Sunflower Star

Pycnopodia helianthoides

Kingdom: Animalia

Phylum: Echinodermata

Class: Asteroidea

Order: Forcipulatida

Family: Asteriidae

Genus: Pycnopodia

Species: P. helianthoides

The sunflower sea star is one of the largest sea stars, with 15-24 arms, and weighing up to 11 lbs. An average arm is 15 inches long, making their diameter 30 inches across. The average lifespan is 3-5 years. Common colors of this species are orange, red, and purple. The underbelly is typically a lighter color with yellow or orange tube feet. Most sunflower sea stars have around 15,000 tube feet. It has a soft, flexible skeleton which gives the species incredible agility. This species is the fastest sea star and it can move 3.3 ft/min. They are usually found in the intertidal zone in the northeast Pacific from Alaska to Southern California.

Diet and Ecological Roles

The diet of sunflower stars consists of sea urchins, clams, snails, sea cucumbers and other sea stars. This sea star has a cardiac stomach that can envelop and digest prey outside its body. It is considered to be one of the most active and voracious subtidal invertebrate predators on echinoids, however some studies challenge this idea. One study found that this species is actually more of a scavenger that depends on chemoreceptive abilities to locate damaged or dead prey. There appears to be a fundamental preference for damaged/dead clams over live clams, even when a live clam is encountered on the way to damaged individuals. Although this study showed how sunflower stars scavange, they are still considered the most important predator of sea urchins.

General Characteristics

If a predator attacks the sunflower star, it is able to easily cast off an arm in order to escape. It is able to do this because of their connective tissue that can rapidly change its tensile strength. It is then able to regenerate missing arms within a few weeks. The image below depicts this arm detachment happening when a Morning Sun Star attacks.

Reproduction and Development

Sea stars are gonochoric with external fertilization. They release their eggs throughout May and June. These eggs then develop into swimming, bilateral larvae that usually remain in the plankton for no more than 10 weeks. They then undergo metamorphosis into young sea stars with 5 arms. One arm is added initally in between the two arms closest to the madreporite, followed by additional arms in pairs on either side of the sixth arm.

Other systems

Sea stars have no special organs for excretion and it occurs through tissues. Sea stars have a complete digestive system, as well as a complex water vascular system which is used for locomotion, food and waste transportation, and respiration. In terms of respiration, tube feet act like gills and function in the exchange between oxygen and carbon dioxide.

Sea Star Wasting Disease (SSWD)

The 2013-2014 sea star wasting disease outbreak is an emergent, rapidly spreading disease, which has led to large population declines of asteroids in the North American Pacific. Evidence suggests that the signs of this disease, including tissue ulcers, inflammation, and necrosis leading to lethargy, limb curling and deflation, limb loss, and death, may be attributed to a viral infection. The mechanisms by which asteroids experiencing SSWD are affected are not yet fully resolved. Furthermore, induction of apoptotic and protein degradation genes suggest that affected stars may excise or degrade compromised tissues.

Sources

Brewer, R. & Konar, B. Marine Biology (2005) 147: 789. https://doi.org/10.1007/s00227-005-1608-7
Eisenlord, M. E., Groner, M. L., Yoshioka, R. M., Elliott, J., Maynard, J., Fradkin, S., … Harvell, C. D. (2016). Ochre star mortality during the 2014 wasting disease epizootic: role of population size structure and temperature. Philosophical Transactions of the Royal Society B: Biological Sciences, 371(1689), 20150212. http://doi.org/10.1098/rstb.2015.0212
Gudenkauf, B. M., & Hewson, I. (2015). Metatranscriptomic Analysis of Pycnopodia helianthoides (Asteroidea) Affected by Sea Star Wasting Disease. PLoS ONE, 10(5), e0128150. http://doi.org/10.1371/journal.pone.0128150
Lambert, P. 2000. Sea Stars of British Columbia, Southeast Alaska and Puget Sound. Vancouver: UBC Press.
Moitoza, D.J. & Phillips, D.W. Marine Biology (1979) 53: 299. https://doi.org/10.1007/BF00391611
Yagoda, S. 2004. "Pycnopodia helianthoides" (On-line), Animal Diversity Web. Accessed November 29, 2017 at
http://animaldiversity.org/accounts/Pycnopodia_helianthoides/
https://www.mindenpictures.com/search/preview/sunflower-sea-star-pycnopodia-asterias-helianthoides-close-up-of-arm/0_90110470.html
https://bangordailynews.com/2013/11/25/environment/sea-stars-stricken-by-mysterious-wasting-disease/
http://echinoblog.blogspot.com/2011/01/secrets-of-starfish-sieve-plate.html

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