This Turbo-Powered Jellyfish Relative Could Inspire Submarines of the Future
This little creature's coordinated swimming system lets it shoot multiple jets of water from the separate units comprising its body.
This series of stills shows the change in orientation of a nectosome following two successive contractions of the top-left nectophore. Image: Costello et. al
Close-up of Nanomia bijuga's multi-jet thrusters.
Researchers are studying the unique swimming techniques of a simply designed yet highly maneuverable jellyfish-like creature in order to inspire designs for underwater vehicles of the future.
Dubbed Nanomia bijuga, it's a member of the siphonophores, a group of gelatinous planktonic creatures that are related to jellyfish, anemones and coral. Similar to coral, the two-inch Nanomia is colonial: It sports a gelatinous body that's motored about by a nectosome made of genetically identical but separate components known as swimming bells (nectophores). Each of these act as mini turbo jets that shoot out streams of water, propelling the creature through the ocean.
In a paper published Tuesday in the journal Nature Communications, an American team of researchers describe collecting samples at night off floating docks at the University of Washington's Friday Harbor Laboratories, in order to understand how exactly Nanomia used their bells to move themselves through the water.
Pulled behind the propulsive nectophores are individuals called zooids, which are specialized for reproduction and feeding. The big question is how such a colony of specialized creatures can all work together. As the researchers found, it's a product of how Nanomia grows: Younger swimming bells steer, while more mature ones give thrust.
"The younger swimming bells at the tip of the colony are responsible for turning. They generate a lot of torque," said Kelly Sutherland, a marine scientist at the University of Oregon, in a release. "The older swimming bells towards the base of the colony are responsible for thrust."
To see Nanomia in action, researchers placed the creatures in small tanks lit with a thin laser light-sheet. They logged its movements with at a rate of 1000 frames per second, then used a technique called particle image velocimetry—a velocity measurement technique into the flows and turbulence of fluids—to analyze the data.
"Although smaller and less powerful, the position of young nectophores near the apex of the nectosome allows them to dominate torque production for turning, whereas older, larger and more powerful individuals near the base of the nectosome contribute predominantly to forward thrust production," the authors write.
This form of locomotion offers insight into a potential new method for powering a man-made craft.
"These jellies have a slight ability to turn their individual jets, but they don't need to do it," added Sutherland in a release. "With multiple static jets they can achieve all the maneuverability they need. Designing a system like this would be simple yet elegant."
According to Sutherland, the jellyfish's unique swimming system means that even if one jet goes down, the creature would lose little propulsion as the other nectophores would keep propelling the creature through the water. While most man-made vehicles and animals rely on a single jet thruster to change direction, these jellyfish use multiple yet static jets to achieve movement and coordination. Instead of moving their jets in a particular direction, they control movement through regulating which units jet out water and at how strongly.
The researchers believe that such simple dependable designs could be transferred onto underwater craft designs to create more effective sea cruisers.
"We believe the identification of those controlling patterns [how the jellyfish move their nectophores] will permit us to understand the high-performance levels of animal swimmers and that perhaps some of this information will be applicable to human-engineered vehicles," said lead author John H. Costello of Providence College in Rhode Island in a release.