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. Some midwater cephalopods, decapod crustaceans, and fishes utilize this form of camouflage. The bioluminescence used can be either autogenic (produced by the animal itself) or bacteriogenic (produced by bacterial symbionts).
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.
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.
- Claes, Julien M., Dag L. Aksnes & Jérôme Mallefet (2010). "Phantom hunter of the fjords: camouflage by counterillumination in a shark (Etmopterus spinax)" (PDF). Journal of Experimental Marine Biology and Ecology 388 (1–2): 28–32. doi:10.1016/j.jembe.2010.03.009. http://www.bio.uib.no/modelling/papers/Claes_2010_Phantom_hunter.pdf.
- Guerrero-Ferreira, R. C. & M. K. Nishiguchi (2009). "Ultrastructure of light organs of loliginid squids and their bacterial symbionts: a novel model system for the study of marine symbioses". Vie Et Milieu-Life and Environment 59 (3–4): 307–313. ISSN 0240-8759.
- Jones, B. W. & M. K. Nishiguchi (2004). "Counterillumination in the hawaiian bobtail squid, Euprymna scolopes Berry (Mollusca : Cephalopoda)" (PDF). Marine Biology 144 (6): 1151–1155. doi:10.1007/s00227-003-1285-3. http://www.medmicro.wisc.edu/labs/mcfall_ruby_papers/pdf/2004/Jones_Nishiguchi_2004_Biol.pdf.
Wikimedia Foundation. 2010.