The distribution and significance of Richelia intracellularis Schmidt in the North Pacific Central Gyre1

Localized blooms of phytoplankton observed in the upper 60 m of the North Pacific Central Gyre during three expeditions are accompanied and often dominated by an increase in the abundance of species of the diatom genus Rhizosolenia that contain the endophytic cyanophyte Richelia intracellularis, which may fix molecular nitrogen. It is hypothesized that the phytoplankton blooms are stimulated and sustained by an increase in the available nitrogenous nutrients resulting from nitrogen fixation by Richelia.