2,000 new marine species are being discovered every year - but they are under serious threat. A new documentary film starring the celebrated David Attenborough hits cinemas this Thursday (May 8) and it's set to bring the triumphs and tragedies of the ocean to life in a way that'll bring tears to your eyes- before revealing what he recommends we do right now to save the planet. Under Attenborough's narration, we see the depths of the ocean transform from an abundance of colour, movement and life to a desert wasteland a mere shadow of its former self, right before our eyes. We also see in HD clarity the haunting look of disappointment in the eyes of starving fishermen as the nets they cast come back empty, or with more shards of plastic waste than actual fish.

The message is clear: careless pollution, over-fishing and global warming are all destroying our oceans - and most of us wouldn't know how much we depend on them, even including for the air that we breathe, until it's too late. Attenborough's on a mission to change that lack of knowledge - and, with a career spanning more than 70 years, there's no-one better placed than him to do so. With just a year to go until he turns 100, he's witnessed the deterioration of the oceans first hand while producing scores of documentaries about the natural world.

In the new film, there's a tear-jerking moment when he shares that, while he's nearing the end of his life, the ocean doesn't have to - and that there is real potential for change.

He shared: "At first I thought the oceans had to be tamed for the good of humanity. Now, as I approach the end of my life, we know the opposite is true."

The documentary shows footage of how British protest groups refused to back down, placing intolerable pressure on the government to ban commercial whaling until it caved in - and now, Attenborough informs us, bluefin whales (which have made a successful comeback) can live over 100 years.

In June, an important meeting will be a pivotal moment in determining the future of the sea, with the UN Ocean Conference in France potentially making history if it agrees to create fully protected marine reserves in 30% of waters. Britain has helped save the whales - but now it needs to help save their home and habitat.

Attenborough declares: "Three billion people rely on the ocean, but just a few ships sent by wealthy nations are starving coastal communities of fish they have depended on for millennia... this is modern colonialism at sea.

"The idea of bull-dozing through a pristine rainforest causes outrage, yet we do the equivalent underwater thousands of times every day."

He laments that £20 billion per year are spent on over-fishing on an "industrial scale", resulting in the total destruction of two-thirds of all ocean life. It's eye-opening to see thousands of fish streaming through chutes in factory production lines and to discover that three-quarters of trawling catches can end up wasted.

"We used to fish in limited areas to feed our communities," Attenborough shares, "but now we fish every day all the time - and I've lived through this change."

It's almost inconceivable that he's just a year away from his milestone 100th birthday, as in this documentary he astounds with how vivacious and articulate he still remains, and in many ways seems to have barely changed since the beginning of his career.

Meanwhile, his enthusiasm for the natural world is infectious as he refers to still-surviving life in the depths of the sea as "meadows", "gardens" and "thriving communities", compelling you to see it in a way you've never imagined before.

He admits that at times he's been so overawed by what's he witnessed under the sea that he momentarily forgot to breathe - and the documentary generously reproduces the scenes that made such an intense impact on him, from the lively Great Barrier Reef to the wilderness of Antarctica.

Didn't know what a peacock mantis shrimp is or why it's special? You will do by the end of the documentary.

Viewers will see through the eyes of a man who really has seen it all - and who thinks he knows how to fix what's gone wrong, if people grasp the magnitude of the struggle facing us.

Coral reefs are set to disappear altogether within 30 years - but he believes that even that stark fate is at least partially reversible.

We'll leave readers with a few poignant words of wisdom from Attenborough himself - "If we just let nature take its course, the sea will save itself".

Ocean With David Attenborough hits cinemas this Thursday (May 9).