Watch How Starfish Walk…and Bounce

starfish walk
Northern sea stars (Asterias rubens) photographed in Massachusetts’ Quincy Bay. The orange dot of a madreporite in the starfish at lower center identifies it as a Forbes sea star (Asterias forbesi).

WITH FIVE ARMS STRETCHING IN FIVE DIRECTIONS, you’d think that starfish could move along the seafloor like Indiana Jones. In fact, usually they creep along on hundreds of little tube feet that line the undersides of those arms. But, researchers studying how starfish walk found something else: sometimes starfish bounce along for speed.

As echinoderms in Class Asteroidea, starfish walk by operating their multitudes of little tiny feet through intricate networks of fluid-filled canals. With this water vascular system, they fill and empty the little tube extremities in random movements to lift feet, swing them forward and plant them firmly to push for locomotion.

Doing this, a starfish like Dermasterias imbricata – a leather star – generally moves along at a whopping six inches a minute. But when disturbed or pursuing prey, it turns out that starfish can speed up with a bouncing motion.

A starfish’s tube feet up close.

HOW TUBE FEET WORK

For animals without brains, starfish are equipped with impressive hydraulic systems that start with taking in seawater through a madreporite, an often-visible porous sieve-like opening on their upper surfaces. A ring canal encircling the mouth on each sea star’s lower surface channels the fluid into canals that run along a groove in each arm. Short branching canals branching ending in ampulla, or blub-shaped organs, lead to the tube feet structures.

In short, muscles in the ampules contract to close off valves in the branching canals, causing the tube feet to fill, expand and grip whatever surface they’re on, using a suction effect to help them push along. The ampulla relax to let the tube feet empty.

starfish walk
A screenshot from the researchers’ video in Science Magazine of a starfish “bouncing” along. Click on it to view the video.

BOUNCING FOR SPEED

Researchers from the U.S. and Japan focused on locomotion in five species of starfish from oceans around the world, filming them from underneath and from the side. They analyzed factors like arm length, animal density, stride frequency, length and speed and the nature of the tube feet in each species.

They found that the starfish overall can speed up their locomotion by synchronizing the filling and emptying of their tubular podia. Starfish create a slight bouncing effect by filling about one-third of them while the rest swung forward.

STARFISH BOUNCE SPEEDS VARY

The sea stars they studied included Asterias forbesi (“Forbes’ starfish,” found in the western Atlantic and Gulf of Mexico), Protoreaster nodosus (“Chocolate chip sea star,” found in the South Pacific), and Luidia clathrata (“striped sea star, found in the tropical Atlantic, Caribbean and Gulf of Mexico).

starfish walk
The most sluggish at bouncing, a chocolate chip sea star from the South Pacific.
starfish walk
A speedy bouncer: a striped sea star from the Caribbean. 

 

 

 

 

 

 

While all the animals bounced when speed was desirable, there were differences between the speed at which they did so. The differing speeds of locomotion reflected reflect the speeds  with which the tube feet empty and refill. Striped starfish bounced at a higher frequency and proved to be five times faster than the chocolate chips. The Forbes sea star bounced along at intermediate speeds.

ON THE OTHER HAND…

There are some 1,500 species of sea stars found in the oceans worldwide. Most starfish walk sluggishly, like the types discussed above. But some species are fast. Burrowing sea stars, like Luidia foliilata (“sand star,” found in the northeastern Pacific) sport points rather than suckers on the tube feet and can move as much as nine feet per minute. One sea star enthusiast reports clocking Asterias vulgaris (a denizen of the northwest Atlantic) at 60 feet per hour.

PRINCIPAL SOURCES: Marine Biology, Fourth Edition, Peter Castro, Michael Huber; Reef Creature Identification, Florida, Caribbean, Bahamas, Reef Creature Identification, Tropical Pacific, Paul Humann, Ned DeLoach; Coral Reef Animals of the Indo-Pacific, Terrence Gosliner, David Behrens, Gary Williams; Marine Life of the North Atlantic, Andrew Martinez; “The oscillatory gait of high-speed sea stars: Do sea stars of varying morphology vary stride length or step frequency to change speed?” Meeting Abstract, Society for Integrative and Comparative Biology, 2019 Annual Meeting; Watch this sea star bounce to get around,” Science Magazine News Feed; “Sea Stars,” Woods Hole Oceanographic Institution; “How Starfish Move — And The Water Vascular System,” The Madreporite Nexus; “Starfish,” National Geographic; “Starfish,” “Tube Feet,” Wikipedia.

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