On the Great Barrier Reef, coral spawning is one of nature's great spectacles — occurring within days of the full moon each November. Corals release buoyant bundles of eggs and sperm simultaneously, cued by moonlight, water temperature (~27–28°C), and sunset timing. Bundles rise to the surface where they break apart; sperm must find eggs from different colonies to fertilize. Fertilized eggs develop into free-swimming planula larvae over 3–5 days before settling on hard substrate and metamorphosing into juvenile polyps. Less than 1 in 1,000 larvae survive to adulthood.