Learn how to say Planktonic correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word plankton:
the small and microscopic organisms drifting or floating in the sea or fresh water, consisting chiefly of diatoms, protozoans, small crustaceans, and the eggs and larval stages of larger animals. Many animals are adapted to feed on plankton, especially by filtering the water:
prawns change their diet from plant plankton to animal plankton
Compare with nekton.
late 19th century: from German, from Greek planktos ‘wandering’, from the base of plazein ‘wander’