In recent years, our knowledge of life beneath the waves has been transformed. Using cutting-edge technology, embark on a journey from the intense heat of the tropics to the frozen poles to reveal new worlds and extraordinary animal behaviours.

The deep is perhaps the most hostile environment on Earth, at least to us - a world of crushing pressure, brutal cold and utter darkness. We have barely begun to explore it, and yet it is the largest living space on the planet.

Corals build themselves homes of limestone in the warm, clear, shallow seas of the tropics. Their reefs occupy less than one tenth of one per cent of the ocean floor, yet they are home to a quarter of all known marine species.

The big blue is the world's greatest wilderness, far from shore and many kilometers deep. It's a vast marine desert where there is little to eat and nowhere to hide.

The most bountiful kelp forests are found off the tip of southern Africa, where two oceans collide. Almost a hundred different species of shark patrol these waters, driving one resident - the common octopus - to become the ultimate escape artist.

Coasts are the most dynamic and challenging habitats in the ocean - that bring great rewards but also great dangers. The extraordinary animals that live here must find ingenious ways to cope with two very different worlds.

The oceans are changing faster than at any point in human history and now, for the first time, we understand why.