Abstract
Sea hares are slow moving animals that have soft body with vestigial shell. Since it is slow and soft, it potentially has high predation risk. However, not many predators attack sea hares and consume them in the field and laboratory environments. How sea hare can defend themselves? “Diet derived chemical defense” has been a hypothetical answer. Actually, the sea hares prefer chemically rich algae. Many researchers have tried to support this “Diet derived chemical defense” hypothesis with well designed experiments; however, the results have been ambiguous. The other hypothetical defense was “defense by inking”. Sea hares release purple secretion when they were attacked by predators. This inking might work as smoke screen by providing a visual obstacle or as deterrent to provide chemical defense. This hypothesis has been anecdotal for many years. However, recently, multiple mechanisms of the chemical defense by inking have been revealed that inking involves two types of secretions, purple ink and white opaline. The ink and opaline contain deterrent molecules which involves seaweed derived secondary metabolites and an enzyme-substrate mixture. The ink and opaline also contains appetitive molecules. These defensive molecules work on chemosensory systems of predators. The ink and opaline works not only against predators but also to conspecifics as alarm cue. This articles reviews recent studies on diet derived chemical defense in their body and ink of sea hares.
