Pycnopodia helianthoides

Geographic Range

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 nearctic
• pacific ocean pacific ocean

Habitat

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.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• benthic benthic

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Physical Description

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 ectothermic
• heterothermic heterothermic
• radial symmetry radial symmetry

• Sexual Dimorphism
• sexes alike

Development

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 metamorphosis

Reproduction

There is no sexual dimorphism within these species. Fertilization is external.

• Mating System
• polygynandrous (promiscuous) 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.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

There is no parental care within this species.

• Parental Investment
• pre-fertilization
  • provisioning

Lifespan/Longevity

Sea stars have a life span usually between 3 and 5 years.

Behavior

Pycnopodia helianthoides is solitary.

Sunflower star have the ability to regenerate its arms which may detach as a means of defense when handled excessively or attacked by a predator. A whole new sea star may form if the detached arm has a portion of the central disk is included.

Pycnopodia helianthoides primarily moves by walking on its tube feet which possess suckers. This particular sea star can move more rapidly because of its flexible body and the aboral skeletal plates are loosely connected to one another.

Pycnopodia helianthoides migrates up and down the shore with the tide and exhibits annual migration as well.

• Key Behaviors
• motile motile
• migratory migratory
• solitary solitary

Communication and Perception

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 chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • eats other marine invertebrates
• herbivore herbivore
  • algivore
• omnivore omnivore

• Animal Foods
• mollusks
• aquatic crustaceans
• echinoderms
• other marine invertebrates

• Plant Foods
• algae

Predation

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.

Ecosystem Roles

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.

Economic Importance for Humans: Positive

There was no information regarding the economic importance of P. helianthoides to humans.

Economic Importance for Humans: Negative

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.

Conservation Status

Other Comments

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.

Additional Links

Encyclopedia of Life

Contributors

Renee Sherman Mulcrone (editor).

Shayna Yagoda (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

References

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Lawrence, J. 1987. A Functional Biology of Echinoderms . Baltimore: The John Hopkins University Press.

Wootton, J. T. 1997. Estimates and Tests of Per Capita Interaction Strength: Diet, Abundance, and Impact of Intertidially Foraging Birds. Ecological Monographs , 67/1: 45-64.

Tropica Beach. 2002. "Sea Stars" (On-line ). Accessed 03/25/03 at http://www.tropicabelize.com/Crab%20Collection/Crabs%20Photos/Sea%20Stars.htm .