View source for Daphnia

{{short description|Genus of crustaceans}}
{{Automatic taxobox
| oldest_fossil = Cretaceous
| image = Daphnia pulex.png
| image_caption = ''[[Daphnia pulex]]''
| taxon = Daphnia
| authority = [[Otto Friedrich Müller|Müller]], 1785
| display_parents = 4
| synonyms = *''Cephaloxus'' {{small|(Sars, 1861)}}
*''Dactylura'' {{small|(Brady, 1898)}}
*''Daphniopsis'' {{small|(Sars, 1903)}}
*''Hyalodaphnia'' {{small|(Schoedler, 1866)}}
*''Leiodaphnia'' {{small|(Dybowski & Grochowski, 1895)}}
| synonyms_ref = &nbsp;<ref name="Kotov">{{cite web |url=http://fada.biodiversity.be/CheckLists/Crustacea-Cladocera.pdf |title=Crustacea-Cladocera checkList |date=March 2, 2012 |author1=A. Kotov |author2=L. Forró |author3=N. M. Korovchinsky |author4=A. Petrusek |work=World checklist of freshwater Cladocera species |publisher=Belgian Biodiversity Platform |access-date=October 29, 2012}}</ref>
| subdivision_ranks = Subgenera
| subdivision = *''[[Daphnia occidentalis|Australodaphnia]]'' {{small|(Colbourne ''et al.'', 2006)}}
*''[[Ctenodaphnia]]'' {{small|(Dybowski & Grochowski, 1895)}}
*''[[Daphnia (Daphnia)|Daphnia]]'' {{small|(O. F. Müller, 1785)}}
| diversity = > 200 spp.
| diversity_link = List of Daphnia species
}}

'''''Daphnia''''' is a genus of small [[plankton]]ic [[crustacean]]s,  {{cvt|0.2|-|6.0|mm|2}} in length. ''Daphnia'' are members of the [[Order (biology)|order]] [[Anomopoda]], and are one of the several small aquatic crustaceans commonly called [[water flea]]s because their [[Saltation (gait)|saltatory]] swimming style resembles the movements of [[flea]]s. ''Daphnia'' spp. live in various aquatic environments ranging from [[acid]]ic [[swamp]]s to [[Fresh water|freshwater]] lakes and ponds.

The two most commonly found species of ''Daphnia'' are ''[[Daphnia pulex|D.&nbsp;pulex]]'' (small and most common) and ''[[Daphnia magna|D.&nbsp;magna]]'' (large). They are often associated with a related genus in the order Cladocera: ''[[Moina]]'', which is in the [[Moinidae]] group instead of the [[Daphniidae]], and is much smaller than ''D.&nbsp;pulex'' (roughly half the maximum length). 

== Appearance and characteristics ==
[[File:Daphnia Heartbeat.ogg|thumb|left|The beating heart of ''Daphnia'' under the microscope]]
The body of a ''Daphnia'' species is usually {{convert|1|-|5|mm|abbr=on}} long,<ref name="Ebert">{{cite book |author=Dieter Ebert |year=2005 |title=Ecology, Epidemiology, and Evolution of Parasitism in ''Daphnia'' |chapter=Introduction to ''Daphnia'' biology |location=Bethesda, MD |publisher=National Center for Biotechnology Information |isbn=978-1-932811-06-3 |url=https://www.ncbi.nlm.nih.gov/books/NBK2042/}}</ref> and is divided into [[Segmentation (biology)|segments]], although this division is not visible.<ref name="Oneida">{{cite web |url=http://www.seagrant.sunysb.edu/OLI/olei-daphnia.htm |title=''Daphnia'' |work=Oneida Lake Education Initiative |publisher=[[Stony Brook University]] |access-date=October 9, 2013}}</ref> The head is fused, and is generally bent down towards the body with a visible notch separating the two. In most species, the rest of the body is covered by a [[carapace]], with a ventral gap in which the five or six pairs of legs lie.<ref name="Oneida"/> The most prominent features are the [[compound eye]]s, the second [[antenna (biology)|antennae]], and a pair of abdominal [[seta]]e.<ref name="Oneida"/> In many species, the carapace is translucent or nearly so, so they make excellent subjects for the [[microscope]], as one can observe the beating heart.<ref name="Oneida"/>
 
Even under relatively low-power [[microscopy]], the feeding mechanism can be observed, with immature young moving in the brood pouch; moreover, the eye being moved by the [[ciliary muscle]]s can be seen, as well as [[blood cell]]s being pumped around the [[circulatory system]] by the simple heart.<ref name="Oneida"/> The heart is at the top of the back, just behind the head, and the average heart rate is about 180&nbsp;bpm under normal conditions. ''Daphnia'' spp., like many animals, are prone to [[ethanol|alcohol]] intoxication as well as caffeine effects, which makes them excellent subjects for studying the effects of the depressant and stimulants on the [[nervous system]] due to the translucent exoskeleton and the visibly altered heart rate. They are tolerant of being observed live under a coverslip and appear to suffer no harm when returned to open water.<ref name="Oneida"/> This experiment can also be performed using [[nicotine]], or [[Epinephrine|adrenaline]], each producing an increase in the heart rate. {{Citation needed|reason=Literature with evidence required|date=October 2018}}

Due to its intermediate size, ''Daphnia'' spp. use both diffusion and circulatory methods, producing [[hemoglobin]] in low-oxygen environments.<ref name="Hemoglobin Sometimes">{{Cite journal |url=http://jeb.biologists.org/content/207/25/i.2 |last=van Bergen |first=Yfke |title=Total Recall |date=2004 |journal=Journal of Experimental Biology |volume=207 |issue=25 |page=i |doi=10.1242/jeb.01364 |bibcode=2004JExpB.207R...1V |s2cid=219208202 |access-date=2018-04-11|url-access=subscription }}</ref>

==Systematics and evolution==
{{main|List of Daphnia species}}
''Daphnia'' is a large genus – comprising over 200 species – belonging to the cladoceran family Daphniidae.<ref name="Kotov"/> It is subdivided into several subgenera (''[[Daphnia (Daphnia)|Daphnia]]'', ''[[Daphnia occidentalis|Australodaphnia]]'', ''[[Ctenodaphnia]]''), but the division has been controversial and is still in development. Each subgenus has been further divided into a number of [[species complex]]es. The understanding of species boundaries has been hindered by phenotypic plasticity, hybridization, intercontinental introductions, and poor taxonomic descriptions.<ref>{{cite journal |author1=Niles Lehman |author2=Michael E. Pfrender |author3=Phillip A. Morin |author4=Teresa J. Crease |author5=Michael Lynch |year=1995 |title=A hierarchical molecular phylogeny within the genus ''Daphnia'' |journal=[[Molecular Phylogenetics and Evolution]] |pmid=8747296 |volume=4 |issue=4 |pages=395–407 |doi=10.1006/mpev.1995.1037|bibcode=1995MolPE...4..395L }}</ref><ref>{{cite journal|author1=Derek J. Taylor |author2=Paul D. N. Hebert |author3=John K. Colbourne |year=1996 |title=Phylogenetics and evolution of the ''Daphnia longispina'' group (Crustacea) based on 12S rDNA sequence and allozyme variation |journal=[[Molecular Phylogenetics and Evolution]] |volume=5 |pmid=8744763 |issue=3 |pages=495–510 |url=http://www.buffalo.edu/~djtaylor/publications_files/Tayloretal1996.pdf |archive-url=https://wayback.archive-it.org/all/20070418040641/http://www.buffalo.edu/~djtaylor/publications_files/Tayloretal1996.pdf |archive-date=2007-04-18 |doi=10.1006/mpev.1996.0045 |bibcode=1996MolPE...5..495T }}</ref><ref>{{cite journal |author1=Sarah J. Adamowicz |author2=Paul D. N. Hebert |author3=María Christina Marinone |year=2004 |title=Species diversity and endemism in the ''Daphnia'' of Argentina: a genetic investigation |journal=[[Zoological Journal of the Linnean Society]] |volume=140 |pages=171–205 |doi=10.1111/j.1096-3642.2003.00089.x |issue=2|doi-access=free |hdl=20.500.12110/paper_00244082_v140_n2_p171_Adamowicz |hdl-access=free }}</ref> Modern members of ''Daphnia'' belonging to the subgenera ''Daphnia'' and ''Ctenodaphnia'' are known since the [[Cretaceous]], though the genus likely originated prior to the beginning of the Cretaceous.<ref>{{Cite journal|last1=Kotov|first1=Alexey A|last2=Taylor|first2=Derek J|date=19 May 2011|title=Mesozoic fossils (>145 Mya) suggest the antiquity of the subgenera of Daphniaand their coevolution with chaoborid predators|journal=BMC Evolutionary Biology|language=en|volume=11|issue=1|page=129|doi=10.1186/1471-2148-11-129|issn=1471-2148|pmc=3123605|pmid=21595889 |bibcode=2011BMCEE..11..129K |doi-access=free }}</ref><ref>{{Cite journal|last1=Van Damme|first1=Kay|last2=Kotov|first2=Alexey A.|date=December 2016|title=The fossil record of the Cladocera (Crustacea: Branchiopoda): Evidence and hypotheses|url=https://linkinghub.elsevier.com/retrieve/pii/S0012825216303701|journal=Earth-Science Reviews|language=en|volume=163|pages=162–189|doi=10.1016/j.earscirev.2016.10.009|bibcode=2016ESRv..163..162V|url-access=subscription}}</ref> There are numerous poorly studied and cryptic species among crustaceans of the genus ''Daphnia''.<ref>
{{ Cite journal | year = 2021 | publisher = [[John Wiley & Sons Ltd]] | issue = 6 | volume = 30 | department = INVITED REVIEWS AND SYNTHESES | first2 = Melania | first1 = Tiffany | last2 = Cristescu | last1 = Chin | pages = 1398–1418 | title = Speciation in ''Daphnia'' | journal = [[Molecular Ecology]] | issn = 0962-1083 | doi = 10.1111/mec.15824 | pmid = 33522056 | bibcode = 2021MolEc..30.1398C | s2cid = 225026378| doi-access = free }}

This review cites this research.

{{Cite journal |last1=Kotov |first1=Alexey A. |last2=Garibian |first2=Petr G. |last3=Bekker |first3=Eugeniya I. |last4=Taylor |first4=Derek J. |last5=Karabanov |first5=Dmitry P. |date=2020-06-17 |title=A new species group from the ''Daphnia curvirostris'' species complex (Cladocera: Anomopoda) from the eastern Palaearctic: taxonomy, phylogeny and phylogeography |journal=[[Zoological Journal of the Linnean Society]] |volume=191 |issue=3 |pages=772–822 |doi=10.1093/zoolinnean/zlaa046 |issn=0024-4082 |doi-access=free}}
</ref>

==Ecology and behaviour==
''Daphnia'' species are normally [[r/K selection theory|''r''-selected]], meaning that they invest in early reproduction, so have short lifespans. An individual ''Daphnia''  lifespan depends on factors such as [[temperature]] and the abundance of [[predator]]s, but can be 13–14 months in some cold, [[oligotrophic]], fish-free lakes.<ref name="Pietrzak">{{cite journal |author1=Barbara Pietrzak |author2=Anna Bednarska |author3=Magdalena Markowska |author4=Maciej Rojek |author5=Ewa Szymanska |author6=Miroslaw Slusarczyk |year=2013 |title=Behavioural and physiological mechanisms behind extreme longevity in ''Daphnia'' |journal=[[Hydrobiologia]] |volume=715 |issue=1 |pages=125–134 |doi=10.1007/s10750-012-1420-6|bibcode=2013HyBio.715..125P |doi-access=free }}</ref> In typical conditions, however, the lifecycle is much shorter, not usually exceeding 5–6 months.<ref name="Pietrzak"/>

''Daphnia'' spp. are typically [[filter feeder]]s, ingesting mainly unicellular [[algae]] and various sorts of organic detritus including [[protist]]s and [[bacteria]].<ref name=Ebert /><ref name="Gliwicz">{{cite book |author=Z. Maciej Gliwicz |year=2008 |chapter=Zooplankton |pages=461–516 |editor1=Patrick O'Sullivan |editor2=C. S. Reynolds |title=The Lakes Handbook: Limnology and Limnetic Ecology |publisher=[[John Wiley & Sons]] |isbn=978-0-470-99926-4 |chapter-url=https://books.google.com/books?id=IEea4VHsgXwC&pg=PA466}}</ref> Beating of the legs produces a constant current through the carapace, which brings such material into the digestive tract. The trapped food particles are formed into a food ''bolus'' which then moves down the digestive tract until voided through the anus located on the ventral surface of the terminal appendage.<ref name="Gliwicz"/> The second and third pairs of legs are used in the organisms' filter-feeding, ensuring large, unabsorbable particles are kept out, while the other sets of legs create the stream of water rushing into the organism.<ref name="Gliwicz"/>

[[File:CladoceraTrunkLimbs.png|thumb|upright=0.7|left| The five trunk limbs, used in filter feeding]]

Swimming is powered mainly by the second set of antennae, which are larger in size than the first set.<ref name="Dodson">{{cite book |author1=Stanley L. Dodson |author2=Carla E. Cáceres |author3=D. Christopher Rogers |year=2009 |chapter=Cladocera and other Branchiopoda |pages=773–828 |editor1=James H. Thorp |editor2=Alan P. Covich |title=Ecology and Classification of North American Freshwater Invertebrates |edition=3rd |publisher=[[Academic Press]] |isbn=978-0-08-088981-8 |chapter-url=https://books.google.com/books?id=gKHmGKqMrgQC&pg=PA776}}</ref> The action of this second set of antennae is responsible for the jumping motion.<ref name="Dodson"/>

''Daphnia'' spp. are known to show behavioral changes or modifications to their morphology in the presence of predator kairomones (chemical signals), including larger size at hatching, increased bulkiness, and the development of "neck-teeth". For example, juveniles of ''D. pulex'' and ''D. magna'' have a larger size after hatching, along with developing neck-teeth at the back of the head, when in the presence of ''[[Chaoborus]]'' kairomones. These morphological defenses have shown to reduce mortality due to ''Chaoborus'' predation, which is a gape-limited predator. Chitin-related genes (deacetylases) are thought to play an important part in the expression/development of these morphological defenses in ''Daphnia''. Chitin-modifying enzymes (chitin deacetylases) have been shown to catalyse the N-deacetylation of chitin to influence the protein-binding affinity of these chitin filaments.<ref>{{Cite journal|last=Christjani|first=Mark|date=2016|title=Phenotypic plasticity in three Daphnia genotypes in response to predator kairomone: evidence for an involvement of chitin deacetylases.|url=https://www.researchgate.net/publication/298897997|journal=The Journal of Experimental Biology|volume=219|issue=Pt 11|pages=1697–704|article-number=jeb.133504 |doi=10.1242/jeb.133504|doi-broken-date=22 October 2025 |pmid=26994174|s2cid=36557263|doi-access=free}}</ref> In case of ''D. magna'' it was shown that the response to different kairomones also differ: While the presence of fish kairomones up-regulated one specific gene in the folding of proteins, whereas ''Chaoborus'' kairomone down-regulated the same gene. Based on this the response is a reduction of size at first reproduction in response to kairomones from fish whereas it shows increased size when confronted with larvae of ''Chaoborus''.<ref name="Schwarzenberger et al. 2009">{{Cite journal|last1=Schwarzenberger|first1=Anke|last2=Courts|first2=Cornelius|last3=von Elert|first3=Eric|date=2009|title=Target gene approaches: Gene expression in Daphnia magna exposed to predator-borne kairomones or to microcystin-producing and microcystin-free Microcystis aeruginosa.|journal=BMC Genomics|volume=10|issue=527|page=527 |doi=10.1186/1471-2164-10-527|pmid= 19917101|s2cid= |doi-access=free|pmc=2784803}}{{Creative Commons text attribution notice|cc=by2|from this source=yes}}</ref> With the same publication it was shown that genes for [[glyceraldehyde 3-phosphate dehydrogenase]] and [[ubiquitin]] conjugating enzyme were up-regulated in the presence of [[microcystins]] in the food of ''D. magna'' and with this the enzymes of [[glycolysis]] and [[protein catabolism]] are significantly upgregulated when daphnids ingest these toxins.<ref name="Schwarzenberger et al. 2009" />

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==Life cycle==
Most ''Daphnia'' species have a [[biological life cycle|lifecycle]] based on "cyclical parthenogenesis", alternating between [[parthenogenesis|parthenogenetic]] (asexual) and [[sexual reproduction]].<ref name="Ebert"/> For most of the growth season, females reproduce asexually. They produce a brood of diploid [[egg (biology)|eggs]] every time they [[ecdysis|molt]]; these broods can contain as few as one or two eggs in smaller species, such as ''[[Daphnia cucullata|D.&nbsp;cucullata]]'', but can be over 100 in larger species, such as ''[[Daphnia magna|D.&nbsp;magna]]''. Under typical conditions, these eggs hatch after a day, and remain in the female's brood pouch for around three days (at 20&nbsp;°C). They are then released into the water, and pass through a further four to six  [[instar]]s over 5–10 days (longer in poor conditions) before reaching an age where they are able to reproduce.<ref name="Ebert"/> The asexually produced offspring are typically female.

[[File:DaphniaMagna LifeCycle DVizoso.svg|thumb|upright=1.75|right| {{center|Cyclic parthenogenesis in the cladoceran ''[[Daphnia magna]]''}}]]

{|
|+
|-
| {{multiple image
 | align = left
 | direction = vertical
 | width     = 180
 | image1    = Daphnia magna-female adult.jpg
 | alt1      = 
 | caption1  = {{center|Female ''Daphnia'' with eggs}}
 | image2    = Daphnid GLERL 1.jpg
 | alt2      = 
 | caption2  = Resting egg pouch (''ephippium'') and the juvenile daphnid that just has hatched from it
}}
! [[File:Rodząca dafnia.jpg|thumb|264px| {{center|''Daphnia'' giving birth}}]]
|}

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Towards the end of the growing season, however, the mode of reproduction changes, and the females produce tough "resting eggs" or "winter eggs".<ref name="Ebert"/> When environmental conditions deteriorate (e.g. crowding), some of the asexually produced offspring develop into males.<ref name="Ebert"/> The females start producing haploid sexual eggs, which the males [[fertilisation|fertilise]]. In species without males, resting eggs are also produced asexually and are diploid. In either case, the resting eggs are protected by a hardened coat (consisting of two [[chitin]]ous plates) called the ''ephippium'', and are cast off at the female's next molt. The ephippia can withstand periods of extreme cold, drought, or poor food availability, and hatch – when conditions improve – into females (They are close to being classed as extremophiles) .<ref name="Ebert"/> 

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==Parasites==
[[File:Pasteuria ramosa LifeCycle DVizoso.svg|thumb|upright=2|left| Life cycle of ''[[Pasteuria ramosa]]'' a bacterial parasite of the cladoceran ''[[Daphnia magna]]''.]]

The diagram on the left shows the lifecycle of ''[[Pasteuria ramosa]]'', a bacterial parasite of ''Daphnia''. Susceptible hosts acquire the infection from spores in the sediment or in suspension. The parasite develops mainly in the host's body cavity and muscle tissue, increasing in density and eventually expanding to occupy the entire host. Typical effects on the host are sterility and gigantism. Spores are released mainly after the host dies and sinks to the substrate, and sometimes directly to the water via clumsy predation.

[[File:Daphnia magna infected with the Pasteuria ramosa.jpg|thumb|upright=0.8|right| ''D. magna'' infected with ''Pasteuria ramosa'']]

{{clear}}

==Conservation==
Several ''Daphnia'' species are considered [[threatened]]. These are listed as vulnerable by [[World Conservation Union|IUCN]]: ''[[Daphnia nivalis]]'', ''[[Daphnia coronata]]'', ''[[Daphnia occidentalis]]'', and ''[[Daphnia jollyi]]''. Some species are [[halophile]]s, and can be found in [[hypersaline lake]] environments, an example of which is the [[Makgadikgadi Pan]].<ref>{{cite web |author=C. Michael Hogan |year=2008 |title=''Makgadikgadi'' |work=The Megalithic Portal |url=http://www.megalithic.co.uk/article.php?sid=22373&mode=&order=0}}</ref>

==Uses==
''Daphnia'' spp. are a popular live food in tropical and marine [[fish keeping]]. They are often fed to tadpoles or small species of amphibians such as the [[African dwarf frog]] (''Hymenochirus boettgeri'').

''Daphnia'' spp. are used in scientific studies as a [[model organism]].<ref name="Altshuler-et-al-2011">{{cite journal | last1=Altshuler | first1=Ianina | last2=Demiri | first2=Bora | last3=Xu | first3=Sen | last4=Constantin | first4=Anna | last5=Yan | first5=Norman D. | last6=Cristescu | first6=Melania E. | title=An Integrated Multi-Disciplinary Approach for Studying Multiple Stressors in Freshwater Ecosystems: ''Daphnia'' as a Model Organism | journal=Integrative and Comparative Biology | publisher=[[Society for Integrative and Comparative Biology]] ([[Oxford University Press|OUP]]) | volume=51 | issue=4 | date=2011-08-27 | issn=1557-7023 | doi=10.1093/icb/icr103 | pages=623–633 | s2cid=205115549 | pmid=21873644| doi-access=free }}</ref> They may be used in certain  environments to test the effects of [[toxin]]s on an [[ecosystem]], which makes them an [[indicator species|indicator genus]], particularly useful because of their short lifespans and reproductive capabilities. Because they are nearly transparent, their internal organs are easy to study in live specimens (e.g. to study the effect of temperature on the heart rate of these [[ectothermic]] organisms). Environmental toxicological testing may be undertaken with researchers assessing mortality rates or metabolic perturbations to evaluate ecological impacts.<ref>{{Cite journal |last1=Oliveira Pereira |first1=Erico A. |last2=Labine |first2=Lisa M. |last3=Kleywegt |first3=Sonya |last4=Jobst |first4=Karl J. |last5=Simpson |first5=André J. |last6=Simpson |first6=Myrna J. |date=2023-04-01 |title=Daphnia magna sub-lethal exposure to phthalate pollutants elicits disruptions in amino acid and energy metabolism |url=https://www.sciencedirect.com/science/article/pii/S0166445X23000395 |journal=Aquatic Toxicology |volume=257 |article-number=106432 |doi=10.1016/j.aquatox.2023.106432 |pmid=36841068 |bibcode=2023AqTox.25706432O |issn=0166-445X|url-access=subscription }}</ref> ''Daphnia'' is also commonly used for experiments to test [[climate change]] aspects, as UVB that seriously damages [[zooplankton]] species (e.g. decrease feeding activity<ref>{{Cite journal|last1=Fernández|first1=Carla Eloisa|last2=Rejas|first2=Danny|date=2017-04-05|title=Effects of UVB radiation on grazing of two cladocerans from high-altitude Andean lakes|journal=PLOS ONE|volume=12|issue=4|article-number=e0174334|doi=10.1371/journal.pone.0174334|pmid=28379975|issn=1932-6203|pmc=5381789|bibcode=2017PLoSO..1274334F|doi-access=free}}</ref>).

Because of their thin membranes, which allow [[drug]]s to be absorbed, they are used to monitor the effects of certain drugs, such as adrenaline or capsaicin, on the heart.

==Invasive species==
[[File:Cercopagidae GLERL 1.jpg|thumb|[[Fishhook waterflea]] (above) and ''[[Bythotrephes longimanus]]'' (spiny water flea) (below)]]

Some species have developed permanent defenses against fish eating them, such as spines and long hooks on the body, which also cause them to become entangled on fishing lines and cloud water with their high numbers. Species such as ''[[Daphnia lumholtzi]]''<ref>USGS: ''[https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=164 Nonindigenous Aquatic Species: Daphnia lumholtzi]''</ref><ref>Center for Freshwater Biology - University of New Hampshire: ''[http://cfb.unh.edu/cfbkey/html/Organisms/CCladocera/FDaphnidae/GDaphnia/Daphnia_lumholtzi/daphnialumholtzi.html Daphnia lumholtzi]''</ref><ref>ISSG: Global Invasive Species Database: ''[http://www.issg.org/database/species/ecology.asp?si=998 Daphnia lumholtzi (crustacean)] {{Webarchive|url=https://web.archive.org/web/20160304195733/http://www.issg.org/database/species/ecology.asp?si=998 |date=2016-03-04 }}''</ref><ref>James A. Stoeckel, Illinois Natural History Survey: ''[http://www.iisgcp.org/catalog/downlds_09/daph.pdf Daphnia lumholtzi: The Next Great Lakes Exotic?] {{Webarchive|url=https://web.archive.org/web/20161220225152/http://www.iisgcp.org/catalog/downlds_09/daph.pdf |date=2016-12-20 }}''</ref> (native to east Africa, the Asian subcontinent of India, and east Australia) have these characteristics and great care should be taken to prevent them from spreading further in North American waters.

Some species of ''Daphnia'' native to North America can develop sharp spines at the end of their bodies and helmet-like structures on their heads when they detect predators,<ref>Elizabeth A. Colburn (2004), ''Vernal Pools: Natural History and Conservation'', page 118 of paperback second edition from 2008</ref><ref>Patrick Lavens and Patrick Sorgeloos, ''Manual on the Production and Use of Live Food for Aquaculture: [http://www.fao.org/docrep/003/w3732e/w3732e0x.htm#6.1.%20Daphnia%20and%20Moina Daphnia and Moina]''</ref> but this is overall temporary for such species and they do not completely overwhelm or discourage native predators from eating them. While ''Daphnia'' spp. are an important base of the food chain in freshwater lakes (and vernal pools), they become a nuisance when they are unable to be eaten by native macroscopic predators, and some concern exists that the original spineless and hookless water fleas and spp. end up outcompeted by the invasive ones. (This may not be the case, however, and the new invaders may mostly be a tangling and clogging nuisance.)

In the water bodies of the world, at least 15 species of ''Daphnia'' and hybrids are non-native species, many of which pose a great threat to aquatic ecosystems.<ref>{{Cite journal |last1=Kotov |first1=Alexey A. |last2=Karabanov |first2=Dmitry P. |last3=Van Damme |first3=Kay |date=2022-09-09 |title=Non-Indigenous Cladocera (Crustacea: Branchiopoda): From a Few Notorious Cases to a Potential Global Faunal Mixing in Aquatic Ecosystems |journal=Water|volume=14 |issue=18 |page=2806 |doi=10.3390/w14182806 |bibcode=2022Water..14.2806K |issn=2073-4441 |doi-access=free}}</ref>

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==See also==
{{Portal|Crustaceans}}
*[[List of Daphnia species|List of ''Daphnia'' species]]
*[[Rotifer]]

==References==
{{Reflist|32em}}

==External links==
{{Commons category|Daphnia}}

* {{Wikispecies-inline|Daphnia|''Daphnia''}}
*[https://web.archive.org/web/20050124131431/http://daphnia.cgb.indiana.edu/ ''Daphnia'' Genomics Consortium]
*[http://www.caudata.org/daphnia/#anatomy ''Daphnia'': An Aquarist's Guide]
*[https://web.archive.org/web/20070928142228/http://www.waterflea.org/ Waterflea.org: a Community resource for cladoceran biology]
*[http://www.geochembio.com/biology/organisms/daphnia/ ''Daphnia'' spp.: taxonomy, facts, life cycle, references at GeoChemBio] {{Webarchive|url=https://web.archive.org/web/20210410195742/http://www.geochembio.com/biology/organisms/daphnia/ |date=2021-04-10 }}

{{Taxonbar|from=Q269354}}
{{Authority control}}

[[Category:Cladocera]]
[[Category:Branchiopoda genera]]
[[Category:Fishkeeping]]
[[Category:Freshwater crustaceans]]
[[Category:Freshwater crustaceans of Europe]]
[[Category:Freshwater crustaceans of Asia]]
[[Category:Freshwater crustaceans of Africa]]
[[Category:Articles containing video clips]]
[[Category:Taxa named by Otto Friedrich Müller]]