BBC Studios Natural History Unit, co-produced by BBC America, ZDF, FTV and The Open University

In Planet Earth III, Ocean, Sir David Attenborough presents a ground-breaking journey from tropical shallow seas, through vast open ocean, to the mysterious depths to reveal extraordinary new worlds and unique animal behaviours. Working closely with scientists and using cutting edge technology the film team capture incredible animal behaviour.

Two miles below the surface, in freezing cold and crushing pressure, a mother octopus heads to a special place - a thermal spa. Here, twenty thousand female octopus gather to develop their eggs in the warm water. This will take two years. In that time these devoted mothers will not feed – this eventually kills them.

Elsewhere, in in the giant kelp forests off North America, a young horn shark reveals its astonishing defence, after being ambushed and seemingly swallowed whole by an angel shark.

The episode explores how humans are impacting animal behaviour. Today, islands of seaweed are being replaced by plastic. It can be lethal, but Columbus crabs are making it a home. Off the coast of Chile, thousands of South American sea lions raid fishermen’s nets. As the net is drawn in, the sea lions must get out quickly or risk being crushed and drowned.