This extraordinary photograph (by David Liittschwager) shows a random splash of seawater, magnified 25 times. The Earth’s open seas are home to countless tiny animals and plants that are known collectively as plankton.
The word “plankton” does not describe a specific type of organism; instead, it is defined by size and by the fact that these life forms are too small to swim against the prevailing ocean currents.
Plankton includes marine viruses (the femtoplankton), microscopic algae and bacteria, tiny worms and crustaceans, as well as the egg, juvenile and larval forms of larger animals and plants such as seaweeds, crabs, lobsters, fish and urchins. Because they drift with ocean currents, even large jellyfish are classed as plankton.
The importance of plankton cannot be overstated; phytoplankton (plants) produce a large proportion of the world’s oxygen supply, upon which all higher life forms are dependent, and both the phytoplankton and zooplankton (animals) prop up the entire aquatic food chain.
(For a key showing what each creature in the photo is go here)