Dhaka, Nov. 19 -- Our oceans have been generous to us. They generate oxygen, help protect us from the sun's heat, provide food and livelihoods to millions of people, and serve humanity in myriad other ways. In return, we are destroying these nurseries for marine life by overharvesting fish and polluting the waters with untreated sewage and plastics.

Marine ecosystems are now threatened by extinction. Over the past 50 years, the world has lost nearly half of its coral reefs and mangrove forests, while marine populations have halved and global fish stocks depleted by a third.

Ocean dead zones - enormous areas where fish can no longer survive and breed -will expand dramatically as nitrogen fertilizer flows unabated at a rate of about 11 mi...