Entire reefs release their eggs on the same night, timed by the moon
Once a year, many coral species on a reef spawn simultaneously, releasing clouds of eggs and sperm into the water within the same narrow window — often just a few nights after a full moon. Moonlight helps synchronize the timing, while water temperature and the length of darkness after sunset fine-tune the exact night. The mass release, visible from satellites over Australia's Great Barrier Reef, boosts each coral's odds its eggs meet sperm from another colony before predators eat them.