Many sea creatures are solitary beings, but for Nanomia bijuga, it seems things are always better when they’re together (*hums Jack Johnson*). Much like their jellyfish cousins, these marine critters squirt out water in order to propel themselves through the ocean. But these team players don’t go about it solo: Stringing themselves into an orderly line, the colony maneuvers itself through the environment by coordinating jets produced by multiple members.
The organization of the individual jellies is also key to the success of this propulsion system. Taking the lead are the younger members, steering the colony with their jets, while bringing up the rear are the older, more sizeable jellies that provide the unit’s thrust.
“This is a highly efficient system in which no developmental stage is wasted,” lead author John H. Costello of the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, said in a statement. “It’s quite a sophisticated design, for what would seem like a simple arrangement.”
Belonging to the same group as corals and jellyfish, N. bijuga is a type of colony-forming marine organism called a physonect siphonophore. These animals spend their days lurking in the depths of the ocean, probably to avoid the mouths of hungry predators, but frequent the surface when the sun goes down to serve themselves a tasty plankton treat.
While the individuals may seem like nothing to write home about, the colonies they form turn out to be something special. The jet-shooting young’uns at the front tend to be a group of genetically identical clones organized into a small propulsive unit termed a nectosome. While this humble gelatinous blob may fit in the palm of your hand, it hauls an impressively long train of other units that have different jobs, such as reproduction and feeding. The distance these colonies can travel each day – up to 200 meters (650 feet) – would be like a human running a marathon while also dragging along their own bodyweight.
To get a better idea of how they achieve this impressive feat, MBL and University of Oregon researchers collected a bunch of specimens from around Friday Harbor, Washington, and examined them in small tanks illuminated with a slim laser sheet. Using cameras capable of capturing 1,000 frames per second, the scientists were able to analyze their locomotion by looking at particle flows around the colony.
As described in the September 2 issue of Nature Communications, the team discovered that the youngest colony members squirted out the least amount of water. This may seem like a copout, but a small push is all that is required from them to steer the group, thanks to their position at the front of the nectosome, distant from the long trailing tentacle of colonies. The older, larger members positioned further back are capable of pushing out more water than those at the front, which provides the thrust needed to travel distances, rather than contributing to the steering.
“These patterns permit all members of the colony to make important contributions to the propulsion and maneuvering traits that are crucial to the success of N. bijuya in its natural environment,” the authors conclude.