HIDE AND SEEK IN THE OPEN SEA:
PELAGIC CAMOUFLAGE AND VISUAL COUNTERMEASURES

Camouflage is exceptionally challenging in pelagic environments, due to their featureless nature. Thus, it is perhaps no surprise that pelagic species have evolved highly sophisticated cryptic strategies, three of which – transparency, mirrors, and counterillumination – are rare or absent in all other habitats. Pelagic visual systems are equally complex, and several visual capabilities, including UV and polarization sensitivity and intraocular filters, are thought to facilitate detection of camouflaged animals. This talk reviews the optical nature of the pelagic realm and both the camouflage and camouflage-breaking strategies of its inhabitants, focusing primarily on underlying principles and what remains to be discovered. A theme throughout is that far more is known about the optical and visual structures involved than about their function, and that this imbalance is primarily due to the rarity of observations of undisturbed behavior.