View image in fullscreen The colourful underwater world of the Red Sea’s coral reef colonies. Photograph: Anadolu/Getty Images These creatures evolved over millenia to create nature’s finest circular economy, but are now struggling to survive There’s no preparing for a first encounter with a thriving coral reef: your attention ricochets between dramas of colour, form and movement. A blaze of fire coral, darting clown fish, crimson sponge, electric blue ray … a turtle! Your heart soars, your head spins. Nowhere else will you encounter such density and diversity of life. Corals are the architects of all this splendour. Their immobile forms suggest plants, but they’re animals – solar-powered ones. Each is a colony of thousands, sometimes millions, of tiny coral polyps, each resembling a slimmed-down sea anemone, just millimetres tall. Coral polyps are invertebrates. They protect their delicate bodies by building tiny cups of pure limestone, the building blocks of every reef. Two hundred and fifty million years before our first cities and pyramids rose, corals were already giving free rein to their monumental architectural impulses. No human structure matches the grandeur of the largest reefs. The Great Barrier Reef spans 344,400 sq km, redirecting ocean currents and deflecting tsunamis. Their engineering creates niches for millions of other species. These living riches sustain an estimated 1 billion coastal and island dwellers worldwide. And they conjure all this magnificence from virtually nothing: tropical waters are nutrient deserts. Darwin was the first to wonder how reefs could possibly create so much from so little. The solution to Darwin’s conundrum is that coral polyps don’t weave their magic alone. Their achievements depend on mutually-beneficial symbioses with other reef organisms, particularly invisible microbes. These partnerships are so pivotal that biologists view corals not as individual animals, but as “holobionts” – living collectives where […]