There are five species of lichens in the monument. They are commonly found growing on recent lava flows and older trees. A lichen is an unusual organism because it is not just one organism, but two organisms that live together in symbiosis. The first is a fungus composed of stringy filaments, and living within these filaments are algae- usually a species of green algae, or cyanobacterium.
Maine ocean islands provide the only nesting sites for Atlantic puffins in the United States. Eastern Egg Rock in the midcoast region, Seal Island and Matinicus Rock at the mouth of Penobscot Bay, and Machias Seal Island and Petit Manan Island off the downeast coast provide habitat for more than 4,000 puffins each summer.