Low-active high-density cells of Noctiluca scintillans cells in surface seawater

•Noctiluca scintillans is a heterotrophic dinoflagellate widely distributed in the temperate and subtropical region.•N. scintillans often forms red tides in coastal water and discolors the surface water.•It is reported that N. scintillans plays a significant role in the marine ecosystem because of its high biomass, even if it does not form a red tide.•N. scintillans cells in subsurface layers with low density were so active and high density cells in the surface water were low active.