Sea cucumbers, marine invertebrates related to starfish and sea urchins, often appear stationary but are capable of movement. While their locomotion is often slow, they employ diverse methods to navigate underwater environments, fulfilling ecological roles.
How Sea Cucumbers Get Around
Sea cucumbers primarily move using specialized structures called tube feet. These small, flexible appendages are arranged in five rows on their undersides. A hydraulic water vascular system powers these tube feet, allowing them to extend, attach, and contract, slowly propelling them forward.
Some species lacking well-developed tube feet rely on muscular contractions of their body wall for movement. This process, known as peristalsis, involves wave-like contractions that push the animal along, similar to an earthworm. This method is often used by burrowing species.
Many sea cucumbers combine these methods, especially for burrowing. They can dig into sand or mud, using muscular action to push through the substrate, while tube feet assist in anchoring or pulling. Movement is generally quite slow, with some crawling species moving between 1.86 and 21.47 meters overnight.
Why Sea Cucumbers Move
Movement serves several purposes, primarily for survival and reproduction. A primary reason is foraging. As detritivores and scavengers, they crawl across the seafloor, sifting through sediment for organic matter, algae, and plankton.
Movement also helps avoid predators. Though slow, some species can gradually shift away from threats or employ defense mechanisms like evisceration. Certain species can also alter buoyancy to float away from danger.
Environmental changes also prompt movement. They might seek areas with more favorable conditions like different sediment types or temperatures. Organic content in the substrate can also influence movement, leading to more rapid movement in areas with higher food concentrations. During reproduction, sea cucumbers aggregate, adopting a cobra-like posture to release eggs and sperm into the water column.
The Diverse Ways Sea Cucumbers Travel
Sea cucumber mobility varies significantly across species, from nearly sessile to surprisingly active. Many species are extremely slow, often remaining in a small area as they feed, especially suspension feeders.
Other sea cucumbers are active burrowers, spending much of their lives moving through sediment. These species are adapted to navigating soft substrates, constantly digging and shifting as they process organic material. Their body shapes and muscular systems are well-suited for this subterranean lifestyle.
A few rare, specialized species, particularly in deep-sea environments, can swim or float. Some achieve this by undulating their bodies, while others, like Pelagothuria natatrix, can take in water to modify buoyancy, allowing them to drift with ocean currents. These pelagic species can cover significant distances, sometimes traveling up to 50 miles per day by floating, a stark contrast to crawling relatives.