Their tests grow to a size of three or four inches. Sea urchins will eat just about anything that floats by. Its sharp teeth can scrape algae off rocks, and grind up plankton , kelp , periwinkles , and sometimes even barnacles and mussels . Sea urchins are sought out as food by birds, sea stars , cod, lobsters, and foxes. In the northwest, sea otters are common predators of the purple sea urchin.
Humans also seek out sea urchin eggs, or roe, for food.
The eggs are considered a delicacy in Asia.