Common Sea Star (Northern Sea Star)

Northern Sea Stars / Jeff Rotman / Getty Images
Northern Sea Stars. Jeff Rotman / Getty Images

The common sea star is also called the northern sea star, northern starfish or common starfish. It is sometimes referred to as Asterias vulgaris, which was the scientific name originally used for the sea star in the western North Atlantic off the eastern coast of the U.S. and Canada, while Asterias rubens referred to the common sea star in the eastern North Atlantic. The two species have now been determined to be the same species, and are referred to as Asterias rubens.

Description

Common sea stars have five arms, a robust body and a visible madreporite on the dorsal surface. This madreporite intakes water that fill the sea star's tube feet.There may also be a visible row of spines down the middle of each arm on the dorsal side.  On their dorsal side, these sea stars also have spines and pedicellariae - pincer-like structures that are used for cleaning the sea star's body surface to keep it from being fouled by encrusting organisms - see a close-up image here

On the underside, common sea stars have four rows of sucker-tipped tube feet, and a mouth in the middle of the central disk that is located in center of the animal's body. 

Common sea stars can be a variety of colors, including orange, purple, brown and pink. These sea stars can grow to about 20 inches across, although they are usually smaller.

Classification

  • Order: Forcipulatida
  • Family: Asteriidae
  • Genus: Asterias
  • Species: rubens

Habitat and Distribution

Common sea stars live in the North Atlantic Ocean along the coasts of Canada, the Northeastern United States, Europe and the northern coast of Africa. Common sea stars are found along rocky shores in intertidal areas, and deeper waters out to about 2000 feet.

They may also be found in kelp beds, and abundance may be correlated with the abundance of blue mussels (Mytilus edulis). 

Diet and Feeding

Common sea stars eat mollusks, including bivalves (a favorite prey item is the blue mussel) and gastropods. They also eat crustaceans and worms. They act both as active predators and scavengers. 

The common sea star's feeding methods may seem bizarre - during feeding, they will use their arms to pry open the shell of their prey, if it has one.  The sea star then turns its stomach inside out and pushes it out through their mouth, and into the shell of their prey, where digestive enzymes help digest the prey. Once the prey is digested, the sea star pulls its stomach back inside its body.

Reproduction

Reproduction occurs sexually or asexually. There are separate male and female common sea stars, and they have a pair of gonads in each arm.  Sexual reproduction occurs through the release of millions of sperm and eggs into the water, which are fertilized in the water. The fertilized eggs develop into a planktonic larva which settles to the ocean floor after 21-87 days. Common sea stars are sexually mature after 1 year, and are thought to live for 5-10 years.

 

During asexual reproduction, the sea star divides its disk so that it breaks into two halves. Each half regenerates into a new sea star. Sea stars can also lose an arm (e.g., when attacked by a predator) and regrow it. Occasionally, common sea stars have 6 arms when two arms grow into the place of one. It takes about a year for a sea star to regrow its arm.

Conservation

Common sea stars are not considered threatened and do not have any special conservation status. Dried sea stars may be used by humans for decoration. 

References and Further Information

  • Beer, A. and D. Hall. 2012. The Illustrated World Encyclopedia of Marine Fish and Sea Creatures. Lorenz Books. 
  • Encyclopedia of Life. Asterias rubensAccessed December 16, 2013.
  • Lewis, C. 2000. Asterias rubens. Animal Diversity Web. Accessed December 16, 2013.
  • Mah, C.; Hansson, H. 2013. Asterias rubens Linnaeus, 1758. In: Mah, C.L. (2013). World Asteroidea database. Accessed through: Mah, C.L. (2013). World Asteroidea database, December 16, 2013.
  • MarLIN. Biotic Species Information for Asterias rubens. Accessed December 16, 2013.
  • Martinez, A.2003. Marine Life of the North Atlantic.  Aqua Quest Publications: New York. 
  • Waller, G. (ed.). 1996. SeaLife: A Complete Guide to the Marine Environment. Smithsonian Institution Press: Washington, D.C.
  • World Association of Zoos and Aquariums. Common Starfish. Accessed December 16, 2013.