Biology/Natural History: This species is a voracious subtidal predator, feeding on bivalves, snails, chitons, urchins, other asteroids, sea cucumbers, sand dollars, and crabs (in other words, just about anything it wants!). It will also scavenge dead animals. It may be the largest and fastest seastar in the world. It can move up to 3 meters per minute, and has been known to travel at least 3 km. It has over 15,000 tube feet. Tiny, newly metamorphosed juveniles of this species have only 5 rays but rays are added as the individual grows. Has very prominent spines and (crossed) pedicellariae, plus purple papulae. Loss of rays upon handling seems to be due to autotomy. In Puget Sound this species excavates butter clams (Saxidomus gigantea) by picking up sediment particles over the clam, passing them out to the ends of the rays, and dropping them. Often eat urchins such as Strongylocentrotus purpuratus, whose spines may pierce through from the stomach to the aboral surface. Can evert its stomach but more often swallows its prey whole. Predators include Alaska King crab and some large Cancer crabs. Individuals are agressive toward one another (and to almost any other seastar). Spawns March to July (some also in winter); has fertilizable eggs at least from December to June. May stand on the tips of their rays while spawning. Pelagic larvae metamorphose to benthic, 5-rayed juveniles at 9-10 weeks.

This species has a large, fleshy body with an only loosely articulated skeleton, and relies on fluid pressure to maintain its body form. It appears to rely more heavily on fluid uptake through the surface than on uptake through the madreporite. Its perivisceral fluid is more hyperosmotic than that of several other local species. This may aid in fluid uptake (Ferguson, 1994) and maintaining body form.

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

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

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

Habitat: Mostly subtidal, rocky, gravelly, or sandy bottoms.

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 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.

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:

• Alaska king crabs (Paralithodes camtschaticus)
• sea otters (Enhydra)
• gulls (Laridae)

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

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

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.

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)

US Federal List: no special status

CITES: no special status

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.