A robot for cleaning submersed marine structures is provided. The robot has a drive system for traversing the robot over the submersed structure. The robot further has an attachment system for attaching the robot to the submersed structure. The robot further has a cleaning arrangement for removing biofouling from the submersed structure as the robot is traversed thereover. The robot further has one or more flexible detector strips which contact the submersed structure as the robot is traversed thereover. The strips have a plurality of electrodes and are formed from electroactive polymer material which produces electrical signals in the electrodes on deflection of the strips. The signals are indicative of the surface roughness of the submersed structure.