Because the national park contains extensive marine environments from the shorelines of four separate islands out to ocean depths beyond the outer reefs we assume that the majority of the 991 fish species representing 113 families are found in or near the park This is about twice the number occurring in Hawaii, but half the number in the Indo-Pacific region. Dominant families are damselfish ( Pomacentridae ), surgeonfish ( Acanthuridae ), wrasse ( Labridae ) and parrotfish ( Scaridae ).
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.