The starfish, also known as a sea star, is an echinoderm often perceived as a largely stationary creature fixed to the ocean floor. This image of stillness is misleading, as these marine invertebrates are capable of purposeful movement. Their unique biological structure allows them to glide slowly across various substrates, a feat accomplished without fins, tails, or conventional limbs. This specialized locomotion is powered by a hydraulic system that uses thousands of tiny appendages to propel the animal. Understanding how fast a sea star moves requires looking closely at the measurements of their travel and the complex mechanism that makes this movement possible.
Understanding Starfish Locomotion Speed
The typical speed of a sea star is slow, yet it is perfectly suited for their predatory lifestyle. Most common species move at a rate measured in centimeters per minute; for example, the Leather Star (Dermasterias imbricata) travels at approximately 15 centimeters per minute. This deliberate pace is adequate for hunting sessile or slow-moving prey like clams, oysters, and sea urchins. Movement rates across the species spectrum show significant variation, ranging from 0.3 to 50 millimeters per second. A common sea star may cover only about 1 to 3 meters in an hour, which represents a considerable distance for an animal relying entirely on a hydraulic-powered system. This slow, steady movement allows the sea star to conserve energy while systematically foraging on the seabed.
The Water Vascular System and Tube Feet
The sea star’s ability to move is powered by a sophisticated internal plumbing system called the water vascular system. This hydraulic network begins with the madreporite, a porous, sieve-like plate on the upper surface that filters seawater into the system. The water then travels down a short channel, known as the stone canal, to the ring canal that encircles the central disc. From the ring canal, five radial canals extend outward, running the length of each arm.
These radial canals supply water to hundreds of tiny, bulb-like structures called ampullae, each connected to a single tube foot. The ampullae and tube feet function together like a miniature piston and cylinder to facilitate movement. When a sea star needs to extend a tube foot, muscles contract the ampulla, forcing the internal fluid into the attached tube foot, causing it to lengthen and press against the substrate. The tube foot’s muscular walls then contract, pulling the body forward while the fluid is simultaneously drawn back into the ampulla. This continuous, coordinated sequence of extension, attachment, contraction, and release across thousands of tube feet creates a smooth gliding motion.
Species Differences in Movement Rates
The speed of sea star movement varies widely, as different species exhibit a range of speeds based on their ecological niches. The most noteworthy example of a faster-moving sea star is the Sunflower Sea Star (Pycnopodia helianthoides). This large species, which can have up to 24 arms, is capable of reaching speeds of up to 1 meter per minute, an impressive rate that makes it an active predator of other echinoderms.
Another fast species is the Sand Star (Luidia foliolata), which can travel at a remarkable speed of up to 2.8 meters per minute. Beyond species, environmental conditions also influence the rate of travel. Sea stars generally move faster over smooth, sandy substrates than they do across rough, consolidated pavement or coral rubble, which makes it harder for their tube feet to gain secure purchase.
Temperature is also a significant factor, as sea stars are ectotherms whose metabolic rate is affected by the surrounding water temperature. Studies on the Crown-of-Thorns Starfish (Acanthaster cf. solaris) show that their movement rate increases considerably as water temperature rises from 26°C to 30°C. However, movement performance drops sharply at extreme temperatures, such as 32°C, suggesting a thermal limit to their activity.