brine shrimp
October 1, 2014

Sea Monkey Study Suggests Zooplankton Migrations May Affect Ocean Currents

April Flowers for - Your Universe Online

In 1957, the world was introduced to Sea Monkeys, and people were fascinated. Sea Monkeys were advertised in nearly every popular comic book, and even made a trip to space with Astronaut John Glenn in 1998 aboard Space Shuttle Discovery. The public's fascination with the tiny brine shrimp known as Sea Monkeys mostly stems from the fact that the dehydrated eggs hatch, develop and mate given little more than a tank of salt water.

Physicists study brine shrimp for even shorter-term patterns than the life cycle. They are interested in the vertical migration that brine shrimp, and other zooplankton, engage in. Large groups migrate from the surface at night to deeper environments during the day in response to changing light conditions.

According to a new study from the California Institute of Technology (Caltech), this pattern of migration creates water currents much larger than the sum of those created by individual organisms. The study, published in Physics of Fluid, suggests that global ocean circulation patterns can be affected by the collective movement of small marine organisms on a level comparable to the wind and tides.

Brine shrimp (Artemia salina) display a tendency to move toward a light source, a phenomenon called phototaxis. Caltech researchers Monica Wilhelmus and John Dabiri induced a vertical migration pattern in a swarm of the tiny crustaceans in a large water tank using lasers of different colors. When the researchers used a blue laser in a rising motion along the side of the tank, the brine shrimp moved upward. When a green laser was kept above the tank, the shrimp stayed centered. Microscopic silver-coated glass spheres were released into the water, allowing the team to visualize the resulting currents by capturing their changing distribution throughout the migration with a high speed camera.

[ Watch the Video: Laser-guided Vertical Migration Experiment ]

The tiny disturbances created by a single individual plankton have been the focus of previous studies. The currents created by a single organism, however, isn't enough to impact broad ocean flow patterns. The new study found that when two or more plankton swim in close proximity, the eddies created by their motion create a more powerful swirling fluid force. These forces could alter water circulation on a much wider scale.

"This research suggests a remarkable and previously unobserved two-way coupling between the biology and the physics of the ocean: the organisms in the ocean appear to have the capacity to influence their environment by their collective swimming," Dabiri said in an American Institute of Physics statement.

"The expectation of any card-carrying oceanographer would be that the effect would be negligible, given how tiny these organisms are," Dabiri told the Washington Post. "But even though we're talking about organisms just a few millimeters in size, they're creating this collective effect."

Mostly attributed to winds and tides, currents distribute nutrients, salt and heat throughout the oceans. These results, however, suggest that living organisms could also play a part in creating ocean currents. The results also provide experimental evidence for a theoretical model proposed by Dabiri and his colleagues in an earlier paper, published in Nature.

The team hopes to replicate their results in a tank where water density increases with depth. This would simulate the reality of ocean conditions. "If similar phenomena occur in the real ocean, it will mean that the biomass in the ocean can redistribute heat, salinity and nutrients," said Dabiri.

Not everyone is convinced, however.

"My friends who are physical oceanographers have a healthy skepticism of [this] idea," Dabiri says. "But you have to remember that there are billions of [plankton] in the ocean, and the whole is greater than its parts."

National Geographic reports that Christian Noss, an environmental physicist at the University of Koblenz-Landau in Germany, says that he's not convinced the effect seen in the laboratory would be the same in the ocean. He concedes that the experiment was well designed, but that the ocean is stratified into layers of density, unlike a small water tank. This is what Dabiri's next experiment hopes to address.