Rocky intertidal zone of the New England sea coast, showing rocks encrusted with blue mussels, periwinkles, red crustose algae, calcareous algae (also known as coral weed), and a green-colored algae, possibly false Irish moss. Blue mussel: Mytilus edulis. Periwinkle: Littorina species. Crustose algae: Hildenbrandia prototypus. Calcareous algae: Corallina species. False Irish moss: Mastocarpus stellatus. Appledore Island, Isles of Shoals, Maine, USA.