Zooplankton, animation. Zooplankton are the tiny organisms that feed on organic matter that are found in sea, oceans and almost all other bodies of water. They primarily feed on phytoplankton photosynthesising plankton and other zooplankton. Although many zooplankton are microscopic, the term also covers larger animals that share the drifting lifestyle, including the larvae and young of fish, molluscs and crustaceans, and even large animals such as jellyfish.