How It Works

Plankton under the microscope

‘Plankton’ is a catchall name for a diverse group of marine or freshwater organisms that are so small and/or weak that they can’t swim against a current. Indeed, this inability alone is what classifies an organism as planktonic, with bacteria, algae, molluscs, crustaceans and more all falling under this label.

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Despite their minuscule size, plankton species number in the hundreds of thousands and are a critical component of food chains. Fish and marine mammals – including those as massive as whales – feed extensively on plankton (some exclusively) and without them many ecosystems in the ocean would simply collapse.

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Plankton are subdivided according to size, with those larger than 20 millimetres (0.8 inches) – such as jellyfish – referred to as megaplankton, while at the other end of the scale, organisms less than 0.2 micrometres – such as marine viruses – are known as femtoplankton. In between these two extremes there are several other categories, containing a wide array of organisms ranging from cephalopoda (like octopus hatchlings) through to flagellates.