The 2,300-kilometre long reef — the world’s biggest — suffered its most severe bleaching in recorded history due to warming sea temperatures during March and April.

Reasons for Coral Bleaching:
Bleaching occurs when abnormal environmental conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae, draining them of their colour. Algae are vital to the coral, which uses the organic products of photosynthesis to help it grow. The loss of algae makes the host vulnerable to disease and means it will eventually die. However, coral can recover if the water temperature drops and the algae are able to recolonise them.

Environmentalists blame the burning of fossil fuels for global warming and repeated calls for Australia to abandon coal mining to help prevent further bleaching disasters.

Long recovery:
Scientists estimate that it will take at least 10-15 years to regain lost corals, but are concerned that a major bleaching event may occur before that, hampering the recovery. 

Given reefs need so long to recover from severe bleaching, it said “we are likely to lose large parts of the Great Barrier Reef in just a couple of decades”. That study noted climate change had added 1.0 degree Celsius of warming to ocean temperatures off the Queensland coast in March, when corals were first seen turning white.