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''Halimeda'' is a genus of green
https://www.algaebase.org ; searched on January 22, 2022. There are 71 species and 67 infraspecific names listed on Algaebase as of 2015.
https://www.algaebase.org ; searched on January 22, 2022. 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.
''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.
https://www.algaebase.org ; searched on January 22, 2022.
https://www.algaebase.org ; searched on January 22, 2022. Those with the "sprawler" type are abundant in forereefs and on coral pinnacles.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.
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. Some species such as ''H. opuntia'' have been found to produce up to 54.37 g CaCO3 m−1 yr−1. 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.
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''. 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.
* ''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''
"Deepwater seagrass and Halimeda: lost lawns of the outer shelf"
, * Australian Institute of Marine Science, retrieved 10 November 2006
"Other species of conservation concern"
* Great Barrier Reef Marine Park Authority, retrieved 10 November 2006
ReefCorner - Halimeda Algae Database Entry
{{Taxonbar, from=Q2707334 Bryopsidales genera Bryopsidales
macroalgae
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
. The algal body (thallus
Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...
) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
s. However one species, ''Halimeda tuna
''Halimeda tuna'' is a species of calcareous green seaweed in the order Bryopsidales. It is found on reefs in the Atlantic Ocean, the Indo-Pacific region and the Mediterranean Sea. ''Halimeda tuna'' is the type species of the genus ''Halimeda'' ...
'', was described as pleasant to eat with oil, vinegar, and salt.
As in other members of the order Bryopsidales, individual organisms are made up of single multi-nucleate cells. Whole meadows may consist of a single individual alga connected by fine threads running through the substrate.
''Halimeda'' is responsible for distinctive circular deposits in various parts of the Great Barrier Reef
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, A ...
on the north-east coast of Queensland
)
, nickname = Sunshine State
, image_map = Queensland in Australia.svg
, map_caption = Location of Queensland in Australia
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, establishe ...
, Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
. ''Halimeda'' beds form in the western or lee side of outer shield reefs where flow of nutrient-rich water from the open sea allows them to flourish, and are the most extensive, actively accumulating ''Halimeda'' beds in the world.
The genus is one of the best studied examples of cryptic species
In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each ot ...
pairs due to morphological convergence
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
within the marine macroalgae.
Kooistra W.H.C.F., Coppejans E.G.G. & Payri C. (2002). Molecular systematics, historical ecology, and phylogeography of ''Halimeda''. (Bryopsidales) ''Molecular Phylogenetics and Evolution'' 24: 121–138
Verbruggen H., De Clerck O., Kooistra W.H.C.F. & Coppejans E. (2005). Molecular and morphometric data pinpoint species boundaries in ''Halimeda'' section ''Rhipsalis'' (Bryopsidales, Chlorophyta). ''Journal of Phycology'' 41: 606-621
Verbruggen H., De Clerck O., Schils T., Kooistra W.H.C.F. & Coppejans E. (2005). Evolution and phylogeography of ''Halimeda'' section ''Halimeda''. ''Molecular Phylogenetics and Evolution'' 37: 789-803
Some species grow so vigorously in tropical lagoons that the sediment is composed solely of the remains of their tissues, forming a calcareous "Halimeda sand". In fact some tropical reef systems, such as atoll
An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gro ...
s, consist largely of Halimeda sand accumulated over the aeons.
Taxonomy and nomenclature
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 - which were based on the differences in the fusions of medullary siphons. ''Halimeda tuna'' serves as theholotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...
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. Morphology
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 and are separated by nodes which are non-calcified.M.D. Guiry in Guiry, M.D. & Guiry, G.M. October 19, 2015. ''AlgaeBase''. World-wide electronic publication, National University of Ireland, Galway.Distribution
''Halimeda'' is highly abundant in the tropics including the Thai-Malay Peninsula, and the Florida Keys. Some species (e.g. ''H. copiosa, discoidea, gracilis, opuntia, simulans,'' and ''tuna'') have a global distribution. ''Halimeda tuna'' is found solely in the Mediterranean.M.D. Guiry in Guiry, M.D. & Guiry, G.M. October 19, 2015. ''AlgaeBase''. World-wide electronic publication, National University of Ireland, Galway.Ecology
Species of ''Halimeda'' with sand-grower type holdfasts grown on sandy or muddy substrates, and are thus common in lagoons and backreefs.M.D. Guiry in Guiry, M.D. & Guiry, G.M. October 19, 2015. ''AlgaeBase''. World-wide electronic publication, National University of Ireland, Galway.Life history
''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. 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. 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''Chemical composition
The genus' photosynthetic pigments are the those typical of class Chlorophyta (chlorophyll ''a'' and ''b'') and also includes siphonoxanthin and siphonein.Exploitation and cultivation
Currently, ''Halimeda'' does not appear to be cultivated for aquaculture purposes.Utilization
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.'' ''Halimeda'' opuntia ethanol extract exhibited activity against hepatitis C virus (HCV) due to polymerase inhibitory (HCV-796) binding sites based on molecular docking simulation. 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. 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. ''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#ch2.3Species
* ''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''
References
External links
"Deepwater seagrass and Halimeda: lost lawns of the outer shelf"
, * Australian Institute of Marine Science, retrieved 10 November 2006
"Other species of conservation concern"
* Great Barrier Reef Marine Park Authority, retrieved 10 November 2006
ReefCorner - Halimeda Algae Database Entry
{{Taxonbar, from=Q2707334 Bryopsidales genera Bryopsidales