Coral disease linked

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Close up view of a tabulate Acropora sp. hard coral colony showing the typical signs associated with White Syndrome.

Coral diseases have become an important research area since they were identified as being responsible for major losses of dominant coral species on Caribbean reefs over the past 20 years. The situation on Australia's Great Barrier Reef (GBR) is different in that coral diseases have not caused major losses to date. However, an international team of scientists working on the GBR has now found a clear link between coral disease and warmer ocean temperature. ‘White syndrome' is one of a number of coral diseases that have increased globally in recent years. An international team of scientists from AIMS, the ARC Centre of Excellence for Coral Reef Studies and the University of North Carolina compared new high-resolution measures of sea surface temperature from NOAA satellites for 1998-2004 with the incidence of white syndrome in that period on 48 reefs that have been surveyed by the AIMS Long-term Monitoring Team since the early 1990s. The main discovery was that high water temperatures are associated with increased disease, but only on reefs with high coral cover.

The surveys included sites on inshore, mid-lagoon and outer barrier reefs spread over 10 degrees of latitude from Lizard Island in the far north to Lady Musgrave Reef at the southern end of the GBR. In 2002, when sea temperatures were abnormally warm and coral bleaching was widespread on the GBR, the incidence of coral disease on the monitored reefs was more than an order of magnitude higher than in years with normal sea temperatures but most notably higher on reefs with high coral cover. This ‘catch–22' relationship means that reefs which, through position and/or good luck have not suffered impacts such as cyclones or pest outbreaks, and are apparently in best condition before summer, are at greater risk of coral disease in abnormally warm years.

This raises concerns that future impacts of increasing temperatures from global warming may disproportionately affect important reservoirs of coral biodiversity.