Abstract:
Cephalopods, are widely considered masters of camouflage, be they cuttlefish, squid or octopus, using their intricate nervous system combined with an array of chromatophore cells and a complex visual system to produce body patterns and colouration to reduce detection and recognition by predator and prey species alike. When measuring the background matching abilities of cephalopods, spectrometers tend to be used to observe the reflectance intensities spectrum of the animal and compare those measurements to those of its immediate backgrounds. These devices tend to require extended exposure times, which tends to reduce efficiency when measuring a mobile organism such as cuttlefish that must be motionless to accurately produce measurements. While studies on the background matching abilities of cuttlefish have been carried out, there is a lack of knowledge on the background matching produced by octopuses. This study will attempt to measure the similarity of Octopus tetricus spectra to the spectra of three backgrounds, brown algae, green algae, and sponges, that would have been encountered by the species in its natural environment. Furthermore, to streamline spectral measurements, reconstructions of spectra will be attempted using coefficients approximated from RGB tristimulus values extracted from digital images taken of the octopus. O. tetricus spectra were found to be distinctly separate to the background spectra in all comparisons within the spectral principal component space furthermore, O. tetricus spectra were unable to be accurately reconstructed using background principal components, and vice versa. These results suggest that O. tetricus does not match to the backgrounds provided in this study. Additionally, O. tetricus spectra were unable to be accurately reconstructed using RGB approximated coefficients. This lack of spectral matching may be caused by the lack of colour vision in octopus, or possibly the lack of appropriate chromophore pigments to match the colours in the chosen backgrounds, amongst other reasons. RGB approximated spectral reconstruction inaccuracies may be down to the sum of inconsistencies in measurements, despite precautions being placed to minimise these errors. Another explanation for the inaccurate reconstructions may be the reflective nature of the octopus and background organic surfaces causing inconsistent measurements depending on location in relation to the illumination source.