UNITED NATIONS, June 8 -- UN Secretary-General Antonio Guterres on Thursday called for more action to protect oceans.

"The ocean is the foundation of life. It supplies the air we breathe and food we eat. It regulates our climate and weather. The ocean is our planet's greatest reservoir of biodiversity," the UN chief said in his video message for World Oceans Day, which is observed annually on June 8.

Guterres said that over a third of global fish stocks are being harvested at unsustainable levels -- just one example of how "human activity is harming oceans," which cover more than 70 percent of the Earth's surface.

The ocean also produces resources that sustain communities, prosperity and health. Worldwide, more than a billion people alone rely on fish as their main source of protein, he said.

"We should be the ocean's best friend. But right now, humanity is its worst enemy," he said.

The top UN official said human-induced climate change is heating the planet, disrupting weather patterns and ocean currents, and altering marine ecosystems and the species living there.

Guterres said that marine biodiversity is also under attack from overfishing, over-exploitation and ocean acidification, fish stocks are being depleted, and coastal waters have been polluted with chemicals, plastics and human wastes.

"But this year's World Oceans Day reminds us that the tides are changing," he said.

Guterres recalled that last December, countries adopted an ambitious global target to conserve and manage 30 percent of land, and marine and coastal areas, by the end of the decade.

The past year also saw a landmark agreement on fisheries subsidies, and the UN Ocean Conference in Lisbon, Portugal, where the world agreed to push for more positive action.

Negotiations for a global, legally binding treaty to end plastic pollutions are currently underway, and in March, countries agreed the historic High Seas Treaty on the conservation and sustainable use of marine biodiversity in areas beyond national jurisdiction.

"Realizing the great promise of these initiatives requires collective commitment," he said.

"This World Oceans Day let's keep pushing for action. Today and every day, let's put the ocean first," he said.