Documentary series presented by David Attenborough which explores the planet's oceans. From the equator to the poles, new worlds and animal behaviours are revealed, from tool-using fish to mother walruses fighting for space on the ice for their tiring pups.
The Deep takes us on an epic journey into the unknown, a world of crushing pressure, brutal cold and utter darkness. It's the largest living space on our planet, and today, scientists think there's more life here than anywhere else on Earth. This is our final frontier.
Coral reefs are home to a quarter of all marine species. Survival in these undersea mega-cities is a challenge with many different solutions.
A turtle heads to the reef's equivalent of a health spa - but she must use trickery to avoid the queue. A remarkable Grouper uses the fish equivalent of sign language to collaborate with an octopus, flushing their prey out of hiding holes.
A metre-long, ferocious-jawed Bobbit Worm hides in its tunnel. Monocle Bream retaliate by squirting water to expose its sandy lair.
Survival in the remote open oceans is tough and baby turtles use debris as rafts to stay afloat while the Portuguese man-of-war sail along hunting for fish. There's also footage of the "boiling sea" effect created by lanternfish being trapped on the surface of the water by predators.
In the undersea forests of kelp, algae and sea-grass, there is competition between species and sea otters are seen helping Garibaldi fish protect their seaweed garden from sea urchins while the common octopus uses shells to create a coat of armour against sharks.