Canberra, April 7 : The Great Barrier Reef, the world's largest coral reef system located in northeast Australia, has suffered its worst mass coral bleaching in recent years, a group of scientists said on Tuesday. This is the third mass bleaching of the reef, which is around 344,000 square kilometers in size, after two other similar devastating events in 2016 and 2017, reports Efe news. "For the first time, severe bleaching has struck all three regions of the Great Barrier Reef Â? the northern, central and now large parts of the southern sectors," Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, said in a statement. The main cause of coral bleaching is rising water temperatures and in the worst of cases, can lead to the death of the corals and life around it. Hughes and his team surveyed 1,036 reefs in the last fortnight of March to measure the extent and severity of coral bleaching in this area, declared a Unesco World Heritage Site and considered one of the seven wonders of the world. Morgan Pratchett, who led underwater surveys of the Great Barrier Reef, explained that when bleaching is severe it is fatal for the corals, as occurred in 2016, when half of the shallow water corals died in the northern region of the reef. "The north was the worst affected region in 2016, followed by the central region in 2017. In 2020, the cumulative footprint of bleaching has expanded further to include the south," Pratchett added. Only a few reefs have escaped severe bleaching so far - those located offshore, in the extreme north and the remote parts of the south, according to the scientists. The distinctive geographic footprint of each bleaching event in these regions reflects the greater or lesser degree of the warming of the waters in the areas affected by these events. "As summers grow hotter and hotter, we no longer need an El Nino event to trigger mass bleaching at the scale of the Great Barrier Reef," Hughes warned. The expert said that of the five bleaching events that occurred in the Great Barrier Reef, only those in 1998 and 2016 were caused by this weather phenomenon and warned that bleaching is occurring at more frequent intervals. /IANS