Obama hasn't settled on the final boundaries for the expanded Pacific Remote Islands Marine National Monument and will solicit input from fishermen, scientists and conservation experts. Obama's senior counselor, John Podesta, said that process would start immediately and wrap up "in the very near future."
President George W. Bush created the monument in 2009 by setting aside waters that encircle an array of remote islands in the south-central Pacific between Hawaii and American Samoa. Bush's protections extend about 50 miles from the shore of the U.S.-administered islands, but maritime law gives the U.S. control up to 200 nautical miles from the coast, forming the outer limit of what Obama could protect using the 1906 Antiquities Act.
If Obama opts for the full 200 miles, conservation groups said, he could roughly double the amount of ocean that's protected worldwide.
A geographic analysis by the Pew Charitable Trusts estimated Obama could protect more than 780,000 square miles almost nine times what Bush set aside and far more if he included the waters around other U.S. islands in the Pacific Ocean.
"Our oceans are feeling the strain of human activity from increased acidification, overfishing and pollution, and we need to take bold action to protect this vital natural resource," said Carol Browner, the former Environmental Protection Agency administrator.
But in practical terms, the expanded sanctuary will likely have a modest impact.
Very little commercial fishing is conducted around the islands. Bob Fryklund, chief upstream strategist for analytics agency IHS Energy, said no one is exploring for oil or gas in the area.
But conservation groups said it's critical to take proactive steps to safeguard underwater ecosystems even if direct human damage isn't imminent.
"These are fairly long distances from any ports, and they're very expensive to get to," said Lance Morgan of the Marine Conservation Institute. "Still, we don't know what all the future uses are going to be."
Obama has increasingly invoked his own authority to impose environmental protections during his second term, wary of ceding control to lawmakers who have shown no appetite for major legislation to fight climate change and other ecological challenges.
Republicans reacted with similar indignation Tuesday and accused Obama of overreaching.
Rep. John Fleming, R-La., who chairs the House sub-panel dealing with oceans and wildlife, said Obama was invoking climate change even though the century-old Antiquities Act wasn't intended to deal with global warming.
"This is clearly way outside of his constitutional boundaries. It's just another step in the wrong direction for our imperial president," he said.
In another environmental move, Obama launched a task force to combat black-market fishing and seafood fraud, in which seafood products are mislabeled to hide their origin. One-fifth of wild marine fish caught each year are considered to be part of the black market, the White House said. The black market for fish cost the legitimate fishing industry $23 billion.