How a jellyfish-like creature could inspire better underwater vehicle design

The jellyfish-like Nanomia bijuga is found throughout the ocean, including off the coast of Oregon and Washington. It’s not much to look at, but the unusual way it moves could help humans design better underwater vehicles. Nanomia moves by jet propulsion — pumping water through its body to push itself forward. University of Oregon researchers found that the animal can control these jets based on its needs, either synching them up for speed or pumping each individually for more efficient swimming. Researchers concluded that the feature could help inform how humans can build more efficient underwater vehicles.

Kelly Sutherland is an associate professor of biology at the University of Oregon. She joins us to talk about jet propulsion and bio-inspired design.

The following transcript was created by a computer and edited by a volunteer:

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. The jellyfish-like sea creature Nanomia bijuga is found throughout the ocean, including off the coasts of Oregon and Washington. It may not look that impressive, but the way it moves sets it apart. It has about two dozen separate small jets that can either be used all at once or in sequence. Researchers at the University of Oregon have been learning more about the benefits of this unique design. They published their results in the prestigious journal, the Proceedings of the National Academy of Sciences. They say Nanomia’s novel way of getting around could help inform the design of more efficient underwater vehicles for humans. Kelly Sutherland is an associate professor of biology at the University of Oregon. She joins us to talk about jet propulsion in these creatures and bio-inspired design. Kelly Sutherland, welcome to the show.

Kelly Sutherland: Thanks so much for having me.

Miller: I thought we could start by having you describe this sea creature. What does Nanomia look like?

Sutherland: Nanomia is, I think, a really beautiful animal that’s actually a colony. So as I think you mentioned, they’re related to jellyfish. They’re related to things like sea anemone and corals. They have multiple swimming units, or propulsers, that are strung together in a chain. So they look a little bit like a bunch of tiny transparent little jellyfish that are strung together. And there can be several of these little swimming units, all the way up to about 20. And these swimming units take in little packets of water and push that water back out by contracting their muscles. So what you have is essentially a string of little jet propellers.

Miller: What do you mean when you say that one of these organisms is actually a colony?

Sutherland: It’s kind of hard to wrap your head around, but they have a bunch of what we call zooids, so they’re identical zooids. And in Nanomia, they actually have the propulsive units on the front end, and on the back end, they have some other units that do other tasks for the colony. So there’s some that are responsible for feeding, others that are responsible for reproduction, and some that are responsible for defense. And so these different individuals are kind of working together to keep the colony going.

Miller: But these aren’t like organs of a single species that all come together to form that organism. These are genetically identical components that we can truly think of, each one, as its own organism?

Sutherland: Yes, more or less. And again, it’s hard to wrap your head around. You have these genetically identical units. With the propulsive units, they all look identical. Some of the units have differentiated to have different tasks, but they are individual kinds of individuals that make up this colony.

Miller: How do they communicate and organize themselves in action?

Sutherland: One of the really interesting and kind of inspiring things about Nanomia is that it’s Cnidarian and like all other Cnidarians, it does not have a centralized nervous system. So there’s no kind of brain or central command station that’s giving orders to the colony. They do have nerves, so they do have wiring for the units to be able to communicate with each other and they likely respond to different stimuli that are sensed at different parts of the colony and then the messages are propagated through the neurons. But they’re able to really achieve this diverse array of behaviors even with a really simple nervous system because they have these distributed propulsion units.

Miller: It’s a biological anarchy where there’s some decentralized control, but still they do work together and there is a kind of decentralized organization.

Sutherland: That’s right. Again, all very weird concepts to wrap one’s head around. I often say that I study really weird organisms in the ocean and I often say you can’t make this stuff up. It’s just really fascinating now.

Miller: Let’s turn to the locomotion because that’s one of the big reasons to have you on today. My understanding is that jet propulsion, or what we could call jet propulsion in sea creatures, that alone is not unusual. Right? I mean, a lot of sea creatures use that way of ejecting water to push themselves forward.

Sutherland: That’s right. Jet propulsion shows up in a lot of different organisms and what we’ve seen is that it’s actually a very effective and efficient way of moving through the water. This idea of pulling water in and then pushing it out in a smoke ring-like structure is a really effective way to move. But most organisms just have a single jet.

Miller: And Nanomia has, as you noted, up to 20.

Sutherland: Right.

Miller: How do they work together?

Sutherland: Having these multiple identical swimming units, even though they have really simple shapes individually, opens up a diversity of movement possibilities and it allows for different swimming modes. In this current study we showed that they have synchronized swimming and that’s where all of the units pulse together, and that results in very high accelerations and high speed. So this would be a good kind of an escape situation. Alternatively, the different units can pulse asynchronously. With asynchronous propulsion, you have pulses that are propagated down the length of the chain. This type of swimming is slower, but it’s also more economical and so it’s better for long distance swims or migrations.

Miller: How much do they need to travel in the course of any given day? What is a Nanomia migration like?

Sutherland: Nanomia, like a lot of other planktonic organisms, undertake a vertical migration each and every day. So they undergo what’s called a diel vertical migration. And that just means that every single night, they swim to the surface and they feed at the surface, and then during the daytime they return to depth. And so having an economical mode of swimming is likely important for migrating long distances. As I said, other organisms are doing this. In fact, it’s the largest migration on the planet that happens every night, that all of these organisms are migrating up to the surface. It is the equivalent of you or me running a marathon each day, in terms of if you put things on their size scale. They’re much smaller than we are. They’re an inch or two in length.

Miller: But based on their size, that’s the distance of traveling. When you say the largest, you mean, in terms of biomass moving itself up and down?

Sutherland: Exactly, yeah. Every single night there’s a huge amount of biomass that moves up to the surface. And Nanomia was actually kind of an early poster child of this migration because they have a little gas filled bladder in their body that was picked up by acoustic methods. Originally, the Navy was using acoustics to look at the particles in the water and they thought, wow all the particles are moving up at nighttime and then going back to depth. And Nanomia was one of the big organisms that was in this migrating layer that was going up and down. And now there’s been a lot more study into this phenomenon.

Miller: When you say that it’s economical to move this way. Is that another way to put it, that it’s efficient that they can actually move pretty quickly without using that much energy when they are asynchronous, or sort of all the different jets firing off sequentially? It’s an efficient way to move, but not necessarily that fast?

Sutherland: They have this efficient mode and that’s exactly right. So it’s hydro dynamically efficient. It’s energetically efficient, and to kind of put it into context, achieving both fast swimming and slower. More economical swimming in the same organism is problematic. So there are animals that are capable of both speedy and long distance modes, but they typically do so with complicated body shapes and multiple propulsar types. Fish are a good example of this. And what’s really compelling about Nanomia is that it achieves these two different modes with these really simple shapes and with a really simple nervous system. And in addition to the economical swimming, we’ve previously shown that having redundant swimming units also allows them to be highly maneuverable so they are very effective at turning and also swimming in reverse. This idea of having distributed propulsars is really the key to opening up these different modes, even with a relatively simple system,

Miller: If it can turn easily and swim in reverse, does that mean that its individual propulsars themselves can move? They can swivel?

Sutherland: So it’s not so much that they swivel, it’s just a matter of firing different pulsars to affect a turn. The colony is kind of a long linear tube. The shape is very tube-like and by just pulsing the one at the very tip, at the apex of the colony, that’s at the end of a really long lever arm, and so you end up getting this really effective turn just by pulsing a single pulsar. And with the reversals, they have these hoes like nozzles at the end of each of those swimming units and when we looked really closely, we saw that they were able to kind of point those hose nozzles backwards so they could direct the flow backwards and reverse their direction.

Miller: It must be exciting for you. You’ve been studying these creatures for years now, right? But you’re still learning things about even something as seemingly basic as the way it moves in the water?

Sutherland: Yeah, it’s a lot of fun. I really enjoyed looking deeply at how organisms work. In earlier work, we started off looking at individual jellyfish and saw that that individual jellyfish were really efficient swimmers. When you start to dig into understanding the shapes and the movements and also the propulsion, you just really get into a deep understanding of how these things work and looking at the colonies was the next natural step.

Miller: As I noted, you wrote in the article that this particular form of locomotion and its novel combination of speed and power, efficiency and distance, using the same set of propulsion, could be a model for human designers of underwater vehicles. What exactly do you have in mind?

Sutherland: I think when you’re looking really deeply at an organism and understanding how it works, there’s a natural progression to start to think about how this understanding might be applied to solve human design bottlenecks. That kind of gets into this concept of bio-inspired design, which is really just looking to nature to find new solutions to solve our design challenges. And the way I look at this is that there are just limits to our ingenuity, there’s just limits to what ideas we can come up with. And animals have evolved a diversity of ways–in this case ways to move around–and maybe some of their modes of swimming can be useful in reimagining underwater propulsion.

Something that I like to be really careful about is that when you’re looking to nature for inspiration, it doesn’t necessarily mean that you’re going to design something that looks exactly like Nanomia, in this case. But taking some of those fundamental principles - this idea of having multiple, distributed propulsar, having them coordinate in different ways to achieve different swimming modes - that kind of basic understanding is something that could be applied in a lot of different contexts.

Miller: What are some of the other big questions you still have about Nanomia?

Sutherland: I would say that the questions I have are really broader questions about colonial organisms. It turns out that having distributed propulsars is more common than most people realize. It’s hard to wrap one’s head around again, but out in the open ocean, this strategy of having multiple propulsars is not that uncommon, even though it only appears in a couple of animal lineages. The next thing that I’m interested in doing is looking more broadly across different species that have multiple propulsars and understanding how the different arrangements and coordination of those propulsars give rise to different ways of swimming.

Miller: Kelly Sutherland, thanks very much for joining us.

Sutherland: Thanks for having me.

Miller: Kelly Sutherland is an associate professor of biology at the University of Oregon. She joined us to talk about a jellyfish-like sea creature called Nanomia and the way it propels itself through the water.

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