Sea fans are made up of polyps -- small finger-like cylinders of tissue -- attached in a fan-like pattern to a central internal skeleton.
(ENN) -- A fungus called Aspergillus sydowii has been responsible for the mass destruction of sea fan coral over the last 15 years, according to researchers at the University of California, Berkeley, and their collaborators.

The same fungus causing disease in sea-fan coral from the Florida Keys to San Salvador has actually inhabited Caribbean waters for a very long time but appears to have begun killing coral on a large scale only recently, said John W. Taylor, UC Berkeley professor of plant and microbial biology.

Coral is an animal and is an extremely important component of the marine ecosystem. It hosts many reef organisms and provides a refuge for reef fish.

The researchers are entertaining a number of possibilities for why the fungus has suddenly become a killer. One explanation is that the fungus mutated in recent years. Other, more likely possibilities include the weakening of the sea fan's immune system or some other damage to the organism, possibly from changes in the environment, making the coral more vulnerable to infection.

The fungus was identified by genetic studies of DNA taken from infected corals at a number of sites. A. sydowii was first described in the scientific literature in 1913 but probably existed even 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.

Alarmingly, the incidence of the coral reef disease "is increasing at a pretty intense rate," said Kim B. Ritchie of the University of North Carolina, Chapel Hill and a collaborator on the study. "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. Older colonies can get up to about five feet or more.

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.

The researchers are not expecting an easy answer to the question of what to do now.

There is no safe, effective cure at the moment, and even if there were, Taylor doesn't think it would be economically possible to treat sea fans in their natural environment.

"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," said Taylor

The researchers' work was published in the July 9 issue of the journal Nature. Taylor's collaborators include 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.