Seventy-one percent of the Earth's surface is covered by water, but much of the oceans' depths have so far kept their secrets from scientists. In the inky depths, an unfamiliar world is home to amazing, strange and colourful creatures, whose lives remain mysterious to experts. `World of Oceans' explores this hidden realm, taking a close-up look at different underwater habitats. Their inhabitants fight for survival against predators, a changing environment and harsh conditions, many relying on speed or strength to survive, while others have evolved very different innovations.