Ochre Sea Star
Pisaster ochraceus

 

Physical Description 

  • Five-armed sea star, rather large (length can be up to 10 inches).
  • Bumpy rough back, covered in short spines arranged in a wavy pattern.
  • Most commonly orange or purple, but can be red or brown.

Range 

  • Found from Alaska to Baja California, Mexico.

Habitat

  • Live in the intertidal zone and tide pools.
  • When the tide goes out, they can be seen hiding from the sun under shady ledges and crevices.

Reproduction

  • Males and females are indistinguishable externally.
  • They spawn during the summer months, starting from the age of 5.
  • Females can produce 40 million tiny eggs, which are fertilized in the water by sperm released by males.
  • The fertilized eggs turn into bilaterally symmetrical larvae (symmetrical on only one line of symmetry) that float around as plankton before settling out of the plankton a few months later and growing into pentaradially symmetric (symmetrical on 5 lines of symmetry) adults.

Diet

  • Eat chitons, limpets, snails, barnacles, clams, sea urchins, and mussels.
  • The sea star eats these animals by opening the animals’ shells with the sea star’s strong tube feet. It then releases its stomach through its mouth, located in the middle of its body, into the animals’ shell and digests the animal whole.

Predators 

  • Sea otters and gulls.

Interesting Facts 

  • They are a keystone species, which means they significantly affect the entire community of the intertidal zone. They eat many other species, especially mussels. By eating a lot of mussels, sea stars allow other animals to come in and settle in the areas where mussel beds were.
  • Sea stars are in turn eaten by otters and sea gulls.
  • Ochre sea stars are vulnerable to sea star wasting disease, a disease that scientists are actively studying to help rescue these important species.
  • Scientists still don’t know why some Ochre sea stars are bright orange and some are bright purple.
  • Sea stars can regrow a lost arm. Regeneration may take up to a year, depending on food supply, water temperature, and other factors.

Sources: Slater Museum of Natural History, University of Puget Sound; Oceana; Georgia Aquarium

Photo: Jeremy Smith