Counter-illumination

Counterillumination is a method of camouflage in which bioluminescent light from within an organismon the ventral surface[1] 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.[2] Some midwater cephalopods, decapod crustaceans, and fishes utilize this form of camouflage.[3] The bioluminescence used can be either autogenic (produced by the animal itself) or bacteriogenic (produced by bacterial symbionts).[4]. The bacteria is often Vibrio ficheri.[5] 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[6].[7][8]

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.[2]

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.[9] This strategy has been shown to significantly reduce predation among individuals employing it over those not employing it in the fish species Porichthys notatus.[10]

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.[11] another example would be the Bobtail squid who also uses counter-illumination as a means of predation.[12]

Other well-studied examples include the cookiecutter shark, the marine hatchetfish, and the Hawaiian bobtail squid.[13]

Footnotes

  1. ^ Young. R.E, Roper. C.F.E. 1977. Intensity Regulation of Bioluminesence during Countershading in Living midwater animals. Science, New Series. Vol 191,4231: 1046-1048.
  2. ^ a b Jones(2004): p.1151
  3. ^ Jones(2004): Young 1977, as cited by Jones et al. 2004
  4. ^ (Jones et al. 2004)
  5. ^ Jones. B.W, Nishiguchi. M.K. 2004. Counterillumination in the Hawaiian bobtail squid, Euprymna scolpes Berry (Mollusca: Cephalopoda). Marine Biology. 144:1151-1155.
  6. ^ http://www.bbc.co.uk/nature/blueplanet/infobursts/counter_illumination_bg.shtml
  7. ^ Young. R.E, Roper. C.F.E. 1976. Bioluminescent countershading in Midwater Animals from living Squid. Science, New Series. Vol 191,4231: 1046-1048.
  8. ^ Young. R.E, Roper. C.F.E. 1977. Intensity Regulation of Bioluminesence during Countershading in Living midwater animals. Science, New Series. Vol 191,4231: 1046-1048.
  9. ^ Guerrero-Ferreira(2009): p.307
  10. ^ Jones(2004): Harper 1999, as cited by Jones et al. 2004
  11. ^ Claeus(2010): p.28
  12. ^ Jones. B.W, Nishiguchi. M.K. 2004. Counterillumination in the Hawaiian bobtail squid, Euprymna scolpes Berry (Mollusca: Cephalopoda). Marine Biology. 144:1151-1155.
  13. ^ Jones(2004): p.1154

Paper by Young Bioluminescence in Mesopelagic Squid.

References