Prince William has warned that oceans have been reduced to "barren deserts" by humans

William dec lared the situation to be "simply heartbreaking" and called for action so "change the course of history" by saving the world's oceans, though he noted "the clock is ticking" on a global commitment to protect 30 per cent of land and sea by the end of the decade, noting just 3% of the ocean is fully protects.

He said: "Put simply: the ocean is under enormous threat, but it can revive itself.

"But, only if together, we act now...

"This challenge is like none that we have faced before."

He quoted Sir David Attenborough and said: "If we save the sea, we save our world".

William called for "urgency and optimism" to tackle the issue.

He said: "I believe that urgency and optimism have the power to bring about the action needed to change the course of history," he said.

"With creativity, ingenuity, investment and support, we can unlock exciting innovations and solutions that protect our planet, create jobs, sustain livelihoods and encourage prosperity...

"Watching human activity reduce beautiful sea forests to barren deserts at the base of our oceans is heartbreaking.

"For many, it is an urgent wake-up call to just what is going on in our oceans. But it can no longer be a matter of 'out of sight, out of mind.'"

William dec lared that looking after the oceans was an "incredibly important issue" held "dear to my heart", but warned many forget just how "vital" the seas of the world are.

He said at the Grimaldi Forum conference hall: "We come together today united by our deep connection to the ocean and our concern for its safety. For many of us, it is a place where some of our happiest memories are made... where we have explored the wonders of the natural world... and we have all relied on its great abundance for our food and livelihoods.

"And yet, all too often, it can feel distant and disconnected from our everyday lives, allowing us to forget just how vital it is. The truth is that healthy oceans are essential to all life on earth.

"They generate half of the world's oxygen, regulate our climate and provide food for more than three billion people.

"And today, they need our help.

"Rising sea temperatures, plastic pollution and overfishing are putting pressure on these fragile ecosystems... and on the people and communities who depend upon them.

"What once seemed an abundant resource is diminishing before our eyes.?We all stand to be impacted. And we are all responsible for change - both negative and positive."

William met delegates from the Earthshot Prize before addressing those gathered for the forum, which was held in honour of World Oceans Day.

And after helping Sir David launch his new film 'Ocean', the prince - who has Prince George, 11, Princess Charlotte, 10, and seven-year-old Prince Louis with wife Catherine, Princess of Wales- admitted he was "very emotional" after seeing the documentary.

He told Enric Sala, a marine ecologist who had worked on the film: "I was very emotional after watching it. I got angry then I got sad then I got frustrated then I got happy - every single range of emotions.

"It was really powerful. I'm working out how to show my children as well."