抄録
We focused on the phototaxis of cypris larvae to prevent their settlement on a ship's hull. Preventing settlement on the top surface （3 mm thickness） was particularly important so as not to increase the shade from the juveniles settled there. The maximum irradiance at the top surface was 550.0－ 560.0 （W m-2）. A cylinder （diameter 15.4 cm; axial length 40 cm） was used to compare the efficiency of phototaxis attracted by the different colors of light from a source placed inside the closed end. A total of 1,101 individuals settled on the surface when red light was being emitted, while only 2 individuals were on it when there was no light. All individuals settled above the tip of a blue LED stopped metamorphosing, indicating that a higher irradiance blue light inhibits some metamorphosis processes. That indirectly contributes to a reduction of biofouling on the plate surface. The effectiveness of blue light sources composed of three, nine, and thirty-six LEDs on the reduction of the settlement frequency was quantified when the emission was performed from a distance of 40 cm from the center on the flat surface （40 cm square）. The value of the relative population density in the central area was drastically reduced from 0.2 to 0.06 （％ cm-2） in response to an increase in the number of LEDs from three to nine. The value decreased slightly to 0.04 （％ cm-2） with thirty-six LEDs. We also examined the effectiveness of the arrangement of four light sources, each of which was composed of nine LEDs and was emitting equally toward a quarter the area of a surface. In that case, an 80.8 ％ reduction of the settlement frequency was obtained as compared to that of the control, while the value was 61.6 ％ when a single light source of thirty-six LEDs was emitting toward the central area on the plate surface, indicating that an emission that covers a wider area reduces the settlement frequency by attracting cypris larvae effectively toward the light source. The blue LED light with higher irradiance was found to have application for maintaining a smooth hull surface.
