Australian Great Barrier Reef. In the liquid skin of planet Earth live creatures of unearthly beauty. These tiny animals have crossed oceans of space and time in an epic bid for survival. Wanderers through inner space, they carry the future of their species. On their odyssey they have faced extinction and awesome planetary force. Theirs is an evolutionary success story, made possible by a remarkable reproductive strategy. Reefs are exotic interruptions in otherwise barren tropical seas. They're oases of life, vibrant, colorful and competitive. But this vast canvas of living art has not just materialized out of the blue. Coral and its cohorts have arrived from somewhere. Though they seem solid and unmoving, reefs have spread themselves throughout the tropical oceans. How have they overcome their immobility? The answer has its origin in one of life's most fundamental acts - sex. But the reproductive rites of coral communities are shrouded in mystery. It's only in the last ten years that the reef has begun to reveal its private life. For animals sex is a fact of life, but for the 'rocks' of the reef a sex life would seem out of the question. But corals are not rocks, they're colonies of tiny animals. Only the outer surface of these colonies is alive; a living skin populated by polyps.