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. (Lambert, 2000)
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. (Ahearn and Benhnke, 1991; Esquivel, 2003; Lambert, 2000; )
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. (Alender, et al., 1966; Lambert, 2000)
There is no sexual dimorphism within these species. Fertilization is external. (Lawrence, 1987)
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. (Alender, et al., 1966; Lambert, 2000)
There is no parental care within this species.
Sea stars have a life span usually between 3 and 5 years. ("Sea Stars", 2002)
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.
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. (Lambert, 2000)
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. (Ahearn and Benhnke, 1991; Esquivel, 2003; Lambert, 2000; )
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. (Lambert, 2000; Wootton, 1997)
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. (Dayton, 1975; Duggins, 1983; )
There was no information regarding the economic importance of P. helianthoides to humans.
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. (Holmes, 1994)
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. (Lambert, 2000; Lawrence, 1987; )
Renee Sherman Mulcrone (editor).
Shayna Yagoda (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
an animal that mainly eats meat
uses smells or other chemicals to communicate
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
An animal that eats mainly plants or parts of plants.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
makes seasonal movements between breeding and wintering grounds
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
uses sight to communicate
Tropica Beach. 2002. "Sea Stars" (On-line ). Accessed 03/25/03 at http://www.tropicabelize.com/Crab%20Collection/Crabs%20Photos/Sea%20Stars.htm.
Ahearn, G., R. Benhnke. 1991. Diet, Feeding-Behaviour, and Surface-Morphology of the Multiarmed Antartic Sea Star Labidiaster-Annulatus. Marine Ecology- Progress Series, 77/1: 65-84.
Alender, C., J. Anderson, J. Binyon, R. Boolootian, D. Davenport. 1966. Physiology of Echinodermata. New York: Interscience.
Dayton, P. 1975. Experimental Evaluation of Ecological Dominance in a Rocky Intertidal Algal Community. Ecological Monographs, 45/2: 137-159.
Duggins, D. 1983. Starfish Predation and the Creation of Mosaic Patterns in a Kelp-Dominated Community. Ecology, 64/6: 1610-1619.
Esquivel, C. 2003. "Critter Care Club-species list: Invertebrates" (On-line). Accessed December 08, 2004 at http://www.cabrilloaq.org/critter1.htm.
Holmes, P. 1994. "Star Fish" (On-line). Accessed December 09, 2004 at http://www.adfg.state.ak.us/pubs/notebook/shellfsh/starfish.php.
Lambert, P. 2000. Sea Stars of British Columbia, Southeast Alaska and Puget Sound. Vancouver: UBC Press.
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.