Assessment of five markers as potential barcodes for identifying Sargassum subgenus Sargassum species (Phaeophyceae, Fucales)

Abstract -D NA barcoding has been the focus of numerous publications, but only limited studies are available for marine macroalgae and even less are specific to Phaeophyceae. The case study presented here assesses the potential of five different markers for use as DNA barcodes in the genus Sargassum:the nuclear ITS-2, aportion of the chloroplastic RubisCO operon and amitochondrial spacer (mtsp), COI and cox3. To assess and compare the identification success of the five markers we used three criteria based on distance methods: Best Match, Best Close Match and All Species Barcodes applied to five datasets representing 13 closely related species of Sargassum subgenus Sargassum.Results demonstrated the inadequacy of ITS-2 and RubisCO as barcode markers while they suggested the potential of the mitochondrial markers. Additional research is needed based on numerically and geographically larger datasets to further assess the identification success of these markers. ITS-2 / cox3/CO

Patch dynamics driven by wave exposure in subtidal temperate seaweeds are exacerbated by warming oceans

Over the past decades, ocean temperatures have been steadily increasing and are projected to continue to do so, stressing many temperate marine organisms. Changing temperatures do not affect ecosystems in isolation, but interact with many other factors in shaping ecological communities. We investigated the changes over 2 decades in subtidal temperate seaweed communities over a wave exposure gradient in Western Australia, a global warming hotspot. We found higher diversity in the seaweed community and a higher proportion of biomass of species with a warm affinity (expressed as the tropicalization index: TI) over time. There was no decline in biomass of the dominant habitat-forming kelp Ecklonia radiata on low wave exposure reefs, while it was patchier and comprised a lower proportion of the total seaweed biomass on the medium and high wave exposure reefs. Furthermore, the presence of E. radiata was disproportionally associated with low abundances of seaweeds with warm affinity. The increasing patchiness of E. radiata likely provided a competitive release for other seaweeds, and the increase in abundance of Scytothalia dorycarpa likely provided a compensatory effect which resulted in a lower than expected TI. We found no indication of an ameliorating effect by wave exposure, and conclude that the patch dynamics driven by wave exposure are more likely exacerbated by increasing ocean temperatures on subtidal temperate reefs. If this continues, the reduction in E. radiata and increase in warm affiliated seaweeds will result in a more diverse seaweed community, but one with a lower standing biomass

Seaweed diversification driven by Taiwan’s emergence and the Kuroshio Current: insights from the cryptic diversity and phylogeography of Dichotomaria (Galaxauraceae, Rhodophyta)

Ocean currents play a role in both facilitating and impeding connectivity of marine organisms’ populations, serving as key drivers and potential barriers. The emergence of Taiwan around five million years ago (Mya) impacted the Kuroshio Current which later shaped the distribution of marine organisms. In this study, we examined how the Kuroshio Current influenced the distribution and population divergence of the marine red alga Dichotomaria elegans (Galaxauraceae, Nemaliales). Through phylogenetic analysis, species delimitation, and morphological comparison of Taiwanese species, we determined its phylogenetic position relative to other species within the D. marginata complex of the genus Dichotomaria. We uncovered the hidden cryptic diversity within the D. marginata complex in Taiwan and proposed the new combinations D. elegans and D. latifolia based on Galaxaura elegans and G. latifolia. Genetic analysis based on three loci (mitochondrial cox2-3 and cox1, and plastid rbcL) from 32 locations across the Philippines, Taiwan, and Japan revealed three allopatric lineages within D. elegans. The first lineage is restricted to the northern Philippines and southern Taiwan, while the second has a broader latitudinal range along the Kuroshio Current. The third lineage is found in southeast Luzon, Philippines, close to the bifurcation of the North Equatorial Current, near the start of the Kuroshio Current. The divergence of the first two lineages during the mid-Pliocene (~3.7 Mya) coincided with the emergence of Taiwan, with the current dynamics accentuating their separation. The Kuroshio Current exhibited a dual impact on the biogeography of D. elegans: promoting the dispersal of the second lineage towards higher latitudes and preventing the first lineage from moving northward. Principal component analysis showed that habitat conditions and morphologies differed between the two D. elegans lineages. This study provides insights into the cryptic diversity of Dichotomaria in Taiwan, as well as the genetic divergence, biogeographical patterns, and ecological associations of D. elegans, highlighting the interplay of island formation and currents shaping the diversification of seaweeds in the Northwest Pacific Ocean

Taxonomie du genre Sargassum (Fucales, Phaeophyceae) en Nouvelle-Calédonie et dans le Pacifique Sud. Approches morphologique et moléculaire

Sargassum C. Agardh is a genus of marine brown macrophyte classified in the class Phaeophyceae. This genus is distributed worldwide and recognized as the most diversified of the order Fucales. It is especially well represented in the tropical and inter-tropical Pacific where it forms large underwater forests of well known ecological and economical importance. But with more than a thousand taxa described over the last 200 years, and an old and complex classification, identifying a Sargassum species is a difficult task. The Sargassum diversity of the south Pacific islands has been studied here in its Indo-Pacific biogeographical context. A combined morphological and DNA analyses method was applied to recent collections from several Pacific regions. The classification, as well as the taxonomic value of classic morphological characters, was revised. More than 52 news synonymies have been proposed as well as significant revisions of the traditional classification of Sargassum subgenus Sargassum.Sargassum C. Agardh est un genre de macrophyte marine appartenant à la classe des Phaeophyceae. Ce genre est réparti mondialement et reconnu comme un des plus diversifiés de l'ordre des Fucales. Il est particulièrement bien représenté dans le Pacifique tropical et intertropical où il forme de grandes algueraies dont l'importance écologique et l'intérêt économique sont reconnus. Néanmoins, avec près d'un millier de taxons décrits depuis 200 ans, et une classification complexe et ancienne, identifier une espèce de Sargassum est une tâche difficile. La diversité du genre Sargassum des îles du Pacifique Sud a été analysée ici dans son contexte biogéographique Indopacifique. L'étude a été réalisée grâce à une méthode combinée utilisant des analyses morphologiques et ADN sur des collections récentes provenant de plusieurs régions du bassin Pacifique. La classification ainsi que la valeur taxonomique des caractères morphologiques traditionnellement utilisés ont été remis en question. Plus de 52 nouvelles synonymies ont été proposées ainsi que des révisions significatives de la classification traditionnelle du sous-genre Sargassum

190 years of Sargassum taxonomy, facing the advent of DNA phylogenies

Sargassum C. Agardh is one of the morphologically most complex phaeophyceaen genera and represents the most species-rich genus of the brown algal order Fucales Bory de Saint-Vincent (Phaeophyceae). The genus' classification system dates back to the 19th century and is based on observed differences in macro-morphological characters. Those morphological characters may display important variation within individual species, and several authors have linked the taxonomic complexity of the genus to its highly polymorphic nature and phenotypic plasticity. Among the large choice of existing species and subspecies epithets (about 1000), identifying taxa accurately is a difficult task, often relying on authors' interpretation of short Latin diagnoses or descriptions published in local Floras. Recently, the study of individual species' morphological range and DNA phylogenies underlined inconsistencies within low taxonomic levels (sections, subsections, series and species groups). Results highlighted the weak taxonomic value of traditional characters used to classify species, and pointed out significant taxonomic issues. The four Sargassum subgenera (S. subgen. Arthrophycus, Bactrophycus, Sargassum and Phyllotrichia) are now subdivided into a total of 12 sections and further subdivisions were abandoned. Two possible new sections need to be assessed. In the present paper, we raise the hypothesis that S. subgen. Arthrophycus could be merged to S. subgen. Bactrophycus, and that S. subgen. Phyllotrichia could be transferred to the recently reinstated genus Sargassopsis Trevisan. We also propose that two sections of the S. subgen. Bactrophycus: S. sect. Halochloa and Repentia be merged. A summary of the actual classification is given along with an identification key for Sargassum subdivisions

Taxonomic revision of Sargassum species (fucales, phaeophyceae) from New Caledonia based on morphological and molecular analyses

Sargassum C. Agardh (1820) is a taxonomically difficult genus distributed worldwide and reported as the most species-rich genus of the Fucales. It is especially abundant in the Pacific where decreasing species richness is reported to occur from west to east. New Caledonia has been recognized as one of the hotspots of Sargassum diversity; however, species lists available for this region are old and incomplete and have not yet been updated with regard to the latest taxonomic revisions published. This study aimed at revising Sargassum diversity in New Caledonia and to assess its geographic affinities with neighboring Pacific regions. We used combined morphological and DNA analyses on new collections and examined numerous type specimens. Although 45 taxa have been listed in the literature, most of them have been either transferred to synonymy since or misidentified, and in this study, only 12 taxa were recognized as occurring in New Caledonia. They belong to the subgenus Sargassum sect. Binderianae (Grunow) Mattio et Payri (2), sect. Ilicifoliae (J. Agardh) Mattio et Payri (2), sect. Polycystae Mattio et Payri. (1), sect. Sargassum (4), sect. Zygocarpicae (J. Agardh) Setch. (2), and subgenus Phyllotrichia (Aresh.) J. Agardh (1). New Caledonian Sargassum flora appeared as the second richest in the region after the Pacific coast of Australia, with which it has shown high similarity, and shared species with all neighboring regions. One species, S. turbinarioides Grunow, is considered as endemic to New Caledonia. The low genetic diversity detected among several polymorphic species belonging to sect. Sargassum is also discussed

Taxonomie du genre Sargassum (Fucales, Phaeophyceae) en Nouvelle-Calédonie et dans le Pacifique Sud (approches morphologique et moléculaire)

Sargassum C. Agardh est un genre appartenant à la classe des Phaeophyceae (algue brune). Ce genre est réparti mondialement et reconnu comme un des plus diversifiés de l ordre des Fucales. Il est particulièrement bien représenté dans le Pacifique tropical et intertropical où il forme de grandes algueraies dont l importance écologique et l intérêt économique sont reconnus. Néanmoins, avec près d un millier de taxons décrits depuis 200 ans, et une classification complexe et ancienne, identifier une espèce de Sargassum est une tâche difficile. La Nouvelle-Calédonie est répertoriée comme un des hot-spots de la biodiversité du genre Sargassum, pourtant les listes d espèces disponibles pour cette région sont une compilation de travaux anciens et incomplets. La situation est comparable dans les autres îles du Pacifique Sud en particulier aux îles Salomon, à Fidji, au Vanuatu et en Polynésie française. Le but de cette étude était d analyser la diversité du genre Sargassum de Nouvelle- Calédonie et des îles du Pacifique Sud dans le contexte biogéographique de l Indopacifique. Pour atteindre cet objectif, une méthode combinée utilisant des analyses morphologiques et moléculaires des régions ADN nucléaire ITS-2, chloroplastique RubisCO et mitochondriale cox3 a été utilisée sur des collections récentes provenant de plusieurs régions du bassin Pacifique. D autre part, de nombreux spécimens types ont été examinés. La classification ainsi que la valeur taxonomique des caractères morphologiques traditionnellement utilisés ont été remis en question. Plus de 52 nouvelles synonymies sont proposées ainsi que des révisions significatives de la classification traditionnelle du sous-genre Sargassum, avec en particulier trois nouvelles sections et l abandon des rangs taxonomiques inférieurs. Au terme de cette étude, il est proposé que le sous-genre Sargassum soit sous-divisé en cinq sections : (i) Binderianae (Grunow) Mattio et al., (ii) Ilicifoliae (J. Agardh) Mattio et al., (iii) Polycystae Mattio et Payri, (iv) Sargassum (=Malacocarpicae (J. Agardh) Abbott et al.), et (v) Zygocarpicae (J. Agardh) Setchell. Par ailleurs, la faible diversité génétique observée entre plusieurs taxons polymorphes appartenant à la sect. Sargassum est discutée. Des 67 épithètes recensées dans la littérature intéressant les îles du Pacifique Sud, seuls 14 taxons appartenant aux sous-genres Sargassum et Phyllotrichia sont finalement reconnus dans cette étude. La flore de Sargassum néocalédonienne apparaît comme la plus riche des localités étudiées avec 12 taxons montrant une large répartition à l échelle de l Indopacifique. Plusieurs hypothèses concernant les régions ayant pu jouer un rôle de refuge durant le dernier maximum glaciaire et à partir desquelles se seraient dispersées et diversifiées les flores actuelles, sont discutées. Il en ressort que, le Pacifique Ouest pourrait représenter un refuge pour les sections Ilicifoliae Binderianae, Polycystae et Zygocarpicae, et les sous-genres Arthrophycus, Bactrophycus et Phyllotrichia. A l est du Pacifique le Golfe de Californie pourrait représenter un refuge pour la section Sargassum.Sargassum C. Agardh is a genus belonging to the class Phaeophyceae (brown algae). This genus is distributed worldwide and is recognized as one of the most diverse of the order Fucales. It is especially well represented in the tropical and intertropical Pacific where is forms large beds with a well known ecological importance and economic potential. However, with about a thousand taxa described during the last 200 years and a complex and old classification, Sargassum species are difficult to identify accurately. New Caledonia is recorded as one of the Sargassum biodiversity hot spots but species lists available for this region are old and incomplete. The situation is similar in other south Pacific islands, especially in the Solomon Islands, Fiji, Vanuatu and French Polynesia. The aim of this study was to analyse Sargassum diversity from New Caledonia and other Pacific islands in the Indopacific biogeographic context. To reach this goal, a method combining the analysis of morphology and nuclear ITS-2, chloroplastic RubisCo, and mitochondrial cox3 DNA regions was used on new collections from several regions in the Pacific basin. In addition, numerous type specimens were examined. The subgenus Sargassum s classification, as well as the taxonomic value of traditional morphological characters, were re-evaluated. Fifty-two new synonymies are proposed as well as significant revisions of the subgenus Sargassum s traditional classification, especially three new sections and the abandon of lower taxonomic ranks. We propose that the subgenus Sargassum be divided into fives section as follows : (i) Binderianae (Grunow) Mattio et al., (ii) Ilicifoliae (J. Agardh) Mattio et al., (iii) Polycystae Mattio et Payri, (iv) Sargassum (=Malacocarpicae (J. Agardh) Abbott et al.), and (v) Zygocarpicae (J. Agardh) Setchell. The low genetic diversity observed between several polymorphic taxa of section Sargassum is discussed. In addition among the 67 epithets listed in the available literature for Pacific islands, only 14 taxa belonging to the subgnera Sargassum and Phyllotrichia are recognized in this study. The New Caledonian Sargassum flora appear as on of the richest among the studied localities with 12 taxa showing a large Indopacific distribution. Several hypotheses about the regions potentially involved as refuges during the Last Glacial Maximum, and from which actual floras could have dispersed and diversified, are discussed. The western Pacific region could represent a refuge for sections Ilicifoliae Binderianae, Polycystae and Zygocarpicae, as well as subgenera Arthrophycus, Bactrophycus and Phyllotrichia. To the east, the Gulf of California could have played the role of a refuge for section Sargassum.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

The vegetation on ultramafic rocks in New Caledonia

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Taxonomic revison of Sargassum (Fucales, Phaeophyceae) from French Polynesia based on morphological and molecular analyses

An assessment of Sargassum in French Polynesia was done through the critical revision of the literature, type specimens, and specimens from type localities. Sargassum samples were newly collected, and four morphotypes were identified on the basis of morphological characters. Molecular analysis of the nuclear ITS2, chloroplastic partial rbcLS, and mitochondrial cox3 markers generated two clades and confirmed the recent divergence suspected between closely related species. Although 18 different epithets have been attributed to French Polynesian Sargassum since 1828, only three species are considered valid in this study. Most of these species were transferred to S. pacificum Bory, the only species present in the Society Archipelago, while S. obtusifolium J. Agardh was restricted to the Austral Archipelago, and S. echinocarpum J. Agardh was confirmed for the Austral and Gambier Archipelagos. A morphological identification key is provided, along with descriptions and illustrations for each polymorphic species. Moreover, the study of several regional collections underlined similar and low specific diversity among Sargassum populations in the southeastern Pacific. As a result of this study, we propose that S. bacciferum J. Agardh var. latiuscula Grunow, S. bisserula f. pacifica Grunow, S. boraborense (Grunow) Setch., S. mangarevense (Grunow) Setch., S. sociale (Grunow) Setch., and S. tahitense Grunow be considered as heterotypic synonyms of S. pacificum. Sargassum skottsbergii Sjostedt, S. hawaiiensis Doty et Newhouse, S. divaricatum var. chilensis Grunow, S. obtusifolium J. Agardh f. chamberlainii Grunow, and S. obtusifolium J. Agardh f. lendigeroides Grunow are further regarded as heterotypic synonyms of S. obtusifolium

Taxonomic revision of Sargassum sect. Acanthocarpicae (Fucales, Phaeophyceae)

Sargassum is one of the morphologically most complex phaeophyceaen genera, and is divided into subgenera, sections, subsections, series and species groups based on highly polymorphic characters. Recent DNA analyses have highlighted incongruities in the traditional classification of the genus and especially within Sargassum subg. Sargassum sect. Acanthocalpicae. Our goal was to re-assess the relationships among taxa currently attributed to this section in the Pacific basin. We undertook the taxonomic study in two main steps: (I) the morphological examination of large collections from inter-tropical Pacific islands and type specimens from worldwide localities; and (2) DNA analyses using a set of three markers (ITS-2, partial rbcLS-operon, cox3). Morphological and DNA analyses confirmed that S. sect. Acanthocarpicae is based on unsuitable morphological characters and is not monophyletic. On the basis of this study, we propose (1) abandoning subsections within S. sect. Acanthocarpicae; (2) synonymization of S. sect. Acanthocarpicae and sect. Malacocarpicae with sect. Sargassum; and (3) the elevation of S. ser. Ilicifoliae and ser. Binderianae to sectional rank as well as their re-description according to new sets of morphological characters