Jellyfish help mix the world's oceans

Small sea creatures such as jellyfish may contribute to ocean mixing by pulling water along as they swim, according to a new study. The collective movement of animals could generate stirring of the same order as winds and tides.

Pulsating jellyfish stir up the oceans with as much vigor as tides and winds, scientists have found. The new study, which is published in the July 30 issue of the journal Nature, reveals a mixing mechanism first described by Charles Darwin's grandson that is actually enhanced by the ocean's viscosity, making these tiny sea creatures major players in ocean mixing.

In their field experiments, the researchers squirt fluorescent dye into the water in front of the Mastigias jellyfish and watched what happened as the animals swam through the dyed water. Rather than being left behind as the jellyfish swam by, the dyed water travelled along with the swimming creatures.

As the jellyfish swims, water gets pulled along with the animal, seen as swirls of red or green dye that was injected into the water.

Here's how the researchers think it works: As a jellyfish swims, it pushes water aside and creates a high-pressure area ahead of the animal. The region behind the jellyfish becomes a low-pressure zone. Then, the ocean water rushes in behind the animal to fill in this lower pressure gap. The result: Jellyfish drag water with them as they swim.

Jelliy fishes have huge variation in their body shapes. Moon jellyfish (the kind typically seen at aquariums) have saucer-shaped bodies and can carry a lot of water with them. But other bullet-shaped jellyfish would drag smaller volumes of water.

Global impact
The ocean churning has broader implications.
With this mechanism the animals can pull nutrient-rich fluid up to nutrient-poor areas and pull oxygen-rich fluid down to oxygen-poor regions,".
On larger scales, the biologic blender could impact the ocean circulation, which affects the Earth's climate.