Starfish, also known as sea stars, are fascinating marine invertebrates belonging to the phylum Echinodermata. Their lack of a visible head, brain, or eyes, combined with extremely slow movement, makes it difficult to determine if a specimen is alive or simply a dried-out shell. Identifying signs of life requires understanding their unique physiology and observing subtle behavioral cues.
Understanding Starfish Movement and Physiology
Starfish possess a hydraulic system called the water vascular system, which powers their movement and life processes. This system draws in filtered seawater through a porous plate on the upper surface, known as the madreporite, and circulates it through internal canals. The seawater provides the fluid pressure necessary to operate their thousands of tube feet, which are the primary structures for locomotion.
The tube feet are tiny, sucker-tipped appendages lining the grooves on the underside of each arm. When internal muscular bulbs, called ampullae, contract, they force water into the attached tube feet, causing them to extend and adhere to a surface. By coordinating the extension and retraction of these feet, the starfish slowly glides across rocks and sand. This movement is highly efficient but often too slow for the casual observer to notice immediately.
Key Indicators of a Living Starfish
Observing subtle movement in the tube feet is the most reliable indicator of a living starfish, even if the animal appears stationary. If a specimen is submerged and appears dormant, watching the underside of its arms for several minutes may reveal minute, wave-like motions as the tube feet search for purchase or perform gas exchange. They are also sensitive to touch, and a gentle probe may elicit a retraction response if the animal is viable.
Another behavioral sign is the defensive curling or twitching of the arm tips. Healthy starfish arms often exhibit a slight flex or curve upward, particularly at the ends. If a starfish is found inverted, its attempt to flip over, known as the righting reflex, confirms it is alive. This reflex is a deliberate, slow process where the arms twist and turn to regain contact with the substrate, and it can take several minutes to complete.
A living starfish will possess turgor, a noticeable firmness due to the pressurized fluid within its water vascular system and coelomic cavities. The body will feel solid and slightly resilient to a gentle touch. While color varies widely by species, a vibrant, consistent coloration characteristic of the local species suggests living cells and good health.
Identifying Non-Viable and Deceased Specimens
The absence of movement after prolonged observation in water strongly suggests the specimen is deceased or non-viable. The most obvious indicator of a recently deceased specimen is a strong, foul odor, often described as putrid or intensely fishy. This smell is caused by the rapid decomposition of soft tissues and bacteria, which begins shortly after death.
Non-viable starfish that have washed ashore and dried naturally lose their body turgor. They feel brittle and rigid, lacking the resilience of a living animal, or they may feel mushy and fall apart if decomposition is advanced. Dried specimens often show significant color loss or bleaching, as the pigments degrade upon exposure to air and sunlight. If the arms are curled tightly upward and feel like hard, calcified bone, the specimen is fully dried and dead.
Responsible Interaction with Wild Starfish
When encountering a starfish in the wild, responsible interaction is paramount for its survival. Starfish are highly sensitive to being removed from the water, as they rely on their water vascular system for gas exchange, making removal akin to suffocation. Brief exposure to air can cause harm, and the risk of desiccation is severe, especially in warm or windy conditions.
If a starfish is found stranded above the low tide line, gently return it to a safe, submerged habitat, such as a rock pool or the ocean. When handling is necessary, use minimal contact, avoiding the central disk, which houses many internal organs. The goal is to minimize disturbance and ensure the animal remains in its natural, wet environment.