This urchin’s body and spines are typically bright purple. Juveniles are occasionally pale green or greenish with tinges of purple. They are domed above and flattened below. These urchins can regenerate broken spines. They are related to other invertebrates including Sea Stars, Sea Cucumbers and Sand Dollars. Purple Sea Urchins eat a variety of red and brown algae, but the giant kelp Macrocystis is their first choice. As a result of their appetite, urchins can affect the growth of kelp beds. Historically, their numbers were controlled by Sea Otters which allowed kelp beds to flourish. When the sea otters were hunted to extinction along the Oregon coast in the late nineteenth century however, the urchin populations grew quickly and decimated many of the kelp forests offshore. Since these forests provided food and shelter to a variety of important marine species, the reduction had a cumulative effect that conservation efforts still struggle to control.
Urchins can be found from British Columbia to Baja California. They live in burrows or depressions on rocky shores and pilings from the lower intertidal zone to 525 feet (160 m) deep. They prefer areas of moderate to strong wave action.