As mineral resources on land decline, manganese nodules on the ocean floor are seen as a potential source of metals such as nickel, cobalt and copper. Its mining technology is also gaining attention. However, the fine ore particles produced during the mining process and the discharge of tailings are bound to affect the  phytoplankton, which may cause pollution to the ocean. In this study, the effects of crushed manganese nodules on marine surface phytoplankton were explored by adding manganese nodules of different sizes and concentrations to dinoflagellates and diatoms to detect changes in chlorophyll fluorescence and photosynthetic efficiency.