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Scientists now know why jellyfish-like salps swimming together move better than a single salp pulsing all by itself. According to marine biologist Kelly Sutherland, these findings could guide the development of jet-propelled underwater vehicles.
At a research station on a Pacific island off Panama, researchers are using high-resolution camera systems to study the propulsion of these elusive, hand-sized planktonic tunicates both underwater and in the lab.
But wait, what the heck is a salp? Salps, also sometimes called “the ocean’s vacuum cleaners,” are small barrel-shaped invertebrates that feed on plankton. They swim by producing a jet from a rear-facing siphon and refilling with water from a forward facing siphon. The same water that helps propel them forward also contains food particles that they collect on a feeding filter as the water passes through their mostly hollow bodies. They can be found individually or in colonies up to 15 feet long.
Previous research focused mostly on how much thrust they produce, overlooking side effects of their periodic pulsing motion such as drag caused by acceleration and deceleration.
“Salps are fairly difficult to access and are notoriously patchy,” said Sutherland, a biology professor at the UO’s Oregon Institute of Marine Biology in Charleston and the Clark Honors College. “We’ve been able to do this work because we’ve found the right field sites where their presence is pretty reliable. Our underwater camera systems allowed us to get good quantitative information about how they achieve such effective swimming.”
The most interesting feature about these organisms is that they have multiple jets. Jellyfish propel themselves by using pulsed jets, but this requires them to speed up and slow down each time. Salps, on the other hand, can time their jets to move at a constant speed to propel the whole colony, allowing them to migrate up to depths of 3,280 feet.
The new study was published online on August 2, 2017 in the Royal Society’s journal Interface.
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