The United States joined forces with other nations to declare a vast swathe of the Pacific Ocean a marine sanctuary and take "historic" steps to combat illegal fishing.
Taking the helm in a stepped up fight to save the planet's oceans, President Barack Obama on Tuesday ordered his administration to chart a way to expand an existing US reserve and create what would be the world's largest marine park.
And a two-day conference hosted by the State Department was given a sprinkle of stardust by Hollywood A-lister Leonardo DiCaprio, who pledged US$7 million from his foundation to help clean up the seas.
The US is planning to expand the Pacific Remote Islands National Monument, which together with action taken by other nations such as the Cook Islands and Kiribati, would mean three million square kilometers are declared off-limits to all fishing fleets and drilling activities.
A total of US$1.8 billion - with US$1 billion alone coming from Norway to combat climate change - was pledged at the conference seeking to draw up an action plan to fight pollution, acidification and overfishing.
"Right now only a small fraction of the world's ocean ... is protected," US Secretary of State John Kerry said.
More had to be done but the new commitments were "a terrific start", he said, after leaders from more than 80 countries met for two days with scientists and industry experts.
Obama said he would use his executive powers to expand the Pacific Islands marine park, where the White House said "tropical coral reefs and associated marine ecosystems are among the most vulnerable areas to the impacts of climate change and ocean acidification".
In a video address, Obama said he had also directed the US government to "build a national strategy to combat black-market fishing."
"Rising levels of carbon dioxide are causing our oceans to acidify. Pollution endangers marine life. Overfishing threatens whole species as well as the people who depend on them for food and their livelihoods," Obama said.
But the White House pledged that fishermen, scientists and conservation experts would be consulted before the outlines of the marine sanctuary were defined.
The plan could ignite a new battle with Republicans in Congress, angered by Obama again using his executive powers to bypass the US legislature.
"If we ignore these problems, if we drain our oceans of the resources, we won't just be squandering one of humanity's greatest treasures, we'll be cutting off one of the world's major sources of food and economic growth," Obama warned.
He won support from Hollywood actor DiCaprio, an avid diver, who said his love for the oceans had led him to explore underwater worlds.
"I've witnessed environmental devastation first hand," DiCaprio said, recalling two dives he made some 18 years apart at the coral reef in Australia.
"What once had looked like an endless underwater utopia is now riddled with bleached coral reefs and massive dead zones."
"Unfortunately today, there's no proper law enforcement capacity and little accountability for violating the law. It's the Wild West on the high seas," warned the star.