Study: Jellyfish, lampreys pull their weight in ocean swimming

Other than living in water, the bulbous jellyfish and the sinuous lamprey may seem to have little in common. And yet these two animals share a remarkable secret ability that allows them to move with great efficiency — they essentially pull, rather than push, their way through the water.

Instead of creating high-pressure zones by pushing against the water, these two very different animals create areas of low pressure that force water past their bodies, according to new research out of Stanford University and the Marine Biological Laboratory.

The discovery, published in the journal Nature Communications, might force scientists to rethink some of the fundamental assumptions about animal propulsion.

Humans swim by using our arms and legs to push against the water, generating high-pressure regions in the places where we push it out of the way.

It’s long been thought that this is essentially how the ocean’s more naturally gifted swimmers move: A fish swings its tail back and forth, pushing against the water. Given the way that we move, it seems to make intuitive sense.

For this paper, the researchers studied two ocean-dwellers: lampreys and jellyfish. These animals may look different, but they share a common distinction: They’re both among the ocean’s most efficient swimmers.

The scientists filled a tank with millions of tiny silver-coated glass beads just 10 micrometres across and outfitted it with lasers and cameras; the lasers would highlight the movement of the glass beads, as the animals swam through the water, revealing patterns in its complex dynamics.

The researchers found that the jellyfish and normal lampreys were bending their bodies in a way that created low-pressure zones at the curves, causing water ahead of them to rush in and fill those zones. By creating these low-pressure areas, the animals essentially were sucking their bodies forward through the water. And while there were high-pressure zones created in this process, Dabiri’s team found that those zones were essentially the byproduct of the animal’s motion, not the reason for it.