Walk along the beach enough times and eventually you'll come across a beached jellyfish. It looks like a squishy mass of tentacles and membranes drying out in the sun.
But in its marine home, the jellyfish can band together with millions of others. They're capable of achieving high enough numbers that they forced the Oskarshamn nuclear power plant to shut off.
A new paper from the Marine Biological Laboratory in Massachusetts and a new robot from the Korean Advanced Institute of Science and Technology (KAIST) attempt to explain how jellyfish got to be one of the most prolific species in the world's oceans, as well as how to deal with their increasing numbers.
Jellyfish Get an Extra Boost When Swimming
Brad Gemmell, a post-doctoral researcher at the Marine Biological Laboratory, said that the jellyfish propels itself forward by contracting its muscles and creating spinning, donut-shaped vortices of water. "They're similar to smoke rings in the air," he told ABC News. "The jellyfish sheds one vortex and that's where most of the locomotion comes from, when the animal achieves its fastest speed."
Other jellyfish researchers had focused on the initial vortex created immediately after the muscle contraction, but Gemmell noticed that there was an additional and unexpected boost following its contraction. "At first I didn't think too much about it, since it could have just been some noise in the data," he said. "But it ended up being in every contraction cycle in a variety of different species and sizes."
The jellyfish creates a second vortex of water without contracting its muscles and expending any additional energy. "The second one actually rolls up underneath the animal," said Gemmell. "It accounts for 30 percent of the length it travels in each contraction cycle."
The jellyfish itself doesn't travel particularly fast or far with each muscle contraction, but those energy savings add up. "It's one of the most energetically efficient animals that we've ever measured, even compared to other animals that fly or run," said Gemmell.
He adds in the paper that by saving energy while swimming, jellyfish can allocate the energy they obtain from food into both growth and reproduction. His findings are published in the journal Proceedings of the National Academy of Sciences.