Healthiest coral reefs hardest hit by climate change

Warmer sea temperatures help create ideal conditions for the spread of a coral disease threatening the world's reefs, according to a study on Australia's Great Barrier Reef released on Tuesday.

The study, which appeared in the journal PLoS Biology, offers a grim picture of the potential impact of global warming on coral reefs, which are among the world's richest ecosystems.

The authors found warmer sea temperatures around the densest and healthiest sections of the Great Barrier Reef provide the perfect conditions for white syndrome, a deadly disease that is spreading rapidly.

The authors looked at weekly ocean surface temperatures in areas around 48 reefs within the Great Barrier Reef and took note of instances when temperatures were higher byat least one degree Celcius from mean records for that week.

They compared those results to both the observed instances of white syndrome and the extent of coral cover.

Coral reefs that had living coral covering less than 50 per of the ocean floor were not more susceptible to white syndrome even with warmer water temperatures.

"Ironically, it's the very healthiest reefs, the ones with the healthiest coral populations, where the disease outbreaks occur," researcher John Bruno from the University of North Carolina told ABC Radio in Australia.

Coral reefs live atop a foundation of limestone built from calcium carbonate secreted from each tiny coral. The corals have a symbiotic relationship with single-celled algae that live within the coral and supply much of the food needed to survive.

When the corals are hit with white syndrome they expel their algae, causing the coral to lose their colour and their means of nourishment.

The Great Barrier Reef and coral reefs like it form the basis of a rich marine ecosystem in the Earth's oceans. Their rapid decline in health over the past decade worries marine biologists, who fear the loss of biodiversity could affect the planet's food chain.

The UN-led Intergovernmental Panel on Climate Change also suggested the reefs could lose a significant portion of their biodiversity by 2020, in part because of the the progressive acidification of oceans due to increasing atmospheric carbon dioxide.