Sea stars are diverse marine invertebrates found in oceans worldwide, recognized by their radial symmetry. These creatures come in a wide array of sizes, shapes, and vibrant colors, adapting to various marine environments. They typically move using thousands of tube feet on their undersides, which also aid in feeding.
The Sunflower Sea Star: A Giant Among Starfish
The Sunflower Sea Star (Pycnopodia helianthoides) is one of the largest sea stars. An adult can achieve an arm span of up to 1 meter (3.3 feet), making it one of the largest in terms of diameter. It is also recognized as the heaviest known sea star, with individuals capable of weighing up to 5 kilograms (13.4 pounds).
Its body typically has 16 to 24 arms, considerably more than the five arms seen in most other sea star species.
Habitat, Diet, and Unique Characteristics
The Sunflower Sea Star lives along the eastern Pacific coast, with its range extending from the Aleutian Islands in Alaska down to Baja California, Mexico. These sea stars inhabit a variety of underwater landscapes, including rocky intertidal zones, kelp forests, and sandy or muddy flats. They can be found from shallow intertidal areas to depths of up to 435 meters (1427 feet), though they are most commonly observed in shallower waters between zero and 30 meters.
As active predators, Sunflower Sea Stars play a significant role in their ecosystems, preying on a wide range of marine invertebrates. Their diet primarily consists of sea urchins, mussels, clams, sea cucumbers, snails, and crabs. They are also known to scavenge on dead fish and other organisms.
They are notably fast, moving at up to 1 meter (3.3 feet) per minute, which is fast for a sea star. This movement is facilitated by an estimated 15,000 tube feet. Their soft, velvet-textured bodies display a range of colors, including orange, yellow, red, brown, and purple.
These sea stars possess a skeletal structure composed of disjointed pieces, allowing for greater flexibility and enabling them to engulf large prey. They can also regrow lost or damaged arms. In some instances, a detached arm containing a portion of the central disc can even regenerate into a complete new individual.
Ecological Role and Conservation Status
The Sunflower Sea Star is a keystone species in its marine environment. Its predatory habits, particularly its consumption of sea urchins, are instrumental in maintaining the balance of kelp forest ecosystems. By controlling sea urchin populations, the Sunflower Sea Star helps prevent overgrazing of kelp, which in turn supports the health and biodiversity of these vital underwater forests.
Despite its ecological significance, the Sunflower Sea Star faces severe threats to its survival. It is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN). The species has experienced a rapid and drastic decline since 2013, with some populations, such as those in Washington waters, seeing a reduction of over 99%. This widespread die-off has led to the species becoming nearly extinct in California.
The primary cause of this decline is Sea Star Wasting Syndrome (SSWS), a devastating disease that has affected numerous sea star species along the Pacific coast. Symptoms of SSWS include white lesions, tissue decay, and body fragmentation and death, often occurring within a few days. Recent research suggests that the bacterium Vibrio pectenicida is a cause of this disease, and its outbreaks have coincided with anomalous ocean heat waves, indicating a link between rising water temperatures and disease progression. Efforts are underway, including captive breeding programs, to help recover this species and restore its populations in affected areas.