Scientists at the University of Oregon say a type of tiny jellyfish – colonial siphonophores – that swims rapidly by coordinating multiple water-shooting jets from separate but genetically identical units, may hold the key to future design for manmade underwater craft.
“This is a very interesting system for studying propulsion, because these jellies have multiple swimming bells to use for propulsion,” says biologist Kelly Sutherland.
“This is relatively rare in the animal kingdom. Most organisms that swim with propulsion do so with a single jet. These siphonophores can turn on a dime, and very rapidly.”
The system may provide “a natural solution to multi-engine organization that may contribute to the expanding field of underwater-distributed propulsion vehicle design,” Sutherland and her co-authors conclude in their paper, published in Nature Communications.
The jellies studied are Nanomia bijuga. They are members of the phylum Cnidaria, whose members have specialised stinging cells that are used mainly for capturing prey.
N. bijuga rarely exceed five centimetres in length but has tentacles that can extend to a 30 centimetres long.
The scientists monitored the colony’s swimming technique by putting them in small tanks and adding buoyant particles as tracers. The tanks were lit with a thin, 2-D laser sheet and the jellies’ movement was captured at 1,000 frames a second.
The data was analyzed with particle image velocimetry, a technique that provides instantaneous velocity measurements.
“The younger swimming bells at the tip of the colony are responsible for turning,” Sutherland said.
“They generate a lot of torque. The older swimming bells toward the base of the colony are responsible for thrust.” Their tentacles capture zooplankton, the tiny organisms that these jellyfish consume, she added.
Bill Condie is a science journalist based in Adelaide, Australia.
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