The open ocean is enormous. Also called the pelagic zone, it includes all the world’s oceans except for coastal waters and the sea floor. Pelagic waters are not all the same. Some areas are teeming with life, while others are nearly lifeless. Enormously long currents flow like rivers under the surface, influencing everything from the concentration of marine life to weather systems on land. There’s also a huge 'vertical' variety, from sunlit surface waters down through the twilight zone to almost complete darkness and crushing pressures below 1,000m. Despite its size, only around 10% of all marine species live in the open ocean. But these include the world’s biggest, fastest, deepest diving, furthest travelling ... and some of the strangest-looking underwater animals. And some of these are of immense commercial value to people.