Predator-induced behavioral plasticity of juvenile red king crabs (Paralithodes camtschaticus)

Predation and adaptations to avoid predation during early life stages have great potential to structure population dynamics and resultant community structure. Crypsis is the primary predator-avoidance mechanism for recently-settled red king crabs (Paralithodes camtschaticus); however, it is unknown if this behavioral adaptation is innate or gained with experience. Hatchery-cultured individuals may be at a disadvantage once released into the wild if they have no experience with predators. We conducted experiments with Pacific halibut (Hippoglossus stenolepis) and Pacific cod (Gadus macrocephalus) predators to determine if red king crab predator responses could be enhanced with experience. We exposed crabs to predators for 48h either with limited exposure (chemical and visual cues only) or complete exposure (chemical, visual, and physical cues) and used video recordings to compare (1) crab crypsis, (2) crab survival, and (3) predator behavior (attack rates, capture success) among naïve and experienced crabs. Halibut and cod exposure enhanced crab crypsis and survival, but only halibut exposure resulted in a significant effect. Crabs with limited and complete halibut exposure had higher initial crypsis, and both naïve and conditioned crabs increased crypsis by the end of the experiment. Complete exposure initiated a stronger response compared to limited exposure. Physical interactions with predators are likely important to initiate enhanced avoidance responses. Halibut and cod attack rates and capture success did not vary when crabs had prior experience, but halibut were generally more successful at capturing prey than cod. Our results show that juvenile red king crabs respond to some predators by increasing their cryptic behavior and that this response may be enhanced with experience. For stock enhancement programs, exposing juveniles to predators in the hatchery prior to release may enhance predator avoidance and allow quick adaptation to the natural environment.