picoplankton

Picoplankton is the fraction of plankton composed by cells between 0.2 and 2 µm that can be either prokaryotic and eukaryotic phototrophs and heterotrophs:

• photosynthetic 
• heterotrophic 

They are prevalent amongst microbial plankton communities of both freshwater and marine ecosystems. They have an important role in making up a significant portion of the total biomass of phytoplankton communities