View source for Seagrass

{{Short description|Plants that grow in marine environments}}
{{Hatnote|Not to be confused with [[seaweed]], plant-like algae, or with [[Ammophila (plant)|beachgrass]], a terrestrial plant}}
{{use British English|date=August 2021}}
{{use dmy dates|date=August 2021}}
{{Automatic taxobox
| name = Seagrasses
| fossil_range = {{Geological range|70|0|earliest=100|latest=0}}
| image = Zostera marina - National Museum of Nature and Science, Tokyo - DSC07663.JPG
| image_caption = ''[[Zostera marina]]'' – the most abundant seagrass species in the Northern Hemisphere
| image_upright = 1.15
| taxon = Alismatales
| authority = [[Robert Brown (Scottish botanist from Montrose)|R.Br.]] ''ex'' [[Friedrich von Berchtold|Bercht.]] & [[Jan Svatopluk Presl|J.Presl]]
| subdivision_ranks = Families
| subdivision = See ''[[#Taxonomy|Taxonomy]]''
}}

'''Seagrasses''' are the only [[flowering plant]]s which grow in [[marine (ocean)|marine]] environments. There are about 60 species of fully marine seagrasses which belong to four [[Family (biology)|families]] ([[Posidoniaceae]], [[Zosteraceae]], [[Hydrocharitaceae]] and [[Cymodoceaceae]]), all in the order [[Alismatales]] (in the clade of [[monocotyledon]]s).<ref>{{Cite journal |last=Tomlinson and Vargo |date=1966 |title=On the morphology and anatomy of turtle grass, Thalassia testudinum (Hydrocharitaceae). I. Vegetative Morphology. |journal=Bulletin of Marine Science |volume=16 |pages=748–761 |url=https://www.ingentaconnect.com/contentone/umrsmas/bullmar/1966/00000016/00000004/art00007#}}</ref> Seagrasses evolved from [[terrestrial plant]]s which recolonised the ocean 70 to 100 million years ago.

The name ''seagrass'' stems from the many species with long and narrow [[Leaf|leaves]], which grow by [[rhizome]] extension and often spread across large "[[Seagrass meadow|meadows]]" resembling [[grassland]]; many species superficially resemble terrestrial [[grass]]es of the family [[Poaceae]].

Like all [[autotrophic]] plants, seagrasses [[photosynthesize]], in the submerged [[photic zone]], and most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. Most species undergo submarine [[pollination]] and complete their life cycle underwater. While it was previously believed this pollination was carried out without pollinators and purely by sea current drift, this has been shown to be false for at least one species, ''[[Thalassia testudinum]]'', which carries out a mixed biotic-abiotic strategy. Crustaceans (such as crabs, ''[[Majidae]] zoae'', ''[[Thalassinidea]] zoea'') and [[syllid]] [[polychaete]] worm larvae have both been found with pollen grains, the plant producing nutritious mucigenous clumps of pollen to attract and stick to them instead of nectar as terrestrial flowers do.<ref>{{cite journal |last1=van Tussenbroek |first1=Brigitta I. |last2=Villamil |first2=Nora |last3=Márquez-Guzmán |first3=Judith |last4=Wong |first4=Ricardo |last5=Monroy-Velázquez |first5=L. Verónica |last6=Solis-Weiss |first6=Vivianne |title=Experimental evidence of pollination in marine flowers by invertebrate fauna |journal=Nature Communications |date=29 September 2016 |volume=7 |issue=1 |pages=12980 |doi=10.1038/ncomms12980 |pmid=27680661 |pmc=5056424 |bibcode=2016NatCo...712980V |language=en |issn=2041-1723}}</ref>

Seagrasses form dense underwater [[seagrass meadow]]s which are among the most productive ecosystems in the world. They function as important [[carbon sink]]s<ref>{{cite web |title=39 Ways to Save the Planet - Sublime Seagrass |url=https://www.bbc.co.uk/sounds/play/m000qx0t |website=BBC Radio 4 |publisher=BBC |access-date=12 February 2022}}</ref> and provide habitats and food for a diversity of [[marine life]] comparable to that of [[coral reef]]s.

==Overview==
Seagrasses are a paraphyletic group of marine [[angiosperm]]s which evolved [[Parallel evolution|in parallel]] three to four times from land plants back to the sea. The following characteristics can be used to define a seagrass species:

* It lives in an [[estuarine]] or in the [[marine environment]], and nowhere else.
* The [[pollination]] takes place underwater with specialized pollen.
* The seeds which are dispersed by both [[biotic component|biotic]] and [[abiotic component|abiotic agents]] are produced underwater.<ref name="Papenbrock2012">{{cite journal |doi=10.5402/2012/103892 |title=Highlights in Seagrasses' Phylogeny, Physiology, and Metabolism: What Makes Them Special? |year=2012 |last1=Papenbrock |first1=Jutta |journal=ISRN Botany |volume=2012 |pages=1–15 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License].</ref> 
* The seagrass species have specialized leaves with a reduced [[cuticle]], an [[epidermis]] which lacks [[stomata]] and is the main [[photosynthetic]] tissue.
* The [[rhizome]] or underground stem is important in [[anchoring]].
* The roots can live in an [[Hypoxia (environmental)|anoxic environment]] and depend on oxygen transport from the leaves and rhizomes but are also important in the [[nutrient]] transfer processes.<ref name="Papenbrock2012" /><ref>Larkum A. W. D., R. J. Orth, and C. M. Duarte (2006) ''Seagrass: Biology, Ecology and Conservation'', Springer, The Netherlands.</ref>

Seagrasses profoundly influence the physical, chemical, and biological environments of coastal waters.<ref name=Papenbrock2012 /> Though seagrasses provide invaluable [[ecosystem service]]s by acting as breeding and nursery ground for a variety of organisms and promote [[commercial fisheries]], many aspects of their physiology are not well investigated. There are 26 species of seagrasses in North American coastal waters.<ref>{{Cite web |title=Seagrasses |url=https://www.nwf.org/Educational-Resources/Wildlife-Guide/Plants-and-Fungi/Seagrasses }}</ref> Several studies have indicated that seagrass habitat is declining worldwide.<ref>{{cite journal |doi=10.1641/0006-3568(2006)56[987:AGCFSE]2.0.CO;2 |issn=0006-3568 |year=2006 |volume=56 |page=987 |title=A Global Crisis for Seagrass Ecosystems |last1=Orth |first1=Robert J. |last2=Carruthers |first2=TIM J. B. |last3=Dennison |first3=William C. |last4=Duarte |first4=Carlos M. |last5=Fourqurean |first5=James W. |last6=Heck |first6=Kenneth L. |last7=Hughes |first7=A. Randall |last8=Kendrick |first8=Gary A. |last9=Kenworthy |first9=W. Judson |last10=Olyarnik |first10=Suzanne |last11=Short |first11=Frederick T. |last12=Waycott |first12=Michelle |last13=Williams |first13=Susan L. |journal=BioScience |issue=12 |s2cid=4936412 |doi-access=free }}</ref><ref name=Waycott2009 /> Ten seagrass species are at elevated risk of extinction (14% of all seagrass species) with three species qualifying as [[Endangered species|endangered]]. Seagrass loss and degradation of seagrass [[biodiversity]] will have serious repercussions for marine biodiversity and the human population that depends upon the resources and ecosystem services that seagrasses provide.<ref>{{cite journal |doi=10.1016/j.biocon.2011.04.010 |title=Extinction risk assessment of the world's seagrass species |year=2011 |last1=Short |first1=Frederick T. |last2=Polidoro |first2=Beth |last3=Livingstone |first3=Suzanne R. |last4=Carpenter |first4=Kent E. |last5=Bandeira |first5=Salomão |last6=Bujang |first6=Japar Sidik |last7=Calumpong |first7=Hilconida P. |last8=Carruthers |first8=Tim J.B. |last9=Coles |first9=Robert G. |last10=Dennison |first10=William C. |last11=Erftemeijer |first11=Paul L.A. |last12=Fortes |first12=Miguel D. |last13=Freeman |first13=Aaren S. |last14=Jagtap |first14=T.G. |last15=Kamal |first15=Abu Hena M. |last16=Kendrick |first16=Gary A. |last17=Judson Kenworthy |first17=W. |last18=La Nafie |first18=Yayu A. |last19=Nasution |first19=Ichwan M. |last20=Orth |first20=Robert J. |last21=Prathep |first21=Anchana |last22=Sanciangco |first22=Jonnell C. |last23=Tussenbroek |first23=Brigitta van |last24=Vergara |first24=Sheila G. |last25=Waycott |first25=Michelle |last26=Zieman |first26=Joseph C. |journal=Biological Conservation |volume=144 |issue=7 |pages=1961–1971 |bibcode=2011BCons.144.1961S |s2cid=32533417 |url=http://psasir.upm.edu.my/id/eprint/22177/1/Extinction%20risk%20assessment%20of%20the%20world.pdf}}</ref><ref name=Papenbrock2012 />

Seagrasses form important [[Marine coastal ecosystem|coastal ecosystems]].<ref>Hemminga, M. A., and Duarte, C. M. eds (2000). “Seagrasses in the human environment,” in Seagrass Ecology (Cambridge: Cambridge University Press), 248–291.</ref> The worldwide endangering of these sea meadows, which provide food and habitat for many [[marine species]], prompts the need for protection and understanding of these valuable resources.<ref name=Pfeifer2020 />

==Evolution==
[[File:Seagrass evolution.png|thumb|upright=2|right| Evolution of seagrass, showing the progression onto land from marine origins, the diversification of land plants and the subsequent return to the sea by the seagrasses]]

Around 140 million years ago, seagrasses evolved from early monocots which succeeded in conquering the marine environment.<ref name=Pfeifer2020 /> [[Monocot]]s are grass and grass-like [[flowering plant]]s (angiosperms), the seeds of which typically contain only one embryonic leaf or [[cotyledon]].<ref>{{cite book |last1=Rudall |first1=Paula J. |title=Developmental Genetics and Plant Evolution |volume=20020544 |author-link=Paula Rudall |last2=Buzgo |first2=Matyas |chapter=Evolutionary history of the monocot leaf |chapter-url=https://www.researchgate.net/publication/260967325 |pages=431–458 |doi=10.1201/9781420024982.ch23 |series=Systematics Association Special Volumes |year=2002 |isbn=978-0-415-25790-9}}, in {{harvtxt|Cronk|Bateman|Hawkins|2002}}</ref>

[[Terrestrial plant]]s evolved perhaps as early as 450 million years ago from a group of [[green algae]].<ref name="Knauth">{{cite journal |first1=L. Paul |last1=Knauth |first2=Martin J. |last2=Kennedy |date=2009 |title=The late Precambrian greening of the Earth |journal=Nature |volume=460 |issue=7256 |pages=728–732 |doi=10.1038/nature08213 |pmid=19587681 |bibcode=2009Natur.460..728K |s2cid=4398942 }}</ref> Seagrasses then evolved from terrestrial plants which migrated back into the ocean.<ref name=":03">{{Cite journal |last=Orth |display-authors=etal |date=2006 |title=A global crisis for seagrass ecosystems |journal=BioScience |volume=56 |issue=12 |pages=987–996 |doi=10.1641/0006-3568(2006)56[987:AGCFSE]2.0.CO;2 |hdl=10261/88476 |s2cid=4936412 |doi-access=free }}</ref><ref name=":13">{{Cite journal |last=Papenbrock |first=J |date=2012 |title=Highlights in seagrass' phylogeny, physiology, and metabolism: what makes them so species? |journal=International Scholarly Research Network |pages=1–15}}</ref> Between about 70 million and 100 million years ago, three independent seagrass lineages ([[Hydrocharitaceae]], [[Cymodoceaceae]] complex, and [[Zosteraceae]]) evolved from a single lineage of the [[monocotyledonous]] flowering plants.<ref>Les, D.H., Cleland, M.A. and Waycott, M. (1997) "Phylogenetic studies in Alismatidae, II: evolution of marine angiosperms (seagrasses) and hydrophily". ''Systematic Botany'' '''22'''(3): 443–463.</ref>

Other plants that colonised the sea, such as [[salt marsh]] plants, [[mangrove]]s, and [[marine algae]], have more diverse evolutionary lineages. In spite of their low species diversity, seagrasses have succeeded in colonising the continental shelves of all continents except Antarctica.<ref>{{Cite journal |doi=10.1641/0006-3568(2006)56[987:AGCFSE]2.0.CO;2 |issn=0006-3568 |year=2006 |volume=56 |page=987 |title=A Global Crisis for Seagrass Ecosystems |last1=Orth |first1=Robert J. |last2=Carruthers |first2=TIM J. B. |last3=Dennison |first3=William C. |last4=Duarte |first4=Carlos M. |last5=Fourqurean |first5=James W. |last6=Heck |first6=Kenneth L. |last7=Hughes |first7=A. Randall |last8=Kendrick |first8=Gary A. |last9=Kenworthy |first9=W. Judson |last10=Olyarnik |first10=Suzanne |last11=Short |first11=Frederick T. |last12=Waycott |first12=Michelle |last13=Williams |first13=Susan L. |journal=BioScience |issue=12 |s2cid=4936412 |doi-access=free }}</ref>

Recent [[DNA sequencing|sequencing]] of the genomes of ''[[Zostera marina]]'' and ''[[Zostera muelleri]]'' has given a better understanding of [[angiosperm]] [[adaptation]] to the sea.<ref name=Lee2016>{{cite journal |doi=10.1104/pp.16.00868 |title=The Genome of a Southern Hemisphere Seagrass Species (Zostera muelleri) |year=2016 |last1=Lee |first1=Hueytyng |last2=Golicz |first2=Agnieszka A. |last3=Bayer |first3=Philipp E. |last4=Jiao |first4=Yuannian |last5=Tang |first5=Haibao |last6=Paterson |first6=Andrew H. |last7=Sablok |first7=Gaurav |last8=Krishnaraj |first8=Rahul R. |last9=Chan |first9=Chon-Kit Kenneth |last10=Batley |first10=Jacqueline |last11=Kendrick |first11=Gary A. |last12=Larkum |first12=Anthony W.D. |last13=Ralph |first13=Peter J. |last14=Edwards |first14=David |journal=Plant Physiology |volume=172 |issue=1 |pages=272–283 |pmid=27373688 |pmc=5074622}}</ref><ref name=Olsen2016>{{cite journal |doi = 10.1038/nature16548|title = The genome of the seagrass Zostera marina reveals angiosperm adaptation to the sea|year = 2016|last1 = Olsen|first1 = Jeanine L.|last2 = Rouzé|first2 = Pierre|last3 = Verhelst|first3 = Bram|last4 = Lin|first4 = Yao-Cheng|last5 = Bayer|first5 = Till|last6 = Collen|first6 = Jonas|last7 = Dattolo|first7 = Emanuela|last8 = De Paoli|first8 = Emanuele|last9 = Dittami|first9 = Simon|last10 = Maumus|first10 = Florian|last11 = Michel|first11 = Gurvan|last12 = Kersting|first12 = Anna|last13 = Lauritano|first13 = Chiara|last14 = Lohaus|first14 = Rolf|last15 = Töpel|first15 = Mats|last16 = Tonon|first16 = Thierry|last17 = Vanneste|first17 = Kevin|last18 = Amirebrahimi|first18 = Mojgan|last19 = Brakel|first19 = Janina|last20 = Boström|first20 = Christoffer|last21 = Chovatia|first21 = Mansi|last22 = Grimwood|first22 = Jane|last23 = Jenkins|first23 = Jerry W.|last24 = Jueterbock|first24 = Alexander|last25 = Mraz|first25 = Amy|last26 = Stam|first26 = Wytze T.|last27 = Tice|first27 = Hope|last28 = Bornberg-Bauer|first28 = Erich|last29 = Green|first29 = Pamela J.|last30 = Pearson|first30 = Gareth A.|journal = Nature|volume = 530|issue = 7590|pages = 331–335|pmid = 26814964|bibcode = 2016Natur.530..331O|s2cid = 3713147|display-authors = 1|doi-access = free}}</ref> During the evolutionary step back to the ocean, different genes have been lost (e.g., [[stomatal]] genes) or have been reduced (e.g., genes involved in the synthesis of [[terpenoid]]s) and others have been regained, such as in genes involved in [[sulfation]].<ref name=Olsen2016 /><ref name=Pfeifer2020 />

[[Genomics|Genome information]] has shown further that adaptation to the marine habitat was accomplished by radical changes in [[#Cell walls|cell wall]] composition.<ref name=Lee2016 /><ref name=Olsen2016 /> However the cell walls of seagrasses are not well understood. In addition to the [[ancestral trait]]s of [[land plant]]s one would expect habitat-driven adaptation process to the new environment characterized by multiple [[Abiotic component|abiotic]] (high amounts of salt) and [[Biotic component|biotic]] (different seagrass grazers and bacterial colonization) stressors.<ref name=Pfeifer2020 /> The cell walls of seagrasses seem intricate combinations of features known from both angiosperm land plants and marine macroalgae with new structural elements.<ref name=Pfeifer2020 />

==Taxonomy==
Today, seagrasses are a polyphyletic group of marine angiosperms with around 60 species in five families ([[Zosteraceae]], [[Hydrocharitaceae]], [[Posidoniaceae]], [[Cymodoceaceae]], and [[Ruppiaceae]]), which belong to the order Alismatales according to the [[Angiosperm Phylogeny Group]] IV System.<ref>{{cite journal |doi = 10.1111/boj.12385|title = An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV|journal = Botanical Journal of the Linnean Society|year = 2016|volume = 181|pages = 1–20| s2cid=7498637 |doi-access = free}}</ref> The genus ''[[Ruppia]]'', which occurs in brackish water, is not regarded as a "real" seagrass by all authors and has been shifted to the Cymodoceaceae by some authors.<ref>{{Cite book|url=https://books.google.com/books?id=sEfKwaRHQj4C&q=In+time+and+with+water.the+systematics+of+alismatid+monocotyledons&pg=PA118|title=Early Events in Monocot Evolution|isbn=9781107244603|last1=Wilkin|first1=Paul|last2=Mayo|first2=Simon J.|date=30 May 2013|publisher=Cambridge University Press }}</ref> The [[APG IV system]] and The Plant List Webpage<ref>The Plant List (2020). Ruppia. Available online at: http://www.theplantlist.org/1.1/browse/A/Ruppiaceae/Ruppia/ (accessed September 22, 2020).</ref>  do not share this family assignment.<ref name=Pfeifer2020>{{cite journal |doi = 10.3389/fpls.2020.588754|title = The Cell Wall of Seagrasses: Fascinating, Peculiar and a Blank Canvas for Future Research|year = 2020|last1 = Pfeifer|first1 = Lukas|last2 = Classen|first2 = Birgit|journal = Frontiers in Plant Science|volume = 11|page = 588754|pmid = 33193541|pmc = 7644952|doi-access = free}} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

{| class="wikitable"
|-
! Family
! width=140px | Image
! width=140px | Genera
! Description
|-
! rowspan=3 | [[Zosteraceae]]
| colspan=3 style="text-align:left; background:#ddf8f8;"| The family '''[[Zosteraceae]]''', also known as the '''seagrass family''', includes two genera containing 14 marine species. It is found in [[temperate]] and [[subtropical]] [[coastal]] waters, with the highest diversity located around Korea and Japan.<br />
{{right|Species subtotal:  &nbsp;}}
|-
| [[File:Tectura palacea 3.jpg|center|140px]]
| ''[[Phyllospadix]]''
| {{right|[[Phyllospadix#Species|6 species]] &nbsp;}}
|-
| [[File:Zostera.jpg|center|140px]]
| ''[[Zostera]]''
| {{right|[[Zostera#Species|16 species]] &nbsp;}}
|-
! rowspan=4 | [[Hydrocharitaceae]]
| colspan=3 style="text-align:left; background:#ddf8f8;"| The family '''[[Hydrocharitaceae]]''', also known as '''tape-grasses''', include [[Elodea canadensis|Canadian waterweed]] and frogbit. The family includes both fresh and marine aquatics, although of the sixteen genera currently recognised, only three are marine.<ref>{{Cite journal |last1=Christenhusz |first1=Maarten J.M. |last2=Byng |first2=James W. |date=2016-05-20 |title=The number of known plants species in the world and its annual increase |url=https://biotaxa.org/Phytotaxa/article/view/phytotaxa.261.3.1 |journal=Phytotaxa |volume=261 |issue=3 |pages=201 |doi=10.11646/phytotaxa.261.3.1 |issn=1179-3163 |doi-access=free}}</ref> They are found throughout the world in a wide variety of habitats, but are primarily tropical.<br />
{{right|Species subtotal:  &nbsp;}}
|-
| [[File:Enhalus acoroides01.jpg|center|140px]]
| ''[[Enhalus]]''
| {{right|[[Enhalus#Species|1 species]] &nbsp;}}
|-
| [[File:Johnsons seagrass bed.jpg|center|140px]]
| ''[[Halophila]]''
| {{right|[[Halophila#Species|19 species]] &nbsp;}}
|-
| [[File:Thalassia hemprichii.jpg|center|140px]]
| [[Thalassia (genus)|''Thalassia'']]
| {{right|[[Thalassia (genus)#Species|2 species]] &nbsp;}}
|-
! rowspan=2 | [[Posidoniaceae]]
| colspan=3 style="text-align:left; background:#ddf8f8;"| The family '''[[Posidoniaceae]]''' contains a single genus with two to nine marine species found in the seas of the [[Mediterranean]] and around the south coast of [[Australia]].<br />
{{right|Species subtotal: 2 to 9 &nbsp;}}
|-
| [[File:Posidonia oceanica (L).jpg|center|140px]]
| ''[[Posidonia]]''
| {{right|[[Posidonia#Species|2 to 9 species]] &nbsp;}}
|-
! rowspan=6 | [[Cymodoceaceae]]
| colspan=3 style="text-align:left; background:#ddf8f8;"| The family '''[[Cymodoceaceae]]''', also known as '''manatee-grass''', includes only marine species.<ref>{{cite book |title=A Guide to Southern Temperate Seagrasses |author1=Waycott, Michelle |author2=McMahon, Kathryn |author3=Lavery, Paul |publisher=CSIRO Publishing |year=2014 |isbn=9781486300150}}</ref> Some taxonomists do not recognize this family.<br />
{{right|Species subtotal:  &nbsp;}}
|-
| [[File:Amphibolis griffithii 34184967.jpg|center|140px]]
| ''[[Amphibolis]]''
| {{right|[[Amphibolis#Species|2 species]] &nbsp;}}
|-
| [[File:Cymodocea.JPG|center|140px]]
| ''[[Cymodocea]]''
| {{right|[[Cymodocea#Species|4 species]] &nbsp;}}
|-
| [[File:Halodule wrightii.jpg|center|140px]]
| ''[[Halodule]]''
| {{right|[[Halodule#Species|6 species]] &nbsp;}}
|-
| [[File:Syringodium isoetifolium et Acropora sp..jpg|center|140px]]
| ''[[Syringodium]]''
| {{right|[[Syringodium#Species|2 species]] &nbsp;}}
|-
| [[File:Thalassodendron ciliatum.jpg|center|85px]]
| ''[[Thalassodendron]]''
| {{right|[[Thalassodendron#Species|3 species]] &nbsp;}}
|- style="background:#ddf8f8;"
| colspan=4 style="text-align:right; "| '''Total species: &nbsp;&nbsp;'''
|}

==Sexual recruitment==
[[File:Seeds of Posidonia oceanica.png|thumb|upright=1.7| Seeds from ''Posidonia oceanica''.<ref name=Guerrero-Meseguer2018 /> (A)&nbsp;Newly released seeds inside a fruit, (B)&nbsp;one-week-old seeds. FP:&nbsp;fruit pericarp, NRS:&nbsp;newly released seeds, WS:&nbsp;1-week-old seeds, H:&nbsp;adhesive hairs, S:&nbsp;seed, R1:&nbsp;primary root, Rh:&nbsp;rhizome, L:&nbsp;leaves.]]
[[File:Sexual recruitment stages of Posidonia oceanica.png|thumb|upright=1.7| The sexual recruitment stages of ''[[Posidonia oceanica]]'':<ref name=Guerrero-Meseguer2018 /><br /> dispersion, adhesion and settlement]]

{{See also|Seagrass meadow#Using propagules|Seagrass meadow#Movement ecology}}

Seagrass populations are currently threatened by a variety of [[Human impact on the environment|anthropogenic]] [[stressor]]s.<ref>{{cite journal |doi = 10.1016/j.marpolbul.2014.03.050|title = Temperature extremes reduce seagrass growth and induce mortality|year = 2014|last1 = Collier|first1 = C.J.|last2 = Waycott|first2 = M.|journal = Marine Pollution Bulletin|volume = 83|issue = 2|pages = 483–490|pmid = 24793782| bibcode=2014MarPB..83..483C }}</ref><ref name=Waycott2009>{{cite journal |doi = 10.1073/pnas.0905620106|title = Accelerating loss of seagrasses across the globe threatens coastal ecosystems|year = 2009|last1 = Waycott|first1 = M.|last2 = Duarte|first2 = C. M.|last3 = Carruthers|first3 = T. J. B.|last4 = Orth|first4 = R. J.|last5 = Dennison|first5 = W. C.|last6 = Olyarnik|first6 = S.|last7 = Calladine|first7 = A.|last8 = Fourqurean|first8 = J. W.|last9 = Heck|first9 = K. L.|last10 = Hughes|first10 = A. R.|last11 = Kendrick|first11 = G. A.|last12 = Kenworthy|first12 = W. J.|last13 = Short|first13 = F. T.|last14 = Williams|first14 = S. L.|journal = Proceedings of the National Academy of Sciences|volume = 106|issue = 30|pages = 12377–12381|pmid = 19587236|pmc = 2707273|bibcode = 2009PNAS..10612377W|doi-access = free}}</ref> The ability of seagrasses to cope with environmental [[Disturbance (ecology)|perturbations]] depends, to some extent, on [[genetic variability]], which is obtained through [[Recruitment (biology)|sexual recruitment]].<ref>{{cite journal |doi = 10.1073/pnas.0500008102|title = Ecosystem recovery after climatic extremes enhanced by genotypic diversity|year = 2005|last1 = Reusch|first1 = T. B. H.|last2 = Ehlers|first2 = A.|last3 = Hammerli|first3 = A.|last4 = Worm|first4 = B.|journal = Proceedings of the National Academy of Sciences|volume = 102|issue = 8|pages = 2826–2831|pmid = 15710890|pmc = 549506|bibcode = 2005PNAS..102.2826R|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1371/journal.pone.0207345|title = Understanding the sexual recruitment of one of the oldest and largest organisms on Earth, the seagrass Posidonia oceanica|year = 2018|last1 = Guerrero-Meseguer|first1 = Laura|last2 = Sanz-Lázaro|first2 = Carlos|last3 = Marín|first3 = Arnaldo|journal = PLOS ONE|volume = 13|issue = 11|pages = e0207345|pmid = 30444902|pmc = 6239318|bibcode = 2018PLoSO..1307345G|doi-access = free}}</ref><ref>{{cite journal |doi = 10.3354/meps07369|title = Importance of genetic diversity in eelgrass Zostera marina for its resilience to global warming|year = 2008|last1 = Ehlers|first1 = A.|last2 = Worm|first2 = B.|last3 = Reusch|first3 = TBH|journal = Marine Ecology Progress Series|volume = 355|pages = 1–7|bibcode = 2008MEPS..355....1E|doi-access = free}}</ref> By forming new individuals, seagrasses increase their [[genetic diversity]] and thus their ability to [[Colonisation (biology)|colonise]] new areas and to adapt to environmental changes.<ref>{{cite book |doi = 10.1007/978-1-4020-2983-7_5|chapter = Ecology of Seagrass Seeds and Seagrass Dispersal Processes|title = Seagrasses: Biology, Ecologyand Conservation|year = 2006|last1 = Orth|first1 = Robert J.|last2 = Harwell|first2 = Matthew C.|last3 = Inglis|first3 = Graeme J.|pages = 111–133|isbn = 978-1-4020-2942-4}}</ref><ref>{{cite journal |doi = 10.3354/meps08190|title = High levels of gene flow and low population genetic structure related to high dispersal potential of a tropical marine angiosperm|year = 2009|last1 = Van Dijk|first1 = JK|last2 = Van Tussenbroek|first2 = BI|last3 = Jiménez-Durán|first3 = K.|last4 = Márquez-Guzmán|first4 = GJ|last5 = Ouborg|first5 = J.|journal = Marine Ecology Progress Series|volume = 390|pages = 67–77|bibcode = 2009MEPS..390...67V|doi-access = free|hdl = 2066/75120|hdl-access = free}}</ref><ref>{{cite book |doi = 10.1017/CBO9781107415324.004|chapter = Summary for Policymakers|title = Climate Change 2013 - the Physical Science Basis|year = 2014|pages = 1–30|hdl = 10818/26263|isbn = 9781107415324|editor1-last = Intergovernmental Panel On Climate Change}}</ref><ref>{{cite journal |doi = 10.1098/rspb.2014.0878|title = The movement ecology of seagrasses|year = 2014|last1 = McMahon|first1 = Kathryn|last2 = Van Dijk|first2 = Kor-Jent|last3 = Ruiz-Montoya|first3 = Leonardo|last4 = Kendrick|first4 = Gary A.|last5 = Krauss|first5 = Siegfried L.|last6 = Waycott|first6 = Michelle|last7 = Verduin|first7 = Jennifer|last8 = Lowe|first8 = Ryan|last9 = Statton|first9 = John|last10 = Brown|first10 = Eloise|last11 = Duarte|first11 = Carlos|journal = Proceedings of the Royal Society B: Biological Sciences|volume = 281|issue = 1795|pmid = 25297859|pmc = 4213608}}</ref><ref>{{cite journal |doi = 10.1016/j.marenvres.2016.08.010|title = Spatial variation in reproductive effort of a southern Australian seagrass|year = 2016|last1 = Smith|first1 = Timothy M.|last2 = York|first2 = Paul H.|last3 = MacReadie|first3 = Peter I.|last4 = Keough|first4 = Michael J.|last5 = Ross|first5 = D. Jeff|last6 = Sherman|first6 = Craig D.H.|journal = Marine Environmental Research|volume = 120|pages = 214–224|pmid = 27592387| bibcode=2016MarER.120..214S }}</ref><ref name=Guerrero-Meseguer2018>{{cite journal |doi = 10.1371/journal.pone.0207345|title = Understanding the sexual recruitment of one of the oldest and largest organisms on Earth, the seagrass Posidonia oceanica|year = 2018|last1 = Guerrero-Meseguer|first1 = Laura|last2 = Sanz-Lázaro|first2 = Carlos|last3 = Marín|first3 = Arnaldo|journal = PLOS ONE|volume = 13|issue = 11|pages = e0207345|pmid = 30444902|pmc = 6239318|bibcode = 2018PLoSO..1307345G|doi-access = free}} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>{{Excessive citations inline
|date=March 2021}}

Seagrasses have contrasting [[Colonisation (biology)|colonisation]] strategies.<ref name=Inglis2000>{{cite journal |doi = 10.1071/PC000251|title = Variation in the recruitment behaviour of seagrass seeds: Implications for population dynamics and resource management|year = 1999|last1 = j. Inglis|first1 = Graeme|journal = Pacific Conservation Biology|volume = 5|issue = 4|page = 251}}</ref> Some seagrasses form [[seed bank]]s of small seeds with hard [[pericarp]]s that can remain in the dormancy stage for several months. These seagrasses are generally short-lived and can recover quickly from disturbances by not [[germinating]] far away from [[Seagrass meadow|parent meadows]] (e.g., ''[[Halophila]]'' sp., ''[[Halodule]]'' sp., ''[[Cymodocea]]'' sp., ''[[Zostera]]'' sp. and ''[[Heterozostera]]'' sp.).<ref name="Inglis2000" /><ref>{{cite journal |doi = 10.1016/0304-3770(90)90072-S|title = Fruit anatomy, seed germination and seedling development in the Japanese seagrass Phyllospadix (Zosteraceae)|year = 1990|last1 = Kuo|first1 = John|last2 = Iizumi|first2 = Hitoshi|last3 = Nilsen|first3 = Bjorg E.|last4 = Aioi|first4 = Keiko|journal = Aquatic Botany|volume = 37|issue = 3|pages = 229–245| bibcode=1990AqBot..37..229K }}</ref> In contrast, other seagrasses form [[Seed dispersal|dispersal]] [[propagule]]s. This strategy is typical of long-lived seagrasses that can form buoyant fruits with inner large non-dormant seeds, such as the genera ''[[Posidonia]]'' sp., ''[[Enhalus]]'' sp. and ''[[Thalassia (plant)|Thalassia]]'' sp.<ref name=Inglis2000 /><ref>Kuo J, Den Hartog C. (2006) "Seagrass morphology, anatomy, and ultrastructure". In: Larkum AWD, Orth RJ, Duarte CM (Eds), ''Seagrasses: Biology, Ecology and Conservation'', Springer, pages 51–87.</ref> Accordingly, the seeds of long-lived seagrasses have a large dispersal capacity compared to the seeds of the short-lived type,<ref>{{cite journal |doi = 10.1016/0304-3770(87)90086-6|title = Effects of current on photosynthesis and distribution of seagrasses|year = 1987|last1 = Fonseca|first1 = Mark S.|last2 = Kenworthy|first2 = W.Judson|journal = Aquatic Botany|volume = 27| issue=1 |pages = 59–78| bibcode=1987AqBot..27...59F }}</ref> which permits the evolution of species beyond unfavourable light conditions by the seedling development of parent meadows.<ref name=Guerrero-Meseguer2018 />

The seagrass ''[[Posidonia oceanica]]'' (L.) Delile is one of the oldest and largest species on Earth. An individual can form [[Seagrass meadow|meadows]] measuring nearly 15&nbsp;km wide and can be hundreds to thousands of years old.<ref name="Implications of Extreme Life Span i">{{cite journal |doi = 10.1371/journal.pone.0030454|title = Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica|year = 2012|last1 = Arnaud-Haond|first1 = Sophie|last2 = Duarte|first2 = Carlos M.|last3 = Diaz-Almela|first3 = Elena|last4 = Marbà|first4 = Núria|last5 = Sintes|first5 = Tomas|last6 = Serrão|first6 = Ester A.|journal = PLOS ONE|volume = 7|issue = 2|pages = e30454|pmid = 22312426|pmc = 3270012|bibcode = 2012PLoSO...730454A|doi-access = free}}</ref> ''P. oceanica'' [[Seagrass meadow|meadows]] play important roles in the maintenance of the [[geomorphology]] of Mediterranean coasts, which, among others, makes this seagrass a priority habitat of conservation.<ref>{{cite journal |doi = 10.1002/esp.3932|title = Biogeomorphology of the Mediterranean ''Posidonia'' oceanicaseagrass meadows|year = 2017|last1 = Vacchi|first1 = Matteo|last2 = De Falco|first2 = Giovanni|last3 = Simeone|first3 = Simone|last4 = Montefalcone|first4 = Monica|last5 = Morri|first5 = Carla|last6 = Ferrari|first6 = Marco|last7 = Bianchi|first7 = Carlo Nike|journal = Earth Surface Processes and Landforms|volume = 42|issue = 1|pages = 42–54|bibcode = 2017ESPL...42...42V|s2cid = 130872337|doi-access = free}}</ref> Currently, the flowering and recruitment of ''P. oceanica'' seems to be more frequent than that expected in the past.<ref name=Balestri2017>{{cite journal |doi = 10.3389/fpls.2017.00001|title = Nitric Oxide Ameliorates Zinc Oxide Nanoparticles Phytotoxicity in Wheat Seedlings: Implication of the Ascorbate–Glutathione Cycle|year = 2017|last1 = Tripathi|first1 = Durgesh K.|last2 = Mishra|first2 = Rohit K.|last3 = Singh|first3 = Swati|last4 = Singh|first4 = Samiksha|last5 = Vishwakarma|first5 = Kanchan|last6 = Sharma|first6 = Shivesh|last7 = Singh|first7 = Vijay P.|last8 = Singh|first8 = Prashant K.|last9 = Prasad|first9 = Sheo M.|last10 = Dubey|first10 = Nawal K.|last11 = Pandey|first11 = Avinash C.|last12 = Sahi|first12 = Shivendra|last13 = Chauhan|first13 = Devendra K.|journal = Frontiers in Plant Science|volume = 8|page = 1|pmid = 28220127|pmc = 5292406|doi-access = free}}</ref><ref>{{cite journal |doi = 10.12681/mms.529|title = Flowering of the seagrass Posidonia oceanica in NW Mediterranean: Is there a link with solar activity?|year = 2013|last1 = Montefalcone|first1 = M.|last2 = Giovannetti|first2 = E.|last3 = Morri|first3 = C.|last4 = Peirano|first4 = A.|last5 = Bianchi|first5 = C. N.|journal = Mediterranean Marine Science|volume = 14|issue = 2|page = 416| s2cid=85362624 |doi-access = free}}</ref><ref>{{cite journal |doi = 10.1016/j.marpolbul.2017.10.037|title = Experimental evidence of warming-induced flowering in the Mediterranean seagrass Posidonia oceanica|year = 2018|last1 = Ruiz|first1 = J.M.|last2 = Marín-Guirao|first2 = L.|last3 = García-Muñoz|first3 = R.|last4 = Ramos-Segura|first4 = A.|last5 = Bernardeau-Esteller|first5 = J.|last6 = Pérez|first6 = M.|last7 = Sanmartí|first7 = N.|last8 = Ontoria|first8 = Y.|last9 = Romero|first9 = J.|last10 = Arthur|first10 = R.|last11 = Alcoverro|first11 = T.|last12 = Procaccini|first12 = G.|journal = Marine Pollution Bulletin|volume = 134|pages = 49–54|pmid = 29102072| bibcode=2018MarPB.134...49R |s2cid = 11523686|hdl = 10508/15205|hdl-access = free}}</ref><ref>{{cite journal |doi = 10.1111/j.1365-2486.2006.01260.x|title = Consequences of Mediterranean warming events in seagrass (Posidonia oceanica) flowering records|year = 2007|last1 = Diaz-Almela|first1 = Elena|last2 = Marbà|first2 = Nuria|last3 = Duarte|first3 = Carlos M.|journal = Global Change Biology|volume = 13|issue = 1|pages = 224–235|bibcode = 2007GCBio..13..224D|s2cid = 84055440}}</ref><ref>{{cite journal |doi = 10.3354/meps08104|title = Seed nutrient content and nutritional status of Posidonia oceanica seedlings in the northwestern Mediterranean Sea|year = 2009|last1 = Balestri|first1 = E.|last2 = Gobert|first2 = S.|last3 = Lepoint|first3 = G.|last4 = Lardicci|first4 = C.|journal = Marine Ecology Progress Series|volume = 388|pages = 99–109|bibcode = 2009MEPS..388...99B|doi-access = free|hdl = 11568/132307|hdl-access = free}}</ref> Further, this seagrass has singular adaptations to increase its survival during recruitment. The large amounts of nutrient reserves contained in the seeds of this seagrass support shoot and root growth, even up to the first year of seedling development.<ref name="Implications of Extreme Life Span i"/> In the first months of [[germination]], when leaf development is scarce, ''P. oceanica'' seeds perform [[photosynthetic]] activity, which increases their photosynthetic rates and thus maximises seedling establishment success.<ref>{{cite journal |doi = 10.1007/s00227-010-1612-4|title = Photosynthetic activity of the non-dormant Posidonia oceanica seed|year = 2011|last1 = Celdrán|first1 = David|last2 = Marín|first2 = Arnaldo|journal = Marine Biology|volume = 158|issue = 4|pages = 853–858| bibcode=2011MarBi.158..853C |s2cid = 84357626}}</ref><ref>{{cite journal |doi = 10.1890/ES13-00104.1|title = Seed photosynthesis enhances ''Posidonia'' oceanicaseedling growth|year = 2013|last1 = Celdrán|first1 = David|last2 = Marín|first2 = Arnaldo|journal = Ecosphere|volume = 4|issue = 12|pages = art149|doi-access = free}}</ref> Seedlings also show high morphological plasticity during their [[root system]] development<ref>{{cite journal |doi = 10.1016/j.ecss.2015.01.002|title = First evidence of root morphological and architectural variations in young Posidonia oceanica plants colonizing different substrate typologies|year = 2015|last1 = Balestri|first1 = Elena|last2 = De Battisti|first2 = Davide|last3 = Vallerini|first3 = Flavia|last4 = Lardicci|first4 = Claudio|journal = Estuarine, Coastal and Shelf Science|volume = 154|pages = 205–213|bibcode = 2015ECSS..154..205B| hdl=11568/755031 |hdl-access = free}}</ref><ref>{{cite journal |doi = 10.1111/rec.12438|title = Influence of substrate and burial on the development of Posidonia oceanica : Implications for restoration|year = 2017|last1 = Guerrero-Meseguer|first1 = Laura|last2 = Sanz-Lázaro|first2 = Carlos|last3 = Suk-Ueng|first3 = Krittawit|last4 = Marín|first4 = Arnaldo|journal = Restoration Ecology|volume = 25|issue = 3|pages = 453–458| bibcode=2017ResEc..25..453G |hdl = 10045/66474|s2cid = 88876962|hdl-access = free}}</ref> by forming adhesive [[root hair]]s to help [[Holdfast (biology)|anchor]] themselves to rocky sediments.<ref name=Balestri2017 /><ref>{{cite journal |doi = 10.1038/srep08804|title = Evidences of adaptive traits to rocky substrates undermine paradigm of habitat preference of the Mediterranean seagrass Posidonia oceanica|year = 2015|last1 = Badalamenti|first1 = Fabio|last2 = Alagna|first2 = Adriana|last3 = Fici|first3 = Silvio|journal = Scientific Reports|volume = 5|page = 8804|pmid = 25740176|pmc = 4350093|bibcode = 2015NatSR...5E8804B}}</ref><ref>{{cite journal |doi = 10.1016/j.ecss.2013.01.009|title = Influence of microhabitat on seedling survival and growth of the mediterranean seagrass posidonia oceanica (L.) Delile|year = 2013|last1 = Alagna|first1 = Adriana|last2 = Fernández|first2 = Tomás Vega|last3 = Terlizzi|first3 = Antonio|last4 = Badalamenti|first4 = Fabio|journal = Estuarine, Coastal and Shelf Science|volume = 119|pages = 119–125|bibcode = 2013ECSS..119..119A}}</ref> However, many factors about ''P. oceanica'' sexual recruitment remain unknown, such as when photosynthesis in seeds is active or how seeds can remain anchored to and persist on substrate until their root systems have completely developed.<ref name=Guerrero-Meseguer2018 />

{{Clear}}

==Intertidal and subtidal==
[[File:Morphological and photoacclimatory responses of Zostera marina.png|thumb|upright=2| Morphological and photoacclimatory responses of intertidal and subtidal ''[[Zostera marina]]'' eelgrass<ref>{{cite journal |doi = 10.1371/journal.pone.0156214|title = Photoacclimatory Responses of Zostera marina in the Intertidal and Subtidal Zones|year = 2016|last1 = Park|first1 = Sang Rul|last2 = Kim|first2 = Sangil|last3 = Kim|first3 = Young Kyun|last4 = Kang|first4 = Chang-Keun|last5 = Lee|first5 = Kun-Seop|journal = PLOS ONE|volume = 11|issue = 5|pages = e0156214|pmid = 27227327|pmc = 4881947|bibcode = 2016PLoSO..1156214P|doi-access = free}} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

Seagrasses occurring in the intertidal and subtidal zones are exposed to highly variable environmental conditions due to tidal changes.<ref>{{cite journal |doi = 10.3354/meps257037|title = Daily variation patterns in seagrass photosynthesis along a vertical gradient|year = 2003|last1 = Silva|first1 = J.|last2 = Santos|first2 = R.|journal = Marine Ecology Progress Series|volume = 257|pages = 37–44|bibcode = 2003MEPS..257...37S|doi-access = free|hdl = 10400.1/12140|hdl-access = free}}</ref><ref name=Boese2005>{{cite journal |doi = 10.1515/BOT.2005.037|title = Desiccation is a limiting factor for eelgrass (Zostera marina L.) distribution in the intertidal zone of a northeastern Pacific (USA) estuary|year = 2005|last1 = Boese|first1 = Bruce L.|last2 = Robbins|first2 = Bradley D.|last3 = Thursby|first3 = Glen|journal = Botanica Marina|volume = 48|issue = 4|s2cid = 85105171}}</ref> Subtidal seagrasses are more frequently exposed to lower light conditions, driven by plethora of natural and human-caused influences that reduce light penetration by increasing the density of suspended opaque materials. Subtidal light conditions can be estimated, with high accuracy, using artificial intelligence, enabling more rapid mitigation than was available using ''in situ'' techniques.<ref>{{Cite journal|last1=Pearson|first1=Ryan M.|last2=Collier|first2=Catherine J.|last3=Brown|first3=Christopher J.|last4=Rasheed|first4=Michael A.|last5=Bourner|first5=Jessica|last6=Turschwell|first6=Mischa P.|last7=Sievers|first7=Michael|last8=Connolly|first8=Rod M.|date=2021-08-15|title=Remote estimation of aquatic light environments using machine learning: A new management tool for submerged aquatic vegetation|url=https://www.sciencedirect.com/science/article/abs/pii/S0048969721019562|journal=Science of the Total Environment|language=en|volume=782|pages=146886|doi=10.1016/j.scitotenv.2021.146886|bibcode=2021ScTEn.78246886P|hdl=10072/403729 |s2cid=233519731|issn=0048-9697|hdl-access=free}}</ref> Seagrasses in the [[intertidal zone]] are regularly exposed to air and consequently experience extreme high and low temperatures, high photoinhibitory [[irradiance]], and [[desiccation]] stress relative to subtidal seagrass.<ref name=Boese2005 /><ref>{{cite journal |doi = 10.1007/s00227-003-1038-3|title = Depth-related variability in the photobiology of two populations of Halophila johnsonii and Halophila decipiens|year = 2003|last1 = Durako|first1 = M. J.|last2 = Kunzelman|first2 = J. I.|last3 = Kenworthy|first3 = W. J.|last4 = Hammerstrom|first4 = K. K.|journal = Marine Biology|volume = 142|issue = 6|pages = 1219–1228| bibcode=2003MarBi.142.1219D |s2cid = 85627116}}</ref><ref name=Olivé2013>{{cite journal |doi = 10.1007/s00227-012-2087-2|title = Photosynthetic and morphological photoacclimation of the seagrass Cymodocea nodosa to season, depth and leaf position|year = 2013|last1 = Olivé|first1 = I.|last2 = Vergara|first2 = J. J.|last3 = Pérez-Lloréns|first3 = J. L.|journal = Marine Biology|volume = 160|issue = 2|pages = 285–297| bibcode=2013MarBi.160..285O |s2cid = 86386210}}</ref> Such extreme temperatures can lead to significant seagrass dieback when seagrasses are exposed to air during low tide.<ref>Hemminga M. A. and Durate C. M.  (2000) ''Seagrass ecology''. Cambridge University Press.</ref><ref name="Photosynthetic response of Amphibol">{{cite journal |doi = 10.3354/meps220119|title = Photosynthetic response of Amphibolis antarctica and Posidonia australis to temperature and desiccation using chlorophyll fluorescence|year = 2001|last1 = Seddon|first1 = S.|last2 = Cheshire|first2 = AC|journal = Marine Ecology Progress Series|volume = 220|pages = 119–130|bibcode = 2001MEPS..220..119S|doi-access = free|hdl = 2440/12249|hdl-access = free}}</ref><ref>Hirst A, Ball D, Heislers S, Young P, Blake S, Coots A. Baywide Seagrass Monitoring Program, Milestone Report No. 2 (2008). Fisheries Victoria Technical Report No. 29, January 2009.</ref> Desiccation stress during low tide has been considered the primary factor limiting seagrass distribution at the upper intertidal zone.<ref>{{cite journal |doi = 10.2307/1352808|jstor = 1352808|title = Beyond Light: Physical, Geological, and Geochemical Parameters as Possible Submersed Aquatic Vegetation Habitat Requirements|last1 = Koch|first1 = Evamaria W.|journal = Estuaries|year = 2001|volume = 24|issue = 1|pages = 1–17|s2cid = 85287808}}</ref> Seagrasses residing the intertidal zone are usually smaller than those in the subtidal zone to minimize the effects of emergence stress.<ref>{{cite journal |doi = 10.3354/meps284117|title = Emergence stress and morphological constraints affect the species distribution and growth of subtropical intertidal seagrasses|year = 2004|last1 = Tanaka|first1 = Y.|last2 = Nakaoka|first2 = M.|journal = Marine Ecology Progress Series|volume = 284|pages = 117–131|bibcode = 2004MEPS..284..117T|doi-access = free}}</ref><ref name="Photosynthetic response of Amphibol"/> Intertidal seagrasses also show light-dependent responses, such as decreased photosynthetic efficiency and increased photoprotection during periods of high irradiance and air exposure.<ref>{{cite journal |doi = 10.3354/meps191121|title = Photosynthetic tolerances to desiccation of tropical intertidal seagrasses|year = 1999|last1 = Björk|first1 = M.|last2 = Uku|first2 = J.|last3 = Weil|first3 = A.|last4 = Beer|first4 = S.|journal = Marine Ecology Progress Series|volume = 191|pages = 121–126|bibcode = 1999MEPS..191..121B|doi-access = free}}</ref><ref>{{cite journal |doi = 10.3354/meps10229|title = Seasonal heterogeneity in the photophysiological response to air exposure in two tropical intertidal seagrass species|year = 2013|last1 = Petrou|first1 = K.|last2 = Jimenez-Denness|first2 = I.|last3 = Chartrand|first3 = K.|last4 = McCormack|first4 = C.|last5 = Rasheed|first5 = M.|last6 = Ralph|first6 = PJ|journal = Marine Ecology Progress Series|volume = 482|pages = 93–106|bibcode = 2013MEPS..482...93P|hdl = 10453/23914|url = https://researchonline.jcu.edu.au/30200/1/Petrou%20et%20al%202013%20tidal%20exposure%20photophysiology.pdf}}</ref>

[[File:Zostera marina seedling.jpg|thumb|left| ''[[Zostera marina]]'' seedling<ref>{{cite journal |doi = 10.7717/peerj.2697|title = Salinity and temperature significantly influence seed germination, seedling establishment, and seedling growth of eelgrass ''Zostera'' marinaL|year = 2016|last1 = Xu|first1 = Shaochun|last2 = Zhou|first2 = Yi|last3 = Wang|first3 = Pengmei|last4 = Wang|first4 = Feng|last5 = Zhang|first5 = Xiaomei|last6 = Gu|first6 = Ruiting|journal = PeerJ|volume = 4|pages = e2697|pmid = 27896031|pmc = 5119234 | doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

In contrast, seagrasses in the [[subtidal zone]] adapt to reduced light conditions caused by light attenuation and scattering due to the overlaying water column and suspended particles.<ref>{{cite journal |doi = 10.1007/s002270000433|title = Photosynthetic utilisation of carbon and light by two tropical seagrass species as measured in situ|year = 2000|last1 = Schwarz|first1 = A.-M.|last2 = Björk|first2 = M.|last3 = Buluda|first3 = T.|last4 = Mtolera|first4 = M.|last5 = Beer|first5 = S.|journal = Marine Biology|volume = 137|issue = 5–6|pages = 755–761| bibcode=2000MarBi.137..755S |s2cid = 86384408}}</ref><ref>{{cite journal |doi = 10.1016/j.ecss.2007.02.014|title = Patterns in tropical seagrass photosynthesis in relation to light, depth and habitat|year = 2007|last1 = Campbell|first1 = Stuart J.|last2 = McKenzie|first2 = Len J.|last3 = Kerville|first3 = Simon P.|last4 = Bité|first4 = Juanita S.|journal = Estuarine, Coastal and Shelf Science|volume = 73|issue = 3–4|pages = 551–562|bibcode = 2007ECSS...73..551C}}</ref> Seagrasses in the deep subtidal zone generally have longer leaves and wider leaf blades than those in the shallow subtidal or intertidal zone, which allows more photosynthesis, in turn resulting in greater growth.<ref name=Olivé2013 /> Seagrasses also respond to reduced light conditions by increasing [[chlorophyll]] content and decreasing the [[Chlorophyll b|chlorophyll a/b ratio]] to enhance [[light absorption]] efficiency by using the abundant wavelengths efficiently.<ref>{{cite journal |doi = 10.1016/S0022-0981(96)02720-7|title = Effect of in situ light reduction on the maintenance, growth and partitioning of carbon resources in Thalassia testudinum banks ex König|year = 1997|last1 = Lee|first1 = Kun-Seop|last2 = Dunton|first2 = Kenneth H.|journal = Journal of Experimental Marine Biology and Ecology|volume = 210| issue=1 |pages = 53–73| bibcode=1997JEMBE.210...53L }}</ref><ref>{{cite journal |doi = 10.1016/S0304-3770(99)00035-2|title = Seagrass survival during pulsed turbidity events: The effects of light deprivation on the seagrasses Halodule pinifolia and Halophila ovalis|year = 1999|last1 = Longstaff|first1 = B.J|last2 = Dennison|first2 = W.C|journal = Aquatic Botany|volume = 65|issue = 1–4|pages = 105–121| bibcode=1999AqBot..65..105L }}</ref><ref>{{cite journal |doi = 10.3354/meps07171|title = Physiological characteristics of the seagrass Posidonia sinuosa along a depth-related gradient of light availability|year = 2008|last1 = Collier|first1 = CJ|last2 = Lavery|first2 = PS|last3 = Ralph|first3 = PJ|last4 = Masini|first4 = RJ|journal = Marine Ecology Progress Series|volume = 353|pages = 65–79|bibcode = 2008MEPS..353...65C|doi-access = free|hdl = 10453/8694|hdl-access = free}}</ref> As seagrasses in the intertidal and subtidal zones are under highly different light conditions, they exhibit distinctly different photoacclimatory responses to maximize photosynthetic activity and photoprotection from excess irradiance.{{cn|date=October 2023}}

Seagrasses assimilate large amounts of [[inorganic carbon]] to achieve high level production.<ref>{{cite journal |doi = 10.1016/j.jembe.2007.06.016|title = Effects of irradiance, temperature, and nutrients on growth dynamics of seagrasses: A review|year = 2007|last1 = Lee|first1 = Kun-Seop|last2 = Park|first2 = Sang Rul|last3 = Kim|first3 = Young Kyun|journal = Journal of Experimental Marine Biology and Ecology|volume = 350|issue = 1–2|pages = 144–175| bibcode=2007JEMBE.350..144L }}</ref><ref>{{cite journal |doi = 10.1016/j.jembe.2009.03.010|title = Uptake and resource allocation of inorganic carbon by the temperate seagrasses Posidonia and Amphibolis|year = 2009|last1 = Nayar|first1 = S.|last2 = Collings|first2 = G.J.|last3 = Miller|first3 = D.J.|last4 = Bryars|first4 = S.|last5 = Cheshire|first5 = A.C.|journal = Journal of Experimental Marine Biology and Ecology|volume = 373|issue = 2|pages = 87–95| bibcode=2009JEMBE.373...87N }}</ref> Marine [[Aquatic plant|macrophytes]], including seagrass, use both {{CO2}} and {{chem2|HCO3-}} ([[bicarbonate]]) for photosynthetic carbon reduction.<ref>{{cite journal |doi = 10.1016/0304-3770(89)90054-5|title = Photosynthesis and photorespiration of marine angiosperms|year = 1989|last1 = Beer|first1 = Sven|journal = Aquatic Botany|volume = 34|issue = 1–3|pages = 153–166| bibcode=1989AqBot..34..153B }}</ref><ref>Larkum AWD, James PL. Towards a model for inorganic carbon uptake in seagrasses involving carbonic anhydrase. In Kuo J, Phillips RC, Walker DI, Kirkman H, editors. Seagrass biology: Proceedings of an International Workshop. Nedlands: The University of Western Australia; 1996. pp. 191–196.</ref><ref>{{cite journal |doi = 10.1016/S0304-3770(96)01109-6|title = The acquisition of inorganic carbon by the seagrass Zostera marina|year = 1997|last1 = Beer|first1 = Sven|last2 = Rehnberg|first2 = Jon|journal = Aquatic Botany|volume = 56|issue = 3–4|pages = 277–283| bibcode=1997AqBot..56..277B }}</ref> Despite air exposure during low tide, seagrasses in the intertidal zone can continue to photosynthesize utilizing CO<sub>2</sub> in the air.<ref>{{cite journal |doi = 10.1016/j.jembe.2004.11.010|title = Submerged versus air-exposed intertidal macrophyte productivity: From physiological to community-level assessments|year = 2005|last1 = Silva|first1 = João|last2 = Santos|first2 = Rui|last3 = Calleja|first3 = Maria Ll.|last4 = Duarte|first4 = Carlos M.|journal = Journal of Experimental Marine Biology and Ecology|volume = 317| issue=1 |pages = 87–95| bibcode=2005JEMBE.317...87S }}</ref> Thus, the composition of inorganic carbon sources for seagrass photosynthesis probably varies between intertidal and subtidal plants. Because stable [[carbon isotope ratio]]s of plant tissues change based on the inorganic carbon sources for photosynthesis,<ref>{{cite journal |doi = 10.2307/1310735|jstor = 1310735|last1 = O'Leary|first1 = Marion H.|title = Carbon Isotopes in Photosynthesis|journal = BioScience|year = 1988|volume = 38|issue = 5|pages = 328–336}}</ref><ref>{{cite journal |doi = 10.1071/PP01201|title = Mechanistic interpretation of carbon isotope discrimination by marine macroalgae and seagrasses|year = 2002|last1 = Raven|first1 = John A.|last2 = Johnston|first2 = Andrew M.|last3 = Kübler|first3 = Janet E.|last4 = Korb|first4 = Rebecca|last5 = McInroy|first5 = Shona G.|last6 = Handley|first6 = Linda L.|last7 = Scrimgeour|first7 = Charlie M.|last8 = Walker|first8 = Diana I.|last9 = Beardall|first9 = John|last10 = Vanderklift|first10 = Mathew|last11 = Fredriksen|first11 = Stein|last12 = Dunton|first12 = Kenneth H.|journal = Functional Plant Biology|volume = 29|issue = 3|pages = 355–378|pmid = 32689482}}</ref> seagrasses in the intertidal and subtidal zones may have different stable carbon isotope ratio ranges.

==Seagrass meadows==
[[File:Seagrass Grahams Harbour.jpg|thumb|[[Seagrass bed]] with several echinoids]]
[[File:Strombus gigas Rice Bay.jpg|thumb|Seagrass bed with dense [[Thalassia testudinum|turtle grass]] (''Thalassia testudinum'') and an immature queen conch (''[[Eustrombus gigas]]'')]]
{{main|Seagrass meadow}}

[[Seagrass bed]]s/meadows can be either monospecific (made up of a single species) or in mixed beds. In [[temperate]] areas, usually one or a few species dominate (like the eelgrass ''[[Zostera marina]]'' in the North Atlantic), whereas [[tropical]] beds usually are more diverse, with up to thirteen [[species]] recorded in the [[Philippines]].{{cn|date=October 2023}}

Seagrass beds are diverse and productive [[ecosystem]]s, and can harbor hundreds of associated species from all [[phylum|phyla]], for example juvenile and adult [[fish]], [[epiphytic]] and free-living [[macroalgae]] and [[microalgae]], [[mollusk]]s, [[bristle worm]]s, and [[nematode]]s. Few species were originally considered to feed directly on seagrass [[leaf|leaves]] (partly because of their low nutritional content), but scientific reviews and improved working methods have shown that seagrass [[Herbivore|herbivory]] is an important link in the food chain, feeding hundreds of species, including [[green turtle]]s, [[dugong]]s, [[manatee]]s, [[fish]], [[geese]], [[swan]]s, [[sea urchin]]s and [[crab]]s. Some fish species that visit/feed on seagrasses raise their young in adjacent [[mangrove]]s or [[coral reef]]s.

Seagrasses trap sediment and slow down water movement, causing suspended sediment to settle out. Trapping sediment benefits [[coral]] by reducing sediment loads, improving photosynthesis for both coral and seagrass.<ref>[http://www.seagrasswatch.org/seagrass.html Seagrass-Watch: What is seagrass?] Retrieved 2012-11-16.</ref>

Although often overlooked, seagrasses provide a number of [[ecosystem services]].<ref>{{Cite journal |last1=Nordlund |first1=Lina |last2=Koch |first2=Evamaria W. |last3=Barbier |first3=Edward B. |last4=Creed |first4=Joel C. |date=2016-10-12 |editor-last=Reinhart |editor-first=Kurt O. |title=Seagrass Ecosystem Services and Their Variability across Genera and Geographical Regions |journal=PLOS ONE |language=en |volume=11 |issue=10 |pages=e0163091 |doi=10.1371/journal.pone.0163091 |issn=1932-6203 |pmc=5061329 |pmid=27732600 |bibcode=2016PLoSO..1163091M |doi-access=free}}</ref><ref>United Nations Environment Programme  (2020).  Out of the blue:  The value of seagrasses to the environment and to people. UNEP, Nairobi. https://www.unenvironment.org/resources/report/out-blue-value-seagrasses-environment-and-people</ref> Seagrasses are considered [[ecosystem engineer]]s.<ref name=":2">{{Cite journal|last1=Jones |first1=Clive G. |first2=John H. |last2=Lawton |first3=Moshe |last3=Shachak|date=1994|title=Organisms as ecosystem engineers|journal=[[Oikos (journal)|Oikos]] |volume=69|issue=3 |pages=373–386|doi=10.2307/3545850 |jstor=3545850 |bibcode=1994Oikos..69..373J }}</ref><ref name=":13" /><ref name=":03" /> This means that the plants alter the ecosystem around them. This adjusting occurs in both physical and chemical forms. Many seagrass species produce an extensive underground network of roots and [[rhizome]] which stabilizes sediment and reduces [[coastal erosion]].<ref>{{Cite journal|last1=Grey |first1=William |last2=Moffler |first2=Mark |date=1987|title=Flowering of the seagrass Thalassia testudinum (Hydrocharitacea) in the Tampa Bay, Florida area|journal=Aquatic Botany|volume=5|pages=251–259|doi=10.1016/0304-3770(78)90068-2}}</ref> This system also assists in oxygenating the sediment, providing a hospitable environment for [[sediment-dwelling organism]]s.<ref name=":2" /> Seagrasses also enhance [[water quality]] by stabilizing heavy metals, pollutants, and excess nutrients.<ref name=":3">{{Cite journal |last1=Darnell |first1=Kelly |title=Reproductive phenology of the subtropical seagrasses Thalassia testudinum (Turtle grass) and Halodule wrightii (Shoal grass) in the northwest Gulf of Mexico |journal=Botanica Marina |last2=Dunton |first2=Kenneth |date=2016 |volume=59 |issue=6 |pages=473–483 |doi=10.1515/bot-2016-0080 |s2cid=88685282}}</ref><ref name=":13" /><ref name=":03" /> The long blades of seagrasses slow the movement of water which reduces wave energy and offers further protection against coastal [[erosion]] and [[storm surge]]. Furthermore, because seagrasses are underwater plants, they produce significant amounts of oxygen which oxygenate the water column. These meadows account for more than 10% of the ocean's total carbon storage. Per hectare, it holds twice as much carbon dioxide as rain forests and can sequester about 27.4 million tons of CO<sub>2</sub> annually.<ref>{{Cite journal |first1=P. I. |last1=Macreadie |first2=M. E. |last2=Baird |first3=S. M. |last3=Trevathan-Tackett |first4=A. W. D. |last4=Larkum |first5=P. J. |last5=Ralph |date=2013 |title=Quantifying and modelling the carbon sequestration capacity of seagrass meadows. |doi=10.1016/j.marpolbul.2013.07.038 |pmid=23948090 |journal=Marine Pollution Bulletin |volume=83 |issue=2 |pages=430–439}}</ref>

[[Seagrass meadows]] provide food for many marine herbivores. Sea turtles, manatees, parrotfish, surgeonfish, sea urchins and pinfish feed on seagrasses. Many other smaller animals feed on the epiphytes and invertebrates that live on and among seagrass blades.<ref>{{Cite web|url=https://myfwc.com/research/habitat/seagrasses/faq/|title=Seagrass FAQ|website=Florida Fish And Wildlife Conservation Commission}}</ref> Seagrass meadows also provide physical habitat in areas that would otherwise be bare of any vegetation. Due to this three dimensional structure in the water column, many species occupy seagrass habitats for shelter and foraging. It is estimated that 17 species of coral reef fish spend their entire juvenile life stage solely on seagrass flats.<ref>{{Cite journal |first1=I. |last1=Nagelkerken |first2=C. M. |last2=Roberts |first3=G. |last3=van der Velde |first4=M. |last4=Dorenbosch |first5=M. C. |last5=van Riel |first6=E. |last6=Cocheret de la Morinière |first7=P. H. |last7=Nienhuis |date=2002|title=How important are mangroves and seagrass beds for coral-reef fish? The nursery hypothesis tested on an island scale |journal=Marine Ecology Progress Series |volume=244 |pages=299–305 |doi=10.3354/meps244299 |bibcode=2002MEPS..244..299N |doi-access=free |hdl=2066/126674 |hdl-access=free }}</ref> These habitats also act as a nursery grounds for commercially and recreationally valued fishery species, including the gag grouper (''[[Mycteroperca microlepis]]''), red drum, [[common snook]], and many others.<ref name="Nordlund et al., 2017">{{cite journal |last1=Nordlund |first1=L. M. |last2=Unsworth |first2=R. K. F. |last3=Gullstrom |first3=M. |last4=Cullen-Unsworth |first4=L. C. |title=Global significance of seagrass fishery activity |journal=Fish and Fisheries |volume=19 |issue=3 |pages=399–412 |doi=10.1111/faf.12259 |year=2018 |doi-access=free|bibcode=2018AqFF...19..399N }}</ref><ref name="Unsworth et al., 2018">{{cite journal |last1=Unsworth |first1=R. K. F. |last2=Nordlund |first2=L. M. |last3=Cullen-Unsworth |first3=L. C. |title=Seagrass meadows support global fisheries production |journal=Conserv Lett |volume=e12566 |pages=e12566 |doi=10.1111/conl.12566 |year=2019 |issue=1 |doi-access=free|bibcode=2019ConL...12E2566U }}</ref> Some fish species utilize seagrass meadows and various stages of the life cycle. In a recent publication, Dr. Ross Boucek and colleagues discovered that two highly sought after flats fish, the common snook and [[spotted sea trout]] provide essential foraging habitat during reproduction.<ref name=":9">{{Cite journal |last1=Boucek |first1=Ross E. |last2=Leone |first2=Erin |last3=Bickford |first3=Joel |last4=Walters-Burnsed |first4=Sarah |last5=Lowerre-Barbieri |first5=Susan |date=2017-11-23 |title=More Than Just a Spawning Location: Examining Fine Scale Space Use of Two Estuarine Fish Species at a Spawning Aggregation Site |journal=Frontiers in Marine Science |volume=4 |issue=4 |pages=1–9 |doi=10.3389/fmars.2017.00355 |doi-access=free |issn=2296-7745}}</ref> Sexual reproduction is extremely energetically expensive to be completed with stored energy; therefore, they require seagrass meadows in close proximity to complete reproduction.<ref name=":9" /> Furthermore, many commercially important [[invertebrate]]s also reside in seagrass habitats including bay scallops (''[[Argopecten irradians]]''), [[horseshoe crab]]s, and [[shrimp]]. Charismatic fauna can also be seen visiting the seagrass habitats. These species include [[West Indian manatee]], [[green sea turtle]]s, and various species of sharks. The high diversity of marine organisms that can be found on seagrass habitats promotes them as a tourist attraction and a significant source of income for many coastal economies along the Gulf of Mexico and in the Caribbean.

<gallery mode="packed" style="float:left" heights="170">
File:Floridian seagrass bed.jpg| ''[[Thalassia testudinum]]'' [[seagrass bed]]
File:White-spotted puffer.jpg|[[White-spotted puffer]]s, often found in seagrass areas
File:Seagrass Meadow - Porthdinllaen.webm| Underwater footage of seagrass meadow, [[bull huss]] and [[conger eel]]
</gallery>
{{clear}}

==Seagrass microbiome==
[[File:Processes within the seagrass holobiont.webp|thumb|upright=1.7|right| The most important interconnected processes within the seagrass [[holobiont]] are related to processes in the carbon, nitrogen and sulfur cycles. [[Photosynthetically active radiation]] (PAR) determines the photosynthetic activity of the seagrass plant that determines how much carbon dioxide is fixed, how much [[dissolved organic carbon]] (DOC) is exuded from the leaves and root system, and how much oxygen is transported into the [[rhizosphere]]. Oxygen transportation into the rhizosphere alters the [[redox]] conditions in the rhizosphere, differentiating it from the surrounding sediments that are usually [[Hypoxia (environmental)|anoxic]] and [[sulfidic]].<ref name=Ugarelli2017>Ugarelli, K., Chakrabarti, S., Laas, P. and Stingl, U. (2017) "The seagrass holobiont and its microbiome". ''Microorganisms'', '''5'''(4): 81. {{doi|10.3390/microorganisms5040081}}. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><ref>Tarquinio, F., Hyndes, G.A., Laverock, B., Koenders, A. and Säwström, C. (2019) "The seagrass holobiont: understanding seagrass-bacteria interactions and their role in seagrass ecosystem functioning". ''FEMS microbiology letters'', '''366'''(6): fnz057. {{doi|10.1093/femsle/fnz057}}.</ref>]]

{{Further|microbiome|marine microorganisms}}

===Seagrass holobiont===
{{see also|plant holobiont}}

The concept of the [[holobiont]], which emphasizes the importance and interactions of a microbial host with associated microorganisms and viruses and describes their functioning as a single biological unit,<ref>[[Lynn Margulis|Margulis, Lynn]] (1991) [https://books.google.com/books?id=3sKzeiHUIUQC&dq=%22Symbiosis+as+a+Source+of+Evolutionary+Innovation%22&pg=PA1 "Symbiogenesis and Symbionticism"]. In: ''Symbiosis as a Source of Evolutionary Innovation''; Margulis, L., Fester, R.(Eds.), Cambridge MIT Press. {{ISBN|9780262132695}}.</ref> has been investigated and discussed for many model systems, although there is substantial criticism of a concept that defines diverse host-microbe symbioses as a single biological unit.<ref>Douglas, A.E.; Werren, J.H. (2016) "Holes in the Hologenome: Why Host-Microbe Symbioses Are Not Holobionts". ''mBio'', '''7''': e02099-15. {{doi|10.1128/mBio.02099-15}}.</ref> The holobiont and hologenome concepts have evolved since the original definition,<ref>Theis, K.R.; Dheilly, N.M.; Klassen, J.L.; Brucker, R.M.; Baines, J.F.; Bosch, T.C.G.; Cryan, J.F.; Gilbert, S.F.; Goodnight, C.J.; Lloyd, E.A.; et al. Getting the Hologenome Concept Right: An Eco-Evolutionary Framework for Hosts and Their Microbiomes. mSystems 2016, 1, e00028-16. {{doi|10.1128/mSystems.00028-16}}.</ref> and there is no doubt that symbiotic microorganisms are pivotal for the biology and ecology of the host by providing vitamins, energy and inorganic or organic nutrients, participating in defense mechanisms, or by driving the evolution of the host.<ref>Rosenberg, E. and Zilber-Rosenberg, I. (2016) "Microbes drive evolution of animals and plants: the hologenome concept". ''MBio'', '''7'''(2). {{doi|10.1128/mBio.01395-15}}.</ref>

Although most work on host-microbe interactions has been focused on animal systems such as corals, sponges, or humans, there is a substantial body of literature on [[plant holobiont]]s.<ref>Zilber-Rosenberg, I. and Rosenberg, E. (2008) "Role of microorganisms in the evolution of animals and plants: the hologenome theory of evolution". ''FEMS Microbiology Reviews'', '''32'''(5): 723–735. {{doi|10.1111/j.1574-6976.2008.00123.x}}.</ref> Plant-associated microbial communities impact both key components of the fitness of plants, growth and survival,<ref>Vandenkoornhuyse, P., Quaiser, A., Duhamel, M., Le Van, A. and Dufresne, A. (2015) "The importance of the microbiome of the plant holobiont". ''New Phytologist'', '''206'''(4): 1196-1206. {{doi|10.1111/nph.13312}}.</ref> and are shaped by nutrient availability and plant defense mechanisms.<ref>Sánchez-Cañizares, C., Jorrín, B., Poole, P.S. and Tkacz, A. (2017) "Understanding the holobiont: the interdependence of plants and their microbiome". ''Current Opinion in Microbiology'', '''38''': 188–196. {{doi|10.1016/j.mib.2017.07.001}}.</ref> Several habitats have been described to harbor plant-associated microbes, including the rhizoplane (surface of root tissue), the [[rhizosphere]] (periphery of the roots), the endosphere (inside plant tissue), and the [[phyllosphere]] (total above-ground surface area).<ref name=Ugarelli2017 /> The microbial community in the ''P. oceanica'' rhizosphere shows similar complexity as terrestrial habitats that contain thousands of taxa per gram of soil. In contrast, the chemistry in the rhizosphere of ''P. oceanica'' was dominated by the presence of sugars like sucrose and phenolics.<ref>{{Cite journal |last1=Sogin |first1=E. Maggie |last2=Michellod |first2=Dolma |last3=Gruber-Vodicka |first3=Harald R. |last4=Bourceau |first4=Patric |last5=Geier |first5=Benedikt |last6=Meier |first6=Dimitri V. |last7=Seidel |first7=Michael |last8=Ahmerkamp |first8=Soeren |last9=Schorn |first9=Sina |last10=D’Angelo |first10=Grace |last11=Procaccini |first11=Gabriele |date=2022-05-02 |title=Sugars dominate the seagrass rhizosphere |journal=Nature Ecology & Evolution |volume=6 |issue=7 |language=en |pages=866–877 |doi=10.1038/s41559-022-01740-z| pmid=35501482  |pmc=9262712 |bibcode=2022NatEE...6..866S |issn=2397-334X}}</ref>

{{clear}}

==Cell walls==
[[File:Structures of sulfated galactans from marine organisms.jpg|thumb|upright=1.9| Structures of sulfated [[galactans]] from marine organisms.<ref name=Pfeifer2020 /> [[Sulfated polysaccharide]] structures from left to right: red algae: ''Botryocladia occidentalis'', seagrass: ''[[Ruppia maritima]]'', sea urchin: ''[[Echinometra lucunter]]'', tunicate: ''[[Styela plicata]]''.]]
{{see also|Cell wall}}

Seagrass [[cell wall]]s contain the same [[polysaccharide]]s found in [[angiosperm]] land plants, such as [[cellulose]]<ref>{{cite journal |doi = 10.15376/biores.11.2.5358-5380|title = Fiber Characteristics and Papermaking of Seagrass Using Hand-beaten and Blended Pulp|year = 2016|last1 = Syed|first1 = Nurul Farahin Nur|last2 = Zakaria|first2 = Muta Harah|last3 = Bujang|first3 = Japar Sidik|journal = BioResources|volume = 11|issue = 2|doi-access = free}}</ref> However, the cell walls of some seagrasses are characterised by [[sulfate]]d polysaccharides,<ref name=Aquino2005>{{cite journal |doi = 10.1093/glycob/cwh138|title = Occurrence of sulfated galactans in marine angiosperms: Evolutionary implications|year = 2004|last1 = Aquino|first1 = R. S.|last2 = Landeira-Fernandez|first2 = A. M.|last3 = Valente|first3 = A. P.|last4 = Andrade|first4 = L. R.|last5 = Mourão|first5 = P. A.|journal = Glycobiology|volume = 15|issue = 1|pages = 11–20|pmid = 15317737|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1590/S0102-695X2011005000199|title = Biological activities of the sulfated polysaccharide from the vascular plant Halodule wrightii|year = 2012|last1 = Silva|first1 = Juliana M. C.|last2 = Dantas-Santos|first2 = Nednaldo|last3 = Gomes|first3 = Dayanne L.|last4 = Costa|first4 = Leandro S.|last5 = Cordeiro|first5 = Sara L.|last6 = Costa|first6 = Mariana S. S. P.|last7 = Silva|first7 = Naisandra B.|last8 = Freitas|first8 = Maria L.|last9 = Scortecci|first9 = Katia Castanho|last10 = Leite|first10 = Edda L.|last11 = Rocha|first11 = Hugo A. O.|journal = Revista Brasileira de Farmacognosia|volume = 22|pages = 94–101|doi-access = free}}</ref> which is a common attribute of [[macroalgae]] from the groups of [[red algae|red]], [[brown algae|brown]] and also [[green algae]]. It was proposed in 2005 that the ability to synthesise sulfated polysaccharides was regained by marine angiosperms.<ref name=Aquino2005 /> Another unique feature of cell walls of seagrasses is the occurrence of unusual [[pectic]] polysaccharides called [[apiogalacturonan]]s.<ref>{{cite journal |doi = 10.1021/np100092c|title = Structural Characterization and Cytotoxic Properties of an Apiose-Rich Pectic Polysaccharide Obtained from the Cell Wall of the Marine Phanerogam Zostera marina|year = 2010|last1 = Gloaguen|first1 = Vincent|last2 = Brudieux|first2 = Véronique|last3 = Closs|first3 = Brigitte|last4 = Barbat|first4 = Aline|last5 = Krausz|first5 = Pierre|last6 = Sainte-Catherine|first6 = Odile|last7 = Kraemer|first7 = Michel|last8 = Maes|first8 = Emmanuel|last9 = Guerardel|first9 = Yann|journal = Journal of Natural Products|volume = 73|issue = 6|pages = 1087–1092|pmid = 20465284}}</ref><ref>{{cite journal |doi = 10.3390/md13063710|doi-access = free|title = Extraction, Isolation, Structural Characterization and Anti-Tumor Properties of an Apigalacturonan-Rich Polysaccharide from the Sea Grass Zostera caespitosa Miki|year = 2015|last1 = Lv|first1 = Youjing|last2 = Shan|first2 = Xindi|last3 = Zhao|first3 = Xia|last4 = Cai|first4 = Chao|last5 = Zhao|first5 = Xiaoliang|last6 = Lang|first6 = Yinzhi|last7 = Zhu|first7 = He|last8 = Yu|first8 = Guangli|journal = Marine Drugs|volume = 13|issue = 6|pages = 3710–3731|pmid = 26110894|pmc = 4483652}}</ref><ref name=Pfeifer2020 />

In addition to polysaccharides, [[glycoprotein]]s of the [[hydroxyproline]]-rich glycoprotein family,<ref>{{cite journal |doi = 10.1104/pp.103.031237|title = The Fasciclin-Like Arabinogalactan Proteins of Arabidopsis. A Multigene Family of Putative Cell Adhesion Molecules|year = 2003|last1 = Johnson|first1 = Kim L.|last2 = Jones|first2 = Brian J.|last3 = Bacic|first3 = Antony|last4 = Schultz|first4 = Carolyn J.|journal = Plant Physiology|volume = 133|issue = 4|pages = 1911–1925|pmid = 14645732|pmc = 300743}}</ref> are important components of cell walls of land plants. The highly glycosylated [[arabinogalactan protein]]s are of interest because of their involvement in both wall architecture and cellular regulatory processes.<ref>{{cite journal |doi = 10.1104/pp.110.156000|title = Arabinogalactan-Proteins: Key Regulators at the Cell Surface?|year = 2010|last1 = Ellis|first1 = Miriam|last2 = Egelund|first2 = Jack|last3 = Schultz|first3 = Carolyn J.|last4 = Bacic|first4 = Antony|journal = Plant Physiology|volume = 153|issue = 2|pages = 403–419|pmid = 20388666|pmc = 2879789}}</ref><ref name=Ma2018>{{cite book |doi = 10.1002/9781119312994.apr0608|chapter = AGPs Through Time and Space|title = Annual Plant Reviews online|year = 2018|last1 = Ma|first1 = Yingxuan|last2 = Zeng|first2 = Wei|last3 = Bacic|first3 = Antony|last4 = Johnson|first4 = Kim|pages = 767–804|isbn = 9781119312994|s2cid = 104384164}}</ref> Arabinogalactan proteins are ubiquitous in seed land plants<ref name=Ma2018 /> and have also been found in [[fern]]s, [[lycophyte]]s and [[moss]]es.<ref>{{cite journal |doi = 10.1016/j.carbpol.2019.01.077|title = Arabinogalactan-proteins in spore-producing land plants|year = 2019|last1 = Classen|first1 = Birgit|last2 = Baumann|first2 = Alexander|last3 = Utermoehlen|first3 = Jon|journal = Carbohydrate Polymers|volume = 210|pages = 215–224|pmid = 30732757|s2cid = 73426733}}</ref> They are structurally characterised by large polysaccharide [[moiety (chemistry)|moieties]] composed of [[arabinogalactan]]s (normally over 90% of the molecule) which are covalently linked via [[hydroxyproline]] to relatively small protein/peptide backbones (normally less than 10% of the molecule).<ref name=Ma2018 /> Distinct [[glycan]] modifications have been identified in different species and tissues and it has been suggested these influence physical properties and function. In 2020, AGPs were isolated and structurally characterised for the first time from a seagrass.<ref>{{cite journal |doi = 10.1038/s41598-020-65135-5|title = Arabinogalactan-proteins of Zostera marina L. Contain unique glycan structures and provide insight into adaptation processes to saline environments|year = 2020|last1 = Pfeifer|first1 = Lukas|last2 = Shafee|first2 = Thomas|last3 = Johnson|first3 = Kim L.|last4 = Bacic|first4 = Antony|last5 = Classen|first5 = Birgit|journal = Scientific Reports|volume = 10|issue = 1|page = 8232|pmid = 32427862|pmc = 7237498|bibcode = 2020NatSR..10.8232P}}</ref> Although the common backbone structure of land plant arabinogalactan proteins is conserved, the glycan structures exhibit unique features suggesting a role of seagrass arabinogalactan proteins in [[osmoregulation]].<ref>{{cite journal |doi = 10.1111/j.1469-8137.2005.01591.x|title = Salt stress upregulates periplasmic arabinogalactan proteins: Using salt stress to analyse AGP function|year = 2006|last1 = Lamport|first1 = Derek T. A.|last2 = Kieliszewski|first2 = Marcia J.|last3 = Showalter|first3 = Allan M.|journal = New Phytologist|volume = 169|issue = 3|pages = 479–492|pmid = 16411951}}</ref><ref name=Pfeifer2020 />

Further components of secondary walls of plants are cross-linked [[phenols|phenolic]] polymers called [[lignin]], which are responsible for mechanical strengthening of the wall. In seagrasses, this polymer has also been detected, but often in lower amounts compared to angiosperm land plants.<ref>{{cite journal |doi = 10.3354/meps094191|title = Decomposition of senescent blades of the seagrass Halodule wrightii in a subtropical lagoon|year = 1993|last1 = Opsahl|first1 = S.|last2 = Benner|first2 = R.|journal = Marine Ecology Progress Series|volume = 94|pages = 191–205|bibcode = 1993MEPS...94..191O|doi-access = free}}</ref><ref>{{cite journal |doi = 10.3354/meps194001|title = Retention of lignin in seagrasses:angiosperms that returned to the sea|year = 2000|last1 = Klap|first1 = VA|last2 = Hemminga|first2 = MA|last3 = Boon|first3 = JJ|journal = Marine Ecology Progress Series|volume = 194|pages = 1–11|bibcode = 2000MEPS..194....1K|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1016/j.cub.2008.12.031|title = Discovery of Lignin in Seaweed Reveals Convergent Evolution of Cell-Wall Architecture|year = 2009|last1 = Martone|first1 = Patrick T.|last2 = Estevez|first2 = José M.|last3 = Lu|first3 = Fachuang|last4 = Ruel|first4 = Katia|last5 = Denny|first5 = Mark W.|last6 = Somerville|first6 = Chris|last7 = Ralph|first7 = John|journal = Current Biology|volume = 19|issue = 2|pages = 169–175|pmid = 19167225|s2cid = 17409200|doi-access = free| bibcode=2009CBio...19..169M }}</ref><ref>{{cite journal |doi = 10.1016/j.orggeochem.2018.07.017|title = Radically different lignin composition in Posidonia species may link to differences in organic carbon sequestration capacity|year = 2018|last1 = Kaal|first1 = Joeri|last2 = Serrano|first2 = Oscar|last3 = Del Río|first3 = José C.|last4 = Rencoret|first4 = Jorge|journal = Organic Geochemistry|volume = 124|pages = 247–256| bibcode=2018OrGeo.124..247K | hdl=10261/169361 |s2cid = 105104424|url = https://ro.ecu.edu.au/cgi/viewcontent.cgi?article=5646&context=ecuworkspost2013|hdl-access = free}}</ref><ref name=Pfeifer2020 /> Thus, the cell walls of seagrasses seem to contain combinations of features known from both angiosperm land plants and marine macroalgae together with new structural elements. Dried seagrass leaves might be useful for papermaking or as insulating materials, so knowledge of cell wall composition has some technological relevance.<ref name=Pfeifer2020 />

{{clear}}

== Threats and conservation ==
Despite only covering 0.1 - 0.2% of the ocean’s surface, seagrasses form critically important ecosystems. Much like many other regions of the ocean, seagrasses have been faced with an accelerating global decline.<ref name=duarte>{{Cite journal |last=Duarte |first=Carlos M. |date=June 2002 |title=The future of seagrass meadows |url=https://www.cambridge.org/core/journals/environmental-conservation/article/abs/future-of-seagrass-meadows/AF04B451E1680DF8B00EBA20CBB51B56 |journal=Environmental Conservation |language=en |volume=29 |issue=2 |pages=192–206 |doi=10.1017/S0376892902000127 |bibcode=2002EnvCo..29..192D |hdl=10261/89840 |s2cid=31971900 |issn=1469-4387|hdl-access=free }}</ref>  Since the late 19th century, over 20% of the global seagrass area has been lost, with seagrass bed loss occurring at a rate of 1.5% each year.<ref>{{Cite journal |last1=Waycott |first1=Michelle |last2=Duarte |first2=Carlos M. |last3=Carruthers |first3=Tim J. B. |last4=Orth |first4=Robert J. |last5=Dennison |first5=William C. |last6=Olyarnik |first6=Suzanne |last7=Calladine |first7=Ainsley |last8=Fourqurean |first8=James W. |last9=Heck |first9=Kenneth L. |last10=Hughes |first10=A. Randall |last11=Kendrick |first11=Gary A. |date=2009-07-28 |title=Accelerating loss of seagrasses across the globe threatens coastal ecosystems |journal=Proceedings of the National Academy of Sciences |language=en |volume=106 |issue=30 |pages=12377–12381 |doi=10.1073/pnas.0905620106 |issn=0027-8424 |pmc=2707273 |pmid=19587236|bibcode=2009PNAS..10612377W |doi-access=free }}</ref> Of the 72 global seagrass species, approximately one quarter (15 species) could be considered at a [[Threatened species|Threatened]] or [[Near-threatened species|Near Threatened]] status on the [[IUCN Red List|IUCN’s]] Red List of Threatened Species.<ref name="sciencedirect.com">{{Cite journal |last1=Short |first1=Frederick T. |last2=Polidoro |first2=Beth |last3=Livingstone |first3=Suzanne R. |last4=Carpenter |first4=Kent E. |last5=Bandeira |first5=Salomão |last6=Bujang |first6=Japar Sidik |last7=Calumpong |first7=Hilconida P. |last8=Carruthers |first8=Tim J. B. |last9=Coles |first9=Robert G. |last10=Dennison |first10=William C. |last11=Erftemeijer |first11=Paul L. A. |date=2011-07-01 |title=Extinction risk assessment of the world's seagrass species |url=https://www.sciencedirect.com/science/article/pii/S0006320711001327 |journal=Biological Conservation |language=en |volume=144 |issue=7 |pages=1961–1971 |doi=10.1016/j.biocon.2011.04.010 |bibcode=2011BCons.144.1961S |s2cid=32533417 |issn=0006-3207}}</ref> Threats include a combination of natural factors, such as storms and disease, and anthropogenic in origin, including [[habitat destruction]], [[Marine pollution|pollution]], and [[climate change]].<ref name=duarte/>

By far the most common threat to seagrass is human activity.<ref>{{Cite journal |last1=Heuvel |first1=Michael R. |last2=Hitchcock |first2=Jesse K. |last3=Coffin |first3=Michael R. S. |last4=Pater |first4=Christina C. |last5=Courtenay |first5=Simon C. |date=2019-05-08 |title=Inorganic nitrogen has a dominant impact on estuarine eelgrass distribution in the Southern Gulf of St. Lawrence, Canada |journal=Limnology and Oceanography |language=en |volume=64 |issue=6 |pages=2313–2327 |doi=10.1002/lno.11185 |bibcode=2019LimOc..64.2313H |issn=0024-3590|doi-access=free }}</ref><ref>{{Cite book |last1=Hemminga |first1=Marten A. |url=https://www.cambridge.org/core/books/seagrass-ecology/53A7465F196885C57CF1977DF226C77D |title=Seagrass Ecology |last2=Duarte |first2=Carlos M. |date=2000 |publisher=Cambridge University Press |isbn=978-0-521-66184-3 |location=Cambridge |doi=10.1017/cbo9780511525551}}</ref> Up to 67 species (93%) of seagrasses are affected by human activity along coastal regions.<ref name="sciencedirect.com"/>  Activities such as coastal land development, motorboating, and fishing practices like [[trawling]] either physically destroy seagrass beds or increase [[turbidity]] in the water, causing seagrass die-off. Since seagrasses have some of the highest light requirements of [[angiosperm]] plant species, they are highly affected by environmental conditions that change water clarity and block light.<ref name="doi.org">{{Cite journal |last1=Orth |first1=Robert J. |last2=Carruthers |first2=Tim J. B. |last3=Dennison |first3=William C. |last4=Duarte |first4=Carlos M. |last5=Fourqurean |first5=James W. |last6=Heck |first6=Kenneth L. |last7=Hughes |first7=A. Randall |last8=Kendrick |first8=Gary A. |last9=Kenworthy |first9=W. Judson |last10=Olyarnik |first10=Suzanne |last11=Short |first11=Frederick T. |date=2006-12-01 |title=A Global Crisis for Seagrass Ecosystems |journal=BioScience |volume=56 |issue=12 |pages=987–996 |doi=10.1641/0006-3568(2006)56[987:AGCFSE]2.0.CO;2 |s2cid=4936412 |issn=0006-3568|doi-access=free }}</ref>

Seagrasses are also negatively affected by changing global climatic conditions. Increased weather events, [[sea level rise]], and higher temperatures as a result of [[Climate change|global warming]] all have the potential to induce widespread seagrass loss. An additional threat to seagrass beds is the introduction of non-native species. For seagrass beds worldwide, at least 28 non-native species have become established. Of these [[invasive species]], the majority (64%) have been documented to infer negative effects on the ecosystem.<ref name="doi.org"/>

Another major cause of seagrass disappearance is [[coastal eutrophication]]. Rapidly developing human population density along coastlines has led to high nutrient loads in coastal waters from sewage and other impacts of development. Increased nutrient loads create an accelerating cascade of direct and indirect effects that lead to seagrass decline. While some exposure to high concentrations of nutrients, especially [[nitrogen]] and [[phosphorus]], can result in increased seagrass productivity, high nutrient levels can also stimulate the rapid overgrowth of [[macroalgae]] and [[epiphyte]]s in shallow water, and [[phytoplankton]] in deeper water. In response to high nutrient levels, macroalgae form dense canopies on the surface of the water, limiting the light able to reach the [[Benthic zone|benthic]] seagrasses.<ref name="Seagrasses and eutrophication">{{Cite journal |last1=Burkholder |first1=JoAnn M. |last2=Tomasko |first2=David A. |last3=Touchette |first3=Brant W. |date=2007-11-09 |title=Seagrasses and eutrophication |url=https://www.sciencedirect.com/science/article/pii/S0022098107003255 |journal=Journal of Experimental Marine Biology and Ecology |series=The Biology and Ecology of Seagrasses |language=en |volume=350 |issue=1 |pages=46–72 |doi=10.1016/j.jembe.2007.06.024 |bibcode=2007JEMBE.350...46B |issn=0022-0981}}</ref> [[Algal bloom]]s caused by eutrophication also lead to [[Hypoxia (environmental)|hypoxic]] conditions, which seagrasses are also highly susceptible to. Since coastal sediment is generally [[Anoxic waters|anoxic]], seagrass must supply oxygen to their below-ground roots either through [[photosynthesis]] or by the diffusion of oxygen in the water column. When the water surrounding seagrass becomes hypoxic, so too do seagrass tissues. Hypoxic conditions negatively affect seagrass growth and survival with seagrasses exposed to hypoxic conditions shown to have reduced rates of photosynthesis, increased respiration, and smaller growth. Hypoxic conditions can eventually lead to seagrass die-off which creates a [[positive feedback cycle]], where the decomposition of organic matter further decreases the amount of oxygen present in the water column.<ref name="Seagrasses and eutrophication"/>

Possible seagrass population trajectories have been studied in the [[Mediterranean Sea|Mediterranean sea]]. These studies suggest that the presence of seagrass depends on physical factors such as temperature, salinity, depth and turbidity, along with natural phenomena like climate change and anthropogenic pressure. While there are exceptions, regression was a general trend in many areas of the Mediterranean Sea. There is an estimated 27.7% reduction along the southern coast of [[Latium]], 18%-38% reduction in the Northern Mediterranean basin, 19%-30% reduction on [[Ligurian Sea|Ligurian]] coasts since the 1960s and 23% reduction in [[France]] in the past 50 years. In [[Spain]] the main reason for regression was due to human activity such as illegal [[trawling]] and [[aquaculture]] farming. It was found that areas with medium to high human impact suffered more severe reduction. Overall, it was suggested that 29% of known areal seagrass populations have disappeared since 1879. The reduction in these areas suggests that should warming in the Mediterranean basin continue, it may lead to a functional extinction of ''[[Posidonia oceanica]]'' in the Mediterranean by 2050. Scientists suggested that the trends they identified appear to be part of a large-scale trend worldwide.<ref>{{Cite journal |last1=Telesca |first1=Luca |last2=Belluscio |first2=Andrea |last3=Criscoli |first3=Alessandro |last4=Ardizzone |first4=Giandomenico |last5=Apostolaki |first5=Eugenia T. |last6=Fraschetti |first6=Simonetta |last7=Gristina |first7=Michele |last8=Knittweis |first8=Leyla |last9=Martin |first9=Corinne S. |last10=Pergent |first10=Gérard |last11=Alagna |first11=Adriana |date=2015-07-28 |title=Seagrass meadows (Posidonia oceanica) distribution and trajectories of change |journal=Scientific Reports |language=en |volume=5 |issue=1 |pages=12505 |doi=10.1038/srep12505 |issn=2045-2322 |pmc=4516961 |pmid=26216526|bibcode=2015NatSR...512505T }}</ref>

[[Conservation biology|Conservation]] efforts are imperative to the survival of seagrass species. While there are many challenges to overcome with respect to seagrass conservation there are some major ones that can be addressed. Societal awareness of what seagrasses are and their importance to human well-being is incredibly important. As the majority of people become more urbanized they are increasingly more disconnected from the natural world. This allows for misconceptions and a lack of understanding of seagrass ecology and its importance. Additionally, it is a challenge to obtain and maintain information on the status and condition of seagrass populations. With many populations across the globe, it is difficult to map the current populations. Another challenge faced in seagrass conservation is the ability to identify threatening activities on a local scale. Also, in an ever growing human population, there is a need to balance the needs of the people while also balancing the needs of the planet. Lastly, it is challenging to generate scientific research to support conservation of seagrass. Limited efforts and resources are dedicated to the study of seagrasses.<ref>{{Cite journal |last1=Unsworth |first1=Richard K. F. |last2=McKenzie |first2=Len J. |last3=Collier |first3=Catherine J. |last4=Cullen-Unsworth |first4=Leanne C. |last5=Duarte |first5=Carlos M. |last6=Eklöf |first6=Johan S. |last7=Jarvis |first7=Jessie C. |last8=Jones |first8=Benjamin L. |last9=Nordlund |first9=Lina M. |date=2019-08-01 |title=Global challenges for seagrass conservation |url=https://doi.org/10.1007/s13280-018-1115-y |journal=Ambio |language=en |volume=48 |issue=8 |pages=801–815 |doi=10.1007/s13280-018-1115-y |issn=1654-7209 |pmc=6541581 |pmid=30456457|bibcode=2019Ambio..48..801U }}</ref> This is seen in areas such as [[India]] and [[China]] where there is little to no plan in place to conserve seagrass populations. However, the conservation and restoration of seagrass may contribute to 16 of the 17 [[Sustainable Development Goals|UN Sustainable Development Goals]].<ref>{{Cite journal |last1=Unsworth |first1=Richard K. F. |last2=Cullen-Unsworth |first2=Leanne C. |last3=Jones |first3=Benjamin L. |last4=Lilley |first4=Richard J. |date=2022-08-05 |title=The planetary role of seagrass conservation|url=https://doi.org/10.1126/science.abq6923 |journal=Science |language=en |volume=377 |issue=6606 |pages=609–613 |doi=10.1126/science.abq6923|pmid=35926055 |bibcode=2022Sci...377..609U |s2cid=251347987 }}</ref>

In a study of seagrass conservation in China, several suggestions were made by scientists on how to better conserve seagrass. They suggested that seagrass beds should be included in the Chinese conservation agenda as done in other countries. They called for the Chinese government to forbid land reclamation in areas near or in seagrass beds, to reduce the number and size of culture ponds, to control raft aquaculture and improve sediment quality, to establish seagrass reserves, to increase awareness of seagrass beds to fishermen and policy makers and to carry out seagrass restoration.<ref>{{Cite journal |last1=Xu |first1=Shaochun |last2=Qiao |first2=Yongliang |last3=Xu |first3=Shuai |last4=Yue |first4=Shidong |last5=Zhang |first5=Yu |last6=Liu |first6=Mingjie |last7=Zhang |first7=Xiaomei |last8=Zhou |first8=Yi |date=2021-06-01 |title=Diversity, distribution and conservation of seagrass in coastal waters of the Liaodong Peninsula, North Yellow Sea, northern China: Implications for seagrass conservation |url=https://www.sciencedirect.com/science/article/pii/S0025326X21002952 |journal=Marine Pollution Bulletin |language=en |volume=167 |pages=112261 |doi=10.1016/j.marpolbul.2021.112261 |pmid=33799145 |bibcode=2021MarPB.16712261X |s2cid=232775373 |issn=0025-326X}}</ref> Similar suggestions were made in India where scientists suggested that public engagement was important. Also, scientists, the public, and government officials should work in tandem to integrate [[traditional ecological knowledge]] and socio-cultural practices to evolve conservation policies.<ref>{{Cite journal |last1=Newmaster |first1=AF |last2=Berg |first2=KJ |last3=Ragupathy |first3=S. |last4=Palanisamy |first4=M. |last5=Sambandan |first5=K. |last6=Newmaster |first6=SG |date=2011-11-23 |title=Local Knowledge and Conservation of Seagrasses in the Tamil Nadu State of India |journal=Journal of Ethnobiology and Ethnomedicine |volume=7 |issue=1 |pages=37 |doi=10.1186/1746-4269-7-37 |issn=1746-4269 |pmc=3269989 |pmid=22112297 |doi-access=free }}</ref>

[[World Seagrass Day]] is an annual event held on March 1 to raise awareness about seagrass and its important functions in the marine ecosystem.<ref>{{Cite web|url=https://nationaltoday.com/world-seagrass-day/|title=World Seagrass Day|first=Haroon|last=Mohsin|date=June 24, 2022|website=National Today}}</ref><ref>{{Cite web |date=2018-06-10 |title=World Seagrass Day |url=https://wsa.seagrassonline.org/world-seagrass-day/ |access-date=2022-07-14 |website=World Seagrass Association |language=en-US}}</ref>

==See also==
* [[Alismatales]]
* [[Blue carbon]]
* [[Salt marsh]]
* [[Mangrove]]
* [[Sea rewilding]]
* [[Nursery habitat]]
* [[Ocean Data Viewer]]: contains the global distribution of seagrasses dataset

==References==
{{Reflist}}

==Further references==
{{Refbegin|32em}}
* den Hartog, C. 1970. ''The Sea-grasses of the World''. ''Verhandl. der Koninklijke Nederlandse Akademie van Wetenschappen, Afd. Natuurkunde'', No. 59(1).
* Duarte, Carlos M. and Carina L. Chiscano “Seagrass biomass and production: a reassessment” Aquatic Botany Volume 65, Issues 1–4, November 1999, Pages 159–174.
* Green, E.P. & Short, F.T.(eds). 2003. ''World Atlas of Seagrasses''. University of California Press, Berkeley, CA. 298 pp.
* Hemminga, M.A. & Duarte, C. 2000. ''Seagrass Ecology''. Cambridge University Press, Cambridge. 298 pp.
* Hogarth, Peter ''The Biology of Mangroves and Seagrasses'' (Oxford University Press, 2007)
* Larkum, Anthony W.D., Robert J. Orth, and Carlos M. Duarte (Editors) ''Seagrasses: Biology, Ecology and Conservation'' (Springer, 2006)
* Orth, Robert J. et al. "A Global Crisis for Seagrass Ecosystems" ''BioScience'' December 2006 / Vol. 56 No. 12, Pages 987–996.
* Short, F.T. & Coles, R.G.(eds). 2001. ''Global Seagrass Research Methods''. Elsevier Science, Amsterdam. 473 pp.
* A.W.D. Larkum, R.J. Orth, and C.M. Duarte (eds). Seagrass Biology: A Treatise. CRC Press, Boca Raton, FL, in press.
* A. Schwartz; M. Morrison; I. Hawes; J. Halliday. 2006. Physical and biological characteristics of a rare marine habitat: sub-tidal seagrass beds of offshore islands. ''Science for Conservation 269.'' 39 pp. [http://www.doc.govt.nz/upload/documents/science-and-technical/sfc269.pdf ]
* Waycott, M, McMahon, K, & Lavery, P 2014, A guide to southern temperate seagrasses, CSIRO Publishing, Melbourne
{{Refend}}

==External links==
* {{Cite journal|last1=Cullen-Unsworth|first1=Leanne C.|author-link=Leanne Cullen-Unsworth|last2=Unsworth|first2=Richard|date=2018-08-03|title=A call for seagrass protection| url=https://www.science.org/doi/10.1126/science.aat7318|journal=Science|language=en|volume=361|issue=6401|pages=446–448|doi=10.1126/science.aat7318|issn=0036-8075|pmid=30072524|bibcode=2018Sci...361..446C|s2cid=51908021}}
* [http://www.projectseagrass.org/ Project Seagrass - Charity advancing the conservation of seagrass through community, research and action]
* [https://regeneration.org/index.php/nexus/seagrasses Seagrasses] Project Regeneration.
* [http://www.seagrassspotter.org/ SeagrassSpotter - Citizen Science project raising awaress for seagrass meadows and mapping their locations]
* [http://ocean.si.edu/seagrass-and-seagrass-beds Seagrass and Seagrass Beds] overview from the Smithsonian Ocean Portal
* [http://www.nature.com/ngeo/journal/v5/n7/abs/ngeo1477.html Nature Geoscience article describing the locations of the seagrass meadows around the world]
* [http://www.seagrasswatch.org/ Seagrass-Watch - the largest scientific, non-destructive, seagrass assessment and monitoring program in the world]
* [http://www.restoreascar.org/ Restore-A-Scar - a non-profit campaign to restore seagrass meadows damaged by boat props]
* [http://www.seagrassnet.org/ SeagrassNet - global seagrass monitoring program]
* [http://www.oceanfdn.org/index.php?ht=d/sp/i/378/pid/378/ The Seagrass Fund at The Ocean Foundation]
* [http://www.fiu.edu/~seagrass/class/bot5647/maureen.htm Taxonomy of seagrasses]
* [http://wsa.seagrassonline.org/ World Seagrass Association]
* [http://www.seagrassli.org/ SeagrassLI]
* [http://www.unepscs.org/index.php?option=com_content&task=view&id=52&Itemid=84 Seagrass Science and Management in the South China Sea and Gulf of Thailand]
* [https://web.archive.org/web/20181215171446/http://www.blackwell-synergy.com/toc/mae/27/4 ''Marine Ecology'' (December 2006)] - special issue on seagrasses
* [https://web.archive.org/web/20110727065713/http://www.marineconservationcambodia.org/Marine-Species-Photographic-Database/Cambodian-Marine-Life/Cambodian-Marine-Plants/Seagrasses.html/ Cambodian Seagrasses]
* [https://web.archive.org/web/20110130032609/http://seagrassproductivity.com/ Seagrass Productivity - COST Action ES0906 ]
* [http://www.fish.wa.gov.au/Documents/recreational_fishing/fact_sheets/fact_sheet_seagrasses.pdf Fisheries Western Australia - Seagrass Fact Sheet]

{{aquatic ecosystem topics|expanded=marine}}
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[[Category:Blue carbon]]
[[Category:Seagrass| ]]
[[Category:Plant common names]]
[[Category:Roofing materials]]