This year's World Oceans Day is committed to the goal of protecting at least 30% of the "blue planet" by 2030. Not only for safeguarding marine life that is disappearing at twice the rate of land species, the 30% goal also aims to protect oceans from climate-linked temperature rise that is bleaching coral reefs and reducing the oxygen in water required for life.

Covering more than 70% of the earth's surface, oceans produces at least 50% of the planet’s oxygen, are home to most of Earth’s biodiversity, and are the main source of protein for more than a billion people around the world. Ocean-based or so-called "blue" economies and communities need to become custodians of sustainable seas that are the Earth's life-support system.

Mangroves (such as above, in the Guinea-Bissau Archipelago), seagrass and salt marshes comprise "blue carbon" ecosystems that can sequester up to four times as much CO2 as terrestrial forests on a per-area basis. As a result, they are vital to the world meeting the 2050 Paris climate agreement emissions-reduction targets.

But oceans will only remain a vital source of work and sustenance when so-called blue economies are managed sustainably. Artisanal fishing, for example, allows coastal economies in the Global South to maintain livelihoods while preserving biodiversity and culture. The blue economy also aims to incorporate renewable energy to protect the Earth's life support system from temperature rises.

Central to ocean sustainability is stopping widespread overfishing and illegal fishing, which is threatening highly biodiverse marine life around the world. While Chinese trawlers are in the spotlight for plundering waters in Latin America for example, Greenpeace has long called out the "massacre" of threatened bluefin tuna in the Mediterranean, and is demanding the creation of marine reserves.

The Great Pacific Garbage Patch is a massive island of plastics and microplastics that is now twice the size of Texas. Said to comprise 1.8 trillion plastic pieces — one of which is shown above — and made up of 80,000 tons of waste, the growing sea-borne garbage patch embodies humanity's disconnection from what environment writer Rachel Carsen called "that great mother of life, the seas."

Clean wave and tidal energy from the ocean could provide 10% of Europe's current electricity needs by 2030, according to Ocean Energy Europe. The vast potential of Europe's sea basins to provide energy is the greatest in the United Kingdom. It produces around 50% of Europe's tidal energy and 35% of its wave energy, and could draw one-fifth of its power for electricity from the ocean.

"All of us have in our veins the exact same percentage of salt in our blood that exists in the ocean, and, therefore, we have salt in our blood, in our sweat, in our tears," former United States President John F. Kennedy once said of humanity's symbiotic relation with water. "We are tied to the ocean. And when we go back to the sea," he continued, "we are going back from whence we came."