Depending on their trophic level, plankton may function as producers, consumers, or recyclers. There are three classifications for plankton: phytoplankton, zooplankton, and bacterioplankton.
Phytoplankton, such as algae and cyanobacteria, reside near the water’s surface and use photosynthesis to produce energy. Zooplankton are small, drifting protozoa or creatures that consume other species of plankton. Bacterioplankton consists of bacteria and archaea, which are saprotrophic recyclers that decompose or recycle organic resources into inorganic forms. Plankton is the initial and most essential layer of the aquatic food chain. The aggregate weight of plankton exceeds that of all other marine organisms.