Jellyfish are infamous for invading ecosystems and taking them over, forming huge blooms that drive out other species
Brad Gemmell of the Marine Biological Laboratory in Woods Hole, Massachusetts, and colleagues studied the moon jellyfish (Aurelia aurita), a common species often seen drifting along in currents. Like other jellyfish, it contracts its bell and pushes water out to drive itself forwards – an effort that does not generate much thrust.
But that isn't the only way the jellyfish moves, Gemmell found. After the thrust phase, when the bell relaxes, a ring-shaped vortex of spinning water forms beneath the jellyfish – shown as the red region of high pressure in this image. This area of positive pressure pushes against its body and generates extra thrust. This allows the jellyfish to travel 30 per cent further for each contraction of the bell, without any more effort.
As a result of this extra thrust, which comes essentially for free, the moon jellyfish swims three times as efficiently as a salmon. This leaves jellyfish with enough energy to grow bigger, roam over great distances and hunt more prey.
Gemmell and his team aren't the only ones investigating jellies' smooth moves. Researchers have previously used laser cameras and fluorescent-dyed sand to image the creatures in action.
Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1306983110
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