An apparatus and method for prevention and treatment of marine biofouling on a surface to be treated by the apparatus includes a body defining a cavity, the body terminating in a distal open end that is adapted, in use, to be in the vicinity of a surface to be treated such that the surface forms a first end wall of a chamber within the cavity; an acoustic transducer mounted within the cavity to form an opposite second end wall of the chamber, the acoustic transducer being adapted to cause acoustic pressure fluctuations; and a reservoir for a liquid, the reservoir including an inlet passage and a plurality of mutually spaced outlet passages for liquid flow from the reservoir into the chamber, the outlet passages at least partially surrounding the chamber in the vicinity of the distal open end.