<P> Plankton (singular plankter) are the diverse collection of organisms that live in the water column of large bodies of water and are unable to swim against a current . They provide a crucial source of food to many large aquatic organisms, such as fish and whales . </P> <P> These organisms include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit--for example--the pelagic zone of oceans, seas, or bodies of fresh water . Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification . </P>

The microscopic organism at the base of the marine food chain are known as