Zooplankton

Part of a series on
Plankton
Trophic mode Phytoplankton Zooplankton Mixoplankton Mycoplankton Bacterioplankton Virioplankton
By size Heterotrophic picoplankton Microalgae Microzooplankton Nanophytoplankton calcareous Photosynthetic picoplankton Picoeukaryote Picoplankton Marine microplankton
By taxonomy Algae diatoms coccolithophores dinoflagellates Protozoans radiolarians foraminiferans amoebae ciliates Bacteria cyanobacteria Archaea Viruses
By habitat Aeroplankton Geoplankton Marine plankton prokaryotes protists Freshwater plankton
Other types Gelatinous zooplankton Holoplankton Ichthyoplankton Meroplankton Pseudoplankton Tychoplankton
Blooms Algal bloom Critical depth Cyanobacterial bloom Harmful algal bloom Spring bloom Eutrophication Great Atlantic Sargassum Belt Great Calcite Belt Milky seas effect
Related topics Algaculture CLAW hypothesis CPR Diel vertical migration f-ratio Marine primary production Ocean fertilization iron Paradox of the plankton Planktivore Planktology Thin layers NAAMES
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Zooplankton are the animal (or heterotrophic) component of the planktonic community (the "zoo-" prefix comes from Ancient Greek: ζῷον, romanized: zôion, lit. 'animal'), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.

Zooplankton can be contrasted with phytoplankton (cyanobacteria and microalgae), which are the are the plant-like component of the plankton community (the "phyto-" prefix comes from Ancient Greek: φῠτόν, romanized: phutón, lit. 'plant', although taxonomically not plants). Zooplankton are heterotrophic (other-feeding), whereas phytoplankton are autotrophic (self-feeding), often generating biological energy and macromolecules through chlorophyllic carbon fixation using sunlight — in other words, zooplankton cannot manufacture their own food, while phytoplankton can. As a result, zooplankton must acquire nutrients by feeding on other organisms such as phytoplankton, which are generally smaller than zooplankton. Most zooplankton are microscopic but some (such as jellyfish) are macroscopic, meaning they can be seen with the naked eye.^[1]

Many protozoans (single-celled protists that prey on other microscopic life) are zooplankton, including zooflagellates, foraminiferans, radiolarians, some dinoflagellates and marine microanimals. Macroscopic zooplankton include pelagic cnidarians, ctenophores, molluscs, arthropods and tunicates, as well as planktonic arrow worms and bristle worms.

The distinction between autotrophy and heterotrophy often breaks down in very small organisms. Recent studies of marine microplankton have indicated over half of microscopic plankton are mixotrophs. A mixotroph is an organism that can behave sometimes as though it were a plant and sometimes as though it were an animal, using a mix of autotrophy and heterotrophy. Many marine microzooplankton are mixotrophic, which means they could also be classified as phytoplankton.