• Centimetre-long brine shrimp

    They may be only a centimetre long each, but thousands of brine shrimp swimming together can create powerful eddies in the ocean. (Photo: Isabel Houghton/Stanford University)

Every night, swarms of tiny crustaceans swirl up from the bottom of the oceans to feed on algae at the surface. Although each individual organism is only a centimetre or two long, the collective motion of migrating columns of krill, brine shrimp and zooplankton may play an important role in ocean mixing, according to new research out of Stanford University.

Ocean mixing is the process by which heat, energy and nutrients like nitrogen, silica and phosphorous are redistributed throughout the layers of the ocean. The process plays a role in regulating the climate and creating the marine plant life upon which many species depend for food. Until recently, scientists shrugged off the idea that marine animals had any impact on this mixing, but the results of the Stanford study show the nightly migration of swarms of crustaceans may have an effect greater than the sum of their parts.

“If you have some small force mixing the oceans, then it could cascade into major impacts,” says Isabel Houghton, lead author of the study, which was published in the journal Nature on April 18.

Upward migration of brine shrimp in a tank, at 4x normal speed. (Image courtesy Isabel Houghton/Stanford University)

Houghton and her team studied the water movement created by schools of brine shrimp in specialized tanks, using LED lights to prompt the shrimp to move upward or downward. They found that the combined swimming motion of the shrimp creates a jet powerful enough to mix waters of different density and salinity, possibly delivering nutrient-rich deep water to phytoplankton (microscopic marine plants) at the surface. “That the jets were that striking was surprising,” Houghton says.

Houghton thinks repeating the experiment with organisms like krill may show even more dramatic results. Krill are larger than brine shrimp, and their jet streams could be even stronger.

A swimming brine shrimp propels water backwards behind itself

Using a special imaging technique, the researchers were able to visualize the rearward motion of water behind a swimming brine shrimp. (Image courtesy Isabel Houghton/Stanford University)

John Doward is an oceanographer at the University of Victoria who has studied the effects krill have on water mixing in Saanich Inlet in B.C. According to Doward, to effectively observe the impacts biological creatures have on ocean mixing, there needs to be more collaboration between oceanographers.

Historically, physical oceanographers have studied ocean mixing and biological oceanographers have studied organisms, and there has been little cross-collaboration on the topic. “If you can get people together, then we might have a better chance to find out how wide-spread this phenomenon really is,” Doward says.