Pisaster is a genus of Pacific sea stars that includes three species, P. brevispinus, P. giganteus, and P. ochraceus. Their range extends along the Pacific coast from Alaska to southern California in the intertidal zone. Pisasters can reach up to 70 cm (28 in) in width and typically have five arms. Colour variations include ochre, brown, orange, and purple. Pisaster starfish is an important predator and a key stone species, in the rocky intertidal community of American Pacific Coast. In a field experiment when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year ,because of inter specific competition.This shows the importance of pisaster starfish.