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Avrainvillea is a green macroalgal genus of the family Dichotomosiphonaceae (order Bryopsidales). Many species have been morphologically described, but few studies have addressed the genetic diversity of this genus. Based on a rich collection of specimens from the tropical Western Atlantic, Indian and Pacific Oceans, we aimed to (1) reassess Avrainvillea species diversity through species delimitation analyses, (2) update their distribution ranges, (3) reconstruct the species phylogenetic relationships, based on a concatenated multilocus matrix (tufA, rbcL and 18S rDNA) and (4) revise their taxonomy and describe new species where necessary. Our species delimitation approach highlighted 23 secondary species hypotheses in our collection, including nine known and currently accepted species, four species complexes (A. amadelpha, A. lacerata, A. erecta-obscura and A. mazei-nigricans), and eight new species for which we provide descriptions: A. laciniata (Papua New Guinea), A. minima and A. pyrochroma (Madagascar), A. mollis and A. kanakiensis (New Caledonia), A. pavonina (Fiji), A. spongiosa (Pacific) and A. corticata (Indo-Pacific). We also propose the resurrection of A. gracillima Børgesen, the reinstatement of Avrainvillea lacerata var. robustior A.Gepp & E.S.Gepp, and the synonymy of A. rotumensis A.D.R.N’Yeurt, D.S.Littler & Littler with A. pacifica A.Gepp & E.S.Gepp. We complemented the taxonomic work by providing a contemporary dichotomous key for morphological identification of all extant species. Our multilocus phylogeny included 25 species of Dichotomosiphonaceae and recovered Avrainvillea as a polyphyletic group, divided into three distinct clades, with Cladocephalus luteofuscus positioned within the group. The species determined using the species delimitation approach were all monophyletic and 19 of them were highly supported. For the first time, this study also provided genetic sequences for A. asarifolia, A. clavatiramea, A. digitata, A. elliottii, A. fulva

Udoteaceae is a morphologically diverse family of the order Bryopsidales. Despite being very widespread geographically, this family is little known compared to the closely related Halimedaceae or Caulerpaceae. Using the most extensive Udoteaceae collection to date and a multilocus genetic dataset (tufA, rbcL and 18S rDNA), we reassessed the species diversity of the family, as well as the phylogenetic relationships, the diagnostic morpho‐anatomical characters and evolutionary history of its genera, toward a proposed taxonomic revision. Our approach included a combination of molecular and morphological criteria, including species delimitation methods, phylogenetic reconstruction and mapping of trait evolution. We successfully delimited 62 species hypotheses, of which 29 were assigned (existing) species names and 13 represent putative new species. Our results also led us to revise the genera Udotea s.s., Rhipidosiphon s.s. and Chlorodesmis s.s., to validate the genus Rhipidodesmis and to propose three new genera: Glaukea gen. nov., Ventalia gen. nov., and Udoteopsis gen. nov. We also identified two large species complexes, which we refer to as the “Penicillus‐Rhipidosiphon‐Rhipocephalus‐Udotea complex” and the “Poropsis‐Penicillus‐Rhipidodesmis complex”. Using a time‐calibrated phylogeny, we estimated the origin of the family Udoteaceae at Late Triassic (ca 216 Ma), whereas most of the genera originated during Paleogene. Our morphological inference results indicated that the thallus of the Udoteaceae ancestor was likely entirely corticated and calcified, composed of a creeping axis with a multisiphonous stipe and a pluristromatic flabellate frond. The frond shape, cortication and calcification are still symplesiomorphies for most extant Udoteaceae genera and represent useful diagnostic characters.

To assess the photophysiological capacity of the recently described Ulva batuffolosa to form blooms in coral reefs, we monitored its biomass and photophysiological capacity with pulse amplitude modulated (PAM) fluorometry over a year period on a coastal barrier reef in New Caledonia, along with temperature and light. Effective and maximum quantum efficiencies of the photosystem II measured on this Ulva species indicated that the algae was in a “good health” all over the year with high quantum efficiencies under either light (Fq’/Fm’) or dark incubated conditions and (Fv/Fm). Photo-acclimation and -regulation status used by this Ulva sp. were driven by seasons (i.e., light and temperature) in the lagoon. Although photo-inhibition was an evidence during the warm period, U. batuffolosa was overall well adapted to tolerate the range of irradiance and temperature that characterized the lagoon over the year, which suggests that photosynthesis is not an impediment to green tides by this species.

There is a growing interest in elucidating the biogeographical processes underlying biodiversity patterns of seaweeds, with recent studies largely focusing on red and brown macroalgae. This study focuses on the siphonous green algal family Udoteaceae, which is diverse and globally distributed in tropical to warm-temperate seas, and includes species that form important components of tropical reefs. We explored the historical processes that have shaped current biodiversity patterns in the family by analyzing a comprehensive dataset of 568 specimens sampled across its geographical range, and including 45 species, corresponding to 59% of the known diversity. Historical biogeographical analysis was based on a three-locus time-calibrated phylogeny, and probabilistic modeling of geographical range evolution. Many species were found to have restricted ranges, indicative of low dispersal capacity. Our analysis points toward a Western Tethys origin and early diversification of the Udoteaceae in the Triassic period. Three centers of diversity were identified, which are, in order of highest species richness, the Central Indo-Pacific, the Western Indian Ocean, and the Greater Caribbean. Different drivers have likely played a role in shaping these diversity centres. Species richness in the Central Indo-Pacific likely resulted from speciation within the region, as well as recolonization from neighbouring regions, and overlap of some wider ranged species, corroborating the “biodiversity feedback” model. Species richness in the Western Indian Ocean can be explained by ancient and more recent diversification within the region, and dispersal from the Central Indo-Pacific. The Greater Caribbean region was colonized more recently, followed by diversification within the region.

Genera and species of the tribes Rhipileae and Rhipiliopsideae are abundant in most coral reef ecosystems worldwide. However, the group has been largely overlooked, and very little genetic data is available to accurately assess its diversity, phylogenetic relationships, and geographical distribution. Our study provided an in-depth reassessment of tribes Rhipileae and Rhipiliopsideae based on a species-rich dataset and the combination of molecular species delimitation, multilocus phylogenetic analyses (tufA, rbcL and 18S rDNA), and morpho-anatomical observations. Our results revealed an unexpected diversity of 38 morphologically-validated species hypotheses, including 20 new species, two of which are described in this paper and one resurrected species (Rhipilia diaphana). Based on our phylogenetic results we proposed to redefine the genera Rhipilia and Rhipiliopsis and described two new genera, Kraftalia gen. nov. (Rhipileae) and Rhipiliospina gen. nov. (Rhipiliopsideae). Finally, we validated Rhipiliella Kraft and included it in tribe Rhipileae. Although Rhipilia and Rhipiliopsis have a pantropical distribution, none of the species studied here appeared cosmopolitan; instead, they have restricted distributions.

Les algues sont extrêmement difficiles, voire impossibles, à identifier sur la base de caractères morphologiques ce qui compromet leur étude dans le cadre de la science participative. L’objectif de cet essai est de proposer des pistes pour surmonter ce verrou afin d’acquérir et de valoriser des données citoyennes sur les algues dans des domaines d'étude de la diversité spécifique et fonctionnelle. À cette fin, un état des lieux des programmes de science participative est réalisé. Il considère à la fois les programmes portant sur les algues, aux échelles nationale (française) et internationale, les programmes visant le milieu marin et pouvant intégrer la collecte de données sur les algues, ainsi que des programmes s’inscrivant dans d’autres domaines, mais dont le concept pourrait être transféré ou adapté à la phycologie. Par ailleurs, des outils et réseaux pouvant soutenir la collecte et l’exploitation des données sur les algues sont également recensés. Une première série de recommandations est émise à partir des leviers et freins mis en évidence. Ensuite, différentes voies potentielles pour la valorisation et l’utilisation des données sur les algues, inspirées de la base de données réalisée, sont proposées et décrites. Une évaluation multicritères permet de discriminer leurs perspectives d'application et d’identifier les projets à prioriser. Enfin, les cinq voies sélectionnées à l’issu de l’analyse sont décrites en terme de modalités de mises en œuvre, et des recommandations générales finalisent l’essai. Les principales conclusions de cette évaluation explicitent qu'il est, dans l'immédiat, préférable d'opter pour des voies d'utilisation et de valorisation des données existantes sur les algues en créant, entre autres, des relais français de programmes de science participative internationaux fonctionnels et populaires. Néanmoins, des voies innovantes avec une application inédite sur les algues ont également été proposées et restent très pertinentes, malgré un classem