Laboratory experiments were conducted to evaluate how water temperature mediates the cannibalistic relationship between age 0 and age 1 red king crab (RKC) (Paralithodes camtschaticus), and the role of habitat structure in providing refuge for prey. We also observed the activity levels of age 1 crabs under light and dark conditions, and predator avoidance behavior by the age 0 crabs. Age 1 crabs (15–20 mm in carapace length (CL)) were active 24 h/day, but motion was about 33% higher in light than in dark conditions, and increased in direct proportion with water temperature (2–10°C). Feeding rate was also directly related with temperature for age 1 crabs, which consumed 7% of body weight per day at 2°C, and 20% at 10°C. Both temperature and habitat complexity had significant effects on survival of age 0 RKC (CW, 2.2–2.6 mm) when exposed to age 1 crabs (CL, 17–19 mm), with no significant interaction. Survival diminished 31% in a linear relationship from 2–10°C, and was twice as high in a complex structural environment compared with bare sand habitat. Predator avoidance behavior by age 0 RKC improved from juvenile molt stage 2 to stage 4. Increasing water temperature may serve to increase mortality by cannibalism in RKC, both in aquaculture and in the field, but survival will increase substantially in structurally complex environments.