The world's seas are "under threat as never before," the United Nations Secretary-General has told the group's first oceans conference.
Antonio Guterres told presidents, ministers, diplomats and environmental activists from nearly 200 countries that seas are being severely damaged by pollution, over-fishing and the effects of climate change as well as rubbish.
He cited a recent study that warned discarded plastic rubbish could outweigh fish by 2050 if nothing is done.
Mr Guterres said the aim of the five-day conference is "to turn the tide" and solve the problems that "we created".
He said competing territorial and fights over natural resources have blocked progress for far too long.
"We must put aside short-term national gain to prevent long-term global catastrophe," the Secretary-General said.