Abstract
There is increasing evidence that projected near‐future carbon dioxide ( CO 2 ) levels can alter predator avoidance behaviour in marine invertebrates, yet little is known about the possible effects on predatory behaviours. Here we tested the effects of elevated CO 2 on the predatory behaviours of two ecologically distinct cephalopod species, the pygmy squid, Idiosepius pygmaeus , and the bigfin reef squid, Sepioteuthis lessoniana . Both species exhibited an increased latency to attack and altered body pattern choice during the attack sequence at elevated CO 2 . I. pygmaeus also exhibited a 20% decrease in predation rate, an increased striking distance, and reduced preference for attacking the posterior end of prey at elevated CO 2 . Elevated CO 2 increased activity levels of S. lessoniana comparable to those previously shown in I. pygmaeus , which could adversely affect their energy budget and increase their potential to be preyed upon. The effects of elevated CO 2 on predatory behaviours, predation strategies and activity levels of cephalopods reported here could have far‐reaching consequences in marine ecosystems due to the ecological importance of cephalopods in the marine food web.