Sometimes a stressed coral may appear to be covered with fine white strings. These are its digestive filaments that can be ejected externally for defensive purposes (see photo chapter 3). Acontia are used to attack neighboring corals and where they contact another species, tissue disintegration is sure to follow. The release of terpenoid compounds by soft corals can also stimulate acontia release in stony corals, as can the presence of other noxious compounds in the water. Supersaturation of oxygen, as can occur from too strong illumination or the administration of pure oxygen into a pressurized "oxygen reactor", will also stimulate the ejection of acontia filaments. In the case of Corallimorpharia (mushroom anemones), rough handling can stimulate the release of acontia. In this case, however, the filaments are typically reabsorbed by the coral in a few hours; no harm done.
Treatment: Allow enough space between corals so that their tissues cannot come in contact. Use barriers if relocation is not possible. Perform a water change if a noxious chemical is suspected and add a fresh amount of phosphate-free activated carbon to remove any remaining toxins. Move the coral into a shadier region if over-illumination is suspected. Adjust the protein skimmer to maintain it's peak performance, so that noxious compounds don't accumulate.
If a stony coral appears to be emitting a lot of clear slimy mucus, it has been physically injured, disturbed by a noxious chemical in the water and/or stung by another coral. It is normal for the coral to shed some mucus all the time, but if the polyps are closed and the mucus is thick and trailing off the coral, it is an indication that the coral is irritated. Please note that some species of stony corals normally release more mucus than others. For example, Turhinaria pelt at a will produce copious amounts of slime when slightly handled, and this is not necessarily an indication that it has been greatly stressed.
Release of some clear mucus from around the mantle and upper surface of tridacnid clams, often with attached air bubbles, is normal. This is a means of getting rid of excess carbon from photosynthesis. Excessive mucus production, which may clog mechanical filters, is a sign of irritation from something in the water. It can also be that a neighboring coral is irritating the clam. John Burleson (pers. comm. 1988) observed that a species of Xenia irritated a Tridacna squamosa, causing it to produce copious mucus, which quickly clogged the mechanical filters in his aquarium.
Treatment: Administer a stronger flow of water and avoid handling the coral too much. Perform water changes if the condition does not improve and add a fresh quantity of phosphate-free activated carbon.
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