English: Mareel, bioluminescence caused by (Noctiluca scintillans) in Norra Grundsund harbor, Lysekil Municipality, Sweden. The water was calm so the only way to make the plankton glow was to stir the water with a stick. At the beginning of the photo session the plankton gave off a greenish turquoise light. Later the light became more blue. The dim glow in the photo is from the the general stirring and ripples, but when some if the plankton splashed onto the algae floating in the water, it stayed visible and glowed bright for a longer time. That is what caused the strong streaks of blue light.
The light from the Noctiluca was so faint I had to keep up the splashing for a while. This image is a compilation of 13 photos, each with an exposure time of 30 sek. The light on the jetty is from a boat on the other side of the harbor. The site of the mareel was in deep shadow because of the stone pier I was taking the photo from.