Plankton pertain to the small organisms that drift, float, or weakly swimming in aquatic habitats. Some of them may be capable of diel vertical migration but they, in general, flow with their surrounding currents. They may be classified according to their trophic level groups: (1) phytoplankton, (2) zooplankton, (3) bacterioplankton, and (4) mycoplankton.
Bacterioplankton are the bacterial component of the plankton. They are comprised of prokaryotes. Some of them serve as primary producers and others as primary consumers in aquatic ecosystems (e.g. marine and freshwater ecosystems). Primary producer bacterioplankton are those that are capable of photosynthesis, e.g. blue-green algae (cyanophyta). It should be noted though that cyanophyta are also referred to as phytoplankton since they are also regarded as one of the photosynthetic algal groups. However, they are the only algal group that is prokaryotic and therefore are also considered as bacteria. Bacterioplankton are ecologically essential since they are involved in the remineralization processes of organic material. They drive global biogeochemical cycling of elements (e.g. carbon fixation, nitrogen fixation, denitrification, nitrification, etc.). Many of them are saprotrophic as they obtain energy from organic material they consume.
Word origin: bacterio- (of bacteria) + planktón, (planktós (“wandering”)