Single-celled marine organisms called diatoms can rapidly alter the speed at which they move through the water column, despite lacking structures for motility.
Diatoms are photosynthetic and are a major contributor to ocean productivity. Brad Gemmell and his colleagues at the University of Texas Marine Science Institute in Port Aransas filmed three species of diatom (Coscinodiscus radiatus pictured) as they sank slowly in laboratory tanks. All exhibited stop-start movement: previously unobserved bursts of rapid sinking followed by periods of near-zero sinking. The authors visualized the flow of water around individual diatoms, and suggest that the organisms alter their buoyancy by exchanging ions with the seawater.
Rapid changes in sinking speed could explain how these diatoms compete for nutrients with cells that can actively swim.
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Diatoms sink in fits and starts. Nature 538, 143 (2016). https://doi.org/10.1038/538143b
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DOI: https://doi.org/10.1038/538143b