Science News

Jellyfish stirring things up.

Sun, 2nd Aug 2009

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Jellyfish may spend their lives passively drifting through the open oceans at the mercy of currents and tides, but they could also be stirring things up as they go.

JellyfishTogether, all the swimming things in the oceans – including minute plankton - could contribute as much mixing as the winds and tides. That’s according to KakaniKatijaand JohnDabiri from the California Institute of Technology in Pasadena who’s study appeared this week in the journal Nature. It could mean that climate modelers have been missing an important part of the puzzle.

Katija and Dabiriused computer models to investigate a process in which a body moving through a fluid pulls some of that fluid with it. The more sticky or viscous the fluid is, the more of it is pulled along. This was an idea first reported 50 years ago by Charles Darwin – grandson of famous author of On the Origin of Species.

The computer models showed that a tiny plankton pulls up to four times its volume in water by just moving a few body lengths.

The research duo then set off for Palau, a cluster of beautiful tropical islands in the Pacific, to test out their ideas among swarms of real jellyfish: a very sensible choice because there jellyfish living in land-locked marine lakes have evolved to have no sting.

They squirted luminous dye behind of the jellyfish and filmed them using special laser-equipped underwater cameras. They watched as each jellyfish was followed by a trail of glowing dye. It turns out that up to 90% of the water movement came down to Darwin’s theory and not because of a turbulent wake streaming behind the jellyfish.

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