Sea Sparkle

Blue light swirling in the water of the yacht harbor at Zeebrugge, Belgium, in June 2010, made by Noctiluca scintillans, a single-celled plankton called sea sparkle. Each cell is a barely visible speck that flashes when the water around it is jostled by a wave, a boat or a hand. The leading idea is the burglar alarm: a tiny grazer that bumps a cell lights itself up for the bigger animals that eat grazers. Related glowing plankton are what make breaking waves shine blue on beaches from California to the Maldives.