Abstract: A plankton harvester includes a surface float adapted to be secured to face tidal flow with an open subsurface cylinder secured to the flat and with the fore/aft axis parallel to the axis of said cylinder. A rotatable conical net structure is coaxial with the cylinder with the apex thereof at the mouth of the cylinder and the cone base engaging the opposite end to force fluid passing through the cylinder to pass through the net and deposit solids from the fluid on the surface of the net. Vanes in the conical structure rotates the cone at a rate dependent upon flow. Powered suction means adjacent to a linear surface segment of the net removes solids from the net surface. A storage chamber associated with the float is flow coupled to the suction means to store solids removed from the net surface.