Visual Performance of Horseshoe Crabs: Role of Underwater Lighting

An experiment was conducted to examine the visual abilities of horseshoe crabs under different lighting conditions. Using the method of two-alternative forced choice, black and grey targets were set up to determine the crabs' visual capacities. The experiment revealed that an equal number of crabs hit the black and grey targets. However, lighting influenced the choice of targets resulting in the crabs' preference for the black target under dark lighting conditions.