Cuttlefish (Sepia officinalis) camouflage in varying environmental conditions

Cephalopods first appeared around 500 million years ago. Since then they have developed from the external shelled ammonites, belemnites and nautiloid’s to the soft bodied organisms we find today. By becoming soft bodied, protection which would have been provided by the shell was lost and a different approach to predator avoidance was adopted. Modern day cephalopods such as octopus, squid and cuttlefish frequently use camouflage techniques to avoid detection. In addition to countershading, which is an often used camouflage technique by aquatic species, the presence of chromatophores allow a versatile and rapid response in relation to stimuli. Cuttlefish expression of these chromatic responses can be categorised into chromatic components. It is the intensity and combination of the expression which makes them an interesting organism to study, when looking at how the environment influences camouflage decisions. In this thesis, I present six experiments looking at how external environmental factors influence camouflage in Sepia officinalis. The first experimental chapter looks at how 3D objects and proximity play a role in not only camouflage, but behavioural responses. The first set of experiments discuss how factors such as contrast and size of an object may elicit different responses both behaviourally and chromatically. The proximity of the cuttlefish to the object was then investigated to determine if visual input was a possible cause for the differences. Size of the object, proximity and contrast produced a differing response to that of a cuttlefish on a uniform background. The two subsequent chapters look at differing light information and whether cuttlefish treat these differences similar to that of low contrast. Reaction to turbid and low light levels show similar responses in camouflage, suggesting that similar mechanisms are employed when there is reduced light and high scatter information. In respect to luminance versus reflectance, cuttlefish seem to be able to differentiate between a projected and reflected image where they appear to treat projected images like a lower contrast value. The last experimental chapter investigates motion camouflage in respect to predation. Prey and distance had a large effect on behaviour and how camouflage was expressed. Over greater distances behavioural variance reduced. Darkening of the head region and arm waving was also present over a greater distance. Camouflage varied in relation to background with a more uniform background producing reduced expression when moving. Stationary predation therefore elicits a different response than that of motion camouflage in cuttlefish.