Some organisms use bioluminescence to blend into their surroundings. By producing light that matches the brightness of the ocean surface,they can hide their silhouette from predators below. The cookiecutter shark uses bioluminescence to camouflage its underside by counter-illumination, but a small patch near its pectoral fins remains dark, appearing as a small fish to large predatory fish like tuna and mackerel swimming beneath it. When such fish approach the lure, they are bitten by the shark.
Many species use light signals to communicate with one another. Fireflies, for example, use specific flashing patterns to attract mates and identify members of their own species. Female Photuris fireflies sometimes mimic the light pattern of another firefly, Photinus, to attract its males as prey. In this way they obtain both food and the defensive chemicals named lucibufagins, which Photuris cannot synthesize.
The defense mechanisms for bioluminescent organisms can come in multiple forms; startling prey, counter-illumination, smoke screen or misdirection, distractive body parts, burglar alarm, sacrificial tag or warning coloration. The shrimp family Oplophoridae Dana use their bioluminescence as a way of startling the predator that is after them. Acanthephyra purpurea, within the Oplophoridae family, uses its photophores to emit light, and can secrete a bioluminescent substance when in the presence of a predator. This secretory mechanism is common among prey fish.
Bioluminescence is used by a variety of animals to mimic other species. Many species of deep sea fish such as the anglerfish and dragonfish make use of aggressive mimicry to attract prey. They have an appendage on their heads called an esca that contains bioluminescent bacteria able to produce a long-lasting glow which the fish can control. The glowing esca is dangled or waved about to lure small animals to within striking distance of the fish.