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Photo of Garriet Smith Garriet Smith
Dust Busting

Garriet Smith, a marine biologist at the University of South Carolina, answers question about his work and what he has earned about a disease threatening Caribbean coral reefs.

q As a Florida resident I am interested on the effects your study has on the Keys. Is the aflatoxin from the fungus the causative agent of the coral disease? Is Aspergillus the pathogen on the hard corals as well?

A The species that causes aspergillosis of sea fans is Aspergillis sydowii and A. sydowii is known to produce an aflotoxin. Reinoculations with reference strains (from soil and elsewhere) on healthy seafans, however, do not result in disease. Only those strains isolated from diseased sea fans do. So, there is a difference in the metabolism these types of A. sydowii that we are investigating with Drew Harvell and Kiho Kim at Cornell Univ. and Joan Nielsen at the Univ. of Copenhagen, but we don't yet know why they are pathogenic. Aspergillis has not been identified as the pathogen of hard corals. Most of these are bacteria (see Nature 392:557, 1998).

q My question involves a setup at home. I am getting into the salt water aquariums. (I have 4 freshwater ones right now, and I am 14 but a very well-known fish breeder in my town.) I am getting a lot of living coral when I get my tank and I was wondering if my tank could get this soil disease.

A Unless you are growing seafans, you shouldn't have a problem with Aspergillis. You may very well have problems with other diseases. We worked with the National Aquarium in Baltimore on bacterial diseases among captive corals. There are a number of them.

q Is it possible that the common fungus identified to be the culprit of the diseased coral could have originated from the islands themselves through erosion?

A The fungal inoculum probably does not originate locally. I say this because we have seen sick sea fans in shallows that were many miles from land. Also, this has spread (very quickly) throughout the Caribbean Sea.

q What kind of ideas have scientists thought about to cure this fungus disease?

A A cure is not on the horizon. Once we are satisfied that we know the origin, spread and pathogenesis of the infection, we can think about how to interfere with the overall process. We just need to know more about it for now.

q Has Aspergillus undergone a mutation in order to germinate in salt water or is this a normal characteristic? I associate Aspergillus primarily with food and soil.

A Actually, the spores do germinate in salt water, but the pathogenic strains do not sporulate (produce spores) in salt water. Therefore the normal life cycle is interrupted. We have recently found that hyphal fragments (the vegetative state does all the damage) will sporulate at the water-air interface in the lab. We don't yet know if this happens in the environment or how significant it might be.

q What information did the core sample you drilled from the boulder coral give you?

A This is still being analyzed.

q Why is it that when the fungus attacks the coral that is like a fan, it turns the coral purple?

A Sea fans have structures known as sclerites. These are calcium carbonate deposits that help make up the skeleton. These sclerites can be clear or pigmented (purple). When the fungus invades the coral tissue, the coral produces a higher percentage of purple sclerites, thus purpling the tissue. We think this is a protective response that sea fans have to limit the spread of the fungus.

q Does this fungus disease affect coral reefs in other areas of the world besides the Caribbean?

A We have not received any reports to date of aspergillosis on sea fans outside the Caribbean, but we don't really know.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.