7/7 David Attenborough explores the issues behind the series' most spectacular stories.
6/7 Coasts are the most changeable of the ocean worlds, but they offer great riches.
5/7 From enchanted forests to undersea prairies, the planet's green seas teem with life.
4/7 This vast ocean desert where sperm whales must dive 1,000 metres just to feed.
3/7 The ingenious ways life exists in the undersea cities of tropical reefs.
2/7 A groundbreaking journey to the deepest parts of the oceans.
1/7 New worlds and animal behaviours are uncovered on a journey from the equator to the poles.