SoylentNews

Researchers have confirmed the grim toll of an unusually hot summer on Australia's Great Barrier Reef: Mass bleaching has killed 35% of corals on the northern and central sections of the 2300-kilometerlong system.
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[This] is the worst of three major bleaching events that have occurred in the last 18 years.

Coral bleaching occurs when abnormal environmental conditions, like heightened sea temperatures, cause corals to expel tiny photosynthetic algae, called ‘zooxanthellae’.
The loss of these algae causes the corals to turn white, and ‘bleach’.
Bleached corals can recover if the temperature drops and zooxanthellae are able to recolonise them, otherwise the coral may die.