A new report investigated on the mechanism of movement of jellyfish-like colonies that utilize multiple jets. The understanding of the colonial species' locomotion processes is said to provide valuable insights regarding distributed-propulsion vehicles that are used under the water.

Jet propulsion techniques for swimming is something that is all too common for marine animals such as jellyfish and squid. However, animal colonies that exert extreme coordination to propel themselves using multiple jets are rare. In a new study conducted by scientists from the Eugene Bell Center of the Marine Biological Laboratory (MBL) in Massachusetts, Stanford University and University of Oregon, the exquisite coordinated movements of both young and old members of the Nanomia bijuga, which is a jelly-fish like colony, are analyzed and were found to have interesting mechanisms.

The body of the colonial species is composed of the nectophore, which is the propulsive component; the pneumatophore, which are gas-filled floats; the nectosome, which aids in swimming and the siphosome, which is the nutrient and reproduction center.

The researchers investigated the swimming patterns of the long-stemmed species by capturing it in a videotape off of Friday Harbor in Washington. They they utilized a technology called laser light sheet illumination to analyze the images and ascertain the flow of the particles surrounding the species as it swims. Through this intervention, the scientists were able to see the size and movements of the individual jets, as well as their angle in relation to the main axis of the animal's body.

The findings of the study, published in the journal Nature Communications, show that the least amount of water was propelled through the jets of the youngest members of the colony. Nonetheless, they play an important role in the overall movement of the species because they are situated at the edge of the nectosome, which is highly distant from where the said part is linked to the entire body. Through this position, the youngest individuals exhibit a motion that, although small in force, is a significant factor as the colony turns its entire body,

"The young members have what we call a long lever arm," says John H. Costello, lead author from MBL. He compared the concept to a door; when one pushes the door near the hinges, where the axis of rotation is near, that person may have a difficult time. But when one pushes the door on its handle, where the axis of rotation is far, that person may easily open the door. So even if the young ones project a small force, placing it with a big lever arm makes a difference.

The older members, on the other hand, exerted powerful movements from the back of the pack, as the entire body swims away from the deep ocean towards the surface. Costello describes the design of the species as sophisticated, considering the rather simple arrangement.

In the end, the scientists concluded that the division of labor among the members enables even the smallest and youngest ones to play a critical role in the colony's movement and long diurnal vertical migrations.

Photo: Bernard DUPONT | Flickr

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