There are two primary examples of plankton: zooplankton and phytoplankton. Both of these plankton types are marine plankton, and they are found in the ocean.
Zooplankton eat other smaller plankton in the ocean. They are eaten by bigger animals such as fish. Examples of zooplankton species would be krill, crabs, arrow worms and copepods. They spend most of their time floating throughout the ocean.
Phytoplankton includes species such as cyanobacteria, diatoms and green algae. They are responsible for recycling carbon dioxide and sunlight to provide the world with oxygen. Some studies show that phytoplankton may produce as much as 50 percent of the oxygen that humans breathe as reported by National Geographic.