Bioluminescence occurs when living organisms (bio) produce light (luminesce) using a chemical reaction. While some land animals – like fireflies – have bioluminescent adaptations, this phenomena is far more common in the ocean. This “living light” is especially useful in the ocean depths, where little-to-no light from the sun reaches. All bioluminescent organisms use a reaction between an enzyme and a substrate to make light, but different species use different chemicals in the process. While usually blue in color (because this is the light that travels best through the water), bioluminescence can range from nearly violet to green-yellow and even red.
Many marine organisms have bioluminescent adaptations. Some have bioluminescent lures to attract prey, others have bioluminescent patches that help to see in the deep, while others are bioluminescent all over. One of the most exciting images captured during a NOAA OER expedition is of a shrimp vomiting a cloud of bright blue bioluminescent fluid as a defense mechanism!