Cephalopod ink release is presumed to function as a visual defense. A dense, mucous-bound pseudomorph ('false-body') that mimics the releaser or a smokescreen/cloud that blocks the releaser from view is released and confuses a predator while the cephalopod escapes. Unfortunately the 'obvious' visual effectiveness of shallow-water cephalopod ink release means empircal tests regarding the effectiveness against natural cephalopod predators have not been performed. Recently I documented ink release by numerous deep-sea squid, including ink release forms that had not been previously described (Bush & Robison, 2007). Why deep-sea squids release ink in the deep sea is currently unknown. Light levels rapidly decrease with water depth, therefore by 1000 m in even the clearest oceanic water no surface-derived light remains - for most of the ocean, this depth is considerably shallower. Ink release seems useless as a visual defense. Some researchers have suggested the possibility that deterrent or attractant chemicals may play a role in ink release. Whether deep-sea squid ink release has a visual and/or chemical function remains to be determined. However, it is likely an effective defense. If not, deep-sea squids would likely have lost the ability to produce and/or release ink over evolutionary time, which has occurred for many deep-sea octopuses. To address these questions, I am testing the reaction of cephalopod predators to both shallow and deep-water squid ink to determine whether one or both groups produce chemicals that affect potential predators.

Octopoteuthis deletron is a medium-sized (to 17cm mantle length) deep-sea species which possesses the typical eight arms of squid, but lacks feeding tentacles. Individuals possess a variety of bioluminescent photophores, many of which are ventrally directed and therefore presumed to counter-illuminate the animal. However, each arm is tipped with a photophore and disturbed animals may splay their arms, emitting asynchronous blue bioluminescent light pulses from them. This presumably startles a potential predator, while the squid escapes. Octopoteuthis deletron also seem to be able to drop an arm (autotomize), just as a lizard drops its tail so that this non-essential appendage is attacked and the animal survives.  Several questions are being adressed: When are arms autotomized? How common is arm autotomy? Can O. deletron re-grow its arms and associated photophores? How has such a defense evolved and been maintained in the low-nutrient, slow lifestyle of deep sea?