Tiny Shrimp Mix Up the Ocean

Crowds of zooplankton swimming upward generate large downward jets of water, a study finds.

Catherine Offord
Catherine Offord
Apr 18, 2018

Brine shrimp illuminated by an LED array swim upward in a water tank (4x speed) ISABEL HOUGHTON

Tiny shrimp and other zooplankton swimming in the ocean could play a major role in ocean mixing, according to researchers at Stanford University. The team reports that as large numbers of the creatures swim upward towards light during the day, they generate downward jets—a finding that suggests the animals could have substantial effects on the structure and composition of the world’s oceans. The results were published today (April 18) in Nature.

“Whether or not swarming adds up to genuine mixing has been the big question in this business for the past decade or so,” Nicholas Butterfield, a paleobiologist at the University of Cambridge who was not involved with the work, tells Science. “This study makes a pretty good claim for nailing it.”

To simulate a tiny piece of the ocean in the lab, Stanford biophysicist John Dabiri and colleagues set up two large tanks of water, and added more than 100,000 brine shrimp, Artemia salina, to each. Then, they encouraged the shrimp to swim upward with lights, and visualized the effects using several imaging techniques.

The team found that even when the water in the tanks was stratified—that is, it contained distinct sections differing in salinity and therefore density—the collective movement of many shrimp swimming upward resulted in large, downward jets of water.

The movement has yet to be observed in the open ocean, the authors note in their paper. However, “the results illustrate the potential for marine zooplankton to considerably alter the physical and biogeochemical structure of the water column,” the authors write, “with potentially widespread effects owing to their high abundance in climatically important regions of the ocean.”