Baby starfish whip up whirlpools to snag a meal

starfish larva making vorticies

LUNCH BUFFET Swirling whirlpools are created by a starfish larva, shown in this time-lapse image. These vortices provide the larva with a conveyor belt of food, sucking in algae. Small beads suspended in water create trails showing fluid flow.

W. Gilpin, V.N. Prakash, M. Prakash/Nature Physics 2016

A baby starfish scoops up snacks by spinning miniature whirlpools. These vortices catch tasty algae and draw them close so the larva can slurp them up, scientists from Stanford University report December 19 in Nature Physics.

Before starfish take on their familiar shape, they freely swim ocean waters as millimeter-sized larvae. To swim around on the hunt for food, the larvae paddle the water with hairlike appendages called cilia. But, the scientists found, starfish larvae also adjust the orientation of these cilia to fine-tune their food-grabbing vortices.

Scientists studied larvae of the bat star (Patiria miniata), a starfish found on the U.S. Pacific coast, by observing their activities in seawater suffused with tiny beads that traced the flow of liquid. (Watch a video of the experiment.) Too many swirls can slow a larva down, the scientists found, so the baby starfish adapts to the task at hand, creating fewer vortices while swimming and whipping up more of them when stopping to feed.

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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