User:Chi567/Bioluminescence

Bioluminescence is a common phenomenon, serving many functions for organisms in the deep sea, with around 75% of organisms in the pelagic zone exhibiting the adaption. Observing and quantifying bioluminescence in the benthic zone is less understood but is becoming increasingly studied with the advancements of new technologies. As bioluminescence becomes more studied and understood, so will its’ functions in the marine sea, such as bioluminescent symbiotic relationships.

Pelagic Zone
Organisms often produce bioluminescence themselves, rarely do they generate it from outside phenomena. However, there are occasions where bioluminescence is produced by bacterial symbionts that have a symbiotic relationship with the host organism. Although many luminous bacteria in the marine environment are free-living, a majority are found in symbiotic relationships that involve fish, squids, crustaceans etc. as hosts. Most luminous bacterial inhabit the marine sea, with the remainder found on terrestrial lands. The Photobacterium and Vibrio genera exist in the marine environment, with the last genera of luminous bacterium, Photorhabdus, existing in terrestrial environments.

Bioluminescence is abundant in the pelagic zone, with the most concentration at depths devoid of light and surface waters at night. These organisms participate in diurnal vertical migration from the dark depths to the surface at night dispersing the population of bioluminescent organisms across the different pelagic zones. The dispersal of bioluminescence across different depths in the pelagic has been attributed to the selection pressures imposed by predation and the lack of places to hide in the open sea. In depths where sunlight never penetrates, often below 200m, the significance of bioluminescent is evident in the retainment of functional eyes for organisms to detect bioluminescence. Also, it has driven organisms capable of using bioluminescence to communicate while also able to optically conceal, to deeper depths where light becomes increasingly limited.

Bacterial Symbioses
In the symbiotic relationship, bacterium benefit from having a source of nourishment and a refuge to grow. Hosts obtain these bacterial symbionts either from the environment, spawning, or the luminous bacterium is evolving with their host. Coevolutionary interactions are suggested as host organisms’ anatomical adaptations have become specific to only certain luminous bacteria, to suffice ecological dependence of bioluminescence. In the ceratoid anglerfish, the adaptation of bioluminescence is exclusive to females who harbor a bacterium in the esca that is responsible for the lure display of light from the anglerfish. Across generas of anglerfish, bacterium are specific to each genera of anglerfish, resulting in a specialized and reduced genome of the bacteria in relation to closely related free-living bacteria in the deep sea. It is suggested that the bacterium and the anglerfish evolve independently of one another, revealing bacterium is acquired in the environment by the host. Their symbiotic relationship provides the bacterium with a safe environment to grow as the deep sea lacks the key nutrients they need to survive, while the bacterium provides the anglerfish with bioluminescence that, although its exact use is unknown, is known to help the anglerfish communicate with mates and attract prey.

Benthic Zone
Bioluminescence is widely studied amongst species located in the mesopelagic zone, but the benthic zone has remained widely unknown. Unlike the pelagic zone where the emission of light is undisturbed in the open sea, the occurrence of bioluminescence in the benthic zone is less common. It has been attributed to the blockage of emitted light by a number of sources such as the sea floor, and inorganic and organic structures. Visual signals and communication that is prevalent in the pelagic zone such as counter-illumination may not be functional or relevant in the benthic realm.