The fluid dynamics of swimming jellyfish have provided a plausible mechanism for a once-wild notion: that marine animals, hidden from sight and ignored by geophysicists, may stir Earth's oceans with as much force as its wind and tides. Called induced fluid drift, it involves the tendency of liquid to "stick" to a body as it moves through water -- and a little bit of drift could add up quickly on a global scale.

That the mere motion of animals could play a profound role in water-column commingling was once considered absurd. The sea would surely absorb the force of a flapping fin, to say nothing of a phytoplankton's flagellae. It was a basic principle of friction, applied to water.

But in recent years, this consensus has sprung some leaks. When added up, winds and tides don't quite provide enough energy to account for the amount of water-mixing observed in the seas. In 2004, a study found that a school of fish could cause as much turbulence as a storm. Other researchers soon suggested that ocean swimmers could account for the gap. Soon after that, ocean physicists measured enormous turbulence generated by a swarm of krill, a crustacean considered too small to have meaningful mixing effects.