Background

• The word "plankton" derives from the Greek term meaning "floating," which literally describes what these tiny organisms do. Water currents move and distribute them, and they cannot travel on their own against these currents. Most plankton are invisible to the naked eye, but some species like small jellyfish are easy to see.
  
  

Types

• There are three types of plankton: phytoplankton, zooplankton and bacterioplankton. Phytoplankton are similar to plants on land in that they create their own food to live off of. Because of this, they commonly live in the sunlit zone of water so they can absorb sunlight for photosynthesis.
  
  Zooplankton are plankton with animal-like characteristics that feed on phytoplankton. Even the eggs or larvae of some other sea animals are zooplankton. In this group are some jellyfish whose movements are solely controlled by currents. They are usually food for larger sea creatures.
  
  Finally, bacterioplankton are little organisms that generally break up and thrive on organic waste in the water.
  
  

Categories

• Within the three types of plankton are two categorical divisions as well. There are holoplankton and meroplankton. Holoplankton spend their entire life cycles as plankton. Most algae and bacterioplankton fall under this category. In the other category, meroplankton begin their lives as plankton but eventually grow into larger organisms with more free will of movement. The eggs and larvae of many sea creatures begin life as meroplankton.
  
  

Importance

• Plankton are critically important to life on Earth. They are the second most abundant life form on our planet next to bacteria and are at the bottom of the marine food chain. Many small organisms and fish that feed on plankton in return feed larger animals. Large creatures including whales and the largest fish (whale sharks) are also plankton feeders.
  
  

Environmental Impact

• Plankton are a good indication of environmental and climate conditions on Earth. Any kind of oceanic disaster, for instance, may adversely affect or kill off certain species of plankton, thus affecting the rest of the organisms in the marine food chain. Plankton also remove approximately three billion tons of carbon dioxide from the atmosphere every year. This in effect can help rebuild the ozone layer and slow down damage done by potential global warming.