Some common zooplankton (mostly copepods) collected near the surface over East Diamante volcano. Credit: NOAA.

Zooplankton are free-floating, oceanic animal life as opposed to phytoplankton, the free-floating plant life. They consist of a wide variety of small organisms, such as copepods, krill, and larval forms of higher animals such as crab, jellyfish, and fish. Zooplankton graze upon phytoplankton as they ride the ocean currents, and are themselves eaten by whales, small fish, invertebrates, and birds. Few levels or areas of the ocean are devoid of zooplankton, and they form a central constituent of the oceans' food chains.