Plankton | Definition, Characteristics, Types, Diet, Size, & Facts

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class="md-content"> <div class="md-article-container template-desktop"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="463121"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/plankton">plankton</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/plankton">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref283872"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/plankton#ref283872">Phytoplankton</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref283873"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/plankton#ref283873">Zooplankton</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref283874"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/plankton#ref283874">Bacteria and fungi</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref283875"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/plankton#ref283875">Plankton and biological productivity</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/plankton/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/plankton">Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/science/plankton/images-videos">Images & Videos</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="https://cdn.britannica.com/65/129565-050-E612629B/Pleurosigma-angulatum-Phytoplankton-parts-North-Atlantic-Ocean.jpg" data-href="/media/1/463121/127446" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/65/129565-004-C0EF77C5/Pleurosigma-angulatum-Phytoplankton-parts-North-Atlantic-Ocean.jpg" alt="phytoplankton" height="50" /> </a> <a href="/video/Phytoplankton-foundation-food-chains/160474" data-href="/media/1/463121/160474" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/83/152183-138-C7950260/Phytoplankton-foundation-food-chains.jpg?w=400&h=225&c=crop" alt="The essential role of phytoplankton in ecosystems" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> <a href="/video/Phytoplankton-diatoms-Navicula-Ditylum/18425" data-href="/media/1/463121/18425" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/35/22235-138-ACCBE74C/Phytoplankton-diatoms-Navicula-Ditylum.jpg?w=400&h=225&c=crop" alt="Observe diatoms, microscopic sea organisms encased in silicified cell walls with intricate designs" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> <a href="https://cdn.britannica.com/63/162063-050-D9AB87C6/collection-zooplankton-copepods-animals-Daphnia.jpg" data-href="/media/1/463121/191670" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/63/162063-004-6CAFC1BE/collection-zooplankton-copepods-animals-Daphnia.jpg" alt="marine zooplankton" height="50" /> </a> <a href="/video/crustaceans-appetites/68457" data-href="/media/1/463121/68457" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/73/73073-138-D519DA56/crustaceans-appetites.jpg?w=400&h=225&c=crop" alt="The role of copepods in the marine food chain" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> <a href="/video/Zooplankton-copepods-tintinnids-rotifers-larvaceans-plankton-examples/18491" data-href="/media/1/463121/18491" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/22/22422-138-14260C15/Zooplankton-copepods-tintinnids-rotifers-larvaceans-plankton-examples.jpg?w=400&h=225&c=crop" alt="Observe permanent plankton, including transparent larvaceans, ciliate protozoans, and other zooplankton" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> <a href="https://cdn.britannica.com/69/6569-004-5FCB5F9B/plankton.jpg" data-href="/media/1/463121/33" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/69/6569-004-5FCB5F9B/plankton.jpg" alt="plankton" height="50" /> </a> <a href="/video/foundations-plankton-ocean-food-chain-currents-coasts/128172" data-href="/media/1/463121/128172" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/26/82426-138-FEE9FBF3/foundations-plankton-ocean-food-chain-currents-coasts.jpg?w=400&h=225&c=crop" alt="Take an in-depth look at the variety of plankton, from diatoms and microflagellates to jellyfish" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> </div> <button disabled class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue " aria-label="Previous"> <span class="material-icons md-24" data-icon="keyboard_arrow_left"></span> </button> <button disabled class="next-button js-next-button position-absolute btn btn-circle shadow btn-blue " aria-label="Next"> <span class="material-icons md-24" data-icon="keyboard_arrow_right"></span> </button> </div> 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The term <em>plankton</em> is a <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="collective" href="https://www.merriam-webster.com/dictionary/collective" data-type="MW">collective</a> name for all such organisms—including certain <a href="https://www.britannica.com/science/algae" class="md-crosslink " data-show-preview="true">algae</a>, <a href="https://www.britannica.com/science/bacteria" class="md-crosslink " data-show-preview="true">bacteria</a>, <a href="https://www.britannica.com/science/protozoan" class="md-crosslink " data-show-preview="true">protozoans</a>, <a href="https://www.britannica.com/animal/crustacean" class="md-crosslink " data-show-preview="true">crustaceans</a>, <a href="https://www.britannica.com/animal/mollusk" class="md-crosslink " data-show-preview="true">mollusks</a>, and <a href="https://www.britannica.com/animal/cnidarian" class="md-crosslink " data-show-preview="true">coelenterates</a>, as well as representatives from almost every other phylum of <a href="https://www.britannica.com/animal/animal" class="md-crosslink " data-show-preview="true">animals</a>. Plankton is distinguished from <span id="ref183048"></span><a href="https://www.britannica.com/science/nekton" class="md-crosslink " data-show-preview="true">nekton</a>, which is composed of strong-swimming animals, and from <span id="ref183049"></span><a href="https://www.britannica.com/science/benthos" class="md-crosslink " data-show-preview="true">benthos</a>, which includes sessile, creeping, and burrowing organisms on the seafloor. Large floating <a href="https://www.britannica.com/science/seaweed" class="md-crosslink " data-show-preview="true">seaweeds</a> (for example, <em>Sargassum</em>, which <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="constitutes" href="https://www.merriam-webster.com/dictionary/constitutes" data-type="MW">constitutes</a> the <a href="https://www.britannica.com/place/Sargasso-Sea" class="md-crosslink " data-show-preview="true">Sargasso Sea</a>) and various related multicellular algae are not considered plankton but <span id="ref183050"></span><a href="https://www.britannica.com/science/pleuston" class="md-crosslink ">pleuston</a>. Pleuston are forms of life that live at the interface of air and water. Organisms resting or swimming on the surface film of the water are called <span id="ref183051"></span><a href="https://www.britannica.com/science/neuston" class="md-crosslink " data-show-preview="true">neuston</a> (e.g., the alga <em>Ochromonas</em>).</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">Plankton is the productive base of both marine and freshwater <a href="https://www.britannica.com/science/ecosystem" class="md-crosslink " data-show-preview="true">ecosystems</a>, providing <a href="https://www.britannica.com/topic/food" class="md-crosslink " data-show-preview="true">food</a> for larger animals and indirectly for humans, whose <a href="https://www.britannica.com/topic/fishery" class="md-crosslink " data-show-preview="true">fisheries</a> depend upon plankton. As a human resource, plankton has only begun to be developed and exploited, in view of its high biological productivity and wide extent. It has been demonstrated on several occasions that large-scale <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="cultures" href="https://www.merriam-webster.com/dictionary/cultures" data-type="MW">cultures</a> of algae are technically <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="feasible" href="https://www.merriam-webster.com/dictionary/feasible" data-type="MW">feasible</a>. The unicellular <a href="https://www.britannica.com/science/green-algae" class="md-crosslink " data-show-preview="true">green alga</a> <em>Chlorella</em> has been used particularly in this connection. Through ample <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="culture" href="https://www.merriam-webster.com/dictionary/culture" data-type="MW">culture</a> conditions, production is directed toward <a href="https://www.britannica.com/science/protein" class="md-crosslink " data-show-preview="true">protein</a> content greater than 50 percent. Although this protein has a suitable balance of essential <a href="https://www.britannica.com/science/amino-acid" class="md-crosslink " data-show-preview="true">amino acids</a>, its low degree of digestibility prevents practical use. Phytoplankton may become increasingly important in <a href="https://www.britannica.com/science/space-exploration" class="md-crosslink " data-show-preview="true">space travel</a> as a source for food and for <a href="https://www.britannica.com/science/human-respiratory-system/The-respiratory-pump-and-its-performance#ref66151" class="md-crosslink " data-show-preview="true">gas exchange</a>. The <a href="https://www.britannica.com/science/carbon-dioxide" class="md-crosslink " data-show-preview="true">carbon dioxide</a> released during respiration of spacecraft personnel would be transformed into organic substances by the algae, while the <a href="https://www.britannica.com/science/oxygen" class="md-crosslink " data-show-preview="true">oxygen</a> liberated during this process would support <a href="https://www.britannica.com/science/human-respiratory-system" class="md-crosslink " data-show-preview="true">human respiration</a>.</p><span class="marker MOD2 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref283872"><h2 class="h1"><span id="ref183052"></span><a href="https://www.britannica.com/science/phytoplankton" class="md-crosslink " data-show-preview="true">Phytoplankton</a></h2> <span class="marker PREMOD3 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="160474" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="152183"><a data-id="152183" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/Phytoplankton-foundation-food-chains/-160474"><img src="https://cdn.britannica.com/83/152183-138-C7950260/Phytoplankton-foundation-food-chains.jpg?w=800&h=450&c=crop" alt="Learn how phytoplankton supply oxygen via photosynthesis and serve as the first link in the marine food chain" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/EuU8RZjB.m3u8" } ], "image": "https://cdn.britannica.com/83/152183-138-C7950260/Phytoplankton-foundation-food-chains.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/blLQRR6y", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/SQ2xdZ1j.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="152183">Learn how phytoplankton supply oxygen via photosynthesis and serve as the first link in the marine food chain</span><span>Learn about phytoplankton's role as the oxygen-producing foundation of many marine food chains.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/plankton/images-videos">See all videos for this article</a></figcaption></figure></div></div><p class="topic-paragraph">The plantlike <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="community" href="https://www.merriam-webster.com/dictionary/community" data-type="MW">community</a> of plankton is called phytoplankton, and the animal-like community is known as zooplankton. This convenient division is not without fault, for, strictly speaking, many planktonic organisms are neither clearly <a href="https://www.britannica.com/plant/plant" class="md-crosslink autoxref " data-show-preview="true">plant</a> nor <a href="https://www.britannica.com/animal/animal" class="md-crosslink autoxref " data-show-preview="true">animal</a> but rather are better described as <a href="https://www.britannica.com/science/protist" class="md-crosslink " data-show-preview="true">protists</a>. When size is used as a <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="criterion" href="https://www.merriam-webster.com/dictionary/criterion" data-type="MW">criterion</a>, plankton can be subdivided into macroplankton, microplankton, and nannoplankton, though no sharp lines can be drawn between these categories. Macroplankton can be collected with a coarse net, and morphological details of individual organisms are easily discernible. These forms, 1 mm (0.04 inch) or more in length, ordinarily do not include phytoplankton. <span id="ref183054"></span><a href="https://www.britannica.com/science/microplankton" class="md-crosslink ">Microplankton</a> (also called net plankton) is composed of organisms between 0.05 and 1 mm (0.002 and 0.04 inch) in size and is a mixture of phytoplankton and zooplankton. The lower limit of its size range is fixed by the aperture of the finest cloth used for plankton nets. Nannoplankton (dwarf plankton) passes through all nets and consists of forms of a size less than 0.05 mm. Phytoplanktonic organisms dominate the nannoplankton.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/biology-bonanza" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/12/167112-131-ABF5C65B/greylag-Flock-Greylag-geese-winter-migration-goose.jpg" alt="greylag. Flock of Greylag geese during their winter migration at Bosque del Apache National Refugee, New Mexico. greylag goose (Anser anser)" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">Biology Bonanza</div> </div> </a><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="18425" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="22235"><a data-id="22235" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/Phytoplankton-diatoms-Navicula-Ditylum/-18425"><img src="https://cdn.britannica.com/35/22235-138-ACCBE74C/Phytoplankton-diatoms-Navicula-Ditylum.jpg?w=800&h=450&c=crop" alt="Observe diatoms, microscopic sea organisms encased in silicified cell walls with intricate designs" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/RcWVoVhp.m3u8" } ], "image": "https://cdn.britannica.com/35/22235-138-ACCBE74C/Phytoplankton-diatoms-Navicula-Ditylum.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/5xdUfRsC", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/RYTrXyZb.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="22235">Observe diatoms, microscopic sea organisms encased in silicified cell walls with intricate designs</span><span>Learn about phytoplankton, which include diatoms such as <em>Navicula</em> and <em>Ditylum</em>.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/plankton/images-videos">See all videos for this article</a></figcaption></figure></div></div><p class="topic-paragraph">The chief components of marine phytoplankton are found within the algal groups and include <a href="https://www.britannica.com/science/diatom" class="md-crosslink " data-show-preview="true">diatoms</a>, <a href="https://www.britannica.com/science/dinoflagellate" class="md-crosslink " data-show-preview="true">dinoflagellates</a> and coccolithophorids. Silicoflagellates, <a href="https://www.britannica.com/science/cryptomonad" class="md-crosslink " data-show-preview="true">cryptomonads</a>, and green algae are found in most plankton samples. <a href="https://www.britannica.com/place/Freshwater-England" class="md-crosslink autoxref " data-show-preview="true">Freshwater</a> phytoplankton, usually rich in green algae, also includes diatoms, <a href="https://www.britannica.com/science/blue-green-algae" class="md-crosslink " data-show-preview="true">blue-green algae</a>, and true <a href="https://www.britannica.com/science/flagellate" class="md-crosslink " data-show-preview="true">flagellates</a>.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">In the oceans, phytoplankton <a href="https://www.britannica.com/science/biomass" class="md-crosslink " data-show-preview="true">biomass</a> rises and falls according to multiyear cycles and appears to be sensitive to changes in sea surface temperatures, <a href="https://www.britannica.com/science/climate-change" class="md-crosslink autoxref " data-show-preview="true">climate change</a>, and <a href="https://www.britannica.com/science/ocean-acidification" class="md-crosslink autoxref " data-show-preview="true">ocean acidification</a>. One controversial but influential study, which examined records kept between 1899 and 2010, discovered that phytoplankton biomass declined by 1 percent per year in all but two of Earth’s 10 <a href="https://www.britannica.com/science/ocean" class="md-crosslink autoxref " data-show-preview="true">ocean</a> basins, attributing this reduction, which results in a <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="cumulative" href="https://www.merriam-webster.com/dictionary/cumulative" data-type="MW">cumulative</a> loss of about 40 percent, to increases in sea surface temperatures occurring over the same period. Several other studies examining single <a href="https://www.britannica.com/science/species-taxon" class="md-crosslink autoxref " data-show-preview="true">species</a> or specific regions of the oceans also report slow long-term declines in plankton.</p><span class="marker MOD5 mod-inline"></span></section> <span class="marker h3"></span><section data-level="1" id="ref283873"><h2 class="h1"><span id="ref183053"></span><a href="https://www.britannica.com/science/zooplankton" class="md-crosslink " data-show-preview="true">Zooplankton</a></h2> <span class="marker PREMOD6 mod-inline"></span><div class="assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100" data-type="other"><div class="slider-container js-slider-container overflow-hidden d-flex"><div class="rw-track d-flex align-items-center"><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="191670" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/63/162063-050-D9AB87C6/collection-zooplankton-copepods-animals-Daphnia.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/463121/191670"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/63/162063-050-D9AB87C6/collection-zooplankton-copepods-animals-Daphnia.jpg?w=300"><img src="https://cdn.britannica.com/63/162063-050-D9AB87C6/collection-zooplankton-copepods-animals-Daphnia.jpg?w=300" alt="marine zooplankton" data-width="1600" data-height="1048" loading="eager"></picture><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">1 of 2</div><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/63/162063-050-D9AB87C6/collection-zooplankton-copepods-animals-Daphnia.jpg" data-href="/media/1/463121/191670">marine zooplankton</a><span>A collection of marine zooplankton composed of copepods, <em>Daphnia</em> (water fleas), and other tiny animals.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="68457" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="73073"><a data-id="73073" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/crustaceans-appetites/-68457"><img src="https://cdn.britannica.com/73/73073-138-D519DA56/crustaceans-appetites.jpg?w=800&h=450&c=crop" alt="Discover the copepod's place in the marine food chain and how it develops from a larva into an adult" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/c8zIAYJX.m3u8" } ], "image": "https://cdn.britannica.com/73/73073-138-D519DA56/crustaceans-appetites.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/KGQJs6xw", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/jyxYz1hW.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">2 of 2</div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="73073">Discover the copepod's place in the marine food chain and how it develops from a larva into an adult</span><span>Copepods are tiny oceanic crustaceans with prodigious appetites.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/plankton/images-videos">See all videos for this article</a></figcaption></figure></div></div></div><button disabled="true" class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_left"></span></button><button disabled="true" class="next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_right"></span></button></div><p class="topic-paragraph">The zooplankton is divided into two groups. Temporary plankton consists of planktonic <a href="https://www.britannica.com/science/egg-biology" class="md-crosslink " data-show-preview="true">eggs</a> and <a href="https://www.britannica.com/science/larva" class="md-crosslink " data-show-preview="true">larvae</a> of members of the benthos and nekton; permanent plankton includes all animals that live their complete life cycles in a floating state. The temporary plankton, particularly abundant in coastal areas, is characteristically seasonal in occurrence, though variations in spawning time of different species ensure its presence in all seasons. Representatives from nearly every phylum of the animal kingdom are found in the permanent plankton. Among the protozoans, planktonic <a href="https://www.britannica.com/science/foraminiferan" class="md-crosslink " data-show-preview="true">foraminiferans</a> and <a href="https://www.britannica.com/science/radiolarian" class="md-crosslink " data-show-preview="true">radiolarians</a> are so abundant and widespread that their skeletons <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="constitute" href="https://www.merriam-webster.com/dictionary/constitute" data-type="MW">constitute</a> the bulk of bottom sediments over wide ocean areas. They are absent in fresh water. The <a href="https://www.britannica.com/science/ciliate" class="md-crosslink " data-show-preview="true">ciliate</a> protozoans are represented mainly by the tintinnids, which are between 20 and 640 microns (1 <a href="https://www.britannica.com/science/micrometre" class="md-crosslink autoxref " data-show-preview="true">micron</a> = 10<sup>−6</sup> metre; 0.0008 and 0.025 inch) in size and sometimes occur in vast numbers. Among the planktonic coelenterates are the beautiful siphonophores (e.g., <em>Physalia</em>, the Portuguese man-of-war) and the <a href="https://www.britannica.com/animal/jellyfish" class="md-crosslink " data-show-preview="true">jellyfishes</a>. Planktonic <a href="https://www.britannica.com/animal/ctenophore" class="md-crosslink " data-show-preview="true">ctenophores</a>, called comb jellies, or sea walnuts, are also common. Freshwater <a href="https://www.britannica.com/animal/rotifer" class="md-crosslink " data-show-preview="true">rotifers</a> may be present in plankton in vast numbers during the warmer seasons. A group of organisms that can be found at all latitudes, both in surface water and at great depths, are the marine <a href="https://www.britannica.com/animal/arrowworm" class="md-crosslink " data-show-preview="true">arrowworms</a> (e.g., <em>Sagitta</em>), important planktonic predators. <a href="https://www.britannica.com/animal/oyster" class="md-crosslink " data-show-preview="true">Oysters</a>, <a href="https://www.britannica.com/animal/mussel" class="md-crosslink " data-show-preview="true">mussels</a>, other marine <a href="https://www.britannica.com/animal/bivalve" class="md-crosslink " data-show-preview="true">bivalves</a>, and <a href="https://www.britannica.com/animal/snail" class="md-crosslink " data-show-preview="true">snails</a> begin life as planktonic larvae. The wing snails (Pteropoda) spend their entire life cycles as plankton.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="18491" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="22422"><a data-id="22422" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/Zooplankton-copepods-tintinnids-rotifers-larvaceans-plankton-examples/-18491"><img src="https://cdn.britannica.com/22/22422-138-14260C15/Zooplankton-copepods-tintinnids-rotifers-larvaceans-plankton-examples.jpg?w=800&h=450&c=crop" alt="Observe permanent plankton, including transparent larvaceans, ciliate protozoans, and other zooplankton" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/eKpcbmdu.m3u8" } ], "image": "https://cdn.britannica.com/22/22422-138-14260C15/Zooplankton-copepods-tintinnids-rotifers-larvaceans-plankton-examples.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/c1sYkUpV", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/wtOngcMR.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="22422">Observe permanent plankton, including transparent larvaceans, ciliate protozoans, and other zooplankton</span><span>Learn about zooplankton, such as copepods, rotifers, tintinnids, and larvaceans, that are examples of permanent plankton (holoplankton).</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/plankton/images-videos">See all videos for this article</a></figcaption></figure></div></div><p class="topic-paragraph"><span id="ref183055"></span><a href="https://www.britannica.com/animal/crustacean" class="md-crosslink " data-show-preview="true">Crustaceans</a> are the most important members of the zooplankton. They are the marine counterparts of insects on land; on land as in the sea, the <a href="https://www.britannica.com/animal/arthropod" class="md-crosslink " data-show-preview="true">arthropods</a> are the most <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="diverse" href="https://www.merriam-webster.com/dictionary/diverse" data-type="MW">diverse</a> and numerous of all animal phyla. The <a href="https://www.britannica.com/animal/copepod" class="md-crosslink " data-show-preview="true">copepod</a> <em>Calanus finmarchicus</em> is important as food for the <a href="https://www.britannica.com/animal/herring" class="md-crosslink " data-show-preview="true">herring</a>, and the <a href="https://www.britannica.com/animal/krill" class="md-crosslink " data-show-preview="true">krill</a> <em>Euphausia superba</em>, also known as a euphausiid, is the main food source for <a href="https://www.britannica.com/animal/blue-whale" class="md-crosslink " data-show-preview="true">blue</a> and <a href="https://www.britannica.com/animal/fin-whale" class="md-crosslink " data-show-preview="true">fin</a> <span id="ref183056"></span><a href="https://www.britannica.com/animal/whale" class="md-crosslink " data-show-preview="true">whales</a> in the <a href="https://www.britannica.com/place/Southern-Ocean" class="md-crosslink autoxref " data-show-preview="true">Antarctic Ocean</a>. These whales migrate to waters where the krill spawns, and the rapid growth of these large mammals, feeding entirely on plankton, is impressive.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">There is a pronounced tendency for zooplankton to perform daily (or diurnal) vertical <a href="https://www.britannica.com/science/migration-animal" class="md-crosslink " data-show-preview="true">migrations</a> in both lakes and the sea. This migratory behaviour varies with stages in the <a href="https://www.britannica.com/science/life-cycle" class="md-crosslink " data-show-preview="true">life cycle</a>, <a href="https://www.britannica.com/science/season" class="md-crosslink " data-show-preview="true">seasons</a> of the year, <a href="https://www.britannica.com/science/latitude" class="md-crosslink " data-show-preview="true">latitude</a>, hydrographic structure, and meteorological conditions. Generally, the animals <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="ascend" href="https://www.britannica.com/dictionary/ascend" data-type="EB">ascend</a> toward the surface at sunset from daytime depths. At midnight, if there is no optical stimulus (e.g., the <a href="https://www.britannica.com/place/Moon" class="md-crosslink " data-show-preview="true">Moon</a> or artificial light), some animals return to the daytime depths and then approach the surface once again just before dawn. As the sun rises, all descend to their daytime level.</p><span class="marker MOD8 mod-inline"></span></section> <span class="marker h4"></span><section data-level="1" id="ref283874"><h2 class="h1"><span id="ref183057"></span><a href="https://www.britannica.com/science/bacteria" class="md-crosslink " data-show-preview="true">Bacteria</a> and <span id="ref183058"></span><a href="https://www.britannica.com/science/fungus" class="md-crosslink " data-show-preview="true">fungi</a></h2> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">Bacteria and <a href="https://www.britannica.com/science/fungus" class="md-crosslink " data-show-preview="true">fungi</a> found in water belong by definition to plankton, but, because of special techniques required for sampling and identification, they usually are considered separately. These organisms are important in the transformation of dead organic materials to inorganic plant <a href="https://www.britannica.com/science/nutrient" class="md-crosslink " data-show-preview="true">nutrients</a>. Some of these marine and freshwater microorganisms (including blue-green algae) fix molecular <a href="https://www.britannica.com/science/nitrogen" class="md-crosslink " data-show-preview="true">nitrogen</a> from water containing <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="dissolved" href="https://www.britannica.com/dictionary/dissolved" data-type="EB">dissolved</a> air, forming <a href="https://www.britannica.com/science/ammonia" class="md-crosslink " data-show-preview="true">ammonia</a> or related nutrients important for phytoplankton growth. Although bacteria and fungi always are found in water samples, a peculiar situation exists in the <a href="https://www.britannica.com/place/Black-Sea" class="md-crosslink " data-show-preview="true">Black Sea</a>, where water below 130–180 metres (425–590 feet) contains <a href="https://www.britannica.com/science/hydrogen-sulfide" class="md-crosslink " data-show-preview="true">hydrogen sulfide</a> and no <a href="https://www.britannica.com/science/oxygen" class="md-crosslink " data-show-preview="true">oxygen</a>. Under these conditions only bacteria are found.</p><span class="marker MOD9 mod-inline"></span></section> <span class="marker h5"></span><section data-level="1" id="ref283875"><h2 class="h1">Plankton and biological productivity</h2> <span class="marker PREMOD10 mod-inline"></span><p class="topic-paragraph">The productivity of an area depends on currents and the availability of nutrients. Currents that flow near continents are important to plankton production in an area. The <span id="ref183059"></span><a href="https://www.britannica.com/place/California-Current" class="md-crosslink " data-show-preview="true">California Current</a> (a continuation of the <a href="https://www.britannica.com/place/Kuroshio" class="md-crosslink " data-show-preview="true">Kuroshio</a> from Japan) causes an outland transport of water and <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="combines" href="https://www.britannica.com/dictionary/combines" data-type="EB">combines</a> with a compensating nutrient-rich current along the California coast to make this area highly productive. The same situation exists along the west coast of southern Africa, which is influenced by the <a href="https://www.britannica.com/place/Benguela-Current" class="md-crosslink " data-show-preview="true">Benguela Current</a>, and off the west coast of <a href="https://www.britannica.com/place/South-America" class="md-crosslink autoxref " data-show-preview="true">South America</a>, influenced by the <a href="https://www.britannica.com/place/Peru-Current" class="md-crosslink " data-show-preview="true">Peru Current</a>.</p><div class="one-good-fact-module"> </div><span class="marker MOD10 mod-inline"></span> <span class="marker PREMOD11 mod-inline"></span><p class="topic-paragraph">In the sea an adequate supply of nutrients, including <a href="https://www.britannica.com/science/carbon-dioxide" class="md-crosslink " data-show-preview="true">carbon dioxide</a>, enables phytoplankton and benthic algae to transform the <a href="https://www.britannica.com/science/light" class="md-crosslink autoxref " data-show-preview="true">light</a> energy of the <a href="https://www.britannica.com/place/Sun" class="md-crosslink " data-show-preview="true">Sun</a> into energy-rich chemical components through <a href="https://www.britannica.com/science/photosynthesis" class="md-crosslink " data-show-preview="true">photosynthesis</a>. The bottom-dwelling algae are responsible for about 2 percent of the <a href="https://www.britannica.com/science/primary-productivity" class="md-crosslink autoxref " data-show-preview="true">primary production</a> in the ocean, and the remaining 98 percent is attributable to phytoplankton. Most phytoplankton serves as food for zooplankton, but some is carried below the light zone. After death, this phytoplankton undergoes chemical mineralization, bacterial breakdown, or <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="transformation" href="https://www.britannica.com/dictionary/transformation" data-type="EB">transformation</a> into sediments. Phytoplankton production usually is greatest from 5 to 10 metres (16 to 33 feet) below the surface of the water. High <a href="https://www.britannica.com/science/luminous-intensity" class="md-crosslink autoxref " data-show-preview="true">light intensity</a> and the lack of <a href="https://www.britannica.com/science/nutrient" class="md-crosslink autoxref " data-show-preview="true">nutrient</a> in the regions above a depth of 5 metres may be the causes for suboptimal photosynthesis. Although bacteria are found at all depths, they are most abundant either immediately below great phytoplankton populations or just above the bottom.</p><span class="marker MOD11 mod-inline"></span><span class="md-signature"><a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a></span> </section> <span class="md-signature">This article was most recently revised and updated by <a href="/editor/Adam-Augustyn/6394">Adam Augustyn</a>.</span><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article></div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":1,"pageId":463121,"pageLength":1372,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/topic-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"B","adLeg":"B","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"LARGE","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Plankton | Definition, Characteristics, Types, Diet, Size, & Facts | Britannica