Krill kick up a storm of ocean mixing

A single Pacific krill doesn’t grow as big as its cocktail-shrimp cousins. Yet a swarm of krill making its daily commute in a Canadian inlet boosted water turbulence by factors ranging from 2,000 to 20,000.

That’s the result of the first measurement of a creature’s contribution to the mixing of ocean waters, explains Eric Kunze of the University of Victoria in British Columbia. He says that he hopes the finding will inspire other scientists to measure biological turbulence in addition to mixing from storms and tides.

Turbulence drives many ocean events with global implications. For example, mixing affects gas exchange between the atmosphere and the water.

In recent years, scientists have estimated how much ocean creatures might stir things up. After listening to a talk on such calculations, Kunze says, he and several colleagues realized they had equipment to measure that mixing.

They made several sets of measurements in 2005 at Saanich Inlet on the coast of Vancouver Island. They had located a swarm of Pacific krill spending daylight hours some 100 meters down in the inlet. As the sun went down and light-dependent predators stopped hunting, the krill rushed to the inlet’s surface to feed on plankton.

During the 10 or 15 minutes of the krill commute, the team’s monitors picked up as much turbulence as that produced by a rushing tide. At dawn, the krill swam down, again stirring the water.

These short frantic bursts raised the inlet’s daily average for water mixing 100-fold, Kunze and his colleagues report in the Sept. 22 Science.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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