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

Noctiluca scintillans is an important member of the mesozooplankton in terms of biomass and production in the Seto Inland Sea, Japan. The densities and adenosine triphosphate (ATP) contents of N. scintillans cells were measured. Vertical profiles of N. scintillans cellular activity in the coastal water were determined and the ATP contents were high at middle layers, with a maximum depth of 10 m. ATP contents were low in the surface and lower layers. These results suggest that active N. scintillans cells in subsurface layers with low density play an important role in the coastal ecosystem, and high-density cells in the surface water are not active.