Can Starfish Swim? (Explained)
Starfish, or sea stars – the term scientists prefer because the invertebrates aren’t actually fish – are generally simple animals that we usually see on the bottom of the ocean floor or attached to rocks. But have you ever wondered if they can swim? And if they don’t, how do they move? In this post, we’ll talk all about that. However, let’s start with a quick answer:
Starfish cannot swim but they walk using their tube feet located underside of their bodies. The only time when starfish can swim, or more rather float, is during the larval stage.
However, this certainly doesn’t tell the whole story and in this post, I’ll explain more about how starfish move and how starfish larvae can float in the water. Furthermore, I’ll explain how fast they can move and why they move. Read on!
How do starfish move?
Starfish move using hundreds of tube feet located on their oral side (underside of their bodies). At the end of each foot, they have a small suction cup, which can attach to objects like rocks or corals. Thanks to the suction motion, starfish can also open up the shell of their prey.
See the video below how starfish move their tube feet:
They are able to move their tube feet thanks to the water vascular system – a system of canals that is used by all Echinoderms such as sea urchins, sand dollars, or sea cucumbers. These canals connect each tube feet and create contractions by using sea water.
How does the water vascular system work?
First, the water enters though madreporite (also called a sieve plate) – a small, smooth plate located on the aboral side of the sea star, slightly off the center, and flows to the tube called a stone canal, which is a second part of the water vascular system.
Next, the water goes into a ring canal that circulates the sea stars’ center of the body. It’s wide and pentagonal or five-sided. This ring connects the fourth part of the vascular system – a radial canal.
The radial canal runs throughout the length of each arm of the sea star and it terminates as the lumen of a terminal tentacle. The canal runs immediately to the oral side of the ambulacral muscles. The radial canal spreads into two series of short and narrow branches called lateral canals – the fifth part of the water vascular system.
Each of the lateral canals has a valve inside to prevent a backward flow of the water into the radial canal. Next, these canals are connected to the base of tube feet and their ampulla – the sixth and seventh part of the circulatory system.
The ampulla is the suction cup I already mentioned before. It’s located at the end of sea stars’ tube feet (also called podia) that create contractions. When the sea star wants to make suction, the ampulla pulls water out of the podia. When it wants to extend the tube feet, the suction cup pushes the water into the end of each foot.
As a result, the starfish moves forward steadily and is able to climb or attach to the rocks. Interestingly, the water vascular system doesn’t only allow starfish to move but exchanges gases and nutrients. You can read more about starfish circulatory system in my other blog post, “Do Starfish Have Blood And A Heart?”.
Free-swimming starfish larvae
Interestingly, there is a time during the life of a starfish that it can swim, sort of. It happens during the sea star’s larvae stage. Just like other Echinoderms, starfish reproduce through a behavior called broadcast spawning.
During this process, several females and males release their eggs and sperm into the water column, where fertilization occurs. Once eggs are fertilized, they develop into larvae. During the larval development, sea stars float in the water and, together with other microscopic organisms, are part of the plankton.
These tiny larvae float in the water for several days to several weeks. During this time, they eat smaller microorganisms and start developing arms. Once they’re ready and reach a suitable habitat, they settle on the seafloor, transform, and grow into adult size.
How fast do starfish move?
Starfish are very slow animals, and most of us probably never even notice them moving. In fact, they’re even considered to be one of the slowest animals on the planet, right after a three-toed sloth and a garden snail.
Their specific speed depends on the species and conditions. One of the fastest recorded starfish species is a sand starfish (Luidia foliolata) that can travel at 9 feet (2.8 m) per minute. One of the slowest is a Leather star (Dermasterias imbricata) that can move at 6 inches (15 cm) per minute.
On average, they move about 3 feet (1 m) per minute. According to the National Oceanic and Atmospheric Administration (NOAA), an adult sunflower sea star can travel at 3 feet per minute using its 15,000 tube feet.
Why do starfish move?
Like all animals on the planet, including humans, sea stars move to feed themselves. They mainly eat mollusks such as clams, mussels, and oysters, but some species eat corals or dead organic matter which makes them decomposers of the ocean.
Starfish have a very unique way of eating. Read more about how and what they eat in my other article: “How Do Starfish Eat?”.
Another reason starfish move is to find shelter. Different species developed different defense strategies. Some hide in the sand, some under rocks, and some attach themselves to rocks firmly so they’re not eaten by predators.
But, an excellent place for them to hide and find plenty of food is, of course, coral reefs. They can even locate them with their eyes by seeing large dark structures, so they make sure they don’t walk far away from their home.
How often do starfish move?
Starfish don’t move a lot and the frequency, again, depends on species and conditions. There are about 2,000 species of sea stars that adapted to very different environments, vary in size, or even have different amounts of arms.
Some species barely move and borrow in the sand for most of their time like a sand sifting sea star. Others, are more active and search for food but in general, starfish aren’t in a continuous state of motion. They prefer to attach themselves to the rocks which also protects them from predators.
The most active time of the day for them is when they eat. During this time they use their tube feet to open up the shells of their prey and put their stomach inside.
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