{{Short description|Species of starfish}} {{Speciesbox | image = Ochre_sea_star.jpg | image_caption = [[Ganges, British Columbia|Ganges Harbour]], [[British Columbia]] | genus = Pisaster | species = ochraceus | authority = ([[Johann Friedrich von Brandt|Brandt]], 1835) <ref>{{Cite WoRMS |author=Christopher Mah |year=2010 |title=''Pisaster ochraceus'' (Brandt, 1835) |db=Asteroidea |id=240755 |access-date=February 1, 2012}}</ref> }}
'''''Pisaster ochraceus''''', generally known as the '''purple sea star''', '''ochre sea star''', or '''ochre starfish''', is a common [[seastar]] found among the waters of the [[Pacific Ocean]]. Identified as a [[keystone species]], ''P. ochraceus'' is considered an important indicator for the health of the [[intertidal zone]].<ref name="Power1996">{{cite journal|last1= Power|first1=M. E.|last2= Tilman|first2= D.|last3= Estes|first3=J. A.|last4= Menge|first4=B. A.|last5= Bond|first5=W. J.|last6= Mills|first6=L. S.|last7= Daily|first7= G.|last8= Castilla|first8=J. C.|last9= Lubchenco|first9= J.|last10= Paine|first10= R. T.|title= Challenges in the Quest for Keystones|journal= BioScience|volume= 46|issue= 8|year= 1996|pages= 609–620|doi= 10.2307/1312990|jstor=1312990|doi-access= free}}</ref>
==Description==
[[File:Ochre sea stars.jpg|thumb|right|Cluster of stars, [[Salt Spring Island]], [[British Columbia]]]] [[File:9326 sea stars munsel (7740856110).jpg|thumb|Two sea stars at [[Cape Kiwanda State Natural Area]], Oregon.]] This sea star has five stout rays that range in length from 10 to 25 centimeters (4 to 10 in). The rays are arranged around an ill-defined central disk that needs to be a bit attached to a severed arm to grow a new sea star off of it. While most individuals are purple, they can be orange, orange-ochre, yellow, reddish, or brown. The aboral surface contains many small spines (ossicles) that are arranged in a netlike or pentagonal pattern on the central disk. The ossicles are no higher than 2 mm.<ref name=Kozloff>Kozloff, E. N. (1996). Marine Invertebrates of the Pacific Northwest. Seattle: University of Washington Press.</ref><ref name="McFadden">McFadden, M. (2002). [https://web.archive.org/web/20090412083835/http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Echinodermata/Class%20Asteroidea/Pisaster_ochraceus.html Pisaster ochraceus]. Retrieved May 10, 2010</ref> In ''Pisaster ochraceus'' the tube feet have suckers on their distal ends which allow them to attach to the rocky substrate and live in heavily wave-swept areas.<ref name="Nybakken"/> ''P. ochraceus'' has a simple nervous system and does not have a brain. A [[Circumesophageal nerve ring|nerve ring]] connects and relays impulses between the star's radial nerves.<ref name="Ramirez" />
Two species that can be mistaken for ''P. ochraceus'' are ''[[Pisaster giganteus|P. giganteus]]'', which has blue rings around white or purple spines, and ''[[Pisaster brevispinus|P. brevispinus]]'', which is pink with small white spines. These two species have different aboral spines and coloration which allows one to distinguish between the species. ''[[Evasterias troschelii]]'' may be confused with ''P. ochraceus'' at times as well. It can be distinguished by its smaller disk size and longer, tapering rays which are often thickest a short distance out from their base rather than at the base as in ''P. ochraceus''.<ref name=McFadden/>
== Reproduction and life history==
===Reproduction===
Members of ''Pisaster'' are [[dioecious]] but there is no [[sexual dimorphism]] and sexes can be separated only by the presence of eggs or sperm in the gonads. They reproduce by broadcast spawning, which in the [[Puget Sound]] population occurs around May to July.<ref name=McFadden/> There is no parental investment beyond spawning.<ref name=eol/> Fertilization occurs in the water column and ''Pisaster ochraceous'' develops through several larval stages.<ref name= Ramirez/>
The reproductive system consists of a pair of gonads branching into each ray off a circular genital strand which is along the oral inner surface of the central disc.<ref name=eol/> The gonads look like a feathery collection of tubules. In females there are orange gonads and in males they are whitish.<ref name=Nybakken>Nybakken, J. (1996). Diversity of the invertebrates. Hayward: California State University</ref> During maturation of the gametes, the gonads increase in size and can account for up to 40 percent of the sea star's weight.<ref name=McFadden/> The gonopores are too small to be seen, and can only be found when the sea stars are spawning.<ref name="McFadden"/><ref name=Ramirez>Ramirez, Y. (2002). Pisaster ochraceus, Animal Diversity Web. Retrieved May 10, 2010, from http://animaldiversity.ummz.umich.edu/site/accounts/information/Pisaster_ochraceus.html.</ref>
===Lifespan=== [[File:Ochre Sea Star.jpg|thumb|[[Saint Lazaria Island]], Alaska]] Many sea stars live to a minimal age of four years. ''P. ochraceus'' can live as long as twenty years.<ref name=eol>"Pisaster ochraceus (Brandt, 1835)". Encyclopedia of Life. Retrieved May 10, 2010, from "http://www.eol.org/pages/598469".</ref>
This species of seastar is often considered a [[keystone species]] in many intertidal regions. ''P. ochraceus'' is a predator of the California mussel, ''[[California mussel|Mytilus californianus]]'' and reduces its abundance. This allows for other macroinvertebrates to persist. In an experimental removal of ''P. ochraceus'', it was shown that ''Mytilus californianus'' becomes almost completely dominant of the intertidal community. When ''P. ochraceus'' is present there is a diverse intertidal community.<ref name=Holsinger>Holsinger, K. (2005). Keystone species. Retrieved May 10, 2010, from {{cite web |url=http://darwin.eeb.uconn.edu/eeb310/lecture-notes/interactions/node2.html |title=Keystone species |access-date=2010-05-12 |url-status=dead |archive-url=https://web.archive.org/web/20100630134633/http://darwin.eeb.uconn.edu/eeb310/lecture-notes/interactions/node2.html |archive-date=2010-06-30 }}</ref>
==Feeding==
At the larval stage, ''Pisaster ochraceus'' are filter feeders and their diet consists of [[plankton]]. As an adult, ''P. ochraceus'' feeds on mussels such as ''Mytilus californianus'' and ''[[Mytilus trossulus]]''. They also feed on [[chiton]]s, [[limpet]]s, [[snail]]s, [[barnacle]]s, [[echinoids]], and even [[Decapoda|decapod]] crustacea.<ref name=McFadden/><ref>{{cite journal |author1=C. D. G. Harley |author2=M. S. Pankey |author3=J. P. Wares |author4=R. K. Grosberg |author5=M. J. Wonham |title=Color Polymorphism and Genetic Structure in the Sea Star ''Pisaster ochraceus'' |journal=The Biological Bulletin |volume=211 |pages=248–262 |year=2006 |pmid=17179384 |url=http://www.biolbull.org/cgi/content/full/211/3/248 |doi=10.2307/4134547 |issue=3 |jstor=4134547 |s2cid=18549566 |url-access=subscription }}</ref><ref>{{cite web|url=http://www.beachwatchers.wsu.edu/island/essays/zonation.htm/ |title=Seashore Players Most Successful When They're in Their Zone |author=Holmes, Jan |year=2002 |work=WSU BEACH WATCHERS. Education. Research. Stewardship |access-date=6 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20080724222709/http://www.beachwatchers.wsu.edu/island/essays/zonation.htm |archive-date=July 24, 2008 }}</ref>
''P. ochraceus'' uses its tube feet to handle its [[Predation|prey]]. If the prey is too large to be swallowed whole, then it can use its tube feet to open shells. It can evert its stomach through its mouth and engulf its prey, liquify it with digestive enzymes and ingest the processed food. Mussels hold their valves together very securely but ''P. ochraceus'' can insert part of its everted stomach, or some digestive juices, through the narrow gap that exists where the byssal threads emerge from the shell. The mussel needs to open its valves periodically to feed and breathe and the sea star can exert a powerful traction with its tube feet, pulling the two valves further open. Once the stomach is inside the mussel, digestion takes place. It is thought one sea star can consume eighty Californian mussels in a year.<ref>{{cite book |title=A living bay: the underwater world of Monterey Bay |last=Langstroth |first=Lovell |author2=Libby Langstroth |author3=Todd Newberry |year=2001 |isbn= 9780520221499|page=29 |publisher=University of California Press |url=https://books.google.com/books?id=byqHxbBBb90C&q=Leptasterias&pg=PA31 }}</ref>
==Ecology and distribution== [[File:(2) Starfish, Oregon coast.jpg|thumb|''P. ochraceus'' Oregon coast, near [[Cannon Beach]]]]
=== Conservation === ''Pisaster ochraceus'' has been described as a [[keystone species]]. Experiments by [[zoologist]] [[Robert T. Paine (zoologist)|Robert T. Paine]] in the 1960s demonstrated that a loss of only a few individual ''P. ochraceus'' seastars had a profound impact on mussel bed population, thereby reducing the health of the intertidal environment.<ref name="Power1996" /> With only a few natural predators (sea otters and seagulls) it is suggested that the principal threats to ''P. ochraceus'' are human collectors and casual tidepool visitors.<ref>{{cite book|last1=Ricketts|first1=Edward K.|last2=Calvin|first2=Jack|last3=Hedgepeth|first3=Joel|title=Between Pacific Tides|url=https://archive.org/details/betweenpacificti0000rick|url-access=registration|edition=5th|year=1985|publisher=Stanford University Press|isbn=9780804720687|page=[https://archive.org/details/betweenpacificti0000rick/page/217 217]}}</ref> ''Pisaster ochraceus'' has not been evaluated by the International Union for Conservation of Nature (IUCN).<ref name=eol/>
===Geographic range=== ''P. ochraceus'' can be found from [[Prince William Sound]] in Alaska to [[Point Sal]] in Santa Barbara County, California. The subspecies found within the warmer waters from Santa Barbara County to Baja California is ''P. o. segnis''.<ref name=Humphreys>Humphreys, V. (2003). The Biogeography of the Purple Ochre Sea Star (''Pisaster ochraceus''). Retrieved May 10, 2010, from {{cite web |url=http://bss.sfsu.edu/holzman/courses/Fall%2003%20project/oseastar.htm |title=Biogeography of Ochre Sea Star |access-date=2009-06-09 |url-status=dead |archive-url=https://web.archive.org/web/20090529035845/http://bss.sfsu.edu/holzman/courses/Fall%2003%20project/oseastar.htm |archive-date=2009-05-29 }}</ref>
===Habitat=== This sea star can be found in great numbers on mussel beds and on wave-washed rocky shores. The juveniles are often found in crevices and under rocks.<ref name=Ramirez/> Its depth range is from above the low-tide zone to {{convert|90|m|ft}}. ''P. ochraceous'' is very durable and can tolerate a loss of thirty percent of its body weight in body fluids.<ref name=eol/>
===Effects of ocean acidification=== A study found that ''P. ochraceus'' will not be affected by [[ocean acidification]] in the same way as most [[calcareous]] marine animals. This normally causes decreased growth due to the increased acidity dissolving [[calcium carbonate]]. Researchers found that when ''P. ochraceus'' was exposed to {{convert|21|C|F}} and 770 [[parts per million|ppm]] {{co2}} (beyond rises expected in the next century) they survived. It is thought that this is because the animal's calcium is nodular and so it is able to compensate for the lack of carbonate by growing more fleshy tissue instead.<ref>{{cite news|url=https://www.newscientist.com/article/mg20227104.800-starfish-defy-climate-change-gloom.html|title= Starfish defy climate change gloom|date=30 May 2009 |publisher=[[New Scientist]]|access-date=June 9, 2009}}</ref><ref name="PNAS">{{cite journal|last=Gooding|first=Rebecca |author2=Christopher Harley |author3=Emily Tang|date=June 9, 2009|title=Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm|journal=Proceedings of the National Academy of Sciences|volume=106|issue=23|pages=9316–9321 |doi=10.1073/pnas.0811143106|pmid=19470464|pmc=2695056 |bibcode=2009PNAS..106.9316G |doi-access=free }}</ref>
==References== {{Reflist}}
==External links== {{Commons category}} *[https://web.archive.org/web/20110719193240/http://wikis.evergreen.edu/ize2010/index.php/Pisaster_ochraceus ''Pisaster ochraceus''] *[https://seanet.stanford.edu/rocky-shores Species by zone height] *[https://web.archive.org/web/20090529035845/http://bss.sfsu.edu/holzman/courses/Fall%2003%20project/oseastar.htm Biogeography] *[https://web.archive.org/web/20090412083835/http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Echinodermata/Class%20Asteroidea/Pisaster_ochraceus.html ''Pisaster ochraceus'' (Brandt, 1835)] *[http://animaldiversity.ummz.umich.edu/site/accounts/information/Pisaster_ochraceus.html ''Pisaster ochraceus''] *[https://web.archive.org/web/20140222212328/http://enature.com/fieldguides/detail.asp?allSpecies=y&searchText=pisaster%20ochraceus&curGroupID=8&lgfromWhere=&curPageNum=1 Ochre sea star] *[http://eol.org/pages/598469 ''Pisaster ochraceus'' (Brandt, 1835)] *[https://web.archive.org/web/20090529035845/http://bss.sfsu.edu/holzman/courses/Fall%2003%20project/oseastar.htm The Biogeography of the Purple Ochre Sea Star (''Pisaster ochraceus'')] San Francisco State University *[http://northislandexplorer.com/echinoderms/ochreseastar.htm Ochre Sea Star], North Island Explorer * {{SealifePhotos|240755}}
{{Taxonbar|from=Q2727642}} {{Authority control}}
[[Category:Asteriidae]] [[Category:Echinoderms of the Pacific Ocean]] [[Category:Starfish described in 1835]] [[Category:Taxa named by Johann Friedrich von Brandt]]