halimeda

The genus Halimeda J.V. Lamouroux belongs to the order Bryopsidales under the family Halimedaceae. It has five monophyletic sections - Halimeda J.V. Lamouroux, Micronesicae Hillis-Col, Opuntia J. Agardh ex De Toni, Pseudo-opuntia J. Agardh ex De Toni, and Rhipsalis J. Agardh ex De Toni{{Cite journal|last1=Verbruggen|first1=Heroen|last2=Kooistra|first2=Wiebe HCF|date=2004|title=Morphological characterization of lineages within the calcified tropical seaweed genus Halimeda (Bryopsidales, Chlorophyta)|url=http://www.tandfonline.com/doi/abs/10.1080/0967026042000202163|journal=European Journal of Phycology|language=en|volume=39|issue=2|pages=213–228|doi=10.1080/0967026042000202163|s2cid=85225242 |issn=0967-0262}} - which were based on the differences in the fusions of medullary siphons. Halimeda tuna serves as the holotype for the genus.M.D. Guiry in Guiry, M.D. & Guiry, G.M. October 19, 2015. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org ; searched on January 22, 2022.{{Citation|last=Drew|first=Edward|title=Halimeda|date=2011|url=http://link.springer.com/10.1007/978-90-481-2639-2_92|encyclopedia=Encyclopedia of Modern Coral Reefs|series=Encyclopedia of Earth Sciences Series |pages=535–539|editor-last=Hopley|editor-first=David|place=Dordrecht|publisher=Springer Netherlands|doi=10.1007/978-90-481-2639-2_92|isbn=978-90-481-2638-5|access-date=2022-01-22|url-access=subscription}} There are 71 species and 67 infraspecific names listed on Algaebase as of 2015.

The thalli of Halimeda is distinctly segmented and calcified. Calcium carbonate is deposited as aragonite and calcification begins as early as 36 hours. Their segments are composed of 60-80% aragonite{{Cite journal|last1=Rees|first1=S. A.|last2=Opdyke|first2=B. N.|last3=Wilson|first3=P. A.|last4=Henstock|first4=T. J.|date=2006-11-17|title=Significance of Halimeda bioherms to the global carbonate budget based on a geological sediment budget for the Northern Great Barrier Reef, Australia|url=http://dx.doi.org/10.1007/s00338-006-0166-x|journal=Coral Reefs|volume=26|issue=1|pages=177–188|doi=10.1007/s00338-006-0166-x|hdl=1885/53116 |s2cid=22577289 |issn=0722-4028|hdl-access=free}} and are separated by nodes which are non-calcified. The thalli are composed of siphons which are ramified into medullary filaments surrounded by a cortex. The medullary filaments branch out trichotomously to form peripheral utricles which stick to each other to enclose the intersiphonal spaces of each segment. It is in these spaces that aragonite is precipitated.{{Cite journal|last1=Borowitzka|first1=Michael A.|last2=Larkum|first2=Anthony W. D.|title=Calcification in the Green Alga Halimeda. I. An Ultrastructure Study of Thallus Development1 |date=1977|url=http://dx.doi.org/10.1111/j.1529-8817.1977.tb02879.x|journal=Journal of Phycology|volume=13|issue=1|pages=6–16|doi=10.1111/j.1529-8817.1977.tb02879.x|bibcode=1977JPcgy..13....6B |s2cid=86035589 |issn=0022-3646|url-access=subscription}}

Halimeda has three types of holdfasts which serve as attachment points to the substrate. The "sprawler" type has a few loose filaments growing at the ends or in between the segments (Fig. 1). In the "rock-grower" type, the matted holdfast is composed of branched filaments which secure the thallus to a rock surface. The last type is the "sand-grower", where the filaments hold on to fine sand particles, forming a root-like structure. Halimeda is coenocytic and siphonous, meaning its cells are not divided by cross walls, and is instead a continuous filament of cells. This differentiates the genus from Acetabularia, which is another genus of green seaweed that is calcified.

Halimeda is highly abundant in the tropics including the Thai-Malay PeninsulaSupattra Pongparadon, Giuseppe C. Zuccarello, Siew-Moi Phang, Hiroshi Kawai, Takeaki Hanyuda & Anchana Prathep (2015) Diversity of Halimeda (Chlorophyta) from the Thai–Malay Peninsula, Phycologia, 54:4, 349-366, {{doi|10.2216/14-108.1}} and the Florida Keys.{{Cite journal|last1=Beach|first1=Kevin|last2=Walters|first2=Linda|last3=Vroom|first3=Peter|last4=Smith|first4=Celia|last5=Coyer|first5=James|last6=Hunter|first6=Cynthia|title=Variability in the Ecophysiology of Halimeda SPP. (Chlorophyta, Bryopsidales) on Conch Reef, Florida Keys, Usa1 |date=2003|url=http://dx.doi.org/10.1046/j.1529-8817.2003.02147.x|journal=Journal of Phycology|volume=39|issue=4|pages=633–643|doi=10.1046/j.1529-8817.2003.02147.x|bibcode=2003JPcgy..39..633B |s2cid=83973788 |issn=0022-3646|url-access=subscription}} Some species (e.g. H. copiosa, discoidea, gracilis, opuntia, simulans, and tuna) have a global distribution. Halimeda tuna is found solely in the Mediterranean. Image:Halimeda.svg

Species of Halimeda with sand-grower type holdfasts grow on sandy or muddy substrates, and are thus common in lagoons and backreefs. Those with the "sprawler" type are abundant in forereefs and on coral pinnacles.

Being a calcareous alga, Halimeda has been found to have good potential as a carbon sink and can play an important role in regulating the ocean's carbon budget.{{Cite journal|last1=Mayakun|first1=Jaruwan|last2=Prathep|first2=Anchana|date=2018|title=Calcium carbonate productivity by Halimeda macroloba in the tropical intertidal ecosystem: The significant contributor to global carbonate budgets|url=http://dx.doi.org/10.1111/pre.12361|journal=Phycological Research|volume=67|issue=2|pages=94–101|doi=10.1111/pre.12361|s2cid=91879382 |issn=1322-0829|url-access=subscription}} Some species such as H. opuntia have been found to produce up to 54.37 g CaCO₃ m⁻¹ yr⁻¹.{{Cite journal|last1=Carneiro|first1=Pedro Bastos De Macedo|last2=Pereira|first2=Jamile Ulisses|last3=Matthews-Cascon|first3=Helena|date=2016-08-30|title=Standing stock variations, growth and CaCO3 production by the calcareous green alga Halimeda opuntia|url=http://dx.doi.org/10.1017/s0025315416001247|journal=Journal of the Marine Biological Association of the United Kingdom|volume=98|issue=2|pages=401–409|doi=10.1017/s0025315416001247|s2cid=88674727 |issn=0025-3154|url-access=subscription}} The genus also contributes to reef building, as it is large producer of carbon sediments on reefs, generating a wide range of sediment sizes from coarse particles to silt and clay.{{Cite journal|last=Drew|first=Edward A.|date=1983|title=Halimeda biomass, growth rates and sediment generation on reefs in the central great barrier reef province|url=http://dx.doi.org/10.1007/bf02395280|journal=Coral Reefs|volume=2|issue=2|pages=101–110|doi=10.1007/bf02395280|s2cid=42335322 |issn=0722-4028|url-access=subscription}}Drew, E. A. and Abel, K. M. 1985. Biology, sedimentology and geography of the vast interreefal Halimeda meadows within the Great Barrier Reef province. In Harmelin-Vivien, M. and Salvat, B. (Eds). Proceedings of the 5th International Coral Reef Congress, Vol. 5. Antenne Museum-EPHE, Tahiti, pp. 15–20

Although it was largely assumed that its abundance on reefs is due to it being unpalatable to herbivores, more recent studies have found that Halimeda is in fact subject to grazing by some herbivores such as Scarus rivulatus, Hipposcarus longiceps, and Chlorurus microrhinos.{{Cite journal|last1=Mantyka|first1=CS|last2=Bellwood|first2=DR|date=2007-12-20|title=Macroalgal grazing selectivity among herbivorous coral reef fishes|journal=Marine Ecology Progress Series|volume=352|pages=177–185|doi=10.3354/meps07055|bibcode=2007MEPS..352..177M |issn=0171-8630|doi-access=free}} Hard coral cover can actually play a key role in maintaining Halimeda biomass on reefs, as one study found that thalli growing under the canopy of Acropora colonies were larger than those in open areas exposed to herbivory.{{Cite journal|last1=Castro-Sanguino|first1=Carolina|last2=Lovelock|first2=Catherine|last3=Mumby|first3=Peter J.|date=2016-02-12|title=The effect of structurally complex corals and herbivory on the dynamics of Halimeda|url=http://dx.doi.org/10.1007/s00338-016-1412-5|journal=Coral Reefs|volume=35|issue=2|pages=597–609|doi=10.1007/s00338-016-1412-5|bibcode=2016CorRe..35..597C |s2cid=16561406 |issn=0722-4028|url-access=subscription}}Image:Fossil halimeda.jpg

Halimeda reproduces both sexually and asexually. Sexual reproduction is rarely observed because it is completed in 36 hours. The process begins with gametangia forming on the edges of the segments of the thalli. By the next day, the cells of the thallus will have been entirely converted to gametangia. These will mature overnight and release gametes in the morning of the next day, after which the thallus is left white and dies in a process known as holocarpy.{{Cite journal|last=Clifton|first=Kenneth E.|date=1997-02-21|title=Mass Spawning by Green Algae on Coral Reefs|url=http://dx.doi.org/10.1126/science.275.5303.1116|journal=Science|volume=275|issue=5303|pages=1116–1118|doi=10.1126/science.275.5303.1116|pmid=9027310 |s2cid=38126293 |issn=0036-8075|url-access=subscription}} Some species of Halimeda have been found to reproduce synchronously in mass spawning events similar to that of corals, albeit occurring over several months, with small portions of the population spawning each day.{{Cite journal|last1=Clifton|first1=Kenneth E.|last2=Clifton|first2=Lisa M.|title=The Phenology of Sexual Reproduction by Green Algae (Bryopsidales) on Caribbean Coral Reefs |date=1999|url=http://dx.doi.org/10.1046/j.1529-8817.1999.3510024.x|journal=Journal of Phycology|volume=35|issue=1|pages=24–34|doi=10.1046/j.1529-8817.1999.3510024.x|bibcode=1999JPcgy..35...24C |s2cid=83704320 |issn=0022-3646|url-access=subscription}} Therefore it is likely that the life span of the genus is limited to a few months to a year.

Information on the phases of Halimeda's life cycle are limited. It is thought that there is a haploid gametophyte phase, which might be followed by a sporophyte phase, since it not yet known when meiosis occurs.

Asexual reproduction occurs via vegetative "cloning" through fragmentation and dispersal.{{Cite journal|last1=Walters|first1=Linda J|last2=Smith|first2=Celia M|last3=Coyer|first3=James A|last4=Hunter|first4=Cynthia L|last5=Beach|first5=Kevin S|last6=Vroom|first6=Peter S|date=2002|title=Asexual propagation in the coral reef macroalga Halimeda (Chlorophyta, Bryopsidales): production, dispersal and attachment of small fragments|url=http://dx.doi.org/10.1016/s0022-0981(02)00335-0|journal=Journal of Experimental Marine Biology and Ecology|volume=278|issue=1|pages=47–65|doi=10.1016/s0022-0981(02)00335-0|issn=0022-0981|url-access=subscription}}

The genus' photosynthetic pigments are those typical of class Chlorophyta (chlorophyll a and b) and also include siphonoxanthin and siphonein.

Currently, Halimeda does not appear to be cultivated for aquaculture purposes.

Methanol and dimethyformamide extracts of Halimeda opuntia have been observed to have antibacterial properties against some species of microorganisms, including Saccharomyces cerevisiae, Escherichia coli, Bacillus subtilis, and most significantly, Staphylococcus aureus.Selim, S. A. (2012). Antimicrobial, antiplasmid and cytotoxicity potentials of marine algae Halimeda opuntia and Sarconema filiforme collected from Red Sea Coast. World Academy of Science, Engineering and Technology, 61, 1154-1159. Halimeda opuntia ethanol extract exhibited activity against hepatitis C virus (HCV) due to polymerase inhibitory (HCV-796) binding sites based on molecular docking simulation.{{Cite journal |last1=Abdel-Rahman |first1=Iman A. M. |last2=Attia |first2=Eman Zekry |last3=Aly |first3=Omar M. |last4=Saber |first4=Hani |last5=Rushdi |first5=Mohammed I. |last6=Abdelmohsen |first6=Usama Ramadan |date=2022-12-01 |title=Metabolite profiling of green algae Halimeda opuntia to target hepatitis C virus-796 polymerase inhibitors assisted by molecular docking |url=https://www.sciencedirect.com/science/article/pii/S0254629922005713 |journal=South African Journal of Botany |language=en |volume=151 |pages=538–543 |doi=10.1016/j.sajb.2022.10.038 |s2cid=253209343 |issn=0254-6299|doi-access=free }}{{Cite journal |last1=Attia |first1=Eman Zekry |last2=Youssef |first2=Nora Hassan |last3=Saber |first3=Hani |last4=Rushdi |first4=Mohammed I. |last5=Abdel-Rahman |first5=Iman A. M. |last6=Darwish |first6=Ahmed G. |last7=Abdelmohsen |first7=Usama Ramadan |date=2022-10-13 |title=Halimeda opuntia and Padina pavonica extracts improve growth and metabolic activities in maize under soil-saline conditions |url=https://link.springer.com/10.1007/s10811-022-02844-6 |journal=Journal of Applied Phycology |volume=34 |issue=6 |pages=3189–3203 |language=en |doi=10.1007/s10811-022-02844-6 |s2cid=252938716 |issn=0921-8971|url-access=subscription }} Methanolic extracts of Halimeda macroloba have recently been found to exhibit cytotoxicity towards MCF-7 and HT 29 cells, which are derived from human breast cancer cell lines and colon cancer lines, respectively.{{Cite journal|last1=Nazarudin|first1=Muhammad Farhan|last2=Isha|first2=Azizul|last3=Mastuki|first3=Siti Nurulhuda|last4=Ain|first4=Nooraini Mohd.|last5=Mohd Ikhsan|first5=Natrah Fatin|last6=Abidin|first6=Atifa Zainal|last7=Aliyu-Paiko|first7=Mohammed|date=2020-11-22|title=Chemical Composition and Evaluation of the α-Glucosidase Inhibitory and Cytotoxic Properties of Marine Algae Ulva intestinalis, Halimeda macroloba, and Sargassum ilicifolium|journal=Evidence-Based Complementary and Alternative Medicine|volume=2020|pages=1–13|doi=10.1155/2020/2753945|pmid=33299448 |pmc=7704141 |issn=1741-4288|doi-access=free }} These results therefore suggest the genus' potential for cultivation as a food source. An experiment on rats showed that free phenolic acids of Halimeda monile have antioxidant properties which could aid in protecting against liver problems.{{Cite journal|last1=Mancini-Filho|first1=Jorge|last2=Novoa|first2=Alexis Vidal|last3=González|first3=Ana Elsa Batista|last4=de Andrade-Wartha|first4=Elma Regina S|last5=Mancini|first5=Dalva Assunção Portari|date=2009-10-01|title=Free Phenolic Acids from the Seaweed Halimeda monile with Antioxidant Effect Protecting against Liver Injury|journal=Zeitschrift für Naturforschung C|volume=64|issue=9–10|pages=657–663|doi=10.1515/znc-2009-9-1009|pmid=19957433 |s2cid=8846116 |issn=1865-7125|doi-access=free}} Halimeda tuna appears to be used as fodder in the Philippines.Ganzon-Fortes, E. T. (2022, January). Introduction To The Seaweeds: Their Characteristics And Economic Importance. REPORT ON THE TRAINING COURSE ON GRACILARIA ALGAE Manila, Philippines 1–30 April 1981. Manila; Philippines. Retrieved from https://www.fao.org/fishery/docs/CDrom/aquaculture/a0845t/volume2/docrep/field/009/ag155e/AG155E02.htm#ch2.3

Image:Halimeda fossil.jpg

File:Halimeda copiosa at 10 meters depth in shallow cave.jpg at 10 meters depth in shallow cave]]

{{div col|colwidth=20em}}

• H. bikinensis
• H. borneensis
• H. cereidesmis
• H. copiosa
• H. cryptica
• H. cuneata
• H. cylindracea
• H. discoidea
• H. distorta
• H. favulosa
• H. fragilis
• H. gigas
• H. goreauii
• H. gracilis
• H. heteromorpha
• H. howensis
• H. hummii
• H. incrassata
• H. kanaloana
• H. lacrimosa
• H. lacunalis
• H. macroloba
• H. macrophysa
• H. magnidisca
• H. melanesica
• H. micronesica
• H. minima
• H. monile
• H. opuntia
• H. pumila
• H. pygmaea
• H. renschii
• H. scabra
• H. simulans
• H. stuposa
• H. taenicola
• H. tuna
• H. velasquezii

{{div col end}}

{{Reflist}}

• [http://www.aims.gov.au/pages/research/project-net/ugbr/ugbr-06.html "Deepwater seagrass and Halimeda: lost lawns of the outer shelf"] {{Webarchive|url=https://web.archive.org/web/20060910070926/http://www.aims.gov.au/pages/research/project-net/ugbr/ugbr-06.html |date=2006-09-10 }},
• Australian Institute of Marine Science, retrieved 10 November 2006
• [https://web.archive.org/web/20070831155453/http://www.gbrmpa.gov.au/corp_site/info_services/publications/misc_pub/fauna_flora/appendix_04.html "Other species of conservation concern"],
• Great Barrier Reef Marine Park Authority, retrieved 10 November 2006
• [http://reefcorner.com/reef-database-index/macroalgae-index/halimeda-macroalgae/ ReefCorner - Halimeda Algae Database Entry] {{Webarchive|url=https://web.archive.org/web/20170418080458/http://reefcorner.com/reef-database-index/macroalgae-index/halimeda-macroalgae/ |date=2017-04-18 }}

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Category:Bryopsidales genera

Category:Bryopsidales