DIVE DEEP ENOUGH under the surface of the ocean, and light reigns. Some 90 percent of the fish and crustaceans that dwell at depths of 100 to 1,000 meters are capable of making their own light. Flashlight fish hunt and communicate with a flashing Morse code sent by light pockets that pulse under their eyes. Tubeshoulder fish shoot luminous ink at their attackers. Hatchetfish make themselves appear invisible by generating light on their underbellies to mimic downwelling sunlight; predators prowling below look up to see only a continuous glow.