New study reveals why jellyfish are such efficient swimmers (w/ Video)

(Phys.org) —A team of researchers in the U.S. has found that jellyfish are extremely efficient swimmers. In their paper published in Proceedings of the National Academy of Sciences, the team reports using a technique called particle image velocimetry to measure the secondary thrust jellyfish use to increase their energy efficiency when swimming.

For years, jellyfish have been considered a nuisance—they sting swimmers and crowd out other more desirable ocean dwellers. In more recent times, they have become even more of a problem as they grow in both numbers and size—most scientists attribute this to their adaptability to warmer ocean temperatures and a decrease in other populations due to overfishing by humans. Now, it appears they have another natural advantage that gives them an edge over other ocean dwelling creatures as well—they are far more efficient when swimming leaving them more energy to find food and mate.

Scientists have known for a long time that jellyfish move through the water by squeezing the bell that forms ahead of their body. That squeezing pushes water backwards forcing the jellyfish forward. More recently it has been learned that they also are pushed forward by a secondary thrust that occurs as the bell is refilling with water. Until now, however, it was unknown just how much benefit jellyfish got from this.

To find out, the researchers anesthetized some test specimens and placed them in a tank filled with very tiny glass beads. As the jellyfish moved in the beads, a laser was shone and reflected off the beads, allowing the researchers to measure its speed and how much energy the creature was expending as it moved. They noted that immediately after squeezing its bell, a vortex formed as the bell relaxed. That vortex pushed against the jellyfish's body, propelling it forward. More importantly, the researchers found that the secondary thrust required no energy expenditure by the jellyfish at all—it was purely mechanical, like a rubber-band snapping back to its original size after being stretched. That extra boost the researchers report (which averaged about a thirty percent gain) means that jellyfish are by far the most efficient swimmers in the sea, giving them an advantage over virtually all other sea life.

The findings may lead to increases in efficiency in swimming robots as scientists seek to recreate the mechanics of jellyfish—that could mean swimming robots plying the seas sending back data for years on end, or as some have suggested, new kinds of robots that kill real jellyfish.