“The ocean is the ultimate shared resource,” he told delegates gathered at the port of Nice. “But we are failing it.”

Oceans, he warned, are absorbing 90 per cent of the excess heat from greenhouse gas emissions and buckling under the strain: overfishing, rising temperatures, plastic pollution, acidification. Coral reefs are dying. Fish stocks are collapsing. Rising seas, he said, could soon “submerge deltas, destroy crops, and swallow coastlines — threatening many islands’ survival.”

Port Lympia, Nice’s historic marina, now transformed into a secured diplomatic zone known as the Blue Zone for UNOC3.

Call for stewardship

More than 50 Heads of State and Government took part in the opening ceremony, including Brazilian President Luiz Inácio Lula da Silva and European Commission President Ursula von der Leyen — a show of political force underscoring the summit’s weight.

In total, over 120 countries are participating in the five-day gathering, signaling a growing recognition that ocean health is inseparable from climate stability, food security, and global equity.

French President Emmanuel Macron, whose country is co-hosting the summit alongside Costa Rica, followed with a forceful appeal for science, law, and multilateral resolve.

Brazilian President Luiz Inácio Lula da Silva, at the opening ceremony of UNOC3

“The abyss is not for sale, any more than Greenland is for sale, any more than Antarctica or the high seas are for sale,” he declared. “If the Earth is warming, the ocean is boiling.”

He insisted the fate of the seas could not be left to markets or opinion. “The first response is therefore multilateralism,” Mr. Macron said. “The climate, like biodiversity, is not a matter of opinion; it is a matter of scientifically established facts.”

Costa Rican President Rodrigo Chaves Robles took the podium next, thanking Mr. Guterres for elevating the ocean on the global agenda, then shifting to a stark warning.

“The ocean is speaking to us — with bleached coral reefs, with storms, with wounded mangroves,” he said. “There’s no time left for rhetoric. Now is the time to act.”

Condemning decades of treating the ocean as an “infinite pantry and global waste dump,” Mr. Chaves urged a shift from exploitation to stewardship.

“Costa Rica is a small country, but this change has started,” he said. “We are now declaring peace with the ocean.”

Most notably, the Costa Rican leader called for a moratorium on deep-sea mining in international waters until science can adequately assess the risks — a position already backed by 33 countries, he noted.

A treaty within reach

One of the summit’s core objectives is to help bring into force the landmark High Seas Treaty — known as the BBNJ accord — adopted in 2023 to safeguard life in international waters. Sixty ratifications are required for the treaty to become binding international law. Emmanuel Macron announced that this milestone is now within reach.

“In addition to the 50 or so ratifications already submitted here in the last few hours, 15 countries have formally committed to joining them,” he said. “This means that the political agreement has been reached, which allows us to say that this [Treaty] will be properly implemented.”

Whether the legal threshold is crossed this week or shortly after, the French President added, “it’s a win.”

The plenary hall of the third UN Ocean Conference (UNOC3) in Nice.

High-stakes negotiations in the ‘Blue Zone’

The tone set by the opening speeches made clear that Nice will be the stage for high-stakes negotiations — on finalizing a global treaty on plastic pollution, scaling up ocean finance, and navigating the controversy surrounding seabed mining.

Hundreds of new pledges are expected to be announced, building on more than 2,000 voluntary commitments made since the first UN Ocean Conference in 2017. The week-long talks will culminate in the adoption of a political declaration and the unveiling of the Nice Ocean Action Plan, a blueprint aligned with the landmark Kunming-Montreal Global Biodiversity Framework, a 2022 agreement to protect 30 per cent of marine and terrestrial ecosystems by 2030.

“The deep sea cannot become the Wild West,” António Guterres warned, urging that decisions be “grounded in science, guided by precaution, and in line with the rights and obligations enshrined in the UN Convention on the Law of the Sea.”

The summit is being held in a purpose-built venue overlooking Port Lympia, Nice’s historic marina, now transformed into the secured diplomatic ‘Blue Zone.’ On Sunday, a symbolic ceremony led by Li Junhua, head of the UN Department of Economic and Social Affairs and Secretary-General of the conference, saw the French and UN flags raised above the harbor.

“This ceremony marks not only the formal transfer of this historic port into the hands of the United Nations, but also the beginning of a week of shared commitment, responsibility, and hope,” said Mr. Li.

Ludovic Burns Tuki marked the start of the summit by blowing a pu, a traditional conch shell

Culture, science, and collective memory

Before the negotiations began in earnest, Monday’s opening turned to ritual and reflection. Polynesian climate activist Ludovic Burns Tuki marked the start of the summit by blowing a pu, a traditional conch shell.

“It’s a way to call everyone,” he told UN News after the ceremony. “I blow with the support of our ancestors.” In Polynesian navigation, the conch is sounded upon arrival at a new island to signal peaceful intent. Mr. Tuki, born in Tahiti to parents from the Tuamotu and Easter Islands, sees the ocean as both boundary and bond.

“We are not only countries,” he said. “We need to think like a collective system, because this is one ocean, one people, a future for all.”

The cultural segment also included a blessing by Tahitian historian Hinano Murphy, a martial arts performance by French taekwondo master Olivier Sicard, a scientific reflection by deep-sea explorer Antje Boetius, and a poetic testimony by Mauritanian filmmaker Abderrahmane Sissako, accompanied by kora musician Wassa Kouyaté.

What was lost can return

The goals of the conference are clear — but ambitious: to advance the ‘30 by 30’ pledge, promote sustainable fisheries, decarbonize maritime transport, and unlock new streams of “blue finance,” including ocean bonds and debt-for-nature swaps to support vulnerable coastal states.

In addition to plenary sessions, Monday will feature two high-level action panels: one on conserving and restoring marine ecosystems — including deep-sea habitats — and another on strengthening scientific cooperation, technology exchange, and education to bridge the gap between science and policy.

In his opening statement, António Guterres stressed that Sustainable Development Goal 14 , on ‘Life Below Water’, remains the least funded of the 17 UN’s global goals.

“This must change,” he said. “We need bold models to unlock private capital.”

“What was lost in a generation,” he concluded, “can return in a generation. The ocean of our ancestors — teeming with life and diversity — can be more than legend. It can be our legacy.”