The Papahanaumokuakea Marine National Monument is the single largest conservation area under the U.S. flag, and one of the largest marine conservation areas in the world. It encompasses 139,797 square miles of the Pacific Ocean (362,073 square kilometers) - an area larger than all the country's national parks combined. The extensive coral reefs found in Papahanaumokuakea - truly the rainforests of the sea - are home to over 7,000 marine species, one quarter of which are found only in the Hawaiian Archipelago. Many of the islands and shallow water environments are important habitats for rare species such as the threatened green turtle and the endangered Hawaiian monk seal. On less than six square miles of land over 14 million seabirds representing 22 species breed and nest. Land areas also provide a home for four species of bird found nowhere else in the world, including the world's most endangered duck, the Laysan duck. Papahanaumokuakea is of great cultural importance to Native Hawaiians with significant cultural sites found on the islands of Nihoa and Mokumanamana, both of which are on the National and State Register for Historic Places. Papahanaumokuakea Marine National Monument was created by Presidential proclamation on June 15, 2006.