Importance of coral reefs: they are the "canaries" of the seas

Warning species

Early coal mines did not feature ventilation systems, so miners would routinely bring a caged canary into new coal seams. Canaries are especially sensitive to methane and carbon monoxide, which made them ideal for detecting any dangerous gas build-ups. As long as the canary in a coal mine kept singing, the miners knew their air supply was safe. A dead canary in a coal mine signalled an immediate evacuation.

Today, the practice of using a canary in a coal mine has become part of coal mining lore, but the ideology behind it has become a popular expression. The expression living like a canary in a coal mine often refers to serving as a warning to others. And this is exactly what coral reefs do!

Because of their fragility, coral reefs have been compared to the proverbial "canary in the mine shaft" for the world oceans.

The state of the corals gives an indication of the health of the oceans and much of the wildlife that depends on them. One small event, like coral bleaching in an isolated area, may not seem especially noteworthy, but it may offer the first tangible warning against a much larger upcoming problem (like water pollution or even global warming).

Canary in a coalmine
Canary in the mine shaft.
Source: Seeking Alpha