Habitat structure influences the survival and predator–prey interactions of early juvenile red king crab Paralithodes camtschaticus

Highly structured nursery habitats promote the survival of juvenile stages of many species by providing foraging opportunities and refuge from predators. Through integrated laboratory and field experiments, we demonstrate that nursery habitat structure affects survival and predator-prey interactions of red king crab Paralithodes camtschaticus. Crabs (<1 yr old [Age 0]; 8 to 10 mm carapace length [CL]) preferred complex biogenic habitats formed by structural invertebrates and macroalgae over structural mimics and sand in the absence of predators in laboratory experiments, yet they associated with any available structural habitat when fish predators were present. Survival was higher in the presence of complex habitat for Age 0 crabs (5 to 7.5 mm CL) with Pacific cod Gadus macrocephalus predators in the laboratory and for Age 0 (4 to 8 mm CL) and Age 1 (16 to 28 mm CL) crabs with fish and invertebrate predators in the field. Crab activity and refuge response behavior varied with crab stage and habitat. Age 0 crabs were cryptic, avoiding predators by associating with habitat structure or remaining motionless in the absence of structure, and were less likely to respond to an attack. In contrast, Age 1 crabs were more likely to respond to an attacking predator and were less likely to remain motionless in the absence of structural refuge, suggesting an ontogenetic shift in behavior. Complex habitats, cryptic behavior, and direct defense improve juvenile red king crab survival against certain predators, including demersal fishes.