Scientists have studied the "bleaching" of reefs in the Florida Keys in the US and found that the fan-shaped corals are being attacked, causing lesions, tumours and eventually death.
Drew Harvell, associate professor of ecology at Cornell University, told the meeting that the death of 100-year-old corals from diseases that they would have normally survived could be an early warning of far more serious problems for the global environment.
"When we see corals that have persisted for hundreds of years suddenly die from opportunistic infections, we have to wonder what has changed in their environment," Professor Harvell said.
Up to 40 per cent of the sea fan corals in the Florida Keys are now infected by fungal disease, which scientists have attributed to falling water quality and increased biological stress due to rising ocean temperatures.
Garret Smith, of the University of South Carolina, identified the microbe attacking the coral fans as a common, soil-dwelling fungus called Aspergillus, which was washed out by rivers flowing through intensively farmed agricultural land.
The fungus collects on the flexible, fan-shaped surfaces of the coral and causes an infection that first discolours the reefs and eventually kills them. The scientists believe sea fans, which position themselves perpendicularly to water currents to filter feed, are especially vulnerable to any disease- causing microbe.
Kiho Kim, a post-doctoral research associate at Cornell, said there is a growing consensus that the ocean ecosystems are now being degraded to such an extent that they are becoming havens for new infectious diseases.