Bioluminescence In Biology

As humans, our world would be thrown into chaos if suddenly there were no light. However, deep at the bottom of the world’s oceans many organisms are surviving in the complete absence of light. From 200 metres below the surface of the sea, photosynthesis can no longer occur, as not enough sunlight can penetrate the water. From 1000 metres below the surface exists the “twilight zone” where the only wavelength of light that can penetrate through the vast amount of water is blue light (Yancy, 2011). This absence of light leads to multiple challenges for organisms living in the deep sea, such as obtaining food, escaping prey and finding mates. Many organisms get past these challenges by the use of a spectacular adaptation called bioluminescence,

As the environment is so extreme, not many animals can survive it and so the density of animals living there is low. To add to the difficulty of finding a mate of the same species with such a low density of organisms, there is no light to aid the organisms in finding one. As a result, many animals use bioluminescence to find and attract mates. Different species have different patterns of distributions of photophores in their bodies so that other members can identify them. Some species have patterns that differ between males and females also, which helps mating to occur. For example, Lanternfish have photophores along the belly, on the flank, head and tail. The photophores on the underside of the fish are used for camouflage, but the lateral photophores identify individual species. (Davis, Holcroft, Wiley, Sparks, & Smith, 2014). Most animals in the deep sea can only detect blue light, as it’s wavelength can penetrate water the furthest, and therefore tend to bioluminesce in blue/green colours. However, some organisms have taken advantage of this fact. Dragonfish have red bioluminescent “searchlights” under their eyes so that they can identify organisms of the same species, attract mates, hide from predators and hunt unsuspecting prey who cannot detect their light. This red light is a result of fluorescent proteins which can change blue biolumenescent light into

Most food which reaches the deep sea is composed of ditritus; the decaying remains of plants , algae, microbes and other organisms. This ditritus is eaten by scavengers such as sea cucumbers. Occassionally a carcas of a large animal such as a whale might sink down to the deep sea and is eaten by species such as hagfish. however not frequently enough to sustain life. (Yancy, 2011) No sunlight can penetrate through the 1000 metres of water, rendering photosynthesis impossible, and so there is no plant life. Therefore the majority of animals in the deep sea rely on predation rather than scavenging. Many predators have large mouths with hinged jaws and long, pointy teeth which are curved inwards to trap and eat prey. Often bioluminescence is used as a tool to lure prey to the predator. A well known example of this is the infamous anglerfish (Lophiiformes). Anglerfish posess a modified dorsal fin, the illiceum, at the tip of which is a bulb, the esca, which contains symbiotic luminescent bacteria. This esca is used both as a light to guide the fish, but also to lure prey to the anglerfish’s mouth. (Munk, 1998). The Cookiecutter shark’s bioluminescent cells imitate the faint light of the surface above, camouflaging it when viewed from below and so allowing it to approach its prey without being seen. This tecnique is called counterillumination and is used by numerous organisms in the deep sea; both