So You Decided to Build a Jellyfish Treadmill
John Dabiri, left, with Simon Anuszczyk. Credit: Caltech
by Katie Neith
John Dabiri (PhD ’05), Caltech’s Centennial Professor of Aeronautics and Mechanical Engineering, has studied jellyfish through a variety of lenses over the years. He has sought to understand their energy-saving locomotion strategies so that ocean vessels might copy their efficient form of propulsion. He has found connections between the fluid dynamics of swimming jellyfish and the flow of blood in the human heart, which could help to find indicators of heart disease.
A time-lapse of jellyfish in the treadmill. Credit: Caltech
Starting in 2019, Dabiri’s research focus shifted to trying to augment jellyfish with electronics that can gather data about how the oceans respond to climate change. To undertake this project, however, he knew he was going to need a bigger jellyfish tank. A much bigger one.
To turn jellyfish into deep sea scientists, Dabiri first needed to ensure they could swim for several days with the necessary tiny electronic devices attached to them. And to see if that was possible, he realized, he would need to scale up from the 6-foot-high container in which he had been watching jellies to one nearly 20 feet tall that could house a “jellyfish treadmill” with a controlled flow of water that would let the animals swim in place for as long as necessary.
“We found a space in the Guggenheim Aeronautical Laboratory building that looks like an elevator shaft where they forgot to put in the elevator,” Dabiri remembers. “The idea became this big, 40,000-pound structure that would sit suspended over a region where the researchers can go underneath to gather specific measurements.”
While Dabiri and his lab members pride themselves on building their own instruments, this project was beyond their expertise. So, he consulted the experts: a commercial fish-tank company known for building large aquarium displays for clients that include Las Vegas resorts and wealthy homeowners. A team of civil engineers helped with the design of the support structure for the tank, which is braced against nearly century-old walls.
The Caltech Facilities crew coordinated delivery and installation—no easy task. The team maneuvered hunks of fiberglass and plexiglass through the doors of the lab with about a quarter inch to spare, Dabiri says, then stacked the components up like Legos and bolted it all together.
“I remember when we first filled up the tank, there actually was a moment when we started to hear these cracking sounds,” he says. “I was with one of the vendors underneath the tank and, of course, we bolted out in a hurry. Turns out it was just the normal settling of tank materials, but it highlighted the importance of the engineering having to be very accurate.”
As a final test, a scuba-certified graduate student dove into the tank to ensure a person would be able to enter the tank in the future to fix components and fetch dropped items. “What happens if someone drops their iPhone in?” Dabiri says. “We had to think about protocols for certified divers to be able to go in and retrieve things since this tank is 20 feet deep.”
The now-operating 3,600-gallon tank in Guggenheim contains two motors that control water flows to simulate the upwelling and downwelling of the ocean. A filter system and temperature controls keep the animals healthy. Turning vanes on the tank bottom maintain a uniform flow of water.
The jellyfish treadmill has already led to published science. A recent study in Bioinspiration & Biomimetics outlined results of an experiment that monitored jellyfish implanted with both an electronic device to speed up their natural pulsing motion and an added forebody, which is like a hat that sits atop the jellyfish’s bell. The forebody devices, designed by graduate student and lead author Simon Anuszczyk (MS ’22), are meant to make the jellyfish more streamlined and provide a place to put data-collecting sensors and electronics. Dabiri and Anuszczyk showed that a jellyfish so equipped can swim up to 4.5 times faster than a jellyfish without augmentation, all while carrying a payload.
“I remember when we first filled up the tank, there actually was a moment when we started to hear these cracking sounds.”
Anuszczyk is working on a computer-vision algorithm to recognize the location of each jellyfish with a forebody in the tank and track it over time. “If the animal speeds up a little bit or slows down, you want the tank to increase or decrease its flow to keep the animal in place on the treadmill,” explains Dabiri. This allows it to be continuously monitored. “Simon has come up with a really clever AI-based method to do that using a camera that's looking at the animal.”
New applications like this will help simulate long trips to abyssal depths like the Mariana Trench, which is nearly 7 miles underwater. “We're hoping to be able to let the jellyfish swim in the treadmill for up to three or four days, which is approximately the amount of time it would take for them swim down into the trench from the surface of the ocean,” Dabiri adds.
Dabiri sees the potential for the tank to have many other research applications. For example, he has been investigating brine shrimp, tiny creatures whose swimming motion is similar to the oceanic plankton that migrate vertically every day at sunset in large groups. Understanding the dynamics of the water flow the plankton create each day could be important for understanding carbon sequestration in the ocean bottom or for bringing oxygen and nutrients to the surface. It’s a lot easier to experiment on such flow phenomena in a vertical treadmill than in a 3-foot tank.
“I'm excited that we were able to bring it to life. It's one of the reasons why I'm glad I'm back here at Caltech,” says Dabiri, who returned to the Institute in 2019 after some time at Stanford. “You can have a wild idea and be able to put it into practice.”