Teamwork key to ocean travel for jellies

"Colonial animals with multiple jets -- like salps and siphonophores -- can time their jets so a whole colony moves at a constant speed," said researcher Kelly Sutherland.
By Brooks Hays   |   Aug. 8, 2017 at 1:16 PM
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Aug. 8 (UPI) -- Salps, a jelly fish-like, gelatinous marine invertebrate, can navigate ocean waters more efficiently in large numbers than by themselves.

Researchers at the University of Oregon used a high-speed, underwater camera system to study how the barrel-shaped planktonic tunicates propel themselves through the water.

The invertebrates use a jet-like water propulsion system to move through the ocean. A forward-facing siphon draws in water from the top and a rear-facing siphon expels the water out the bottom of the jelly's barrel-like body. A filter traps food as the water is pulled in and pushed out the mostly hollow body.

Most studies of salps have focused on the propulsive forces generated by a single specimen. But other forces -- like drag during acceleration and declaration -- affect a salp's ability to move through the water.

In the newest study, researchers were able to measure a variety of forces related to salp movements. Their analysis -- detailed this week in the journal Interface -- suggests salps that swim in colonies, often in long chains, enjoy a smoother velocity profile and are less impacted by drag.

"Individual jellyfish swim using pulsed jets, and previous work has shown that this is an efficient means of moving through the water," Kelly Sutherland, a biology professor at the Oregon Institute of Marine Biology, said in a news release. "One disadvantage is that pulsed-jetters like jellyfish speed up and slow down with each pulse. Colonial animals with multiple jets -- like salps and siphonophores -- can time their jets so a whole colony moves at a constant speed."

The efficiency offered by coordination allows colonies of salps to travel longer underwater distances than individuals. Some salp chains can swim to depths of 3,280 feet and back in a single day.

Researchers believe their analysis of salp motions could help scientists design more efficient jet-propelled underwater vehicles.

"We haven't really moved beyond the propeller when it comes to underwater vehicles," Sutherland said. "Multi-jet vehicles present a highly effective means of transport and also allow for swarm-like behavior where individual units could break apart from the colony to carry out different objectives."

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