Why Are Jellyfish Such Good Swimmers? Their 'Vortex' Is The Key, Researchers Say

By Josh Lieberman on October 8, 2013 8:20 PM EDT

jellyfish
Jellyfish are some of the most efficient swimmers in the sea, and now researchers have found out why. (Photo: Wikimedia Commons)

A team of researchers says that a key advantage to the survival of jellyfish over the course of millions of years is its efficient swimming capabilites. Brad Gemmell of the Marine Biological Laboratory in Woods Hole, Mass., found that jellyfish use a swimming technique called "passive energy recapture" to move about the ocean more efficiently than just about any other creature. This evolutionary advantage means that jellyfish expend less of their energy to the task of moving around, energy which they can devote to mating and finding food. 

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Scientists already knew that jellyfish swim by squeezing their open bell, pushing water back and moving themselves. Scientists also knew that jellyfish get a "bonus" thrust as their bells refill with water, but they didn't know how much energy jellyfish were expending during that second thrust. That's where Gemmell and his team came in.

"We saw this expected spike in velocity when the animal was contracting, but we would see this secondary peak during a period of time when the animal was actually pausing between contractions, after it had reopened and relaxed," said Gemmell. "So initially we dismissed it as noise, but it ended up showing up in every contraction and among all different sizes of animals and among different species."

Gemmell and his team took a bunch of moon jellyfish, or common jellyfish, and put them in a tank with small silver-coated glass beads. The researchers shot lasers into the tank, which bounced off the beads and revealed the water flows created by the jellyfish. This method revealed to the researchers that the jellyfish weren't expending energy during the little-understood second thrust portion of their movement. Instead, the jellyfish took advantage of the vortex that formed after the initial thrust, which boosted the creature's movement by 30 percent without using any energy.

While jellyfish may be efficient swimmers, they are not fast ones, and they certainly be able to avoid the shredding machines that may soon be coming for them.

Gemmel and his team's findings appear in the study "Passive energy recapture in jellyfish contributes to propulsive advantage over other metazoans" in Proceedings of the National Academy of Sciences.

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