The near bottom water layer of the ocean represents a boundary system between two oceanic biotopes (pelagial and benthal). Seston in general and phytoplankton in particular have complex features in the epibenthic water layers, due to different components that lye on the sea floor (interaction with the three dimensional alive structures like suspension feeders, seweeds, etc.; a special hydro dynamism; a combination of benthic and pelagic phytoplankton in the competition for nutrients and light; the resuspension and lateral advection of particles and nutrients near the bottom, among other things). Although it is recognized as an important part that explains pelagic-benthic coupling processes, these water layers have been largely neglected. The activity of benthic organisms can exert an influence on seston composition and concentration, but also the sampling frequency and different methodological approaches within different ecosystems has to be carefully considered to understand the dynamics of this boundary system. Differences among habitats, the temporary component of phytoplankton (cysts), the seasonal food availability (seston and phytoplankton) for benthic suspension feeders depending on the studied area, how these animals impact on the phytoplankton abundance and composition, and which is the return to the system (in form of nutrient excretion) from these benthic organisms will be discussed within this chapter

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