Scientists find that a species of jellyfish builds walls of water to swim around the ocean

Scientists found out that at least one species of jellyfish creates vortices that rotate in opposite directions to swim through the ocean. Where the flows of the two vortices meet, the collision creates a region when the water is stationary—thus, creating a wall that the jellyfish use to push off.

This movement of jellyfish is a variation of a technique known as the grounding effect. “It’s been known for a very long time that there’s a well-documented boost in performance that you get when you swim or fly near a solid boundary,” Dr. Gemmell said. The circulation of liquid slows down near something solid so the water cannot be passed easily which makes it easier to propel. As there are generally no walls and surfaces in the ocean, jellyfish create their own surface. 

The scientists captured high-speed video of eight moon jellyfish, Aurelia aurita, to investigate their swimming motion. As a jellyfish completes one of its strokes and relaxes, it generates a doughnut-shaped ring of rotating liquid called the stopping vortex, and the blobby “bell” portion of the animal traps this vortex. As the bell contracts, it creates a second ring of liquid, the starting vortex, rotating in the opposite direction. As the jellyfish rises in the water, the starting and stopping vortices meet, producing a virtual wall that aids propulsion.

Jellyfish “represent a really nice model to understand how animals interact with the water around them, to move very efficiently,” said Bradford J. Gemmell, a professor of integrative biology at the University of South Florida, in a published paper. “[Dr. Gemmell’s] paper documents another in what’s a growing portfolio of approaches that these animals use to swim efficiently,” said John O. Dabiri, a professor of aeronautics and mechanical engineering at the California Institute of Technology. 




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