Common Coral Diseases And How To Treat Them
Saltwater aquariums look best with colorful corals, but before you add corals into your aquarium, you need to know how to care for them, including familiarizing yourself with common coral diseases.
Let’s dive straight in!
Unfortunately, many coral diseases have similar symptoms to the dreaded rapid tissue loss (RTL) but are something else, which is why it is important to understand the difference between common coral diseases.
Black Band Disease
Image Credit: Laurie Richardson, NOAA
Image Credit: NOAA
Black band disease is one of the easiest coral diseases to spot. If your coral is infected, you guessed it, it will have a black bacterial ring between healthy tissue. However, it sometimes appears reddish-brown depending on how many pathogens are present. The bandwidth of the ring is typically 1 mm-5 cm, spreading 1 mm - 1 cm per day if left untreated.
The bacterium (Phormidium corallyticum, a filamentous cyanobacterium) will continue to kill your coral’s tissues, exposing the skeleton, and eventually killing it. The rapid tissue decay is a result of a sulfur-rich excrement at the bottom of the band.
Black band disease is the only coral disease that has successfully been treated in saltwater aquariums.
So, what can you do?
Clay or marine/underwater epoxy putty mixed with chlorine powder can be placed directly on the infected band to prevent further growth. When placing the mix on the band, be careful not to spread the bacteria further, as this can infect neighboring corals.
Although this is the recommended treatment, there is no guarantee it will cure your corals. However, hobbyists that have treated corals with the epoxy mix have seen a decrease in tissue loss compared to untreated corals.
White Band Disease
Image Credits: NOAA
White band disease, or the white plague, is a bacterial infection, yet the pathogen behind the coral disease is not known.
It is thought that the pathogen Vibrio carchariae and zooxanthellae overgrowth is to blame, but this is still not confirmed. This hypothesis comes from treatment studies in the Caribbean, where antibiotics were used to slow down bacterial growth, indicating that the bacteria is most likely a gram-positive bacteria like V. carchariae.
The good news is, white band disease only infects Acropora corals, however, it is very destructive, which has led to endangering Acropora corals in the wild.
Infected corals will type 1 white band disease will suffer from tissue loss, exposing the skeleton as it progresses up the Acropora coral’s branches from the base to the tips. Acropora infected with type 2, experience the opposite; tissue loss starts at the tips and works its way down to the base. The white bands can expand, reaching a thickness of 10 cm, and can grow at a daily rate of 5 mm.
Now, you may already be familiar with what coral bleaching is thanks to media coverage of the mass coral bleaching event in Australia’s Great Barrier Reef.
Even though coral bleaching is more common in the wild, you shouldn’t disregard it yet, as it can also happen inside your saltwater aquarium!
Coral bleaching is the stress response when temperatures and sunlight are heightened. Inside your aquarium, too much lighting can bleach your corals, turning them ghostly white (hence the bleaching part), as they expel the zooxanthellae from their tissues. A sudden increase in temperature, poor water flow, and physical injuries can also cause coral bleaching.
Fun Fact: If you didn’t already know, it is the zooxanthellae inside your coral’s tissues that give your coral its mesmerizing color!
But wait, there's more...
It's not all doom and gloom yet, as bleached corals, usually can regain their color if you maintain stable water conditions and ensure you are providing the right amount of lighting for your coral species.
Yellow Band Disease
Image Credits: NOAA
Yellow band disease is identified by the distinctive yellow band left on the coral. It is highly infectious and known to rapidly spread and expand, damaging the coral’s tissues.
As the disease attacks the zooxanthellae inside the coral’s tissues, it leads to the same signs and symptoms as coral bleaching.
Brown Jelly Disease
Brown jelly disease/syndrome is a rotten-smelling brown slime that spreads over the coral’s surface. Trust me, if you were to remove your infected coral and take a whiff, you will soon realize what I am talking about!
The actual cause of the brown jelly disease is still unclear, however, we do know that the gelatinous mass of brown slime is made up of bacteria and protozoan ciliates which are visible under a microscope. It is also thought that the jelly feeds off dead tissue when the coral breaks down from stress or an infection, instead of the jelly destroying the coral’s tissue.
There is no known treatment, and many reef hobbyists have unsuccessfully tried antiseptic dips. However, that doesn't mean you cannot try an iodine or hydrogen peroxide dip. But, the best advice, if your coral becomes infected, is to frag it and dispose of the diseased areas.
White Pox Disease
Image Credit: James W. Porter, University of Georgia
Image Credit: NOAA
If your coral gets white pox, it will be covered in irregular white patches caused by tissue loss. The cause is still uncertain, but it is believed to be from a pathogen called Serratia marcescens.
Image Credit: NOAA
As the name suggests, corals with dark-spots disease will form dark brown or purple pigmented areas on the tissue. Dark-spots disease (or dark spots syndrome (DSS)) is common in stony corals like LPS and SPS corals.
While dark-spots disease may not look serious because the tissues remain intact, the inside of the pigmented area still experiences tissue death.
As the pathogens which cause dark-spots disease are unknown, unfortunately, there is currently no treatment.
These are just a few coral diseases, and sadly, most of them have no known cure. Therefore, prevention is the best way to control coral diseases.
If you notice your coral has become infected with any of the above diseases, frag an unaffected area so the coral can develop from the cutting. While it is a difficult decision to make, discarding the infected area or often the whole colony is recommended to prevent it from spreading inside your reef aquarium and infecting healthy corals.
So, what can you do to prevent your corals from becoming infected?
Read on to find out more!
How To Prevent Coral Diseases
To prevent any of the above coral diseases, you should:
- Quarantine your corals before adding them into the aquarium, followed by a coral dip. Coral dips are also great at eradicating unwanted pests!
- Create an ideal environment for your corals (lighting, water flow, etc.).
- Maintain stable water parameters by frequently testing the water and performing regular water changes.
- Provide your corals with enough nutrition, including coral food, supplements, and additives needed for your corals to thrive.
Corals are fantastic additions to any saltwater aquarium, but just like any aquatic life, they require a certain level of care. Providing the best care will prevent corals from becoming sick from common coral diseases such as black band disease, brown jelly disease, and coral bleaching.