Eye puncture as a route of entry for saliva during predation on crabs by the octopus Eledone cirrhosa (Lamarck)

Abstract

In 45% of crab carapaces examined after octopus feeding, the surface of an eye was found to have been punctured. Experiments in which green crabs ( Carcinus maenas L.) were retrieved from feeding octopuses ( Eledone cirrhosa Lamarck) showed that this penetration of the eye occurred less than ten min after capture. These findings are consistent with direct observations and visualization by ultrasound showing that initially after capture the anterior of the crab is often held to the mouth of the octopus. In vitro injection of octopus saliva into crabs demonstrated that eye puncture is the most rapid and completely effective route of entry for cephalopod toxins. Comparative feeding experiments using swimming crabs ( Liocarcinus depurator L. and Necora puber L.) showed incidences of eye puncture of up to 75%. These observations provide a new explanation for the means by which the crabs are immobilized so rapidly during octopus predation.