NEWS RELEASE, 07/08/98
Pathogen attacking sea-fan coral in the West Indies
is identified by UC Berkeley researchers
By Robert Sanders, Public Affairs
BERKELEY -- The culprit responsible for killing sea-fan coral from the Florida Keys to San Salvador has been caught in the act and identified for the first time, according to researchers at the University of California, Berkeley, and their collaborators. The group reports in the July 9 issue of the journal Nature that a fungus called Aspergillus sydowii has been responsible for the mass destruction of this coral over the last 15 years.
"Aspergillus sydowii is the fungus causing the disease that's killing them," said John W. Taylor, UC Berkeley professor of plant and microbial biology. "It's the same fungus throughout the West Indies."
Taylor made the finding with David M. Geiser, a UC Berkeley post doctoral researcher who now is a professor at Penn State; Kim B. Ritchie of the University of North Carolina, Chapel Hill; and Garriet W. Smith of the University of South Carolina-Aiken.
The sea fan - a type of animal life, as are all corals - is an extremely important component of coral reefs, said Ritchie. It hosts many reef organisms and provides a refuge for reef fish.
What is interesting about the attacking fungus Aspergillus sydowii, said Taylor, is that it has inhabited Caribbean waters for a very long time but appears to have begun killing coral on a large scale only recently.
One explanation for this is that the fungus mutated in recent years to become more virulent. But more likely, the researchers said, the problem lies with the coral itself. They suspect that weakening of the sea-fan immune system or some other damage to the organism, possibly from changes in the environment, could be making the coral more vulnerable to infection. Thus, the marine creatures may no longer be able to fight off the fungus.
The fungus was identified by genetic studies of DNA taken from infected corals. The studies, done at UC Berkeley from samples provided by researchers at the other two institutions, placed the pathogen solidly among other known samples of A. sydowii, a well-known fungus described in the scientific literature in 1913 but undoubtedly in existence much earlier.
"It's a temptation when you see a new disease to think that you have a new organism," said Taylor, a fungi expert. "But that's not necessarily true."
In this case, explained Taylor, it's a new disease from a well-known fungus. The proof is that healthy sea-fan colonies exposed to A. sydowii from diseased tissue also come down with sickness, the researchers found.
Alarmingly, the incidence of the coral reef disease "is increasing at a pretty intense rate," said Ritchie. "The reasons for this are highly debated and range from global warming to human factors like pollution and land run-off."
Generally, she said, "disease occurs most frequently in organisms that are stressed. If the sea fans are not healthy, that is an indication of trouble, and the reefs are certainly not healthy."
Aspergillus fungi have been found not only in Caribbean waters, but in many other places including soil from Washington, D.C., dried Japanese fish and Mexican bee hives. A close relative of penicillium, the fungus is well adapted to conditions of high salt or other solutes, such as sugar.
"If you open up a jelly jar in the refrigerator and there's mold on it," said Taylor, "chances are it's Aspergillus."
Sea fans are made up of polyps - small finger-like cylinders of tissue - attached in a fan-like pattern to a central internal skeleton. Overlaid by the polyps, the inert skeleton supports all branches of a colony. The polyps produce blue-green spores for reproduction.
"Sea-fan colonies can get up to a meter and a half (about five feet) or even larger, (but) these are really old colonies," said Ritchie. "The colonies that we used for the inoculation experiments in our Nature article were small - around 20 centimeters (about eight inches)."
Two species of sea fan, Gorgonia ventalin and Gorgonia flabellum, are found throughout the Caribbean, said Ritchie. Both are affected by the A. sydowii pathogen. Sea-fan disease has been reported in the Virgin Islands, Puerto Rico, the Bahamas, Mexico, Panama, Venezuela, the Florida Keys and many other coral reef locations. It can be recognized by a characteristic receding of the polyps, revealing the dead central skeleton, or core.
"You can clearly see places where the coral has died," said Taylor. "Visually, the human parallel would be a skin infection like ring worm. A closer human parallel would be the Aspergillus fumigatus infection afflicting people undergoing bone marrow or organ transplants. Like A. sydowii, this fungus is not normally a pathogen, but when the patient's immune system is suppressed for the transplant, it becomes one."
As for the coral, the researchers said not to look for any solutions soon.
Even if there were a safe, effective cure to rescue the sea fans, which
at the moment there doesn't appear to be, "I don't think it would be
economically possible to treat sea fans in their natural environment,"
said Taylor. "We need to understand what is making the infection possible.
If we're lucky, it may be some kind of pollution or something else we could
prevent. But if it's something like rising ocean temperature, good luck."
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