Canary in the coal mine – coral

Corals, Earth’s Canary in Coal Mines, Facing ‘Calamitous’ Global Declines. The current state of most of the world’s coral reefs is so calamitous that it’s difficult to over-dramatize the situation. Reefs have seen massive declines around the globe, and while there is much debate about which particular threat is most responsible, most scientists agree humans are to blame.
Yale Climate Connections, 1 Sep 2009