Starfish, more accurately known as sea stars, are marine invertebrates belonging to the class Asteroidea. Characterized by their radial symmetry and often five arms, these organisms inhabit all the world’s oceans, from tropical reefs to abyssal depths. Their longevity is highly variable, depending on species-specific biology and external environmental factors rather than a fixed biological clock. Understanding their lifespan requires examining the vast differences across the nearly 2,000 known species and the unique physiological traits that enable their extended survival.
The Lifespan Spectrum
The duration of a sea star’s life varies dramatically across species, ranging from only a few years to several decades. Generally, larger species that live in deeper, colder, or more stable environments tend to exhibit greater longevity. The common sea star in the North Atlantic, Asterias rubens, typically lives for about seven to eight years. Smaller species like the Asterina sea stars often have a much shorter life expectancy, sometimes living for only two years in the wild.
The Pacific Northwest’s ochre sea star, Pisaster ochraceus, is a longer-lived example, with individuals commonly reaching 20 years of age and some records suggesting a lifespan up to 34 years. Even more impressive is the sunflower sea star, Pycnopodia helianthoides. While estimated to live between five and seven and a half years on average, some larger individuals potentially survive for more than 60 years.
Internal Biology and Longevity
The potential for a sea star to achieve a long life is rooted in its unique physiological attributes, particularly its capacity for regeneration and indeterminate growth. Sea stars possess the ability to regrow lost or damaged limbs, which is a significant factor in their long-term survival. This allows them to recover from injuries, such as losing an arm to a predator, that would be fatal to most other animals.
This regenerative power is linked to indeterminate growth, where the sea star continues to grow throughout its life rather than reaching a fixed adult size. Their arms continuously grow in length by adding new segments, sustained by specialized cells in the arm tips. This continuous growth and repair mechanism helps them remain resilient and biologically youthful over many years.
Environmental Influences on Survival
While a sea star’s internal biology provides the potential for longevity, external factors determine if it reaches its maximum biological age. The availability of food is a primary driver of growth rate and size, which correlates with greater age in many species. Abundant prey allows sea stars to grow faster, while starvation can slow growth or cause them to shrink. Fluctuations in ocean temperature also severely impact survival by increasing susceptibility to disease.
The most devastating environmental threat has been Sea Star Wasting Syndrome (SSWS), a mass mortality event linked to warmer waters. This syndrome causes lesions and tissue decay, leading to the collapse of the sea star’s body structure. SSWS decimated populations of long-lived species, demonstrating how environmental stress cuts short a species’ potential lifespan. Predation also acts as a consistent pressure, though sea stars use defense mechanisms like autotomy, or intentionally shedding an arm, to escape threats.
Life Stages and Deterioration
A sea star’s life begins with a planktonic larval stage that is bilaterally symmetrical, a stark contrast to the adult’s radial form. After drifting in the water column, the larva settles onto the seabed and undergoes metamorphosis, developing into a tiny juvenile, typically starting with five arms. As the sea star matures, it continues to grow throughout its adult life, adding to its size and reproductive capacity.
Many echinoderms do not experience the physical decline or senescence seen in vertebrates. They are considered to exhibit negligible senescence, meaning the likelihood of death does not appear to increase significantly with age. However, deterioration occurs, often as a result of accumulated damage or disease. The calcium carbonate endoskeleton, composed of small bony plates called ossicles, is continuously maintained. Older, larger individuals may experience a functional slowdown, making them more vulnerable to the wounds or infections that eventually lead to natural mortality.