New diseases erode coral reef

Aisling Irwin reports from the annual meeting of the American Association for the Advancement of Science in Baltimore. Some coral reefs are dying from a new disease, raising fears that their resistance to diseases may have been lowered because of environmental changes.

The disease, dubbed the white plague, was discovered last June in the Florida Keys, near Miami. It has attacked the most hardy of coral species, which are losing tissue at one centimetre per day.

Coral reefs are high in bio-diversity, made up of hard and soft coral, sponges and algae as well as fish, and fauna that bore into reefs or live in their crevices. The disease is the latest in a series that have attacked reefs worldwide. Researchers believe that the diseases may be caused by human activity - either directly, for example by micro-organisms being carried from one side of the globe to the other by ships and escaping in their effluent - or indirectly, for example by causing an increase in water temperature which may lower the coral's resistance to pathogens.

The conference heard that diseases are just the latest of many threats to coral reefs. Some of their deterioration is caused by climate change, for example rising sea temperatures. But other damage is caused by local activity, generally the result of humans congregating in coastal areas and releasing a variety of damaging materials into the water.

The biodiversity of coral reefs has been compared to that of rain forests but the main problem is that little is known about what valuable species may be living in them. Marjorie Reaka-Kudla, of the University of Maryland, said that up to 90 per cent of coral reef species may still be undiscovered. She has calculated that there could be between 600,000 and 900,000 coral reef species.

Esther Peters, senior scientist at Tetra Tech, a Virginia-based company, said that the white plague has affected at least 15 species of coral, including one of the toughest species, the elliptical star. The disease attacks tissue at the base of the corals, which sloughs off, leaving just the white calcium carbonate skeleton. "We still don't know why it is happening," she said.

She also described Black-band disease, caused by a microbe, which was discovered in the Caribbean. It has now spread around the world and is known to increase in incidence with higher nutrient levels in the water. Another disease, discovered in 1993, is Coralline Lethal Orange Disease, which "seems to be spreading throughout the western Pacific".

It attacks particular algae that are important in building reefs. Dr Peters said: "The challenge is to determine the relative contributions of environmental changes and pathogens in the development of such diseases."