Starfish, often called sea stars, are marine invertebrates known for their ability to endure outside their watery environment for limited periods. While aquatic, they possess biological features that allow for some air exposure. Understanding these adaptations and environmental factors offers insight into their survival challenges in coastal habitats. The duration a starfish can spend out of water varies significantly based on its biology and external conditions.
How Starfish Survive Out of Water
Starfish do not possess lungs or gills. Instead, they exchange gases through tiny, thin-walled projections on their body surface called papulae. These structures facilitate oxygen diffusion from the surrounding water into their internal fluids and carbon dioxide release. Starfish also utilize their numerous tube feet for respiration, which similarly have thin walls allowing for gas exchange.
A unique hydraulic system, the water vascular system, supports many functions, including movement, feeding, and gas exchange. Water enters this system through a sieve-like plate called the madreporite, located on their upper surface. It then circulates through a network of canals that extend into their tube feet. This system helps maintain internal hydrostatic pressure and aids in transporting dissolved gases throughout their body. While these adaptations enable some air tolerance, starfish fundamentally depend on water for respiration and fluid balance.
Factors Affecting Survival Time
The length of time a starfish can survive out of water varies considerably, depending on environmental and biological factors. Most starfish endure air exposure for about 3 to 5 minutes before experiencing significant distress or damage. However, species adapted to intertidal zones, which regularly experience exposure during low tides, demonstrate greater resilience. For instance, the ochre sea star, common in Pacific intertidal regions, can withstand air exposure for up to 28 hours. In contrast, more delicate species like brittle stars may perish in just a few minutes or hours.
Environmental conditions play a significant role in determining survival duration. High humidity slows desiccation by reducing water evaporation from the starfish’s tissues. Cooler temperatures extend survival time by slowing metabolic processes and reducing water loss, while higher temperatures accelerate drying and increase physiological stress. Increased airflow or wind can also significantly reduce survival time by promoting faster evaporation. Larger starfish tend to retain moisture longer than smaller ones due to their lower surface area to volume ratio, which influences their desiccation rate.
Protecting Starfish and Their Habitats
Prolonged air exposure can have negative consequences for starfish, leading to desiccation, suffocation, organ damage, and death. When removed from water, their papulae and tube feet collapse and dry out, preventing proper oxygen absorption and carbon dioxide release. This can result in carbon dioxide poisoning and asphyxiation. Beyond physiological impacts, handling can induce stress, further compromising their health and survival.
To protect starfish and their ecosystems, minimize direct interaction. If a starfish is encountered out of water, such as in a tide pool, observe it without touching. Should gentle handling be necessary, ensure hands are wet with seawater to prevent transferring oils, sunscreens, or other harmful substances that can damage their sensitive skin and tube feet. Never lift a starfish by a single arm; instead, support its entire body. Return the starfish gently and promptly to its exact location, or to a nearby body of water if safe, allowing it to resume natural functions.