for National Geographic News
Mass movements of marine crustaceans called krill generate turbulent currents that may help pump nutrients from the ocean depths to surface waters, researchers say.
In British Columbia, Canada, billions of the tiny swimmers churn the seas as they migrate each night between their safe daytime havens deep underwater to food-rich surface waters (related video: "Krill Swarm Seas by the Billions").
A new study, which appears in tomorrow's issue of the journal Science, shows that the creatures' nightly migration greatly increase the daily mixing of deep and shallow waters.
The finding, by Eric Kunze of the University of Victoria and colleagues, is the strongest evidence to date that marine organisms contribute significantly to turbulent mixing in the oceans, particularly in coastal areas.
Turbulent mixing caused by wind and other physical forces circulates nutrients that are vital to the productivity of marine ecosystems.
(Related news: "Ocean 'Conveyor Belt' Sustains Sea Life, Study Says" [June 2004].)
Ocean mixing also strongly affects the exchange of heat and gases, such as carbon dioxide, between the atmosphere and the ocean.
Stir It Up
To determine the crustaceans' mixing effect, researchers looked at the daily migration of the krill species Euphausia pacifica in Saanich Inlet, a fjord-like ocean arm in southern British Columbia (map of British Columbia).
E. pacifica is one of the most common krill species in the northeast Pacific Ocean, reaching densities of up to 10,000 individuals per 1.2 square yards (1 square meter).
The 0.4-inch-long (1-centimeter-long) creatures spend the daylight hours about 328 feet (100 meters) below the ocean surface to avoid detection by visually oriented predators such as herring.
At night the animals rise en masse to feed on algae that predominantly live in surface waters.
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