Counter-illumination

Counter-illumination

Counterillumination is a method of camouflage in which bioluminescent light from within an organism is matched to the light radiating from an environmental source in order to obscure the organism's silhouette produced by the environmental source.[1] Some midwater cephalopods, decapod crustaceans, and fishes utilize this form of camouflage.[2] The bioluminescence used can be either autogenic (produced by the animal itself) or bacteriogenic (produced by bacterial symbionts).[3]

Examples of the strategy

Some species utilize this form of camouflage, especially in 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.[1]

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.[4] This strategy has been shown to significantly reduce predation among individuals employing it over those not employing it in the fish species Porichthys notatus.[5]

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.[6]

Other well-studied examples include the cookiecutter shark, the marine hatchetfish, and the Hawaiian bobtail squid.[7]

Footnotes

  1. ^ a b Jones(2004): p.1151
  2. ^ Jones(2004): Young 1977, as cited by Jones et al. 2004
  3. ^ (Jones et al. 2004)
  4. ^ Guerrero-Ferreira(2009): p.307
  5. ^ Jones(2004): Harper 1999, as cited by Jones et al. 2004
  6. ^ Claeus(2010): p.28
  7. ^ Jones(2004): p.1154

References


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