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Marine explorers have discovered a "pristine" 3km (2-mile) coral reef at depths of 30m (100ft) off the coast of Tahiti, French Polynesia. It is one of the largest discovered at that depth, says the United Nations Educational, Scientific and Cultural Organization, which led the mission. Dr Julian Barbiere, from Unesco, said there were probably many more of these ecosystems "we just don't know about".
