Severe mass bleaching events have now been recorded for the Great Barrier Reef four times: 1998, 2002, 2016, and now in 2017. But this year's findings report the middle third section has experienced more damage.
On Monday, the Australian Research Council's Centre of Excellence for Coral Reef Studies released their recent aerial survey of more than 8,000 kilometres of coral.
The aerial surveys this year covered more than 8,000 kilometres (km) and scored almost 800 individual coral reefs closely matching the aerial surveys last year that were carried out by the same two observers.
Great Barrier Reef coral bleaching composite map shows surveyed coral reefs in 2016 (left panel) and 2017 (right panel).
In 2016, severe bleaching hit the northern third of the reef.
James Cook University's Mia Hoogenboom carried out a number of underwater assessments for the survey, and said she documented damage to mound-shaped corals that tend to be more resistant to bleaching.
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The chance for a hurricane landfall on the Florida Peninsula and the East Coast of the U.S.is 24%, with 31% being the average. Out of those, his department forecasts 4 will become hurricanes, compared to the typical 6 to 7 in any given season.
The damage caused when the intense, slow-moving cyclone system struck a healthier section of the reef outweighed any potential beneficial cooling effect, scientists from the ARC Centre of Excellence for Coral Reef Studies said.
Bleached corals can recover if the temperature drops and algae repopulates, but researchers say global warming threatens to make the problem irreversible. It is composed of more than 2,900 individual reefs and 900 islands stretching over 2,300 kilometers over an area of approximately 344,400 square kilometers.
Australia now faces a rapidly approaching deadline for saving the reef by addressing climate change, Hughes added. According to scientists, the back-to-back severe bleaching events will give damaged coral little time to recover.
When the water is too warm, corals expel algae that live in their tissues, and this causes them to become completely white and to be more vulnerable to disease. "Last year was bad enough, this year is a disaster year", Brodie said.
Aerial view of The Great Barrier Reef as seen from above. Corals are more likely to die during longer and stronger bleaching events, just like the ones that occurred last year and earlier this year.
The Coral Reef Watch forecast is for elevated risk of coral bleaching to continue until at least July around the world, adding further stress to coral.
The back-to-back bleaching events, and the increased spread south of the damage now leaves only the southern third of the reef untouched, and while bleached coral doesn't necessarily mean the coral is dead, the dual impact of these losses decreases the reef's natural ability to fix itself.