Canberra, March 26 : A new mass bleaching event has occurred at Australia's Great Barrier Reef, the third since 2016, officials said on Thursday. Recent aerial surveys of the world's largest coral reef system located in northeast Australia has revealed that bleaching was occurring on the reef with varying degrees of severity, Efe news quoted the Great Barrier Reef Marine Park Authority (GBRMPA) as saying in a statement. "Some southern areas of the Reef that had little or no bleaching in 2016 and 2017 have now experienced moderate or severe bleaching," the government agency said about the impact of the intense heat of Australia's summer on the reef. GBRMPA is responsible for the care and protection of the reef which is around 344,000 sq.km in size and has been declared a World Heritage Site by UNESCO. Corals have a unique symbiotic relationship with microscopic algae called zooxanthellae, which provides them with oxygen and a portion of the organic compounds produced through photosynthesis. When subjected to environmental stress, many coral reefs expel their zooxanthellae en masse, and coral polyps are left without pigmentation, appearing almost transparent on the white skeleton of the animal, a phenomenon known as bleaching. Australia, whose government backs coal-fired power and has been criticized for its indifference to climate change, has experienced one of its worst droughts in the last few months and one of the most devastating bushfire seasons in history as well as one of the worst storms in decades, in addition to the ongoing COVID-19 pandemic. Last August, the GBRMPA downgraded its outlook for the corals' health from "poor" to "very poor" and said the target set by the government's Reef 2050 plan to improve water quality had not been achieved. The government adopted the program, which includes improving water quality among a host of other measures, to prevent the Great Barrier Reef from being put on the World Heritage endangered list. The 2,300-km-long site is home to 400 types of coral, 1,500 species of fish and 4,000 varieties of molluscs, began to deteriorate in the 1990s due to the double threat of warming water and increased acidity caused by more carbon dioxide in the atmosphere. /IANS