Starfish, often called sea stars, are marine invertebrates that cannot survive long outside their aquatic habitat. They are specialized for underwater life and lack adaptations to thrive in air. Exposure to open air quickly becomes detrimental.
Why Starfish Need Water: Their Unique Biology
Starfish are intrinsically tied to their marine environment. They absorb oxygen directly from seawater through tiny, thin-walled projections called papulae (skin gills). These delicate structures, found on their upper surface and tube feet, facilitate gas exchange. Without water, these papulae collapse, hindering their ability to respire.
Their water vascular system, a hydraulic network of fluid-filled canals and tube feet, is essential for movement, feeding, and gas exchange. This system operates by regulating water pressure, enabling the extension and retraction of their tube feet. Out of water, this system cannot function, impairing movement. Furthermore, their skin is permeable and not designed to prevent water loss, making them susceptible to desiccation when exposed to air.
How Long Can They Survive?
The duration a starfish can endure out of water varies based on several factors. Some species, particularly those residing in intertidal zones, exhibit a greater tolerance to air exposure due to their natural adaptation to periods of low tide. For instance, the Ochre sea star can survive out of water for up to 30 hours in cool, shaded conditions, whereas more fragile species like the brittle star might perish in just a few minutes or hours.
Environmental conditions play a substantial role in determining survival time. Higher humidity can prolong survival by reducing the rate of water loss from the starfish’s permeable skin. Conversely, elevated temperatures and direct sunlight accelerate desiccation and overheating, limiting their time out of water. Wind also contributes to faster evaporation.
A starfish’s size can also influence its resilience; larger individuals may retain moisture slightly longer. However, even under optimal conditions, survival is typically measured in minutes to a few hours, not days. Most starfish species can only tolerate being out of water for 3 to 5 minutes before experiencing distress or damage, as their papulae and tube feet collapse without water, preventing oxygen absorption.
The Process of Dying Out of Water
When a starfish is removed from water, a cascade of physiological events begins, leading to its death. Oxygen deprivation is a key issue. Their respiratory structures, the papulae and tube feet, absorb dissolved oxygen from seawater. In air, these projections collapse and dry out, becoming ineffective for gas exchange and causing suffocation.
Simultaneously, their porous bodies rapidly lose water through desiccation. This dehydration disrupts cellular functions and compromises tissue and organ integrity. Without the surrounding seawater, the internal osmotic balance is disturbed, leading to cellular damage.
The combined effects of oxygen starvation, water loss, and osmotic stress cause vital organ and system failure. Unlike some marine organisms that can seal themselves off or burrow to conserve moisture, starfish lack such protective mechanisms, making them vulnerable to air exposure. This physiological breakdown culminates in their demise.
Protecting Starfish: What You Can Do
Given their delicate nature and dependence on water, observing starfish without disturbing them is paramount for their well-being. If a starfish is found stranded but appears alive, gently return it to the ocean. Care should be taken to place it in an area with sufficient water depth and conditions similar to its natural habitat, rather than just a shallow puddle.
When handling a starfish, if absolutely necessary, always wet your hands with seawater first, as dry hands can damage their sensitive skin and introduce harmful substances. Never pull a starfish by a single arm, as this can cause severe injury or autotomy (the self-amputation of an arm). Instead, support its entire body by sliding your hand underneath.
Educating others about the fragility of starfish and the importance of leaving them undisturbed in their environment is also beneficial. Even brief exposure to air or improper handling can inflict significant stress and contribute to their mortality. Promoting responsible beach etiquette helps these creatures thrive in their marine homes.