The vertical distributions of chlorophyll and phytoplankton species in the North Pacific central environment

The phytoplankton species in the North Pacific central environment are known to be distributed into two vertically distinct assemblages during most of the year. Key species are defined for each assemblage. The vertical distributions of these key species indicate that the increase in abundance of deep species closely parallels the increase in chlorophyll a at the top of the chlorophyll maximum layer. The chlorophyll maximum is comprised of species characteristic of the deep assemblage, with only insignificant numbers of shallow species.