US President Barack Obama has quadrupled the size of a marine national park in Hawaii, creating what is now the world's largest protected area of any kind.
Papahānaumokuākea Marine National Monument, established by US President George W. Bush in 2006, will now span 1,510,000 square kilometres - four times the state of California.
The protected area encompasses the Northwestern Hawaiian Islands, an uninhabited archipelago stretching northwest of the islands of Kauai and Niihau.
Papahānaumokuākea Marine National Monument (Pew Charitable Trusts)
The reserve is inhabited by more than 7000 species, including 4500-year-old black corals that are thought to be the oldest animals on Earth.
A quarter of the creatures living at the reserve are found nowhere else in the world, including the last 1100 Hawaiian monk seals.
Mr Obama's action will ban commercial fishing, mineral extraction and other industries that deplete natural resources.
The Papahānaumokuākea Monument is suffering from some of the worst coral bleaching in history as ocean temperatures rise.
The US Geological Survey also found in a 2013 study that Eastern Island - a home for millions of seabirds in the reserve - could all but disappear if sea levels rise by two metres by the end of the century.
Recreational fishing and the removal of resources for Native Hawaiian cultural practices and scientific research is allowed within the expanded territory by permit.
"Papahānaumokuākea is critically important to Native Hawaiian culture - it is our ancestral place, the birthplace of all life," said Sol Kahoʻohalahala, a seventh-generation Hawaiian from the island of Lanai, in a statement from a Pew Charitable Trusts subsidiary.
"The expanded monument will serve as a conservation, climate, and cultural refuge for my granddaughter and future generations," he said.
Mr Obama will head to the Papahānaumokuākea Monument in September to raise awareness for conservation in the area.