Cover Story | Education

Sean Collins studies how marine anatomy relates to faster propulsion

Figuring out how an aquatic animal's shape helps it move

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Why do humans walk upright? Why do dogs run on all fours? Why do organisms move the way they move? This is the basic question that Marine Ecologist Sean Collins is trying to answer – and the answer is not basic at all. To attempt to answer this, he researches jellyfish and other swimming animals. Specifically, he studies how an organism’s shape and movement affects how it swims and feeds. By studying this, he hopes to have a greater understanding of the jellyfish’s impact on coastal ecosystems.

In studying jellyfish, Sean has found that how jellyfish move is directly related to how they eat. As it propels itself forward, it creates a large feeding current that transports its food through its trailing tentacles. Once he learned this, he focused on studying how jellyfish swim, which led him to study how other animals swim. “I am interested in why animals’ swimming appendages are always bendy: a jellyfish’s bell (outer hood), a fish’s fins or a dolphin’s tail,” says Sean. “So, most recently I have been working with swimming lamprey (an eel-like creature) to examine what the effects of body bending are on the surrounding fluid and how bends generate swimming thrust.”

He once collaborated on a project for the Office of Naval Research where he helped design a robotic jellyfish. Sean was trying to quantify how it swam and how the water was flowing around it. Initially, the robotic jellyfish would not move forward. It wasn’t until they added a thin bendy flap around the edge of the bell that the robot took off. This was one of his first clues into the importance of having propulsors that bend.

This work directly relates to engineers who are trying to design better underwater vessels. Sean explains that human engineered vehicles always use rigid parts for propulsion. Think about how a submarine is constructed; it’s basically a long torpedo with a propeller behind it. If engineers could better understand the advantages bending has on propulsion, it may help them to incorporate these concepts into vehicle design.

In the long term, Sean would like to have a real impact on our understanding of why animals have evolved the way they have. Hopefully he’ll be able to use this knowledge to better understand how jellyfish impact ecosystems, how animals swim and how bendy parts mean faster propulsion.

marine ecology, sean collins, roger williams university, rwu, the bay magazine, grace lentini, underwater propulsion, jellyfish,

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