There is an established process for designating a bacterium as a pathogen that requires completing a series of experimental steps (e.g. infecting healthy corals with the pathogen and documenting the appearance of disease symptoms). Some of these steps are especially challenging with reef-building corals, so the list of “official” coral pathogens can lag behind the state of our knowledge about likely pathogens.
In this recently added section of the microbiome report, we screen for several suspected pathogens associated with known coral diseases. There is evidence linking these bacteria to coral diseases, but they have not been formally designated as pathogens yet.
Brown Jelly Disease (BJD)
This disease primarily affects Euphyllia corals including hammers, frogspawns, and torches. Like most coral diseases the name describes the symptoms – in this case, the polyp and internal tissues dissolve into a brown gelatinous blob. By the time these symptoms are visible, the symptomatic polyps are doomed and nearby polyps or other colonies are often already infected.
We’ve identified an unclassified member of the Arcobacter genus that is associated with BJD in Euphyllia corals. This is reported as “Arcobacter sp. type 1103”. Infections with this bacterium have been successfully treated using low doses of Ciprofloxacin. You can read more about this here.
Stony Coral Tissue Loss Disease (SCTLD)
This disease has recently emerged as a major threat to corals throughout the Caribbean region. Researchers have recently completed an extensive study of the microbiome in corals affected by the disease, and identified a group of bacteria associated with SCTLD. Several of these same bacterial types show up occasionally in reef tanks, and are included in this section of the report.
What does it mean for your tank?
First consider the prevalence and average level of the bacterium. The presence of a suspected pathogen would raise greater concerns if the pathogen is occurs rarely (low prevalence) or present at higher than usual levels. A suspected pathogen that occurs frequently or is present at typical low levels would raise less concern.
Also consider the affected species. Brown Jelly Disease is primarily an issue for Euphyllia corals. SCTLD affects a wide range of LPS corals. Concerns about these suspected pathogens will depend on whether the affected species are present in your tank.
What can be done about it? In principle both diseases are treatable with antibiotics, although the specific treatment protocols remain a work in progress. We’ve described an in-tank treatment for BJD using low doses of Ciprofloxacin. Researchers studying SCTLD have used a topical antibiotic putty to treat diseased corals in the field.
Aquarists considering antibiotic treatments should consider the following:
- Antibiotics should only be used therapeutically, never as a preventative measure. The routine preventative use of antibiotics leads to the emergence of antibiotic resistance in microbial communities, which can lead to serious health risks.
- Antibiotic treatments are likely to impact beneficial microbes in addition to pathogens. This can be minimized by the choice of antibiotics and dosages. Testing the microbiome can help users determine whether supplementation is needed to restore the community after an especially aggressive antibiotic treatment.