More than one-third of corals on the northern and central Great Barrier Reef have suffered bleaching due to global warming and acidification of the ocean, scientists said Monday. 
The impact is still unfolding, researchers from the ARC Centre of Excellence for Coral Reef Studies said following months of aerial and underwater surveys. 
At least 35% of corals on that part of the reef are affected, the scientists said. 
"The recovery of coral cover is expected to take a decade or longer, but it will take much longer to regain the largest and oldest corals that have died," the group said. 
"This year is the third time in 18 years that the Great Barrier Reef has experienced mass bleaching due to global warming, and the current event is much more extreme than we've measured before," said Terry Hughes, director of the research centre. 
"We're rapidly running out of time to reduce greenhouse gas emissions," he said. 
Last month, the same team of scientists said an aerial survey showed that coral bleaching had affected 93% of the Great Barrier Reef. 
Bleaching is caused by a die-off of the living organisms, or algae, inside the coral. It can be triggered by small changes in environmental conditions, like a rise in sea temperature. 
It is the loss of these colourful algae that causes the corals to turn white and "bleach." Scientists say mildly bleached corals can recover from a warming if the temperature drops again soon, and the algae is able to recolonize them. Otherwise, the coral may die permanently.

Source: QNA