a result of our being more successful at keeping corals in general because now corals grow to much greater sizes than they did in the past. As the size of these corals increases, so too does their proximity to each other and as a result more of their aggressive nature manifests itself. While their aggressiveness was hardly observable and not a problem when many of these corals were small, their effect on neighboring corals becomes dramatically noticeable when they grow to their normal size.
Before describing the placement of corals, a brief description of coral aggression will illustrate the need for adequate spacing between corals. This spacing of corals is important as corals will grow to their full potential only when sufficient room is provided. When looking at pictures of a reef, the first thing noticed is the diversity of life. All spaces on the reef are filled with different organisms suited to fill every niche. This diversity is the result of the organisms evolving through competition. The factor underlying this competition is aggression; both subtle and overt.
This subtle aggression takes the form of gradual conflicts that occur slowly on a continuous basis. Subtle aggression is particularly prevalent among corals as a result of their constant battle for survival. Corals have to cope with currents, predation by fish and other invertebrates, as well as competition from neighboring corals for light, nutrients and food. Consequently, corals have developed several specialized mechanisms for protection and competition with other corals. These include sweeper tentacles, mesenteric filaments, and terpenoid compounds (Ates, 1989).
Sweeper tentacles are the most common of these defense mechanisms in hard corals. These mouthless elongated tentacles form the outermost portion of the coral colony and act as a "patrol" along the periphery. When these tentacles encounter a competing coral, it may attack the competing coral and literally "burn" the offending coral to the point of either killing it or severely damaging it. This "burning" is the result of specialized stinging cells called nematocysts being present in these tentacles. The chemical present in these nematocysts is an alkali toxin similar to bee venom. This may be why corals are said to "sting one another". The relative toxicity of these tentacles differs among various species of corals, as does the length to which these tentacles can elongate (Sheppard, 1982). This degree of toxicity is important in that if two corals fall into each other the relative toxicity of their nematocysts will determine how long they can be in contact before serious injury results. Some corals will be killed after falling into another coral after just fifteen minutes of contact. When two corals have relatively equal toxicity in their nematocysts it is possible for them to kill each other when they fall together. This is why it is important to take precautions to prevent corals from falling into one another.
The length of these sweeper tentacles is not correlated to the length of the normal coral polyp and may in fact be many times longer. One of the most dramatic illustrations of this is in the sweeper tentacles present the coral Pavona cactus, a small-polyped stony coral who's branches are thick and resemble potato chips. Despite the fact that the branches of this coral are only several millimeters thick, the sweeper tentacles that come out may be four or five centimeters long. Another example of dramatic elongation of sweeper tentacles is seen in the sweeper tentacles of the Crystal Coral (Galaxea fascicularis). In this coral, normal polyps are only one to two centimeters long while sweeper tentacles have been seen that are 30cm. long. These sweeper tentacles are especially toxic and often clear the area completely of any other invertebrates within the colony's proximity. Therefore, when selecting this coral, care should be taken to provide abnormally wide spacing between it and other corals.
These sweeper tentacles not only appear when a coral is placed in close proximity to another, but they also seem to result when a coral senses the presence of another aggressive coral. I have observed this phenomenon first hand with my Crystal coral. When first placed in my tank no sweeper tentacles appeared during the first three months. However, a Hammer coral (Euphyllia species) was placed in this same tank, the sweeper tentacles appeared within three days. These tentacles also appear to be able to sense where the competitor is located in that regardless of where a Crystal coral is placed relative to the Hammer coral, the sweeper tentacles always develop toward the Hammer coral. Interestingly, the Euphyllia also developed sweeper tentacles, but they were present only on the side nearest the Crystal coral.
In addition to these tentacles, several hard coral species can produce mesenteric filaments from their stomachs. Corals of the genera Favia, Favites, Scolymia, Pavona, and Cynarina all have this capacity (Chadwich, 1987). These filaments can also kill or devour other coral polyps through a process similar to digestion. Some corals even have the capacity to produce both of these defensive structures, enabling them to fight a battle on several fronts (Wallace, 1984).
These two defense mechanisms are utilized predominantly by hard corals. It is only until recently that sweeper tentacles have been observed in the soft corals. I had never read or heard about soft corals producing these tentacles, but in my friend Dr. Michael Fontana's 1000 gallon reef aquarium I observed a Leather coral (Sarcophyton sp.) producing very fine sweeper tentacles that were irritating a nearby zooanthid colony. This tentacle did not appear to be as well defined as the sweeper tentacles produced by the stony corals, but they appeared to produce the same result.
The soft corals generally compete with the hard corals by releasing terpenoid or sarcophine compounds into the water to injure or impede the growth or neighboring corals and then overgrow these impeded individuals in a process called allelopathy (Delbeek and Sprung, 1994). Like their name implies, these compounds are similar to turpentine in chemical structure and in most instances are just as toxic. By releasing these compounds, the soft coral injures neighboring stony corals and can thus grow above them and eventually block out the light that they are both dependent upon and thus kill the underlying hard coral.
In a reef aquarium, this aggressiveness can have severe and dire consequences. If it is allowed to progress to its conclusion, a large and expensive coral head could die. If these sweeper tentacles or mesenteric filaments are observed, the reef keeper should make sure to move all invertebrates in their proximity out of the way. However, if these tentacles have reached their target they should immediately be removed from the injured animal. If a portion of tentacle remains attached it should be physically removed, otherwise the toxic substances these tentacles secrete will continue to work and will kill the colony to which they have become attached. Fortunately, if the reef tank is well maintained and no microalgae are allowed to grow on the skeleton, the coral colony may recover and grow back over the damaged area.
(CONT)
