Green Sea Urchin Green Sea Urchin: average size is 50-60 mm, but may reach a maximum size of about 85 mm. Distribution: The green sea urchin is one of the most widely distributed of all Echinoderms. It has a circumpolar distribution, which extends into the Arctic regions of both the Atlantic and Pacific Oceans. It commonly inhabits the rocky subtidal zone from the low-tide mark down to a depth of 1200 m, but also occurs intertidally in tide pools. Diet: The green sea urchin primarily grazes on seaweeds (kelp being its preferred food source), but will also consume a wide variety of organisms including mussels, sand dollars, barnacles, whelks, periwinkles, sponges, bryozoans, dead fish, and - when hungry enough - other sea urchins. They are eaten by: A variety of predators including crabs, sea stars, wolf eels and humans. The Japanese relish the gonads called "uni",