Alarming bleaching at Great Barrier Reef

​Miami: Some corals in the Great Barrier Reef are known to be resilient when subjected to rises in temperature, but a study warned that this protective mechanism could soon disappear.

If ocean surface temperatures rise by as little as 0.5 degrees Celsius over what they are at present, the massive coral bleaching event underway in the famed Australian reef could spread dramatically, said the findings in the journal Science.

The reason has to do with an innate response to the stress of warming waters that corals have shown in the past, which scientists studied by analyzing 27 years of satellite records for the Great Barrier Reef.

"When corals are exposed to a pre-stress period in the weeks before bleaching, as temperatures start to climb, this acts like a practice run and prepares the coral," said lead author Tracy Ainsworth from ARC Centre of Excellence for Coral Reef Studies at James Cook University.

"Corals that are exposed to this pattern are then less stressed and more tolerant when bleaching does occur." But if sea surface temperatures rise more than two degrees Celsius above a given region's monthly average temperature -- calculated over the past three decades -- this protective mechanism could be lost and more corals may be damaged.

Most of the corals that have been protected "will begin to experience single and repetitive bleaching events when sea surface temperatures are approximately 0.5 Celsius higher than present -- which is expected to occur within four decades based on historical warming rates," said the study. Currently, about three-fourths of corals in the Great Barrier Reef benefit from the protective scenario.