Marine Animal Colony Swims Using Multiple Coordinated Jets

Posted on September 2, 2015

A marine animal colony called Nanomia bijuga swims by jet propulsion using multiple coordinated jets. Nanomia bijuga belongs to a group of colonial organisms called physonect siphonophores. The colony has jet-producing members called nectophores. Scientists call the colony's multi-jet propulsion system sophisticated and efficient.

The jet-producing nectophores are genetically identical clones. They are arranged in a propulsive unit called the nectosome. The nectosome is the transparent segment on the right in the above image. The nectosome tows the colony's reproductive and feeding units. The organism can travel over 200 meters a day. The oval structure at the tip of the nectosome is called a pneumatophore. It serves as a float.

John H. Costello of Providence College, an Adjunct Scientist and Whitman Center Investigator at the Marine Biological Laboratory (MBL) in Woods Hole, says in a statement, "This is a highly efficient system in which no developmental stage is wasted. It's a quite sophisticated design, for what would seem like a simple arrangement."

The researchers studying the colony found that young members at the leading end of the colony's propulsive unit use their little jets for turning and steering. The older and bigger members farther back push out more water with their jets and provide a powerful thrust for the colony.

Costello says, "The young members have what we call a long lever arm. They are like the handle of a door. 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."

The first video below shows a laser light sheet illumination of particle tracks generated by the swimming siphonophore. The researchers say that this type of synchronized jet production by all of the nectophores usually occurs when the colony is trying to escape from a threat or when it initiates swimming from rest. The second video shows forward, synchronous swimming by Nanomia bijuga.

A research paper on the findings were published here in the journal, Nature Communications.

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