Counter-illumination
Encyclopedia
Counterillumination is a method of camouflage
in which bioluminescent light from within an organism
on the ventral surface is matched to the light radiating from the environment. The bioluminescent is used to obscure the organism's silhouette produced by the down-welling light. Some midwater cephalopod
s, decapod
crustacean
s, and fish
es utilize this form of camouflage. The bioluminescence used can be either autogenic (produced by the animal itself) or bacteriogenic (produced by bacterial symbionts).. The bacteria is often Vibrio ficheri. Reducing the organism's silhouette is primarily an anti predatory deffence for mesopelagic organism's. The reduction of the silhouette from the highly directional down-welling light is important as there is no refuge in the mesopelagic and predation occurs from below.
At night, nocturnal organisms match the wavelength
and light intensity of their bioluminescence to that of the down-welling moonlight and direct it downward as they swim, attempting to remain unnoticed from any observers below. This strategy has been shown to significantly reduce predation among individuals employing it over those not employing it in the fish species Porichthys notatus.
Besides its effectiveness as a predator avoidance mechanism, counter-illumination also serves as an essential tool to predators themselves. Some shark species, such as the deepwater Etmopterus spinax, use counter-illumination to remain hidden from their prey. another example would be the Bobtail squid who also uses counter-illumination as a means of predation.
Other well-studied examples include the cookiecutter shark
, the marine hatchetfish
, and the Hawaiian bobtail squid
.
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
in which bioluminescent light from within an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
on the ventral surface is matched to the light radiating from the environment. The bioluminescent is used to obscure the organism's silhouette produced by the down-welling light. Some midwater cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, decapod
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es utilize this form of camouflage. The bioluminescence used can be either autogenic (produced by the animal itself) or bacteriogenic (produced by bacterial symbionts).. The bacteria is often Vibrio ficheri. Reducing the organism's silhouette is primarily an anti predatory deffence for mesopelagic organism's. The reduction of the silhouette from the highly directional down-welling light is important as there is no refuge in the mesopelagic and predation occurs from below.
Examples of the strategy
Some species utilize this form of counter shading, especially in the mesopelagic areas of the ocean. For these marine species, counter-illumination best serves them when ambient light levels are low, leaving the diffuse down-welling light from above as the only light source.At night, nocturnal organisms match the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
and light intensity of their bioluminescence to that of the down-welling moonlight and direct it downward as they swim, attempting to remain unnoticed from any observers below. This strategy has been shown to significantly reduce predation among individuals employing it over those not employing it in the fish species Porichthys notatus.
Besides its effectiveness as a predator avoidance mechanism, counter-illumination also serves as an essential tool to predators themselves. Some shark species, such as the deepwater Etmopterus spinax, use counter-illumination to remain hidden from their prey. another example would be the Bobtail squid who also uses counter-illumination as a means of predation.
Other well-studied examples include the cookiecutter shark
Cookiecutter shark
The cookiecutter shark , also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as . It migrates vertically up to every day, approaching the...
, the marine hatchetfish
Marine hatchetfish
Marine hatchetfishes or deep-sea hatchetfishes are small deep-sea mesopelagic ray-finned fish of the stomiiform subfamily Sternoptychinae...
, and the Hawaiian bobtail squid
Hawaiian Bobtail Squid
Euprymna scolopes, also known as the Hawaiian Bobtail Squid, is a species of bobtail squid in the family Sepiolidae. It is native to the central Pacific Ocean, where it occurs in shallow coastal waters off the Hawaiian Islands and Midway Island...
.