Reflective Light Modulation by Cephalopods in Shallow Nearshore Habitats
2008
Hanlon, Roger T.
The central question is: what are the optical principles upon which crypsis is achieved by opaque organisms in shallow, nearshore marine habitats? Camouflage mechanisms are not well known despite the general misconception that they are. Moreover, quantification of camouflage (especially of opaque organisms) is particularly wanting. We have three objectives: (1) Acquire imagery (camouflaged animals and their backgrounds) and corresponding irradiance data from coral reef and temperate rock reef environments. (2) Perform image analyses to quantify the degree of crypsis. (3) Construct a comparative digital photographic library of shallow-water marine animals in the camouflage categories of Uniform, Mottle and Disruptive. The central focus is on octopus, cuttlefish and squid because they have the most diverse and changeable camouflage patterns known in biology. Fish and insects are studied comparatively. High-resolution digital still images (Canon EOS 1Ds, Mark II camera) are acquired under natural marine conditions. No flash is used to avoid making artificial shadows from the flash light. A computer-controlled spectrometer (adapted for underwater use) takes downwelling and sidewelling irradiance data at the exact time of photography; then the animal reflectance data are recorded with the spectrometer (in both gross and fine detail on the animal's body) so that color- and contrast-matching can be quantified in the digital images. HDTV video is used to follow foraging cephalopods and fish to document (a) speed of body patterning changes and (b) the range of microhabitats that they encounter and the pattern they choose to camouflage themselves in each microhabitat.
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