From Coastal Wiki
Small floating or weakly swimming animals that drift with water currents and which, with phytoplankton, make up the planktonic food supply upon which almost all oceanic organisms ultimately depend.
Zooplankton are heterotrophic (non-photosynthetic) planktonic organisms, including protists, small animals, and larvae, which exist within the water column. See Marine microorganisms.
Different types of zooplankton: see Marine Plankton.