Predator avoidance behavior of Japanese sea cucumber Apostichopus japonicus juveniles elicited by contact with and chemical stimuli from predatory sea stars

Abstract

The Japanese sea cucumber Apostichopus japonicus is a major target for fisheries, aquaculture, and stock enhancement because of its high commercial value. Knowledge of their survival strategies is crucial for appropriate management of this species. Therefore, this study aimed to determine the behavioral response of A. japonicus juveniles upon contact with a predator or its chemical stimuli. When hatchery-reared A. japonicus juveniles had direct contact with the predatory sea star, their movement speed increased, and the direction of their body axis changed compared with those before contact. The body lengths of the A. japonicus juveniles were longer when they were closer to the predator, suggesting that stretching their body is among their strategies to avoid predation. When the chemical stimuli from the predator was provided, the A. japonicus juveniles changed their movement similar to how they moved upon direct contact with the predator. These results suggest that the predator avoidance behavior of A. japonicus juveniles is elicited by the chemical and/or tactile stimuli from predators. Considering that we used hatchery-reared seedlings, these responses were innate rather than an acquired behavior. An extension of the present study, including the comparison to wild individuals, should substantially contribute to the management of A. japonicus population.