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Global warming is killing coral reefs

Global warming is killing coral reefs

Global warming is killing coral reefs
Rhett A. Butler,
May 7, 2007

A new study provides further evidence that climate change is adversely affecting coral reefs. While previous studies have linked higher ocean temperatures to coral bleaching events, the new research, published in PLoS Biology, found that climate change may increasing the incidence of disease in Great Barrier Reef corals. Omniously, the research also shows that healthy reefs, with the highest density of corals, are hit the hardest by disease.

The number of weeks that ocean temperature exceeded its long-term weekly average by more than one degree Celsius between 1999 and 2004. Anomalously warm conditions like these can cause outbreaks of the coral disease white syndrome, contributing to reef decline. Credit: Elizabeth Selig

Monitoring 48 reefs along more than 900 miles (1,500 kilometers) of Australia’s coastline for six years, a team of researchers led by John Bruno, a marine biologist at the University of North Carolina at Chapel Hill, tracked white syndrome, an infectious disease that kills coral. They found that “reefs with high coral cover and warm sea surface temperatures had the greatest white syndrome frequency.”

“More diseases are infecting more coral species every year, leading to the global loss of reef-building corals and the decline of other important species dependent on reefs,” said Bruno. “We’ve long suspected climate change is driving disease outbreaks. Our results suggest that warmer temperatures are increasing the severity of disease in the ocean.”

Bruno says that high coral density may facilitate the spread of infection by increasing the number of disease vectors that provide “inroads for infection”. Physical closeness between corals may also make it easier for disease transmission.

White syndrome is a fairly common malady for Great Barrier Reef corals, though it has also had a significant in the Caribbean. Technically a generic name used for a variety of similar diseases, White symdrome manifests as white bands, spots, or patchs on coral. Other research indicates a 20-fold increase in abundance since 2000 on the Great Barrier Reef.

The findings will help researchers better understand the drivers of coral decline in other areas.

“This study developed valuable methods to pinpoint warm temperature as a partial driver of disease outbreaks. These methods will also be used to study climate drivers of disease outbreaks in other regions of the world,” said Drew Harvell, a Cornell University professor of ecology and evolutionary biology and a co-author of the study.

Scientists have expressed a great deal of concern over the potential impact of climate change on coral reef ecosystems. Both increasingly levels of acidity, which reduce the ability of coral to generate their main structural material, and higher sea temperatures, which can cause “bleaching” or expulsion of the symbiotic algae that enable corals to feed, are cited as the primary risks to reefs in a world of higher atmospheric carbon dioxide levels.

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