Sea Stars: Asteroidea

Physical characteristics: Northern Pacific sea stars are 16 to 20 inches (40 to 50 centimeters) across. They have five arms that are turned up at the tips. These sea stars are rosy brown, yellowish brown, red, or purple. Their underside is very flat. The skin is covered with unevenly arranged spines that have jagged ends.

Geographic range: Northern Pacific sea stars live in the western, northern, and eastern parts of the Pacific Ocean.

Habitat: Northern Pacific sea stars live in shallow water on sheltered coasts in sand and mud and among rocks and algae thickets. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves.

Diet: Northern Pacific sea stars eat scallops, oysters, mussels, shrimp, and other sea stars.

Northern Pacific sea stars were accidently introduced into Australia and Tasmania, causing damage to the shellfish business. (Illustration by Barbara Duperron. Reproduced by permission.)

Behavior and reproduction: Northern Pacific sea stars feed by using their tube feet and arms to pull apart the shells of their prey before turning their stomachs inside out. When it is time to release eggs and sperm, the swarms are so dense that the females lift themselves above the ground on their arms and release eggs between the arms while the male sea stars crawl beneath. The females release about twenty million eggs, which when fertilized develop into drifting larvae.

Northern Pacific sea stars and people: Northern Pacific sea stars accidentally introduced into Australia and Tasmania have caused damage to the shellfish business.

Conservation status: Northern Pacific sea stars are not considered threatened or endangered. ∎