![]() ![]() For example, the Hawaiian bobtail squid has a special light organ that is colonized by bioluminescent bacteria within hours of its birth. But usually, the animal itself contains the chemicals necessary for the reaction that produces bioluminescence. The number of species that bioluminesce and the variations in the chemical reactions that produce light are evidence that bioluminescence has evolved many times over-at least 40 separate times! This number continues to grow as research makes new discoveries. In 2018, scientists discovered the ray-finned fishes themselves evolved bioluminescence 27 separate times. That's quite an increase from the handful of times that were known before. Most deep-sea animals produce some bioluminescent light, but the phenomenon isn’t relegated to the deep: one of the most common sightings occurs at the surface of the ocean. Many small planktonic surface dwellers-such as single-celled dinoflagellates-are bioluminescent. When conditions are right, dinoflagellates bloom in dense layers at the surface of the water, causing the ocean to take on a reddish-brown color in daylight and a sparkly sheen as they move in the waves at night. When the dinoflagellates are poisonous to other animals, these events are called harmful algal blooms (HABs). ![]() When they're eaten, the toxic dinoflagellates accumulate in high concentrations in larger fish and filter feeding shellfish. And then when marine mammals or people eat these organisms, it can cause sickness or even death. Light travels in waves of different shapes-known as wavelengths-which determine the color of the light. When the waves hit our eyes, they are translated into colors by the brain depending on their wavelength. The wavelengths that our eyes can see are known as the "visible light spectrum," and we can see all the colors on this spectrum as they travel through the air above land. But light travels differently underwater because longer wavelengths can't travel as far. Most of the bioluminescence produced in the ocean is in the form of blue-green light. This is because these colors are shorter wavelengths of light, which can travel through (and thus be seen) in both shallow and deep water. Light traveling from the sun of longer wavelengths-such as red light-doesn't reach the deep sea. This is why many deep sea animals are red: it's effectively the same as being invisible. Moreover, because it's not present, many deep-water animals have lost the ability to see it altogether. However, some animals evolved to emit and see red light, including the dragonfish ( Malacosteus). By creating their own red light in the deep sea, they are able to see red-colored prey, as well as communicate and even show prey to other dragonfish, while other unsuspecting animals cannot see their red lights as a warning to flee. Often animals use a strong flash of bioluminescence to scare off an impending predator. The bright signal can startle and distract the predator and cause confusion about the whereabouts of its target. From small copepods to the larger vampire squid, this tactic can be very useful in the deep-sea. ![]()
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