The unique appearance and behavior of jellyfish make them a very restful sight to behold. From their gently bellowing umbrella-shaped bodies and soft, feathery tendrils floating behind them to their beautiful colors, watching them swim makes you feel at peace, but if you’re keeping a pet jellyfish, perhaps you are wondering how they’re able to move and why.
Jellyfish move both passively (allowing the strong currents to help them drift along) and actively using a ring of radial muscles around the margin of their bell body. They contract and relax these muscles to open and close the bell which propels them forward when water is drawn in and expelled out again.
When you consider that jellyfish do not possess a brain, fins, or eyes like most sea creatures, it is remarkable that they are able to move and travel with any kind of skill at all! If you’ve ever wondered how a jellyfish moves in the unique way it does, why it moves, and how they’re able to move its tentacles, we’ll feed your curiosity to all of these queries and more below.
How Do Jellyfish Move?
In the absence of a brain, jellyfish use their nervous system to signal movement in their bodies and tentacles in the same way that motor neurons in human brains send chemical signals to our muscles.
This network of nerves in jellyfish are concentrated in the ring around the edge of their dome-shaped bodies, which tell them to contract and relax in succession so that water can enter and be forced out, pushing them forward.
If it appears like jellyfish float a lot of the time, this is because this is their preferred method of moving and traveling. Jellyfish are passive swimmers and often allow the ocean current to move them along to conserve energy so that when it is necessary, they have the strength to propel themselves fast to escape predators or to ambush and catch their prey.
How Fast Can a Jellyfish Move?
On average, jellyfish typically swim at a rate of 2 centimeters per second but can swim at top speeds of up to 4 miles per hour if they need to. Their top speed is impressively twice as fast as the average human swimmer.
Naturally, the size and shape of individual jellyfish species can have an impact on how fast they move. Let’s look at how this works below:
Small jellyfish – Smaller species such as Moon jellyfish (measuring 2 inches in diameter at their smallest) and the tiny Irukandji jellyfish (measuring around 1 to 2 cm) can dart around fast in the water using jet propulsion since their small bodies can expel water much more rapidly, helping them generate extra force.
Larger jellyfish species – Jellyfish with bells larger than 5 centimeters, however, move a bit more laboriously in the water since the volume of water needed to propel them forward is a little too heavy for their weak radial muscles.
Oblate/prolate jellyfish shapes – Another difference between smaller and larger jellyfish species is the specific difference in body shape. Small jellyfish tend to have long bullet-shaped ‘prolate’ bells whilst larger jellies have flatter plate-shaped or ‘oblate’ bells which make movement more cumbersome.
Bionic jellyfish – And then there’s part-robotic jellyfish. Researchers at Stanford and Caltech University developed and attached a tiny prosthetic pulse enhancer that sent electrical impulses, increasing their swimming speed to 6 centimeters per second!
What is the Movement of Jellyfish Called?
A jellyfish’s movement is often referred to as a ‘jet propulsion’ in the case of faster-moving small jellyfish or more commonly as a ‘vortex‘ – describing the rolling movement of water which appears when they pulse through the water, trapping and expelling rings of water.
Can Jellyfish Move their Tentacles?
Yes, but there are no muscles in their tentacles to help them control their movement via their nervous system. Instead, jellyfish tentacles act like coiled springs and snap into action like a harpoon when alarmed by touch.
What Makes a Jellyfish Move?
Jellyfish rely on the current to move them passively along, otherwise, they will move of their own accord using a combination of water propulsion and signals sent via their nervous system to their ring of muscles to contract and relax, causing them to pulse through the water like a bellow.
When Do Jellyfish Move?
Jellyfish will move naturally in the direction of the current and will gently propel themselves forward to stay within their group. But jellyfish mainly move when they are trying to attract and catch their prey or evade and fool predators.
While they are not skilled at maneuvering in the water like sharks or tuna, jellyfish are energy-efficient swimmers, allowing their somewhat elastic bodies and strong currents to help them travel large distances.
Do Jellyfish Move in Groups?
While some stronger, more active jellyfish such as the Box jellyfish prefer to travel and hunt alone, the majority of jellyfish species often travel in large groups known as a “swarm”, a “smack”, or most commonly as a “bloom” of jellyfish.
Jellyfish are commonly observed in large masses together due to the ocean current carrying them together, which is in the interest of each one since they are all in search of the same thing – food.
Although scientists can’t say for certain whether jellyfish communicate with each other in the group, some point out the possibility that blooms of jellyfish may respond to and share information about the availability of food in nearby waters.