In 2009, John Dabiri, a Caltech professor of aeronautics and bioengineering, and a colleague found that jellyfish can actually move water over distances greater than their body length just by swimming. This he said “was the first hint that animals could transport water over distances much longer than their body size.”
The scientist next wondered if the same would be true for smaller animals that are found in the world’s oceans like krill and copepods. Swarms of these animals rise up during the night to feed on phytoplankton and sink back into the darker depths during the day. He and graduate student Monica Wilhelmus wondered if such dramatic vertical migrations might produce currents large enough to mix seawater. If so, then this mixing may need to be accounted for in simulations of Earth’s future climate.
The scientists spent a lot of time trying to figure out how to study these animals. Krill are common in the ocean, but difficult to keep in the laboratory so they decided to use brine shrimp also known as sea monkeys. The brine shrimp have a swimming motion that is similar to that of krill, are easier to raise and are highly attracted to light.
To get a sense of the brine shrimps’ collective power, they were placed in a special aquarium that contained lasers. A blue laser that rose from the bottom to the top of the tank triggered upward migration. A green laser shone in the middle of the tank kept the brine shrimp away from the edges, centered in the tank, similar to how they stick together in the ocean. A red laser sheet was used to track the water movements, because brine shrimp don’t seem to notice that color. The red light reflected off small silver coated beads that were added to the water and revealed how the water was flowing with the help of a high speed camera.
Dabiri and Wilhelmus recently published their findings in the journal Physics of Fluids.
The scientists found that although an individual shrimp couldn’t move much water very far, together they had a powerful effect, particularly when they were swimming near one another. The collective movement of such tiny swimming animals like krill could be contributing an estimated 1 trillion watts of power to the ocean, comparable to the combined effect from the winds and tides, which contribute an estimated 2 trillion watts.
“This research suggests a remarkable and previously unobserved two-way coupling between the biology and the physics of the ocean,” John Dabiri said. “The organisms in the ocean appear to have the capacity to influence their environment by their collective swimming.”
