Click, clack and pop: sounds indicate health of coral reefs, study finds

Monitoring the planet's ailing coral is costly and arduous. Now new research shows that scientists can do it by listening in

The popping sound, like milk hitting puffed rice cereal, that you hear when putting your head underwater is not your ear adjusting to a different atmosphere - it is the sound of the submarine world. Fish chat to each other, or move water with their fins; hard-shelled creatures scrape against the surfaces; molluscs drag themselves to their nooks.