Climate Change May Be a Factor in Ailing Sea Fans

by Suzanna Engman

Pollution. Disease. African dust. Warmer water. These factors or a combination of them are killing coal reefs worldwide, and especially in the Caribbean where the death rate is critical. Scientists believe that disease poses the most severe threat to corals here, and some say that the soil fungus Aspergillus sydowii, carried by the wind in dust clouds from Africa, is the pathogen that causes aspergillosis disease in sea fans. But a study funded by CATEC, NOAA Sea Grant, and NIH-SCORE is turning up evidence that the soil fungus might not be the culprit after all. CATEC research on genetic variability and distribution of the pathogen could help predict how climate change will affect the disease and suggest ways to control its spread.

The study uses genetic markers to identify the species of fungus in diseased Gorgonia ventalina (the common sea fan) lesions. A type of coral, sea fans are made up of thousands of polyps, hollow cylindrical sacs attached to a fan-shaped skeleton that supports the branches of a colony. Sea fans anchor in the sand, position themselves toward the current, and spread their tentacles out to form a net to catch prey. Sea fan polyps are interconnected, which can be beneficial for feeding, but their union also means that disease can spread quickly. Sea fans are suffering from an epizootic. Derived from Greek epi (upon) and zoion (animal), an epizootic is a disease that appears in an animal population and spreads at an accelerated rate. An “epidemic” is the same concept applied to humans. “Sea fan disease in the Caribbean is pretty serious and it has only been noticed in the last 15 years or less. It was identified as aspergillois, which is a type of infection that humans get, too, especially in the lungs,” says Paul Bayman, Ph.D., professor of biology at the University of Puerto Rico, Rio Piedras Campus.

About five years ago, Professor Alberto Sabat’s students, who were working with population biology of sea fans, began to see a lot of aspergillois lesions, or purple spots, on the sea fans off the coast of Puerto Rico. Under the direction of Sabat and Bayman, doctoral candidate Carlos Toledo-Hernández began to study the lesions. He never found the supposed pathogen in the lesions, but he did find a lot of it in healthy sea fan tissue. “Nobody had looked at what’s in the healthy sea fans before. We think that the literature is wrong and what is really important is how susceptible the sea fan is to disease or the condition it is in. If the sea fan is stressed because of poor water quality or high water temperature, then there are already opportunistic microorganisms around that can cause disease. The fungi are all around; it’s the stress that weakens the sea fans and makes them more susceptible,” says Bayman.

To test their hypothesis, Toledo-Hernández is researching healthy and diseased sea fans in their natural environment and in the laboratory. In the laboratory he inoculates healthy areas of sea fans with different fungi in an attempt to recreate the disease. These controlled experiments suggest that Aspergillus sydowii alone is not enough to cause aspergillosis.

Toledo-Hernández is testing other fungi that may be the cause of the disease. “We surveyed tissue samples from the healthy areas and diseased areas. We haven’t identified the pathogen yet, although we have some candidates that may be involved in the disease,” says Toldeo-Hernández.

Two papers on their findings have been submitted by Toledo-Hernández to the journal Coral Reefs, one of which was published last year. Another doctoral candidate, Anabella Zuluaga, is studying spatial variation of fungi in sea fans to trace the source of inoculum.

photo by Anabella Zuluaga