The ochre sea star (Pisaster ochraceus) is among the most commonly encountered sea stars on rocky coasts from Alaska to Baja California. It is considered a keystone species because it helps control the diversity and abundance of many other rocky intertidal invertebrates such as the California mussel (Mytilus californianus), one of its prey species. The sea star doesn’t need to pull the mussel’s shell very far apart, a crack will do. Once an opening has been created, the sea star extrudes its stomach from its body and will actually push it into the opening of the shells. Digestive processes then go to work, turning the mussel’s flesh into a slurry that the sea star’s stomach can then absorb.
An amazingly resilient animal, the sea star is very well adapted to the severe stresses faced in rugged intertidal environments. It is able to grip onto rock through the constant pounding of waves, and is often exposed to the open air for up to six hours during low tide.