Sunflower Star, Pycnopodia helianthoides
Sunflower Star, Pycnopodia helianthoides. Star collected from coastal waters of Loreto Bay, Baja California Sur, May 2024. Pictured stars wingspan: 15 cm (5.9 inches).
Phylogeny: The Sunflower Star, Pycnopodia helianthoides (Brandt, 1835), is a member of the Asteriidae Family of Starfish. The genus Pycnopodia is one of thirty-nine genera in this family, and it contains only this species. This species is also known as the Many-legged Star and the Twenty-ray Star. In Mexico it is called estrella girasol.
Morphology: The Sunflower Star has a wide disc and up to twenty-five fairly limp and flaccid arms. Their aboral surface is covered with numerous pedicellariae and short spines and they have a row of slightly longer spines along the margins of the arms and they may have more than 15,000 tube feet. Depending on their diet, they may be brown, orange, purple, pink, red, purple in color, with white spines. The Sunflower Star is the largest member of its family and reaches 1.0 m (3 feet 3 inches) in diameter.
Habitat and Distribution: The Sunflower Star is found on and within mud, rock and sand substrate. They are found from the low intertidal zone to depths of up to 435 m (1,425 feet). The Sunflower Star has historically been a resident of Mexican waters of the Pacific Ocean, with a limited distribution from Isla Todos Santos (Ensenada), Baja California, northward along the northwest coast of Baja. They are currently extirpated from this region.
Diet: Sunflower Stars are predatory carnivores. They are considered to be one of the fastest moving sea stars, “clocked” at up to 2.1 m (6 feet 9 inches) per minute. They chase down their prey and consume it by everting their stomachs. Their main food source is sea urchins. They also eat clams, gastropods, sea cucumbers, and other sea stars.
Predators: Sunflower Stars are prey for crabs, fish, and other sea stars. They are most vulnerable to predation during their larval and juvenile stages.
Reproduction: Sunflower Stars are gonochoric (male or female for life). They reproduce sexually through broadcast spawning, with external fertilization. Sunflower Stars breed from May through June. The eggs hatch into planktonic larva. When their larvae settle out they only have 5 arms, quickly add a sixth arm, and then add future arms in pairs, on either side of the sixth arm. The lifespan of most sunflower sea stars is three to five years.
Ecosystem Interactions: Sunflower Stars play an important role in maintaining the health of kelp forests. Sea urchins graze on kelp holdfasts. When sea star populations are not sufficient to keep urchin populations in check, urchins can quickly decimate a kelp forest. The IUCN estimates that five billion Sunflower Stars have perished from Sea Star Wasting Disease since 2013. That constitutes about 90 percent of the global population. They have been extirpated from the southern half of their previous range. Surveys in 2023 showed very slight improvements in populations in northern California (five individuals instead of zero) and Oregon (eight individuals). Southern California populations show no improvement. Data from Mexico is insufficient to show a trend. Sea Star Wasting Disease is poorly understood. Studies showing it was caused by a densovirus have been discredited. The disease seems to work more quickly in warmer water temperatures, but cold water environments have still been decimated. The disease could possibly be exacerbated by warmer sea temperatures, but the evidence is insufficient to blame the “Climate Crisis”. The cause is still not understood.
Human Interactions: Sunflower Stars have limited direct impact on human activity. From a conservation perspective they are currently considered to be Critically Endangered. In the United States they are considered Threatened under the Endangered Species Act. Efforts are being taken to increase populations through captive breeding and habitat restoration.
Synonyms: Asterias helianthoides.