Kakani Katija on Ocean Currents: Jellyfish & the Moon

Kakani Katija

Can a tiny ocean organism affect weather around the world? Kakani Katija dives into the emerging field of biogenic ocean mixing for answers. She’s exploring the external power sources that propel the perpetual motion of oceans. Winds and tides have long been known to drive currents circulating within the ocean. But as Katija’s evidence increasingly shows, the movements of swimming animals could have an equally powerful effect.

Our ever-undulating seas play a huge role in global climate systems by transferring heat back and forth from the Equator to the Poles. If this watery “conveyer belt” of heat were to stop, extreme climate changes would occur. The continuous mixing of seawater also serves other key purposes. “Ocean water is stratified from top to bottom with a wide range of different temperatures, salinities, and pressures,” Katija describes. “Ocean mixing acts as an essential delivery system, carrying oxygen and nutrients from one layer to another, literally sustaining life as we know it.”

Sea creatures, from the miniscule to the monumental, may influence mixing to a surprising degree.

Katija admits that “when people compare the size of a fish, to the huge depth and volume of Earth’s oceans, it’s hard to believe something so small could ever affect something so large.” A background in engineering and mechanics made her skeptical as well. “But through fieldwork and lab experiments we’ve identified mechanisms to explain how animals swimming in concert could indeed affect things on a much larger scale. Some of our findings show this impact may be the same magnitude as winds and tides.” It seems strength lies in numbers. Smaller creatures make up a large percentage of the total biomass in oceans, in many cases numbering thousands per square meter. Lab measurements show that swarms of tiny krill or copepods may in fact have the greatest potential of all to mix fluids. “We want to know where these big populations are located, how they act together to shape mixing, and what happens when whole populations migrate simultaneously in the same direction.”

To discover the answers, Katija hopes to study everything from jellyfish traversing a Pacific island’s saltwater lake, to migrating krill swarming a Canadian inlet. “I prefer the tropics, since more often than not, I’m the one who gets in the water,” she comments. Katija and the biologists she works with record and measure the flow of water around animals using fluorescent dyes and a sophisticated underwater laser-video camera system the team developed.

Katija’s research could provide important new reasons to protect endangered sea life since, while winds and tides are renewable, animals are not. “The decline and collapse of fisheries may have already severely changed the amount of biogenic energy animals can contribute to mixing our oceans,” she warns. “Our data could underscore the need for drastic conservation measures.”

The team’s deep-sea observations could also help engineers craft new bio-inspired designs on land. “We spend a lot of time examining how animals’ shapes and swimming mechanisms affect propulsion as they move through the water. Biomechanics research shows that biological propulsion is often more efficient than anything humans engineer.”

So what can we learn from swimming animals and apply to our own designs? One major automobile manufacturer has already created a concept car based on boxfish, a species known to have great structural strength and maneuverability but extremely low mass, flow resistance, and drag. The sea is swimming with other ideas: jellyfish that can feed and move simultaneously, squid that employ a complex interaction of jet propulsion and fins, and tuna that set speed records with their aerodynamic body planforms. Perhaps most amazing of all is a one-millimeter-long copepod shown to be the world’s strongest, fastest mechanical system. In relation to its size, the tiny shrimp-like organism is ten times stronger than any other animal or motorized system thanks to two independent propulsion mechanisms and an extremely hydrodynamic shape.

Katija’s academic background in aeronautics might have propelled her to explore heights rather than depths. “My collaborators took a real gamble bringing in an engineer. Coming in to this world of oceanography from the outside, what struck me most is how little we know about our seas, the processes driving them, and the animals they contain. I know of scientists who conduct marine life surveys and identify new species every time they go out on a dive. My work is just beginning to peel away the outer layer of what might be important to the state of our oceans. We’ve explored only a sliver of our seas. They’re really our final frontier here on Earth.”