sunflower seastar

''Pycnopodia helianthoides'', commonly known as the sunflower sea star, is a large sea star found in the northeast Pacific. The only species of its genus, it is among the largest sea stars in the world, with a maximum arm span of . Adult sunflower sea stars usually have 16 to 24 limbs; their color can vary widely. They are predatory, feeding mostly on sea urchins, clams, snails, and other small invertebrates. Although the species had been widely distributed throughout the northeast Pacific, its population has rapidly declined since 2013. The sea star has been on IUCN list of endangered animals since 2021.

Description

Sunflower sea stars can grow to have an arm span of in diameter. They are the second-biggest sea star in the world, only second to the poorly known deep water '' Midgardia xandaros'', whose arm span is and its body is 2.6 cm (roughly 1 inch) wide, although ''P. helianthoides'' is the largest known echinoderm by mass. Growth of the sea star begins rapidly, but slows as the animal ages. Researchers estimate a growth rate of 8 cm (3.1 in)/year in the first several years of life, and a rate of 2.5 cm (0.98 in)/year later.

Their color ranges from bright orange, yellow-red to brown, and sometimes purple, with soft, velvet-textured bodies and 5–24 arms with powerful suckers. Most sea star species have a mesh-like skeleton that protects their internal organs.

Distribution and habitat

Sunflower sea stars were once common in the northeast Pacific from Alaska to southern California, and were largest in Puget Sound, British Columbia, northern California, and southern Alaska. Between 2013–2015, the species underwent a rapid population decline due to sea star wasting disease, warmer water temperatures and abnormally high water temperatures caused by global climate change. The species disappeared from its habitats in the waters off the coast of California and Oregon, and saw its population reduced by 99.2% in the waters near Washington state. A team of ecologists using shallow water observations and deep offshore trawl surveys found declines of 80–100% from 2013 population levels across a 3,000 kilometer range. As of 2020, the species has been declared critically endangered by the International Union for Conservation of Nature. There have been suggestions of the sea star wasting disease being caused by bacterial pathogens or parasites and being contagious, due to its tendency to spread to multiples locations.

Sunflower sea stars generally inhabit low subtidal and intertidal areas rich in seaweed, kelp, sand, mud, shells, gravel, or rocky bottoms. They do not venture into high- and mid-tide areas because their body structure is heavy, and requires water to support it.

Diet

Sunflower sea stars are quick, efficient hunters, moving at a speed of using 15,000 tube feet which lie on the undersides of their bodies. They are commonly found around urchin barrens, as the sea urchin is a favorite food. They also eat clams, snails, abalone, sea cucumbers and other sea stars. In Monterey Bay, California, they will feed on dead or dying squid. Sea star appetites and favorite food can depend on environmental factors in their habitats, such as climate, amount of prey in the area, and latitude.
Although the sunflower sea star can greatly extend its mouth, for larger prey, the stomach can extend outside the mouth to digest prey, such as gastropods like abalone.

Easily stressed by predators such as large fish and other sea stars, they can shed arms to escape, which will grow back within a few weeks. They are preyed upon by the king crab.

Reproduction

Sunflower sea stars can reproduce sexually through broadcast spawning. They also have separate sexes. Sunflower sea stars breed from May through June. In preparing to spawn, they arch up using a dozen or so arms to hoist their fleshy central mass free of the seafloor and release gametes into the water for external fertilization. The microscopic sea star larvae float and feed near the surface for two to ten weeks. After the planktonic larval period, the larvae settle to the bottom and transform into juveniles. Juvenile sunflower sea stars begin life with five arms, and grow the rest as they mature. The lifespans of most sunflower sea stars is three to five years.

Conservation Efforts

Since 2013, sunflower sea star populations have been in a rapid decline due to disease and changes in climate affecting sea star habitats. Efforts have been made to spread awareness of this issue. In 2020, the IUCN first assessed that the sunflower sea star was critically endangered. The Nature Conservancy and its partnered institutions, along with the University of Washington are working together to start the first captive breeding of sunflower sea stars in order to increase the population. Captive breeding efforts include seasonal reproduction of sea stars, the development of their larvae, and growth and feeding experiments for juvenile sea stars. On August 18, 2021, the Center for Biological Diversity created a petition asking that the sunflower sea star be protected under the Endangered Species Act.

Threats

Sunflower sea stars are one of the main predators of sea urchins. By feeding on sea urchins, the sea stars control their population and help maintain the health of kelp forests. Due to the decrease in sea star population resulting from sea star wasting disease, there is now an influx of sea urchins which pose a threat to biodiversity, particularly in kelp forests. The sea star wasting disease affects the sea star's whole body by spreading throughout the whole body. The limbs become affected and eventually fall off from the sea star ultimately ending in death from degradation. There is evidence to suggest the sea star wasting disease affecting sunflower sea stars is a Sea Star-associated Densovirus (SSaDV). The disease also creates behavioral changes and lesions within the species. This disease is known to be more prevalent and harmful towards sea stars when the water is at a warmer temperature, which is seen in the habitats of the sun flower sea stars. The constant rate of the waters warming in California, Washington, and Oregon have coincided with the increased risk of the sea star wasting disease within the ''Pycnopodia helianthoides'' species in said areas.

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{{DEFAULTSORT:Sunflower Sea Star
Starfish described in 1835
Asteriidae