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Sci-Tech

Age determines the transportation jobs in this sea-creature colony

New research finds that members of a group of jellyfish-like marine animals use their jets in different ways -- depending on age -- to steer the colony. No word on retirement age.

The nectosome that serves as the engine of this Nanomia bijuga colony is the transparent section at right.

John H. Costello

Nanomia bijuga!

It might sound like a spell Harry Potter learned to cast at Hogworts, but N. bijuga (as it's known to its scientific friends) is actually a jellyfish-like species that lives in a colony.

What makes the creatures so interesting, as just revealed by a team of scientists publishing in Nature Communication is that when they're all banded together, members of the colony propel the group through the water based on how old they are.

To understand the mechanism by which this happens -- and to add another mouthful to this story -- it's helpful to know that N. bijuga is part of a group of organisms known as physonect siphonophores (but you can just call them physonects). Within a physonect colony, there are things called nectophores, which are "genetically identical clones arranged in a propulsive unit called a nectosome."

Got that? The nectosome is like the engine of an N. bijuga colony and it consists of individual clones called nectophores.

As the colony thrives and new nectophores are born, they emerge at the tip of the nectosome. When they're little, the nectophores can't really produce much thrust, so they use their jets to turn the entire colony, something they're very good at. Their action can make the colony redirect itself very quickly or even go in reverse.

"The young members have what we call a long lever arm," lead author John H. Costello said in a statement. Costello is a biology professor at Providence Collage and an adjunct scientist at the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts.

"They are like the handle of a door," Costello adds." If you push on a door near its hinges -- its axis of rotation -- the door is hard to open. But if you push on the door handle, which is far from the axis of rotation, the door opens easily. A little force placed with a big lever arm has a big effect on turning."

As nectophores age and get bigger, they naturally move back in the colony where their larger jets can be put to use purely as thrust -- a handy ability as the colony sinks to the darker depths of the ocean by day and rises at night to consume plankton.

"The nectosome is only a few centimeters in length, but it tows behind it much longer groups of reproduction and feeding units over distances that can reach 200 meters (656 feet) a day," says the MBL report about the research. "It's the equivalent of a human adult running a marathon every day while towing the equivalent of its body mass behind it."

Costello and his team suggest that the discovery of the way in which N. bijuga colonies move could help in the design of new underwater vehicles.

In conducting their research, the team videotaped physonects in the waters off of Friday Harbor in Washington and measured the flow of particles around the colony as it jetted around the water, as you can see in the following video. The oval object at the head of the colony is known as a pneumatophore, which acts as a float.