Inking as a defensive mechanism in Aplysia dactylomela : (Gastropoda: Opisthobranchia)

The defensive mechanisms of opisthobranch molluscs have received much attention in recent years. They are equipped with a wide array of protective devices, with many species free of all predation. The sea hare, Aplysia dactylomela is a circumtropical member of this subclass, which is known to secrete a purple ink. The role this ink might serve as a defensive mechanism was investigated.

The study was designed to determine whether or not the ink would repel potential predators by being in itself distasteful and/or noxious to predators frequenting the same habitat as A. dactylomela. Tests were set up in aquaria exposing scavenging crabs to food items, with and without the ink present. The effect color alone played in repelling other animals by the ink was also investigated. Experiments were also performed to observe whether or not laughing gulls would reject a preferred food item (local baitfish) once this food had been coated with sea hare ink.

The results of these various experiments indicated that the ink does serve a defensive function by repelling crabs, and that color alone was not responsible. The gull feeding experiment showed that gulls would reject pieces of baitfish which had been thoroughly coated with ink.

The study indicates that the inking behavior of A. dactylomela is one of several means of defense possessed by these soft-bodied molluscs, that enables them to effectively avoid most predation as mature animals in the Florida Keys.