longest reef

The great barrier reef (gbr) off north eastern Australia is 2,027 km (1,260 mi) in length rough roughly the distance between the UK and Malta The gbr is in fact a reef  system comprising some 2, 900 separate colonies that cover 207,200 km2. (80,000 sq mi) living coral grows on deed polyps that can date back as much as 20 million  years. The reef os a doverse but fragile ecosystem that  faces nemerous threats not least  bleaching  where warming ocean waters cause symbiotic algae to be expelled leaving the coral withe a 2018 study revealed that the gbr suffered an unprecedented nine moth marine heatwave in 2016 during which almost 30% of coral in the reef died off. from called book Guinness world records.