If everything is everywhere, do they share a common gene pool?

Marine phytoplanktons are highly dispersed with large population sizes and are often considered to be homogenous over their entire range. Thus, using this definition, one would predict that everything is everywhere for these microbes. However, recent molecular analyses have shown both spatial and temporal compartmentalisation in phytoplankton communities, thus calling into question the idea that everything is everywhere, especially if they do not share a global gene pool. Examples are present to document the range of biogeography that has been reported in the phytoplankton and a hypothesis as to how this relates to species evolution on a geological time scale is provided.