The moon jellyfish in the video above might seem like an odd candidate for the underwater Olympics. But these creatures are actually some of the most energy-efficient swimmers in the animal kingdom. Their secret weapon, according to new research, is a “wall” of water the jellies create underneath their bodies to propel themselves forward.
Scientists tracked the ghostly moves of moon jellyfish (Aurelia aurita) in the lab by recording them with high-speed video. They filled a tank of water with illuminated glass beads to quantify the movement of fluid around the animals. The researchers found that the jellyfish create a vortex ring in the water underneath their bells after each thrust forward, generating higher pressure below that they can more efficiently push off of with their next move. (In the video, you can spot the swirling colored vortices meeting under the jelly as it swims upward.) The vortex acts like a solid wall, which allows the jellies to get a better lift each time their mushroom-top bodies contract, the team reports today in the Proceedings of the Royal Society B: Biological Sciences.
Known as the “ground effect,” this phenomenon helps explain why you might feel like you’re floating on a cushion of air in a plane that’s just about to touch down on the runway. Scientists have documented the effect in animals like crustaceans and fish moving or swimming near a solid boundary, but moon jellies are able to do it despite having muscle tissues that are only one cell layer thick.
The jellies’ technique could provide inspiration for our own underwater travel, the researchers say. Engineers could design underwater vehicles that emit similar pressure, for example, boosting their efficiency as they zoom along.