What Is Zooplankton?

zooplankton Credit: Roland Birke/Photographer's Choice/Getty Images

Zooplankton are small animals that live in water. They are generally weak swimmers and range in size from 2 micrometers to 8 inches long; they also live close to the surface.

Zooplankton are one of the basic elements of the marine food web. One commonly known plankton is krill, which is eaten by whales. There are many different types of zooplankton that are distinct from one another. For example, meroplankton are only considered plankton during one phase of their lives. Meroplankton are larvae that grow into full-sized animals, such as fish, insects and mollosks. Holoplankton remain classified as plankton throughout all of their life stages and include larvaceans and copepods.