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Extreme heat across the globe is causing coral reef bleaching, threatening the delicate ecosystem and fisheries, which feed millions.
Hundreds of the world's top ocean scientists are gathered in Sydney, Australia for the 12th International Coral Reef Symposium. They are meeting to discuss a potential environmental crisis. Increased carbon dioxide in the atmosphere is causing more acidity in the oceans which is killing the coral. Conservationists say urgent action is needed to save what's left.
Matthew Huelsenbeck is a marine scientist with conservation organization Oceana.