Ink is a conspecific alarm cue in the Caribbean reef squid, Sepioteuthis sepioidea

Animals often respond to attacks from predators with behaviors directed at the predator that increase the probability of escape. Some animals also respond to attacks with behaviors that release signals or cues that are detected by conspecifics and enhance escape. Cephalopods, with their complex nervous systems, produce many behaviors, one of which is ejecting ink when attacked by predators. Ink is thought to enhance the ability of the inking cephalopod to escape from the predator, which is a reasonable idea but is lacking experimental support and description of mechanisms. Inking might also serve as an alarm cue, evoking alarm responses in conspecifics. The aim of our study was to determine if ink of the Caribbean reef squid, Sepioteuthis sepioidea, is a conspecific alarm cue. We studied freely behaving animals in the laboratory to determine if they produced alarm or escape behavior in response to ink. We observed that squid responded to conspecific ink introduced into their aquarium with deimatic behaviors containing chromatophore elements (‘eye spots’, ‘all brown’, and ‘flashing’), cryptic behaviors with chromatophore elements (‘clear’, ‘plaid’, ‘dark arms’), cryptic behaviors with postural responses (‘sargassum’, ‘bad hair’), and protean behavior (‘fin movement’, ‘inking’, ‘jetting’). Squid also responded to ink introduced into an adjacent aquarium within view, thus demonstrating that vision can contribute to the alarm response. Melanin-free ink did not evoke a significant alarm response. This is the first experimental demonstration that squid respond to ink of conspecifics as a visual alarm cue. Ink may also provide a chemical alarm cue for S. sepioidea, though further behavioral studies are needed to explore this.