Most of us have observed jellyfish in action at one time or another. In my experience, I have watched them as they surrounded the small boat I was on, on a sunny summer day with no way to swim until they’d made their way past. I’ve also watched them in an exhibition at the National Aquarium in Baltimore. From the vantage point there, I was able to see the portions of the jellyfish that were below the waterline. It was a beautiful site.
This is the first post in a series on jellyfish. It explores the way jellyfish move through deep water. Sometimes it appears that jellyfish simply float and move with the water in the waves. Other times it seems that the wind blowing across the surface of the water is pushing the jellyfish along the surface.
The first situation is not true. The jellyfish do not float in a moving column of water any more than a water molecule floats along in that same moving column. In fact, if you observe a bottle in the water, you’ll notice that it moves in an oval with the motion of the wave. That is to say that it is the energy of the wave that moves the water – or bottle – with the motion of the wave. In reality, the bottle – or water molecule – remains pretty much steadily in place.
Because of this, a jellyfish that simply floated on the surface on a calm day in a place with no wind would be a jellyfish who made no significant forward progress.This clip from the Office of Naval Research will give you an excellent idea of the way it works. (See it in action.) To make any significant progress would require the wind.
So how do jelly fish get anywhere?
In the next post in the series, we’ll take a look at the newest research by Brad Gemmell and his colleagues at the Marine Biological Laboratory in Woods Hole, Massachusetts.