ウニ
All species of sea urchin eat algae. They eat all sizes of algae, from something as small as macroalgae to something as large as kelp, and have been known to eat Coralline algae. In cooler waters, sea urchins have even been known to eat enough to control the size and compositions of kelp forests. Sea urchins act as scavengers and will also eat dead algae that they find. Some sea urchins, such as the variegated sea urchin or the red sea urchin, have become popular as pets for home aquariums because of their ability to proficiently eat algae.