Conditioning the crab Carcinus maenas against instinctive light avoidance

Carcinus maenas is an invasive species found in Northern American waters overtaking the less adaptable species and responding to various forms of conditioning. In this study, we conditioned C. maenas to reverse its innate light avoidance behavior. Within 6 days of testing, 21 out of 30 crabs were successfully trained to enter a beam of light to receive food, although their instincts are to seek shelter from predators in dark areas. Some took as little as 2 days to reverse their light aversion. They also responded faster once trained. Larger crabs had faster response times than smaller ones, while there was no difference between sexes. The conditioned response lasted for at least 4 days without reinforcement. The rapid learning abilities observed during this experiment may help to explain the pervasive success of C. maenas as an invasive species.