The tropical Indian Ocean is home to the Spice Islands. Characterised by beautiful sandy beaches, fringing coral reefs and coastal mangrove forests, this is a vibrant nursery area for marine life, such as whale sharks, crabs, seahorses and a great variety of fish. The coastal areas are where humans have the most direct impact on the ocean's resources.

Fly across iridescent tropical reefs, brush through a cloud of a million jellyfish, visit an alien world where the closer you look, the more you see, where the tiniest creatures support the greatest predators... We think of reefs as exotic, distant places with little or no connection to our everyday world. Yet every reef is a living city beneath the sea with a parallel existence to ours, distant yet undeniably connected. Reefs are hotspots of biodiversity as vital to life on earth as the rain-forests. They have been shaping our shorelines, literally forming islands and mountains, for millions of years. The fossil record shows that given time they have recovered from all of earth's major extinction events. Even reefs pulverised by atomic blasts at Bikini Atoll have regenerated. Yet within our lifetime reefs have come to face their greatest threat...

The fifth programme explores the alliances formed between the animal and plant worlds. Attenborough dives into Australia's Great Barrier Reef and contrasts the nocturnal feeding of coral, on microscopic creatures, with its daytime diet of algae. Some acacias are protected by ants, which will defend their refuge from any predator. Besides accommodation, the guards are rewarded with nectar and, from certain species, protein for their larvae as well. Fungi feed on plants but can also provide essential nutriment to saplings (Mycorrhiza). The connection is never broken throughout a tree's life and a quarter of the sugars and starches produced in its leaves is channelled back to its fungal partners. Meanwhile, fungi that feed on dead wood leave a hollow trunk, which also benefits the tree. Orchids enjoy a similar affiliation. Lichens are the product of a relationship between fungi and a photosynthetic associate, usually algae. They are extremely slow-growing, and a graveyard is the perfect location to discover their exact longevity. Mistletoe is a hemiparasite that obtains its moisture from a host tree, while using own leaves to manufacture food. Its seeds are deposited on another by the mistletoe tyrannulet, following digestion of the fruit. The dodder (Cuscuta) is also parasitic, generally favouring nettles, and siphons its nourishment through periodic 'plugs' along its stem. The rafflesia has no stem or leaves and only emerges from its host in order to bloom — and it produces the largest single flower: one metre across.

The stunning beauty of an island paradise on a quest to find the perfect wave-riding experience. Nine-time world surfing champion Kelly Slater and Tahitian surfer Raimana Van Bastolaer and a group of friends seek out the best waves breaking on the reef at Tahiti's famed surf site Teahupo'o. As their quest unfolds, the audience is plunged beneath the surface of things, to explore the hidden forces at work shaping ocean waves and the islands that lie in their path. Amidst playful surfing action, we navigate the cosmos and an ocean storm in a search for the source and nature of a wave's energy. Exploring mountainous Tahiti, we are thrust into the turbulent volcanic past of the island and its neighbours and discover the seagoing, wave-riding roots of the islanders themselves -- a culture still rich in the music, dance and lore of the sea. Beneath the ocean, swimming with our surfers, we explore the stunning, fragile beauty of the reef habitat -- a turbulent, wave-shaping interface that envelops the island and nurtures the ocean's multitudes in motion -- fish, dolphins, sharks and whales. When the truly big surf arrives at Teahupo'o, surfing play becomes surfing survival as the riders artfully tackle some of the heaviest surf on the planet -- spectacularly captured for the giant screen in 3D for the first time.