Animal Diversity Web

Ge­o­graphic Range

As­te­r­ias forbesi are com­monly found in in­ter­tidal areas and shal­low wa­ters of the At­lantic Ocean on the North Amer­i­can Coast from the Gulf of Maine to the Gulf of Mex­ico (Dale, 2000; Pf­ef­fer, 1989).

• Biogeographic Regions
• atlantic ocean
  • native

Habi­tat

As­te­r­ias forbesi is found in the lit­toral zones of the North Amer­i­can At­lantic. They may be found in abun­dance, but they don't form colonies. They like rocks, boul­ders, and oys­ter/clam/scal­lop/mus­sel beds. Rocks are im­por­tant to help pre­vent wash­ing away and oys­ter beds have plenty of food within range (Moore, 1997).

• Aquatic Biomes
• coastal

Phys­i­cal De­scrip­tion

Most A. forbesi range from 7-15 cm in di­am­e­ter. They are tan, brown, or olive with tomes of or­ange, red, or pink. Like all sea stars, A. forbesi have "spiny skin" (a thin layer of skin cov­er­ing spiny os­si­cles) cov­er­ing their skele­ton. The skele­ton is made of plates called os­si­cles and bound by con­nec­tive tis­sue so that they move like flex­i­ble joints. The small spines are sur­rounded at the base by pedi­cel­lar­iae which are lit­tle jaws that keep the body free of de­bris and maybe catch a lit­tle food, too. The spines of A. forbesi are large in di­am­e­ter and are an ob­vi­ous fea­ture of the ex­ter­nal ap­pear­ance. There are lit­tle tufts of skin on the sur­face that serve as gills. The mouth is on the ven­tral (oral) side and the anus is on the dor­sal (ab­o­ral) side. A. forbesi along with the rest of the echin­o­derms are ra­di­ally sym­met­ri­cal. They have five arms that are ca­pa­ble of re­gen­er­at­ing. The ven­tral sides of the sea star's arms are cov­ered with tube feet. These tube feet have suc­tions at the bot­tom that suck in water and chan­nel it to canals that run through the body. There is a small hard spot on the dor­sal sur­face of the body called the madreporite or sieve plate. In A. forbesi, the madreporite is pink in col­ors. The madreporite has pores that allow it to fil­ter the water be­fore it en­ters the sea star's water vas­cu­lar sys­tem. The madreporite feeds into the ring canal in the mid­dle of the sea star. At­tached to the ring canal are ra­dial canals that branch off. Each ra­dial canal runs down an arm. The ra­dial canals are sur­rounded by am­pul­lae and tube feet on each side. Am­pul­lae are the bulbs at the top of the tube feet. (Ama­ral, 2000; Amos and Amos, 1985; Bertin, 1967; Dale, 2000; Fox, 1999; Raven, 1999; Vodopich, 1999).

• Other Physical Features
• ectothermic

Re­pro­duc­tion

Sea stars in gen­eral have sep­a­rate sexes. There are go­nads in each arm on the ven­tral side. There is ex­ter­nal fer­til­iza­tion be­cause sperm and eggs are shed into the water. Fe­males can re­lease up to 2.5 mil­lion eggs. When one fe­male sheds her eggs, other fe­males in the area are stim­u­lated to shed their eggs and then males are stim­u­lated to shed their milt. The eggs de­velop into bip­in­naria lar­vae, which lasts for about 3 weeks be­fore set­tling and meta­mor­phos­ing. The lar­vae are free-swim­ming and bi­lat­er­ally sym­met­ri­cal. They de­velop into ses­sile ra­dial adults (Bertin, 1967; Raven, 1999).

Be­hav­ior

A. forbesi can move at a rate of 15-20 cm per minute in un­threat­ened ocean water, but when under at­tack, can speed up to 25-35 cm per minute. Sea stars move via their water vas­cu­lar sys­tem by chang­ing the water pres­sure and mov­ing the tube feet. A. forbesi re­lies heav­ily on chemore­cep­tion to ori­ent them­selves and get around. A. forbesi re­sponds to chemosen­sory stim­uli and can lo­cate the source of odors. They use dif­fer­ent ori­en­ta­tion paths for dif­fer­ent odors. When there is prey around, A. forbesi walks faster and at more di­rect an­gles to the food. If a sea star is turned on its back, it turns one arm so that it grips the ground sur­face with its tube feet. The arm turns until the body has com­pleted a slow som­er­sault into its nor­mal po­si­tion. Sea stars do not move like wheels. They move in straight lines with one arm in ad­vance when they are mov­ing their fastest. Dur­ing times of great wave ac­tion in shal­low water, sea stars cling to rocks, flat­ten­ing them­selves against the rocks with all the power their tube feet can exert (Bertin, 1967; Dale, 2000; Grz­imek, 1972).

Food Habits

Sea stars are car­niv­o­rous and like to eat other in­ver­te­brates, ma­rine worms, crus­taceans, gas­tropods, sea urchins, and mol­lus­can bi­valves like mus­sels, clams, and oys­ters. A. forbesi feeds chiefly on bi­valve mol­luscs. They grasp the mol­lusk and use their tube feet to suc­tion and pull the shells apart enough to ex­tend their stom­achs out through their mouth into the mol­lusk. Di­ges­tion (via pos­si­ble toxic juices) oc­curs in­side the shell, turn­ing the mol­lusk into liq­uid that is guided into the sea star's mouth by the cilia on its arms. The sea star will win in the bat­tle against the bi­valve due to mus­cle en­durance and its abil­ity to in­sert its stom­ach through thin open­ings (Ama­ral, 2000; Amos and Amos 1985; Bertin, 1967; Dale, 2000; Pf­ef­fer, 1989).

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

An­other species of starfish in the genus Pisas­ter is a key­stone preda­tor in the rocky in­ter­tidal zone off the Pa­cific Coast. It main­tained di­ver­sity in the tidal re­gion by keep­ing the strongly com­pet­i­tive bi­valves at a low enough pop­u­la­tion level that they could not mo­nop­o­lize all the re­sources and form a mono­cul­ture. Al­though not stud­ied, it is con­ceiv­able that A. forbesi plays a sim­i­lar role on the At­lantic and Gulf Coast. (Raven and John­son 1999)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

As­te­r­ias forbesi can get into mol­lusk beds and com­pete with the farm­ers and fish­er­men for food. If there is an over­pop­u­la­tion of sea stars, they are hard to get rid of be­cause if they break, they will re­gen­er­ate, and then there will be many more.

Con­ser­va­tion Sta­tus

As­te­r­ias forbesi is doing fine. Cur­rently, there is no spe­cial need to save the starfish. The pop­u­la­tion is thriv­ing with­out human help.

• IUCN Red List

  No special status

Other Com­ments

Sea stars aren't highly preyed upon due to their tough, non-nu­tri­tious cal­ci­fied skin. There are some kinds of crus­taceans and fish that will eat them, though. A. forbesi is also known as Forbes' Sea Star and as the com­mon sea star. It is one of the most com­mon starfish species on the North Amer­i­can At­lantic coast (Dale, 2000).

Sea stars can com­pletely re­gen­er­ate as long as they have one fifth of the cen­tral disk and one arm. There is one eye­spot at the end of each arm.

Con­trib­u­tors

Kim Chau (au­thor), South­west­ern Uni­ver­sity, Stephanie Fab­ri­tius (ed­i­tor), South­west­ern Uni­ver­sity.

Ref­er­ences

Ama­ral, K. 2/1/95. "Sea stars" (On-line). Ac­cessed Feb­ru­ary 19, 2000 at http://​www.​umassd.​edu/​Public/​People/​Kamaral/​thesis/​SeaStar.​html.

Amos, W., S. Amos. 1985. The Audubon So­ci­ety Na­ture Guides: At­lantic and Gulf Coasts. New York: Al­fred A. Knopf.

Bertin, L. 1967. The Larousse En­cy­clo­pe­dia of An­i­mal Life. Verona: Mc­Graw-Hill.

Dale, J. 01/26/2000. "Madreporite Nexus" (On-line). Ac­cessed Feb­ru­ary 20, 2000 at http://​www.​vsf.​cape.​com/​~jdale/.

Fox, R. 04/04/99. "As­te­r­ias" (On-line). Ac­cessed Feb­ru­ary 28, 2000 at http://​www.​science.​lander.​edu/​rsfox/​asterias.​html.

Grz­imek, B. 1972. Grz­imek's An­i­mal Life En­cy­clo­pe­dia, Vol­ume 3: Mol­lusks and Echin­o­derms. New York: Van Nos­trand Rein­hold Com­pany.

Moore, P., D. Lep­per. June 1997. Role of chem­i­cal sig­nals in the ori­en­ta­tion be­hav­ior of the sea star As­te­r­ias forbesi. Bi­o­log­i­cal Bul­letin, 192: 410-417.

Pf­ef­fer, P. 1989. Preda­tors and Pre­da­tion: The Strug­gle for Life in the An­i­mal World. New York: Facts On File.

Raven, P., G. John­son. 1999. Bi­ol­ogy (5th ed.). Boston: Mc­Graw-Hill.

Vodopich, D., R. Moore. 1999. Bi­ol­ogy Lab­o­ra­tory Man­ual (5th ed.). Boston: Mc­Graw-Hill.