In this second episode, David Attenborough continues his exploration of the Great Barrier Reef aboard the research vessel The Alucia. This time he discovers the incredible animals that visit the Reef every year, some travelling thousands of miles to get there.
David travels out to one of the most inaccessible corners of the Coral Sea, the stunning Osprey Reef - a mountain in the ocean just off the edge of the Great Barrier. Here he dives into shark infested waters in the Triton submersible, to take a closer look at the animals that use Osprey to navigate huge distances to particular locations on the Barrier Reef. One of these is the tiny Raine Island, a destination for tiger sharks because of another arriving visitor - the green sea turtle. David witnessed a baby turtle hatching here almost 60 years ago. Now, the tens of thousands of turtles that return to lay eggs every year are under threat, but an incredible plan by scientists may save this island and its turtles from disaster.
David's journey also takes him to the forested Heron Island to witness thousands of nesting birds, the waters of Lady Elliot Island to marvel at the manta rays that come here for a good clean, and to the Ribbon Reefs to meet a mysterious dwarf minke whale who visits each winter and seeks out human contact. When David first visited the Reef, science knew very little about visiting creatures and why they came, but new tracking technology allows him to follow the story of these visitors like never before, revealing their surprising reasons for returning, and why the Reef is vital for their survival.