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Presented by Charles & Linda Raabe
Mactan Island, The Philippines
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  While most problems that occur with corals stem from water quality and lighting issues, there are the occasional problems with disease and parasites of corals. Just as with everything else we keep in our systems, water quality plays a major role in the health of our corals, being put under any type of stress makes any animal more susceptible to other problems, such as disease. As such, any attempt at a cure or a solution should take water quality into account first and corrected if need be.

  I have never personally had to deal with many coral diseases or parasites, yet. But since it is my goal to provide or at least gather as much information as possible about any and all topics within our hobby, I have gathered the following links to what I feel are the best informational sites on the web concerning diseases and parasites of corals. I hope I have at least, saved you some searching time.

Noted Coral Problems / Reactions

Coral Bleaching  -  " What is bleaching? Bleaching occurs in corals that maintain a symbiosis with various types of dinoflagellates called zooxanthellae. By one common definition, bleaching is the release, rejection, or loss of zooxanthellae from coral tissue.

Bleaching and Disease "Look Alikes" -  "In this article, I limit myself to those corals having white areas that are not caused by bleaching or disease"

Starvation  -  "We investigated the effect of zooplankton feeding on tissue and skeletal growth of the scleractinian coral Stylophora pistillata. Micro colonies were divided into two groups "

  Tissue Recession  -  Not a very specific term other than to describe an effect of any number of causes, which could be anything from poor water quality, such as high phosphate levels, poor water flow, too much or not enough light, starvation, abrasion wounds, puncture wounds and of course any number of diseases and parasites. I suspect the majority of causes stem from an improper environment and would be on the top of my list of things to check.
   Note:  This effect can be very confusing because while it may be an actual pathogen at work, the appearance of a bacterial line forming on the edge of the tissue loss may only be the result of bacteria consuming the dead tissue matter just as it would any other dead animal. In short, a bacterial clean up crew could easily be mistaken for the cause of the coral's tissue loss while ignoring other possibilities such as poor water quality, nutrition, lack of water flow and so on.

  Coral Allelopathy : It is extremely common to see any number of aquariums keeping a wide assortment of corals species all within the same aquarium. This is extremely stressfull to the "sps" corals when they are subjected to the toxins released by other corals, such as many of the "soft" corals, the Coralliamorphs (mushrooms) and Gorgonians. All of which, when enclosed in such relatively small amounts of water makes for a very toxic soup. Even other stony coral species can be the cause as well. Species such as Galaxea, Hydnophoras and even Anemones all release either free floating stinging cells or other irritants as they shed mucus.

  Coral Neoplasia : A neoplasm is an abnormal mass of tissue that grows through the proliferation of undifferentiated coral cells. These cells grow and multiply more rapidly than normal and lack the structural organization and function of the normal tissue which gives the calcified formation the appearance of being another organism growing on the coral.   The exact cause of this condition is unknown but is thought to be a genetic mutation that may be the result of environmental conditions.  Please see the above link for more information.

Photo Credit : LarryK  Photo Credit : LarryK
                                                        Coral Neoplasm :  Photos by LarryK

  Coral Hyperplasia :  Some corals can have circular areas in which the pattern of the corallites are distinctly different, usually enlarged and protruding above the surface of the colony and altering the pattern of the corallites adjacent to it so that it appears to be compressing the growing tissues. Microscopic examination of tissues from such an area revealed an increase in the number and size of cells and proliferation of all types of tissues. This type of growth has been termed a hyperplasm. It appears that such growths originate from a single budded polyp that undergoes localized, rapid growth, while retaining functional fusion of its tissues with those covering the normal colony skeleton.  As with Neoplasia, the cause of this skeletal or growth anomaly is unknown but is also thought to be a genetic mutation brought on by environmental factors. 

Photo by E.C. Peters
      Coral Hyperplasm : Photo by E.C. Peters

  Coral Starvation :  Yes, it is very possible to starve a coral, even those that are considered to rely heavily upon light for their needs. When tanks are low in nutrients, the corals have lower amounts of zooxanthellae and their pigment content declines. If there is not enough Nitrogen to produce protectant pigments like MAAs and probably other things like SOD and other enzymes and proteins, then the effects of UV and strong lighting become too much, causing the demise of the coral.

  Tissue / polyp expansion : At times what we perceive as the coral doing well, the expansion of polyps such as a goniopora for example, may also be an indication that it is attempting to gather more light in a poorly lighted aquarium. In the LPS coral species, besides an attempt to gather more light, it may also be an attempt to flush itself of poor water conditions or a feeding attempt to gather nutrients from excessively nutrient poor water. If this condition occurs after you have made a change to the system, such as increased carbon use, or a binding agent, that could be the most likely candidate for the cause of the problem.

  Coral Tissue Bubbles : At times, a coral may exhibit what appears to be bubble shaped voids under the corals tissue, its usually a damage induced reproductive strategy that (may) lead to a polyp bailout. It can simply be caused by stress (as with light shock from a change of lamps, increase in light, sudden use of carbon or water changes that drastically clarifies water, etc)... or it can be stimulated by a burn from another attacking coral.


  Photo by Charles Raabe    Is this Rapid Tissue Necrosis or a Parasite at work?  Of course having to figure out what you are actually looking at needs to be accomplished before a treatment plan can be decided upon. Since most parasites / predators are nocturnal, it may take a few nights of diligent watching to determine if there is a predator or not at play. I must stress that environmental factors should be ruled out first.
   I have seen a great many online questions regarding the loss of Acropora species as well as having other corals slowly becoming unhealthy and eventualy dieing. A great many times, this can be attributed to an improperly stocked aquarium. In that, we all would like to see a nice mixture of coral species within our systems. Yet this same mixture will most always lead to trouble in being able to maintain the more sensative species such as the acroporas. Of course, elevated levels of nutrients and the overall quality of the water can play a large role as well. But if you are trying to keep coralliamorphs (mushrooms), gorgonians, large polyped corals and others, such as hydnophora, galaxea or any of the "soft" corals. You are in effect creating a toxic soup within your aquarium through the release of such coral's chemicaly defesensive methods (aleopathy). So if you see your Acropora species losing tissue fairly quickly, you might want to take a hard look at what species you are keeping together. If you wish to keep species such as the Acroporas and Montiporas, I suggest you keep only those species in your aquarium.

  Coral Pathogens Identified for White Syndrome - " White Syndrome (WS), a general term for scleractinian coral diseases with acute signs of advancing tissue lesions often resulting in total colony mortality."

  Characterized Diseases  -  NOAA's Coral disease identification and information

  Uncharacterized Diseases  - " Many coral diseases have not been characterized under peer-reviewed venues. At the present time much confusion and disagreement exists about these diseases "

  Field Guide to Coral Diseases  -  "  This section of the guide presents some of the common coral diseases. For each disease an illustrated description of the disease characteristics is given as well as an illustrated list of species the disease is known to afflict.

  Information on Coral Diseases  -  "  This cross section of disciplines was an intentional effort to enlist techniques and ideas from various fields to help accelerate the slow progression of advances in the study of coral disease. "

  Major Reef-building Coral Diseases  -  "  Coral diseases and syndromes generally occur in response to biotic stresses such as bacteria, fungi and viruses, and/or abiotic stresses such as increased sea water temperatures, ultraviolet radiation, sedimentation and pollutants. One type of stress may exacerbate the other (Santavy and Peters, 1997). "


  Bacterial Diseases  -  " Most of the bacteria in the ocean are one kind of Vibrio or another. Many of them are good citizens. Some of them are luminescent, and help deep water fish and squid be bioluminescent. This is a symbiotic relationship between the larger host organism and the bacteria. Moreover, the symbiosis is often intracellular. So Vibrio can get inside cells of higher organisms.  "

  Rapid Tissue Necrosis (RTN)  -  "  RTN has been described in the wild as 'Shut-down reaction' by Antonius as early as the late-70's. So far, I have not seen a paper that describes this as a proper 'disease', per se. (i.e. fulfills Koch's postulates...) "

  Note: From a lot of reading, I have noticed that the only effective treatment of just about any coral disease involves the use of an Iodine dip, there are a few commercially prepared mixes that you can buy. I would recommend the use of a prepared mix over trying to make one yourself. So far, the most popular brand seems to be "Lugols". Keep in mind that all such treatments have to be done outside of the main tank. Do not ever try to treat the entire tank. Also, do not use a freshwater dip on corals, this alone will probably kill the coral.

  Home made Lugols Dip  -  The most common recipe is 10g potassium iodide dissolved in 100ml distilled water, add 5g iodine crystals till dissolved. Be careful with iodine crystals, they are rather caustic and need to be handled with care. Store it in a dark or amber glass bottle away from light. No need to refrigerate.


 A Tip :  Since most parasites / predators tend to be extremely small, I have found that by using my digital camera as a magnifying lens helps to look over a specimen using the camera's zoom capabilities  while watching the camera's monitor screen, if a suspect animal is found, a photo can be taken of it since you already have the camera in focus and aimed at the suspect, which the photo can then be used for further study and also to submit to experts in this field for identification purposes.

Gastropod Parasites and their Coral hosts

  With the wide variety of snail species coming into our aquariums as hitch hikers, we stand a fairly good chance of getting some coral predators as well. Most of these will be small and difficult to detect and are usually only detected when we notice visible damage to a coral . Since such predators are usually always nocturnal, they are best looked for after the lights have been off for a few hours. This same nocturnal feeding behavior is also typical of most other coral predators / parasites.  This is where I have to stress the importance of a quarantine routine, a coral, once in the landscape, makes detection of such problems very difficult to do.

 Feeding Method : Snails such as the drupella genus have specialized mouth parts that are used to rasp away the living tissue of the coral.

 Treatment / Removal Method :  When discovered the visible adults / juveniles can be picked off of the coral and disposed of. It is also recommended that the effected coral be dipped in a lugols (Iodine) solution to kill any possible egg masses left by the adults.

  The below photos are of the species that I have personally found to be feeding on my acropora corals, and were removed right away while having no eggs masses discovered. I am not sure if the lack of egg masses was due to the snails being unable to breed in my system, or if I had just caught them before they had a chance to do so.

Acropora coral predator, very small and hard to seeCoral Predator Time to get it out of the pool!Zoanthid Predator, must be removed. 
              Drupella cornis                                  Coralliophila Sp                                  Unknown species                       Heliacus - Zooanthid predator

Photo by Charles Raabe Photo by Charles Raabe Photo by Stann
           Calpurnus verrucosus                               Primovula sp.                                   Calpurnus lacteus  
        Predator of leather corals                     Predator of Gorgonians                       Predator of soft corals

  Copepods in the Reef Aquarium

  These are probably the most insidious and difficult of the coral parasites to detect and remove owing to their small size and breeding potentials, as well as some species embedding themselves into the coral's tissue as well.

 Treatment(s) :  
 Red Bugs ( harpacticoid copepods )    Note: Any and all treatments should be performed outside of the main tank.

           Acropora "red bugs"


Aeolid Nudibranch Coral Predation

   There are numerous nudibranch and flatworm species that specialize in feeding on specific coral species. Most, but not all of which can only predate a specific coral species, which in itself is a good thing since as a last resort, we can simply remove the effected coral and isolate it for treatment without concern that other coral species may be in danger.

 Treatments:  Note: All treatments should be performed outside of the main aquarium in a quarantine setting.

Two Potential Molluscicides Against Pest Aeolid Nudibranch  - "A molluscicide is a compound that kills molluscs, of which nudibranchs are an unshelled type. Most of the agents I found that are used in terrestrial studies and practice would be toxic to either the aquarium or the coral."

- Metronidazole Is a highly pure, crystalline metronidazole. Use 1 to 2 measures (each about 100 mg) for every 40 L (10 gallons). Repeat every 2 days as required.

- Iodine - (ex. lugols iodine, Tropic Marin pro-coral cure, Seachem reef dip) when used at recommended dosages and times, these medications will kill most if not all adults.  Throughout the procedure it is important to stir the coral in an effort to detach any adults from the coral.   Once the dip is complete, the coral should be inspected for any nudibranch remnants which can be removed using a toothpick.

- Fragmenting - As a last ditch effort, you can also fragment off healthy, nudibranch free sections of the coral and throw away the effected coral areas.

- Manual Removal - Since most nudibranch are very prey specific, you can also remove the effected coral species from the main aquarium and place into a quarantine tank. Once removed, the coral can then be closely inspected for adult nudibranch and egg masses which can be manualy picked off and removed. The only downside to this method is that it can take a good many months for the nudibranchs that were left behind in the main aquarium to die off from starvation.

- Levamisole - A drug created to treat worm infestations in animals. It acts as a contact poison blocking nerve transmission to kill or stun the parasite. This drug has proven to be a very effective treatment for both parasitic nudibranchs and flatworms.  A recommended minimum dosage of 50ppm for a total duration of 10 hours or more is advised. At this dosage the nudibranchs become paralyzed and fall off the coral. Note, Levamisole is only available with a prescription from a licensed Veterinarian.

Natural predators - Fish such as certain members of the Pseudocheilinus (Sixline wrasses), Coris (Coris wrasses), and certain Thalassoma (Banana wrasses) Genus’ are known to actively feed on these nudibranchs.  While this can be an effective control mechanism, it may not completely get rid of all nudibranchs.  Most of these wrasses lack the mobility to get to most of the places where the nudibranchs hide.  There are many other natural predators, including certain crabs, several other nudibranchs, and perhaps more, however these are not as commonly available to the aquarist as the aforementioned fish.

Freshwater dipping is a very dangerous yet very effective treatment option. Freshwater creates a large difference in osmotic pressure between the inside and outside of the body of the nudibranchs. This sudden change in osmotic pressure causes the cells to rupture and quickly kills the nudibranch. The dip must be done with de-chlorinated water adjusted to the pH and temperature of the tank and must last no longer than 15 seconds. Note, this is not recommended as a safe treatment option as it can be very harmful to the zooxanthellae in the coral, longer exposure times can and will kill coral. I would not recommend this method unless all else has failed.

Photo by Charles RaabePhoto by Charles Raabe Photo by Charles Raabe
 Nudibranch consuming a Montipora   Acropora predator (Aeolid nudibranch)                             Porites Predator and its egg mass


   These potential problems not only can be a direct cause of  coral damage but as most of us have found out already, can also be a secondary problem in that any damaged coral skeleton can easily be used as a surface area for the growth of many other life forms to take up residence on. Once established, the coral will find it all but impossible to regain any lost ground simply because the sponge and/or algae are so much faster in their growth that the coral just can not compete, and may find itself losing even more ground.

  Treatment : In the case of sponge, it may just be a case of having to cut out / off the effected area of the coral. For algae, keeping the surface cleaned of it by either manual removal or placing a herbivore snail onto the area on a regular basis to do the cleaning.  For cyanobacteria, increasing the water flow over the corals will usually prevent this problem, assuming of course that phosphate levels are also controlled.
              Encrusting sponge                                Algae competition                             Surface CyanoBacteria


  These two animal groups are a good reason to always do your best to identify any and all hitch hikers into your system. While interesting and beautiful, many of these animals are in fact very predatory. A few examples are shown below.

  Treatment : Only physical removal as they are found

  Photo by Charles Raabe   Photo by Charles Raabe   Photo by Charles Raabe
     Unidentified Coral Predator - Found consuming an entire Lithophyllon coral colony within my system.

  Photo by Charles Raabe   Photo by Charles Raabe
             Echinaster luzonicus                                  Cidarid Urchin  


   While I have only seen or found a few species of worms that could be considered a threat to corals,  they are none the less a few species that can become a problem for corals. I do want to stress that the vast majority of worms found as hitch hikers are valuable members of a clean up crew and it is very important to properly identify the species of worm before you condemn it. Shown below are examples of worm genus groups that do have members that could pose a risk. For identification of worm species, please see the relevant section of my hitch hiker pages.

  Treatment : Actively trapping them or introducing a biological control to the aquarium such as some wrasse species.

  Photo by Charles Raabe Photo by Charles Raabe Photo by Charles Raabe
        The  Amphinomidae                      The Syllidae                            The Eunicids

 Burrowing Worms :
 While unable to obtain the actual organism that created the below problem, it is apparent due to the formation of calcified tubes that a worm species is most likely the cause.  As this pest species first infests a coral colony, it first builds its own structure on top of the corallite's walls, which block light and water flow to the underlying polyp.  The polyp then slowly dies over the course of weeks and months allowing these and other organisms to further colonize the coral skeleton substrate, effectively killing the coral colony little by little.

   Formation of dead and soon to be dead areas on the coral colony.  Even in seemingly healthy areas of the colony, these organisms are already present as individual formations on top of the corallites.  In the most affected areas, the organism has burrowed through the walls of the corallites.

 Photo by Charles Raabe Photo by Charles Raabe Photo by Charles Raabe
Photo by Charles Raabe Photo by Charles Raabe Photo by Charles Raabe

Below, what appears to be a burrowing worm that leaves behind its drilled coral skeletal fragments in a ball of mucus, below the mucus ball the coral's tissue is dead.
 Photo by Charles Raabe Photo by Charles Raabe Photo by Charles Raabe


  While normally not direct predators of corals, they can cause enough damage as to cause the coral's death . Many of the xanthid species of crabs burrow into coral skeletons as shelter and as they themselves grow, they enlarge the cavity, much to the detriment of the coral. Other species, such as some of the arrow crabs will readily learn that they can rip open a coral polyp and remove the gut contents of the coral polyp. There are of course very small species of crabs that do act as a true parasite of corals.

   Treatment :  Physical removal

  Destructive xanthid rock crab   Destructive Xanthid type crab, outta the pool!!!   Not normaly considered reef safe
                Xanthid Crab                                          Xanthid Crab                                        Arrow Crab    

  All of the above demonstrates another very good reason to use a strict quarantine procedure for everything that you will place into your aquarium. As small as most parasites are, they will be much easier to detect in a small quarantine than once placed in the main tank. It will also help to prevent the spread of such problems.


  It is quite common to find any number of sessile worms, crustaceons or snails that have bored through a corals tissue to get at a substrate to attach onto. Such animals while normaly small in comparasin to the coral and pose no real danger to the coral, they can however start to become a problem in enclosed systems such as our aquariums. If such an animal reproduces well within our systems, their numbers can become so great as to start causing the coral health issues, thankfully this is an extremely rare event.

Photo by Charles Raabe Photo by Charles Raabe Photo by Charles Raabe
               Spionid Worm                                 Flabelligerid Worm                                   Barnacle                                          Vermetid Snail

 There are however, some sessile inverts that are relatively large and if they do invade a single coral polyp, they can cause the death or slow decline of that individual polyp. It would be these that I would take the effort to remove. To do so, remove the coral from the water, very slowly to give the polyp(s) time to retract. Then with a needle nose plier, or a pair of tweezer, pinch or break off the offending animal as close to the coral's tissue as possible without disturbing or damaging the corals tissue. Any remains of the offending animal, such as a calcified tube will be overgrown by the coral in due time.

 Photo by Scott (Dentoid)
         A large invasive barnacle.


   Eric Borneman's Web Forum  -  Ask Eric specific questions within his forum.
  Predators and Parasites of Corals  - There are many species of predators that specialize in eating coral, the most common are nudibranch, snails and copepods. Each predator or parasite will usually have one specific species of coral that they can eat. While any of these predators may destroy a single specimen within our aquariums, the bright side is that the other species of corals within the aquarium are safe.  The removal and treatment of the effected coral will usually stop the predator in its tracks. Most notably nudibranch and "red bugs".


  Coralline Lethal Disease  -  "  A second disease of coralline algae was recognized by Tom Goreau in the Caribbean in 1996. It lacks the characteristic orange color of CLOD, but is lethal, nonetheless.  "

  Coralline Lethal Orange Disease  -  "  Given the importance of coralline algae in contributing material to the reef framework, it was particularly disturbing when a disease of coralline algae was discovered  "

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