Bioluminescence is a captivating display of nature’s light found in the ocean’s depths. While many marine organisms produce their own light, certain crustaceans, often mistaken for shrimp, create enchanting glows. These small creatures transform dark waters into a spectacle of living light.
The Science of Their Glow
The light produced by these organisms results from a biochemical process, known as “cold light” due to generating very little heat. This reaction involves two chemical components: luciferin, a light-emitting compound, and luciferase, an enzyme. When luciferin reacts with oxygen in the presence of luciferase and certain salts, it produces a blue-green luminescence.
Many creatures called “bioluminescent shrimp” are actually ostracods, also known as “sea fireflies.” These tiny crustaceans possess specialized glands that secrete light-producing chemicals into the water. Other true shrimp species also exhibit bioluminescence, sometimes through similar secreted fluids or specialized light organs called photophores embedded in their tissue.
Purpose of the Light
The light emitted by these ostracods serves various functions, primarily for defense and mating. For defense, some species eject a luminous fluid or mucus when threatened. This sudden burst of light can startle a predator, creating a distracting cloud that allows the ostracod to escape. Sometimes, if a predator consumes the ostracod, the light continues to be emitted, potentially making the predator more visible to its own predators, often leading it to regurgitate the glowing meal.
Bioluminescence also plays a role in attracting mates, particularly among male ostracods. Species like Photeros annecohenae and Vargula hilgendorfii engage in courtship displays, emitting distinct patterns of light pulses. These displays can involve synchronized dances, where males release glowing secretions in specific sequences, such as vertical streaks, horizontal trails, or complex spiraling movements. Females observe these species-specific light shows and are drawn to males exhibiting the patterns of their own kind.
Habitat and Human Interaction
Bioluminescent ostracods inhabit various aquatic environments globally, from shallow coastal waters to deep ocean floors. A well-known example, Vargula hilgendorfii, also called “umi-hotaru” or “sea firefly” in Japan, is commonly found in the sandy sea bottoms around the Japanese islands. They typically reside on the seabed during the day and ascend into the water column at night to feed.
These glowing crustaceans have played a role in human history. During World War II, Japanese soldiers utilized dried umi-hotaru as a subdued, smokeless light source for reading maps and documents. When mixed with water, the dried ostracods would rehydrate and emit a faint blue glow, providing discreet illumination without revealing their position. These bioluminescent creatures are wild animals and are not typically kept as pets. Their light displays are best appreciated in their natural marine habitats.