This is a very difficult topic to learn about, as for the most part, not enough scientific study has been completed yet. Coral disease research really did not get a lot of focus until the mid 1970s with many of the common diseases only becoming properly identified in the early 1990s. With the increasing levels of pollutants in the waters of the coral reefs, combined with the effects of global warming, more and more diseases have be developing, along with the frequency they are being found in among the ocean’s coral reefs.
This is (IMO) a very serious threat to the long-term health of our coral reefs today. For example, White band disease has had a devastating impact in the coral reefs in the Florida Keys (killing ~95% of all Acropora SPS corals), and in the Caribbean (infecting ~50% of the shallow water, mostly Elkhorn SPS corals within the first five years after this disease was discovered there). During the past 10 years, the Caribbean coral reefs are being affected more and more each year. New diseases have even started to surface that affect coralline algae (Coralline Lethal Algae Disease) which could also have a significant impact on health of our coral reefs.
Common Elements that Contribute to Disease
Two common elements in all coral disease causes / factors are: stress from any environment factors, and/or water parameter changes. These environmental factors can include: stress/injury from opportunistic organisms such as nematodes or flatworms, and bites/nips from fish or invertebrates combined with the presence of certain types of bacteria and/or fungus. The most common elements of water parameters that can lead to coral diseases are higher than normal temperatures and higher than normal nutrients in the water (typically Nitrate levels 5 ppm or higher and Phosphate levels 0.5 ppm or higher). SPS (stony polyp corals) are more prone to coral diseases as compared to other corals due to fact that SPS are less tolerant to changes in water parameters and not very tolerant of less than ideal water parameters.
In most cases, the exact causes of the majority of coral diseases is still unknown, along with a understanding of why some coral disease only effect a small number of species and others effect a wide range of corals. Most of the current studies being completed today are focused on identifying the pathogens that cause disease and understanding how other corals develop resistance to these diseases.
Removing and treating a coral just as you would with a sick fish is not recommended. That typically would add more stress to the coral which would help the progress of disease regardless of the treatment applied. Adding medications to your tank is often out of the question due to the negative side effects it can have on the rest of the tank. Not to mention most coral medications are still in the experimental stages (and not yet available for sale to hobbyists). There are two fairly successfully strategies when dealing with coral disease: 1) Improving and stabilizing water parameters, and 2) In the case of corals that can be fragged, fragging the coral to save some of the healthy coral and remove/dispose of the infected areas.
There are is at least one treatment option that is currently being tested. This experimental treatment involves dosing a tank with non-pathogenic bacteria. The theory behind this is the non-pathogenic bacteria will out compete the pathogenic bacteria for resources preventing its growth in the aquarium and consequently helping to prevent the coral diseases related to bacterial infections. However, it is not clearly understood which type(s) of pathogenic bacteria actually leads to a bacterial infection in corals which makes this testing a little time consuming and problematic. I’m looking forward to reading about the results of this testing.
Some Preventative Measures:
As all of you football fans out there already know, the best defense is a good offense. It is always easier to attempt to prevent a disease rather than trying to treat it. Following these few simple guidelines will help you do that.
– Maintaining water parameters close to that of actual sea water of the coral reefs
– Maintaining the above mentioned water parameters stable.
– Weekly water changes to replenish trace elements.
– Using coral dips prior to adding new corals to your tank.
Identifying Coral Diseases
Many coral diseases (especially with SPS ) have symptoms that look very similar to other coral diseases, making proper identification difficult. This becomes even more problematic when trying to tell the difference between tissue damage (from fish nipping or other corals) and a coral disease.
The terminology used can also create some difficulties. Diseases effecting SPS will be commonly be referred to as either Rapid tissue narcosis (RTN) AKA Rapid Wasting Syndrome, or slow-tissue narcosis (STN). Up until a few years ago, RTN and STN were thought to be actual diseases. Through further scientific study, a more specific disease has been identified and discovered to be the cause of RTN and STN. These are now common terms (not actual catalogued diseases) used to describe an actual condition of the coral due to the difficulties that come with trying to properly identify the disease.
The below will help you identify which type of disease you may be dealing with. At the end of this article you will find links to some helpful sites with pictures to which can also help you identify them.
Name: Black-Bad Disease
Symptoms: In almost all cases there is a noticeable, black colored narrow band, about 1/8 to 1/2 inch in width which moves along the surface of the coral, consuming the tissue as it passes over the surface. This will leave the coral’s skeleton exposed. Black band is primary a SPS disease which can affect many different species of SPS and some LPS corals.
Cause: For the most part the causes are still unknown. However, in the majority of cases, cyanobacteria in combination with another bacteria called Phormidium corallyticum will cause this diseas
Name: White-Band and White Plague Disease
Symptoms: It can be identified by a white band that starts at the base of a coral. It will progress from there, moving towards the tips, until the coral is completely dead. As the moves from the base to the tip, the flesh dies and falls off the skeleton. This disease can move at rate of up to 1/10th inch or more per day. Very similar white band disease is white plague disease. The physical symptoms appear the same white plague diseases. The only visible difference is that white plague moves faster (consuming up to 1/8 of an inch or more of tissue each day) and effects mostly Milleporas. White-band disease affects a larger range of corals and is prominent in SPS corals, specifically certain Acropora like Elkhorn and Staghorn, but has been found other species of branching corals in the Indo-Pacific area.
Cause: Remains unknown. Although marine scientists do believe a certain type of bacteria will lead to both of these diseases, though completed studies have so far proven inconclusive. In some cases of white band disease, the pathogen responsible has identified as Serratia marcescens, which is a common fecal intestinal bacterium found in many different species of fish and animals.
Name: Yellow Blotch Disease
Symptoms: Yellow blotch disease starts as circular spots of translucent tissue with a yellow color tone, or as a narrow band of pale tissue at the coral’s base. The areas surrounding the affected areas will remain / keep their natural or normal coloring and look healthy. As the disease progresses, the tissue in the center of the patch dies, and exposed skeleton which is usually followed by algae forming on the exposed skeleton as these spots as the grow. This disease mostly affects some of the star corals and brain corals but can be found on other types of LPS and SPS.
Cause: Still Unknown. What is known is that the bacteria associated with Yellow blotch disease produces the characteristic pale yellow lesions and eventually kills the zooxanthellae algae within the coral eliminating the coral’s ability to complete photosynthesis
Name: Red Band Disease
Symptoms: This disease usually starts as dark purple, brown, or dark red circular patches of tissue, that are scattered on the surface of a colony. These patches are also found in irregular shapes. The discolored tissue grows in size, killing the tissue as it gets larger. When the polyps become darkened, they will often appear smaller in size than normal polyps. This disease is most commonly found on starlet coral and blushing star corals.
Cause: Mostly Unknown. Study have shown the presence of a bacteria called Beggiatoa, but no clear indication linking this bacteria to an actual cause as of yet.
Name: Coral Bleaching
Symptoms: The color of the corals flesh become translucent, allowing the skeleton to become visible through the coral’s tissue. This can be one of the easier conditions to recognize as the tissue remains on the coral. Bleaching occurs when the symbiotic algae (zooxanthellae) found in almost all living coral tissue is lost / expelled from the coral. The zooxanthellae is responsible for giving healthy coral a brownish or greenish coloration or color undertone. There can also be a partial bleaching when only some of the zooxanthellae are lost. A partial loss of zooxanthellae affects growth rates and overall health of the coral, leaving it at high risk of other coral diseases, while a complete loss is normally fatal. This disease can affect almost any type of coral.
Cause: There are several conditions that can cause bleaching: increases in lighting / ultraviolet radiation, extreme temperatures, extreme temperature changes, extreme salinities, extreme changes to the salinity, and too high levels of water flow are the most common. This could also be a coral’s natural reaction to an infection (bacteria, fungal, or parasitic) which further complicates a proper diagnosis
Symptoms: This disease will appear as white or purple spots randomly appearing all over the coral. As these spots get bigger, the disease will kill the tissue as these spots grow. It mostly affects soft corals originating from the Caribbean Sea and is very common in sea fans and sea whips.
Cause: Aspergillosis is caused by an infection of a fungal pathogen called Aspergillosis sydowii.
Name: Dark Spot / Black Spot Disease
Symptoms: This disease can be identified by its dark colored spots appearing at random across surface of the coral. The coloring can also be dark brown or dark purple in color. These colored spots may or may not grow in size. Sometimes the dark spots will grow, consuming the coral’s tissue as it does. It has been known to affect both SPS and LPS corals.
Cause: Still unknown. There has not yet been any one bacteria or fungus linked to cause this disease.
Name: White Pox / White Spot
Symptoms: The coral will start to show white spots at random on its surface. Over a short period of time, more and more spots will appear. Most of the time, these spots will come to form a band across the coral’s surface, but this doesn’t happen in all cases. These white spots will increase in size very quickly as the bacteria starts to consume the coral’s tissue. This is most commonly found on SPS and some LPS corals. It is very difficult to tell the difference between this disease and damage due to fish / invert bites. It has been found in both LPS and SPS corals.
Cause: It is caused by a gram negative bacteria called Serratia marcescens
Name: Brown Lime or Brown Jelly Disease
Symptoms: You will first notice brown filaments, or masses floating over and above a coral. This typically is the first sign of the disease. The brown filaments tend to develop slowly at first followed by explosive growth of a thick brown slime covering the coral. This can affect almost all corals and is very common in LPS corals.
Cause: This is a bacterial infection that takes hold when a coral gets physical damage, combined with less than ideal water quality.
Treatment: The below link can be very helpful in the identification of brown jelly disease and suggest treatment options that may help
The above article is based on what I had learned dealing with a two separate occurrences of finding a coral disease and the information that I researched when trying to identify and determine how to handle that situation. As scientific studies continue to uncover more information on these diseases, it will become even more important to identify the disease should specific treatments become available. These are the diseases that I have come to understand as the most common ones encountered in the hobby, based on my limited experience dealing with coral diseases, combined with those that I have read about.
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Below are some of the websites I found a lot of pictures showing the above diseases and some of the information. These pictures that can help you identify any of the above described coral diseases.