French Polynesia's 118 islands are scattered across one of the most remote and biodiverse stretches of ocean on Earth. Its reefs shelter fish, sharks, whales and turtles, while coastal lagoons support communities that have lived along the sea for generations.

Last year, French Polynesia made a historic move to protect all of its waters — an expanse roughly the size of the European Union. Today, they went further.

The French Polynesian government announced that 520,000 square kilometers (200,000 square miles) of ocean surrounding the Austral and Marquesas Islands — two of the most biologically rich archipelagos on Earth — would receive the highest level of protection, where no mining, trawling or industrial fishing is permitted.

The move marks the single largest national contribution to the global goal of protecting 30 percent of the planet's lands and waters by 2030, said Maël Imirizaldu, a regional lead for the Blue Nature Alliance — a global coalition co-founded by Conservation International.

“This…