The City Beneath the Waves | Great Barrier Reef – Solar Bargains, Sand Factories & the Sound of Home

It's the only living structure large enough to be photographed from the International Space Station. It stretches further than the distance from London to Moscow. It has been under construction, without interruption, for 6,000 to 8,000 years. And right now, it is losing.In this episode, we stop calling the Great Barrier Reef a reef — and start calling it what it actually is: a city. A biological metropolis with a foundation, an energy grid, a sanitation department, a diplomatic corps, and a communications network. And like every city, it only works because of the relationships between its residents.We start at the bottom, with the coral polyp — a creature barely visible to the naked eye that has spent thousands of years extracting calcium from seawater and depositing it as limestone, one molecule at a time. Inside its tissue, a hidden partnership with microscopic algae provides up to 90 percent of the polyp's energy. We explain exactly what bleaching is, why it's happening six times per generation, and why the reef has lost more than half its coral cover since 1985.Then we meet the maintenance crew: the parrotfish, whose fused beak grinds through solid limestone and whose excretions are — literally — the white sand beaches of the tropical Pacific. We visit the cleaning stations, where sharks and barracudas queue patiently to let a fish the size of your hand swim inside their mouths. And we follow the sound of the reef itself — the crackling, snapping, drumming acoustic signature that travels for kilometers through the water column and guides the larvae of the next generation home to a place they have never seen.A silent reef, it turns out, is invisible to its own future.The biology of the Great Barrier Reef knows exactly what to do. The question is what we choose to do with the land and atmosphere around it.Secrets of Earth is a nature documentary podcast for all ages, exploring the why and how behind the planet's most extraordinary life.