Sea stars have very few predators, especially P. helianthoides. Sometimes Alaska king crab and sea otters may attack sea stars. Birds such as gulls have been known to prey upon sunflower stars. The magnitude of loss of intertidal P. helianthoides is enough to explain the near absence of these soft-bodied sea stars in the intertidal zone of Tatoosh. Pycnopodia helianthoides can have large subtidal populations that do not experience bird predation resulting in a little effect on their total population sizes. Predators mainly eat the sea stars during their larval and juvenile stages. The availability of food, rather than predation, limits the number of adult sunflower stars.
Known Predators:
Pycnopodia helianthoides, the largest of the sea stars, is radially symmetrical. The sunflower star has more arms than any other species, numbering between 15 and 24 (most sea stars have between 5 and 14), and is the heaviest known sea star, weighing about 5 kg. Their arms are up to 40 cm long and they are usually around 80 cm in diameter. The colors vary. Some are reddish-orange to yellow, violet brown, purplish or slatey purple. The stomach is found on the underside of the center body, or the oral surface. This area is usually a lighter color with yellow or orange tube feet. Pycnopodia helianthoides has over 15,000 tube feet which have suction cups that allow the stars to cling to rocks. The suctions cups are so strong that if you try to pull a sea star of a rock, the suctions cups may break lose from the sea star and continue to stick on the rock.
Other Physical Features: ectothermic ; heterothermic ; radial symmetry
Sexual Dimorphism: sexes alike
Sea stars have a life span usually between 3 and 5 years.
Typical lifespan
Status: wild: 3 to 5 years.
Average lifespan
Status: wild: 3-5 years.
Sunflower stars are commonly found on various substrates like mud, sand, gravel, boulders and rock. They are found from the intertidal zone to 435 m, however, most are found no more than 120 m.
Range depth: 435 (high) m.
Habitat Regions: temperate ; saltwater or marine
Aquatic Biomes: benthic
Other Habitat Features: intertidal or littoral
Pycnopodia helianthoides is one of the most interesting and unique sea stars in its class. It is one of the biggest, has the most arms, and also can move the fastest. Its radiant colors and shape are also unique.
If a predator attacks, P. helianthoides can let its arm drop off and send a chemical that causes an alarm response to other sunflower stars in the area. If its arm is irritated or disturbed by a predator, it will drop it off or autotomize its arm. The autotomy is triggered by a chemical that is released by injured tissues. This allows sunflower stars to escape from the predator holding onto its arm.
Communication Channels: chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; chemical
US Federal List: no special status
CITES: no special status
The eggs develop into swimming, bilateral larvae that usually remain in the plankton for no more than 10 weeks. The larval form feeds on single-celled plants. When the larva settles on the bottom it metamorphoses into a young sea star with five arms. The young P. helianthoides initially feeds on the thin layer skin-celled plants that coat the bottom of their marine habitat. The juvenille soon adds an arm clockwise from the bivium. Additional arms are added bilaterally in pairs to either side of the sixth ray. Each new pair is inserted between the last pair formed and the adjacent original arms.
Development - Life Cycle: metamorphosis
This species is viewed by many commercial fishers as a pest. The results of the sunflower star's predacious behavior fouls long-line gear and crab pots.
There was no information regarding the economic importance of P. helianthoides to humans.
Pycnopodia helianthoides regulates the structure of the benthic community. Between Oregon and the northern Gulf of Alaska, this abudant sea star is the only species considered to be an important sea urchin predator. Pycnopodia helianthoides coexists with its prey while otters decimate urchin populations; therefore, they have a more subtle effect. Pycnopodia helianthoides creates small-scale, prey-free patches by consuming few prey individuals, while the remaining prey exhibit a strong escape response. Since the urchins are herbivorous, the short-term existence of prey-free patches can influence plant diversity and community primary productivity.
Pycnopodia helianthoides is primarily carnivorous, feeding on mussels, sea urchins, fish, crustaceans (crabs and barnacles), sea cucumbers, clams, gastropods, sand dollars, and occasionally algae and sponges. However, the diet varies with geographic location and the availability of prey. For example, on the west coast, studies show that sea urchins are its main prey. For most sunflower stars, sea urchins make up 21-98% of their diet. Sunflower stars use their strong sense of smell and very sensitive indicators of light and dark to find their prey, and can move at a quick rate of 10 cm per second or 18 feet per minute. While moving, it puts its leading 8 arms in front and when it contacts the prey, it throws the leading arms down on top of the prey. Pycnopodia helianthoides then protrudes its stomach, envelops the entire prey, and digests it. The arms and greatly expandable tube feet are the basic tools of prey capture. Many species have developed escape responses to sunflower stars. For example, the abalone Haliotis accelerates and at the same time whips it shell back and forth to break the grasp of the tube feet of the sea star.
Animal Foods: mollusks; aquatic crustaceans; echinoderms; other marine invertebrates
Plant Foods: algae
Primary Diet: carnivore (Eats non-insect arthropods, Molluscivore , Eats other marine invertebrates); herbivore (Algivore); omnivore
Pycnopodia helianthoides is commonly found in marine environments ranging from the shallow waters of the Aleutian Islands, Alaska, to San Diego, California.
Biogeographic Regions: nearctic ; pacific ocean
There is no sexual dimorphism within these species. Fertilization is external.
Mating System: polygynandrous (promiscuous)
Pycnopodia helianthoides breeds by broadcast fertilization between March and July. However, the main peak is May and June. Each separate sex sheds its eggs or sperm into the water where the fertilization takes place by chance.
Breeding interval: Between March and July
Key Reproductive Features: seasonal breeding ; sexual ; fertilization (External ); oviparous
There is no parental care within this species.
Parental Investment: pre-fertilization (Provisioning)
Pycnopodia helianthoides, commonly known as the sunflower sea star, is a large sea star found in the northeastern Pacific Ocean. The only species of its genus, it is among the largest sea stars in the world, with a maximum arm span of 1 m (3.3 ft). Adult sunflower sea stars usually have 16 to 24 limbs. They vary in color.
They are predatory, feeding mostly on sea urchins, clams, sea snails, and other small invertebrates. Although the species was widely distributed throughout the northeast Pacific, its population rapidly declined from 2013.[3] The sunflower sea star is classified as Critically Endangered on the IUCN Red List.[4]
Sunflower sea stars can reach an arm span of 1 m (3.3 ft). They are the second-biggest sea star in the world, second only to the little known deep water Midgardia xandaros, whose arm span is 134 cm (53 in) and whose body is 2.6 cm (roughly 1 inch) wide, although P. helianthoides is the largest known echinoderm by mass.[4] Growth 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.[5]
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.[4][6] Most sea star species have a mesh-like skeleton that protects their internal organs.[7]
Sunflower sea stars were once common in the northeast Pacific from Alaska to southern California,[4] and were dominant in Puget Sound, British Columbia, northern California, and southern Alaska.[7] Between 2013 and 2015, the population declined rapidly due to sea star wasting disease[8] and warmer water temperatures[9] caused by global climate change.[10] 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.[3] 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.[11] In 2020, the species was declared critically endangered by the International Union for Conservation of Nature.[5] Suggestions that sea star wasting disease was caused by bacterial pathogens or parasites and was contagious, due to its tendency to spread to multiple locations.[12]
Sunflower sea stars generally inhabit low subtidal and intertidal areas rich in seaweed,[13] kelp,[14] sand, mud, shells, gravel, or rocky bottoms.[15] They do not venture into high- and mid-tide areas because their body structure is heavy, and requires water to support it.[16][7]
Sunflower sea stars are efficient hunters, moving at a speed of 1 m/min (3.3 ft/min) using 15,000 tube feet that lie on their undersides.[4][6] 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.[4] In Monterey Bay, California, they may feed on dead or dying squid.[17] Sea star appetites and food can depend on environmental factors in their habitats, such as climate, amount of prey in the area, and latitude.[15] Although the sunflower sea star can extend its mouth for larger prey, the stomach can extend outside the mouth to digest prey, such as abalone.[18]
Easily stressed by predators such as large fish and other sea stars, they can shed arms to escape, which regrow within a few weeks. They are preyed upon by the king crab.[7]
Sunflower sea stars can reproduce sexually through broadcast spawning.[19] They have separate sexes.[18] 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 above the seafloor and release gametes into the water for external fertilization.[18] The larvae float and feed near the surface for two to ten weeks. After the planktonic larval period, the larvae settle to the bottom and mature into juveniles.[7] Juvenile sunflower sea stars begin life with five arms, and grow the rest as they mature.[17] The lifespans of most sunflower sea stars is three to five years.
Since 2013, sunflower sea star populations have been in a rapid decline due to disease and changes in climate. In 2020, the IUCN first assessed that the sunflower sea star was critically endangered.[20] The Nature Conservancy and its partner institutions, along with the University of Washington are working to initiate captive breeding.[21] Captive breeding efforts include seasonal production, larval development, and growth and feeding experiments.[22] 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.[23] In March 2023, the National Marine Fisheries Service proposed listing the sunflower sea star as threatened under the act.[24]
Sunflower sea stars are one of sea urchins' main predators.[25] Sea stars control their population and help maintain the health of kelp forests.[26] Due to the decrease in sea star population, sea urchin populations are exploding, which pose a threat to biodiversity, particularly in kelp forests.[9] Sea star wasting disease spreads throughout the whole body. The limbs become affected and eventually fall off, ultimately causing death from degradation.[11] Sea star wasting disease appears to be a Sea Star-associated Densovirus (SSaDV).[8][27] The disease creates behavioral changes and lesions.[8] This disease is known to be more prevalent and harmful in wamer water. The warming waters in California, Washington, and Oregon have coincided with the increased risk of sea star wasting disease.[11]
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{{cite web}}: CS1 maint: url-status (link) {{cite web}}: CS1 maint: url-status (link) {{cite web}}: CS1 maint: url-status (link) {{cite news}}: CS1 maint: url-status (link) Pycnopodia helianthoides, commonly known as the sunflower sea star, is a large sea star found in the northeastern Pacific Ocean. The only species of its genus, it is among the largest sea stars in the world, with a maximum arm span of 1 m (3.3 ft). Adult sunflower sea stars usually have 16 to 24 limbs. They vary in color.
They are predatory, feeding mostly on sea urchins, clams, sea snails, and other small invertebrates. Although the species was widely distributed throughout the northeast Pacific, its population rapidly declined from 2013. The sunflower sea star is classified as Critically Endangered on the IUCN Red List.
