coral/bacteria

[Bruce Carlson]

Observations re: bacterial infections of captive corals 

Aquarists around the country who maintain corals in home aquariums have 
observed a syndrome dubbed Rapid Tissue Necrosis (RTN) where corals 
rapidly degenerate.  Small polyp corals such as Acropora spp. seem 
to be most susceptible.  Usually this begins at the base of the coral as a 
white area and rapidly spreads over the entire coral within 24 hours or 
so.  The tissue in the white areas peels off or otherwise degenerates, ie, 
it is not a simple bleaching event.  Under the microscope the usual 
protozoa (cf. Helicostoma sp.) associated with other cases of RTN in large 
polyp corals (e.g.Euphyllia spp.) are NOT observed. 

Craig Bingman in New York has tested an antibiotic treatment which worked 
in his aquarium.  I wish to report that we have had similar success.  This 
may be of interest to those studying corals diseases in the field.  IN our 
case, one of our exhibit aquariums was accidentally overdosed with an 
iodine solution.  This (or something else) we surmise stressed the 
acroporid corals in the exhibit.  All of the acroporids in this exhibit 
were cloned and the parent colonies in separate aquarium systems remained 
healthy.  Acropora microphthalma and A. austera both deteriorated rapidly 
and were lost. 

The remaining acroporids were treated when signs of the RTN appeared. 
These species included A. cytheria, A. grandis, A. palifera, A. 
gemmifera,and A. sp.  Following Bingman's recommendation, these corals 
were isolated in a 16 liter aquarium and treated with 5mg/liter 
chloramphenicol.  An airstone was added to the tank.  After 24 hours the 
treatment was repeated.  Water from the "infected" tank was used to treat 
the corals rather than "clean" water from our main source.  After 48 hours 
the corals were moved to our outdoor facilities.  The RTN had "consumed" 
up to 50% of some of these colonies before they were treated.  The 
treatment completely halted the progress of the "disease" and all of these 
corals remain alive. 

We did not conduct a test for bacteria but the lack of any other visible 
pathogen and the fact that the progress of the RTN was halted by the use 
of chloramphenical strongly suggests that bacteria were the primary 
pathogen.  The fact that we used "infected" water in the treatment tank 
helps us rule out the possiblity that simply transferring the corals to a 
different tank with different water elliminated the problem. 
Additionally, Craig Bingman reports that he treated his entire aquarium 
system with chloramphenicol with the similar results, ie, the RTN 
disappeared. 

I am reporting this partly to benefit those who are maintaining corals in 
either aquariums or laboratory conditions.  It may or may not have any 
applicability to field situations.  I am not familiar with the literature 
on bacterial infections in corals but I assume that this in itself is 
nothing new.  Finally, just a warning to anyone using chloramphenicol -- 
it is considered very hazardous and should be used with extreme caution. 
Other antibiotics may be safer and just as effective in treating corals. 

For those who may be wondering:  effluent from our coral systems flows 
into the sanitary sewer system, not into the ocean. 

Bruce Carlson 
Waikiki Aquarium