For the first time, United Nations members have agreed on a unified treaty to protect biodiversity in the high seas – nearly half the planet’s surface – concluding two weeks of talks in New York.

The U.N. Convention on the Law of the Sea came into force in 1994, before marine biodiversity was a well-established concept.

An updated framework to protect marine life in the regions outside national boundary waters, known as the high seas, had been in discussions for over 20 years. Still, previous efforts to reach an agreement had repeatedly stalled. Finally, the unified agreement treaty was reached late Saturday.

"We only have two major global commons – the atmosphere and the oceans," said Georgetown marine biologist Rebecca Helm. While the oceans may draw less attention, "protecting this half of earth’s surface is critical to the health of our planet."

Now that the long-awaited treaty text has been finalized, Nichola Clark, an oceans expert at the Pew Charitable Trusts who observed the talks in New York, said, "This is a once-in-a-generation opportunity to protect the oceans – a major win for biodiversity."

The treaty will create a new body to manage the conservation of ocean life and establish marine protected areas on the high seas. And Clark said that’s critical to achieve the U.N. Biodiversity Conference’s recent pledge to save 30% of the planet’s waters and land for conservation.

The treaty also establishes ground rules for conducting environmental impact assessments for commercial ocean activities.

"It means all activities planned for the high seas need to be looked at, though not all will go through a full assessment," said Jessica Battle, an oceans governance expert at the Worldwide Fund for Nature.

Many marine species – including dolphins, whales, sea turtles, and fish – make long annual migrations, crossing national borders and the high seas. However, efforts to protect them – and human communities that rely on fishing or tourism related to marine life – have previously been hampered by a confusing patchwork of laws.

"This treaty will help to knit together the different regional treaties to address threats and concerns across species’ ranges," said Battle.

That protection also helps coastal biodiversity and economies, said Gladys Martínez de Lemos, executive director of the nonprofit Interamerican Association for Environmental Defense, focusing on environmental issues across Latin America.

"Governments have taken an important step that strengthens the legal protection of two-thirds of the ocean and with it marine biodiversity and the livelihoods of coastal communities," she said.

The question now is how well the ambitious treaty will be implemented.

The high seas have long suffered exploitation due to commercial fishing, mining, and pollution from chemicals and plastics. The new agreement is about "acknowledging that the ocean is not a limitless resource, and it requires global cooperation to use the ocean sustainably," said Malin Pinsky, a biologist at Rutgers University.

What’s high seas?

The high seas begin at the border of countries’ exclusive economic zones, which extend up to 200 nautical miles (370 kilometers) from coastlines. They thus fall under the jurisdiction of no country.

Even though the high seas comprise more than 60% of the world’s oceans and nearly half the planet’s surface, they have long drawn far less attention than coastal waters and a few iconic species.

Ocean ecosystems create half the oxygen humans breathe and limit global warming by absorbing much of the carbon dioxide emitted by human activities.

But they are threatened by climate change, pollution, and overfishing.

Only about one percent of the high seas are currently protected.

When the new treaty comes into force, it will allow the creation of marine protected areas in these international waters.