Sunlight disappears in the deep ocean, but darkness there is filled with signals made by living animals. Discover how bioluminescence works, why blue light dominates underwater, and how glowing jellies, fish, squid, shrimp, and plankton use light for camouflage, defense, hunting, and communication. Inside this episode: - How ocean depth changes the available colors of light - The chemistry behind luciferin and luciferase - Why blue and blue-green light travel well through seawater - Counterillumination, lures, warnings, and defensive flashes - How researchers observe natural light in the deep ocean Sources include NOAA Ocean Exploration, Monterey Bay Aquarium Research Institute field research, and peer-reviewed studies of marine bioluminescence. This episode is a researched narrative summary. Historical records may be incomplete, translated diff ...