Dictyota is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end of 2017, some 237 different diterpenes had been identified from across the genus.
Taxonomy and Nomenclature The genus Dictyota was first described by Jean Vincent Lamouroux in 1809. The name Dictyota is derived from the Greek word "Διχτυον" meaning "net" or "network", referring to the inner cellular structure of specimens when viewed under a microscope, which features netted cortical and medullary cells.
Dictyota belongs to the order Dictyotales and the SSDO-clade, which also includes the orders Sphacelariales, Syringodermatales, and Onslowiales. The family Dictyotaceae is divided into two tribes: Dictyoteae and Zonarieae. The former have a single lens-shaped apical cell from which the thallus grows, while the latter are characterized by a row or cluster of apical cells. The genera Glossophora, Glossophorella, and Pachdictyon are synonyms of Dictyota as DNA sequencing revealed that they were closely related.
Morphology
External characteristics Dictyota has "flat, ribbon-like axes" which exhibit dichotomous branching that may be either isotomous (equal or symmetrical) or anisotomous (unequal). Isotomous branches may be recurved, while anisotomous branches may become falcate (hooked), or cervicorn, if combined with twisting axes. Apical meristems of Dictyota species have been reported to be either truncate, rounded, or acute. A considerable degree of morphological plasticity has been observed from branching patterns, thus making molecular analyses indispensable when identifying species.
Colors of living thalli range from dark brown to green (as in D. friabilis) or blue (as in D. cyanoloma). The thalli grow from apical cells which differentiate into an outer cortical and an inner medullary cell layer. Cortical cells on the margins of the thalli may grow into leaf-like projections or teeth (as in D. ciliolata and D. cyanoloma) while adventitious branches may grow from the central cortical cells. Thalli may also grow hair (20-50 um in diameter). Thalli attach to the substrate via rhizoids which are multicellular, uniseriate, branching, and hyaline (glassy or transparent). Different species may have one or several attachment points which can lead to a wide range of growth forms (i.e. creeping thalli or fully erect).
Internal anatomy The thalli are parenchymatous and are characterized by one or more apical cells that divide into an outer cortical and an inner medullary cell layer which can have several different configurations (e.g. uni-layered cortex with unilayered medulla, uni-layered cortex with multi-layered medulla, etc.).
Distribution Dictyota is distributed along tropical to temperate waters with species having generally restricted geographic ranges. It is the most abundant genus of brown algae in the Mediterranean Sea as well as the Atlantic coasts of Europe.
Ecology Species of the genus are commonly found in subtidal to intertidal rocky pools. Seasonality in species' abundances as well as fertility are driven mainly by temperature, photoperiod, and solar radiation. For instance, populations of D. dichotoma in the southern hemisphere are highly abundant for a majority of the year but are largely absent in the warmer months, which is when its northern counterparts are most abundant and fertile.
Life History Dictyota exhibits an isomorphic life cycle wherein the alternating gametophyte and sporophyte phases appear morphologically similar. This alternation co-occurs with a change in ploidy. The gametophytes produce gametes which undergo fertilization to produce the diploid sporophyte, which then produces sporangia which will release 4 haploid spores through meiosis. Half of the haploid spores will develop into the female gametophytes while the other half will develop into male gametophytes, starting the process over again.
Dictyota is dioecious and reproduces both sexually and asexually. Release of gametes follows a diurnal and lunar periodicity. Gametes are often released 20–30 minutes after first light, with peaks occurring once or twice a month depending on the species. Asexual reproduction may occur via adventitious branching following the loss of the apical meristem.
Chemical Composition Dictyota is known to have high levels of fatty acids and lipids which makes the genus ideal for use as feedstock. The pigments found in Dictyota are Chlorophyll a, c, fucoxanthin and violaxanthin which are present in a ratio of 13:3:10:1. This ratio may be altered by depth.
Exploitation/Utilization and Management The genus is not currently cultivated nor harvested on an industrial scale. It is mainly exploited for its secondary metabolites which are known to have anticoagulant, antibacterial, anti-inflammatory properties, among others, making them useful for a wide range of pharmaceutical applications. For instance, there is evidence that methanolic extracts of Dictyota inhibits the butyrylcholinesterase (BuChE) enzyme in humans, which could potentially treat Alzheimer's disease.
Other applications include its use as biofuel - due to the high lipid content of some species - and as supplemental feeds for poultry, cattle, and fish. A study in 2014 found that feeds with D. bartayresiana supplements could potentially reduce in vitro methane production of ruminants by 92.2%, which may have implications for reducing emissions from the agricultural sector.
Species
The genus Dictyota contains the following species:Guiry, M.D. & Guiry, G.M. (2018). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway (taxonomic information republished from AlgaeBase with permission of M.D. Guiry). Dictyota J.V.Lamouroux, 1809. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=144086 on 2018-07-12M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2018. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org/search/genus/detail/?genus_id=oe101e7b01e405395 ; searched on 12 July 2018.
Dictyota acutiloba J.Agardh, 1848 Dictyota adhaerens Noda, 1965 Dictyota adnata Zanardini, 1878 Dictyota adnata f. nana Post Dictyota aegerrima (Allender & Kraft) De Clerck, 2006 Dictyota alternifida J.Agardh, 1894 Dictyota anastomosans Steen et al. Dictyota apiculata var. Agardh Weber-van Bosse Dictyota asiatica I.K.Hwang Dictyota attenuata P.Crouan & H.Crouan, 1842 Dictyota bartayresiana J.V.Lamouroux, 1809 Dictyota bartayresiana var. divaricata Kützing Dictyota bifurca J.Agardh, 1894 Dictyota binghamiae J.Agardh, 1894 Dictyota canaliculata O.De Clerck & E.Coppejans, 1997 Dictyota canariensis (Grunow) Tronholm, 2013 Dictyota caribaea Hörnig & Schnetter, 1992 Dictyota cervicornis f. pseudodichotoma Taylor Dictyota cervicornis f. spiralis Taylor<ref name="AB" Dictyota ceylanica var. anastomosans Yamada Dictyota chalchicueyecanensis Lozano-Orozco & Sentíes Dictyota ciliata var. humilis Grunow Dictyota ciliolata Sonder ex Kützing, 1859 Dictyota concrescens W.R.Taylor, 1945 Dictyota coriacea (Holmes) I.K.Wang, H.-S.Kim & W.J.Lee, 2004 Dictyota crenulata J.Agardh, 1847 Dictyota cribrosa Setchell & N.L.Gardner, 1930 Dictyota crinita (J.Agardh) Hörnig, Schnetter & Prud'Homme van Reine, 1992 Dictyota crux Dictyota crux f. parva A.Bachmann Dictyota cuneata Dickie, 1874 Dictyota cyanoloma Tronholm, De Clerck, A.Gómez-Garreta & Rull Lluch, 2010 Dictyota cymatophila Tronholm, M.Sanson & Afonso-Carrillo, 2010 Dictyota decumbens (R.W.Ricker) Hörnig, Schnetter & Prud'homme van Reine, 1992 Dictyota detergenda Kraft, 2009 Dictyota dhofarensis (Nizamuddin & A.C.Campbell) De Clerck, 2006 Dictyota dichotoma (Hudson) J.V.Lamouroux, 1809 Dictyota dichotoma Suhr, 1839 Dictyota dichotoma f. angustior Schiffner Dictyota dichotoma var. fimbriata Piccone & Grunow Dictyota dichotoma var. genuina Grunow Dictyota dichotoma var. guinea Grunow Dictyota dichotoma var. inequalis S.F.Gray Dictyota dichotoma var. intricata (C.Agardh) Greville Dictyota dichotoma var. patens Dictyota dichotoma f. proliferans Ercegovic Dictyota diemensis Sonder ex Kützing, 1859 Dictyota dilatata Yamada, 1925 Dictyota divaricata P.L.Crouan & H.M.Crouan, 1865 Dictyota dolabellana De Paula, Yoneshigue-Valentin & Teixeira, 2008 Dictyota dumosa Børgesen, 1935 Dictyota fasciculata Sperk, 1869 Dictyota fascida J.Agardh, 1898 Dictyota fasciola var. abyssinica J.Agardh Dictyota fasciola (Roth) J.V.Lamouroux, 1809 Dictyota fasciola var. divergens f. major Schiffner Dictyota fasciola var. divergens f. minor Schiffner Dictyota fasciola var. elongata De Notaris Dictyota fasciola f. major Schiffner Dictyota fasciola f. minor Schiffner Dictyota fasciola var. repens (J.Agardh) Ardissone Dictyota fastigiata Sonder, 1845 Dictyota fenestrata J.Agardh, 1894 Dictyota flabellata (F.S.Collins) Setchell & N.L.Gardner, 1924 Dictyota flabellulata Foster & Schiel Dictyota flagellifera Kraft, 2009 Dictyota foliosa J.Agardh, 1892 Dictyota friabilis Setchell, 1926 Dictyota furcellata (C.Agardh) Greville, 1830 Dictyota galapagensis (Farlow) De Clerck, 2006 Dictyota grossedentata De Clerck & Coppejans, 1999 Dictyota guajirae Hörnig, Schnetter & J.M.Over, 1992 Dictyota guineënsis (Kützing) P.L.Crouan & H.M.Crouan, 1878 Dictyota gunniana (J.Agardh) I.Hörnig, R.Schnetter & Prud'homme van Reine, 1992 Dictyota hamifera Setchell, 1926 Dictyota harveyana Dictyota hauckiana Nizamuddin, 1975 Dictyota humifusa Hörnig, Schnetter & Coppejans, 1992 Dictyota implexa (Desfontaines) J.V.Lamouroux, 1809 Dictyota indica Anand, 1965 Dictyota inscripta J.Agardh, 1893 Dictyota intermedia Zanardini, 1874 Dictyota jamaicensis W.R.Taylor, 1960 Dictyota kunthii (C.Agardh) Greville, 1830 Dictyota laciniata J.V.Lamouroux, 1809 Dictyota lata J.V.Lamouroux, 1809 Dictyota linearis var. campsosticha Montagne Dictyota linearis f. intricata Kützing Dictyota linearis var. major P.Crouan & H.Crouan Dictyota linearis var. minor Sonder Dictyota littoralis P.Anand, 1965 Dictyota liturata J.Agardh, 1848 Dictyota major W.R.Taylor, 1945 Dictyota masonii Setchell & N.L.Gardner, 1930 Dictyota mayae Lozano-Orozco & Sentíes Dictyota mediterranea (Schiffner) G.Furnari, 1997 Dictyota menstrualis (Hoyt) Schnetter, Hörnig & Weber-Peukert, 1987 Dictyota mertensii (C.Martius) Kützing, 1859 Dictyota moniliformis (J.Agardh) Hörnig, Schnetter & Prud'homme van Reine, 1992 Dictyota multifida (J.E.Smith) Bory, 1838 Dictyota naevosa (Suhr) Montagne, 1840 Dictyota nigrescens Zanardini, 1878 Dictyota nigricans J.Agardh, 1882 Dictyota ocellata J.Agardh, 1894 Dictyota pachyderma Luan Rixiao & Ding Lanping Dictyota paniculata J.Agardh, 1841 Dictyota papenfussii Lindauer, 1949 Dictyota pavonia var. maxima J.V.Lamouroux Dictyota pedrochei Lozano-Orozco & Sentíes Dictyota pellucida J.Agardh, 1892 Dictyota penicellata J.V.Lamouroux Dictyota phlyctaenodes Montagne, 1852 Dictyota pinnata (E.Y.Dawson) I.Hörnig, R.Schnetter & Prud'homme van Reine, 1993 Dictyota pinnatifida Kützing, 1859 Dictyota pinnatifida var. rigida Grunow Dictyota plantaginea J.V.Lamouroux ex Frauenfeld, 1855 Dictyota plectens (Allender & Kraft) Kraft, 2009 Dictyota pleiacantha Tronholm, 2013 Dictyota polyclada Sonder ex Kützing Dictyota pontica Sperk, 1869 Dictyota pulchella Hörnig & Schnetter, 1988 Dictyota rhizodes (Turner) J.V.Lamouroux Dictyota rigida De Clerck & Coppejans, 1999 Dictyota robusta J.Agardh, 1894 Dictyota rotunda C.Agardh, 1820 Dictyota sandvicensis Sonder, 1859 Dictyota serrulata J.V.Lamouroux, 1809 Dictyota spathulata Yamada, 1928 Dictyota spinulosa J.D.Hooker & Arnott, 1838 Dictyota spiralis Montagne, 1846 Dictyota stolonifera E.Y.Dawson, 1962 Dictyota suhrii (Kützing) I.Hörnig, R.Schnetter & W.F.Prud'homme van Reine, 1992 Dictyota vieillardii Kützing, 1863