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Ulva , a green marine macroalga, lives in a symbiotic relationship with bacteria like Roseovarius sp. and  Maribacter sp., which produce algal growth- and morphogenesis-promoting factors (AGMPFs) crucial for algal development. In the absence of all AGMPFs including thallusin Ulva exhibit a callus-like morphotype characterised by a lack of cellular differentiation. This study introduces calli as a novel model to investigate the AGMPF action. The metabolic impacts of AGMPFs were investigated by comparing the axenic calli of  Ulva compressa (cultivar Ulva mutabilis ) with those exposed to AGMPFs. Adding AGMPFs regenerated the callus and promoted germling-like structures, along with changes in the metabolome. The bouquet of AGMPFs, containing (−)-thallusin, induced significant variations in fatty acid metabolism, notably an increase of palmitic acid and several polyunsaturated fatty acids, along with a change of the ω6:ω3 ratio (<0.7), which may directly affect growth as well as membrane and cell wall formation. The results highlight the significant implications of bacterial-derived AGMPFs instead of live bacteria and underscore the necessity of optimising AGMPF distribution in cultivation to improve the nutritional quality of Ulva for food and feed.

Cymodocea nodosa and Ruppia maritima constitute key seagrasses that provide habitat, stabilize sediment, and support nutrient cycling and carbon sequestration in coastal ecosystems. This study aims to investigate the composition and abundance of epiphytic macroalgae on C. nodosa and R. maritima at the coastal sites of Epanomi and Vravrona, parts of Natura 2000 network in Greece. Seasonal plant material collection was conducted from 2022 to 2023 and epiphytic macroalgae were removed and identified to species or genera level. The coverage and number of epiphytic macroalgal taxa were determined and species were classified into Ecological Status Groups (ESGs). The similarity of macroalgal composition and coverage between seasons, locations and hosts was analyzed using cluster analysis. Vravrona exhibited higher epiphyte coverage compared to Epanomi, while Rhodophyta dominated qualitatively and quantitatively throughout the year. In Epanomi, seasonal shifts in dominance were observed, with different algal groups prevailing in each season. Cluster analysis revealed distinct clusters of epiphyte communities, indicating significant differences between sites and seasons, suggesting that local environmental conditions play a role in determining the composition and structure of epiphytic communities. The findings underscore the need for continuous environmental assessments to protect coastal waters and support conservation strategies for these critical ecosystems.

The Egadi Islands Marine Protected Area (MPA) (west of Sicily) is one of the largest MPAs in the Mediterranean Sea. Nevertheless, studies of benthic macroalgae in this MPA are few and quite outdated. The latest study, performed about 20 years ago, documented the disappearance of cold affinity species (mainly Cystoseira s.l. and Sargassum species) in favour of warm affinity ones. In this study, we conducted a visual census activity through snorkelling and scuba dives on the island of Marettimo, and we found a total of 17 Fucales: four belonging to Cystoseira , eight to Ericaria , two to Gongolaria , and three to Sargassum . The obtained data were compared with previous studies conducted in the 1970s and in the early 2000s in the E-MPA reporting data on the Fucales stands to understand the dynamics that have occurred during this period. Five species, not previously reported from the island of Marettimo, were found during this study: Cystoseira cf micheleae , Ericaria barbatula , Ericaria brachycarpa var. claudiae , Gongolaria montagnei var. compressa and Sargassum cf furcatum .

Chnoospora is one of the genera in Scytosiphonaceae with many taxonomic changes, comprising only two currently taxonomically accepted species. Chnoospora minima , its type species, has the widest distribution range and is characterized by a simple morphology with cylindrical or flattened thalli and dichotomous branching. On the Mexican coasts, its distribution is disjunct, being recorded on both the Pacific and Atlantic sides. In the present study we aim to characterize morphologically and molecularly the Mexican populations of C. minima . Our results revealed two phylogenetically independent groups, corresponding with different species with sympatric distribution in the tropical Mexican Pacific, C. minima and C. ramosissima sp. nov. Chnoospora ramosissima has the typical morphology of the genus, however, it is distinct in having relatively constant length of the branching segments, that are gradually reducing towards the apical portions, giving the thallus a profusely branched appearance; in addition, cellular measurements also differ between them. In contrast, C. minima , presented five different morphotypes on the Mexican coasts, however, all of them were different from C. ramosissima by having a central branching segment longer than the rest, subsequently reducing towards the apical portions, giving the thallus the appearance of being elongated and little branched.

Recent and future coastal habitat degradation and climate change can result in the loss of genetic diversity, especially in Southeast Asia. Despite its economic importance for the agar industry, the phylogeography of the intertidal red alga Gracilaria salicornia from Vietnam remains unexplored. Here we used 399 mitochondrial COI sequences, including 55 newly generated from Vietnam, to decipher the phylogeographic pattern of G. salicornia . The COI phylogeny and haplotype network revealed the presence of three haplogroups in G. salicornia . Haplogroup I, comprising 18 haplotypes, predominantly inhabited the west of the South China Sea, while haplogroup II, consisting of eight haplotypes from Japan and the Philippines, likely reflecting the influence of the Kuroshio Current. A single haplotype from the Philippines was placed in haplogroup III. G. salicornia exhibited high genetic diversity, with neutrality test, mismatch distribution, and Bayesian skyline plot suggesting a sudden demographic or range expansion during the mid-Pleistocene. The divergence of haplogroups I and II, occupying the eastern and western sides of the South China Sea, likely resulted from sea currents and glacial sea-level changes. Our study on historical phylogeography offers valuable insights that will encourage further research into the population history of tropical red algae in Southeast Asia, a region for its remarkable marine biodiversity.

Recent comprehensive phylogenetic and morphological analyses have led to the recognition of the Grateloupiaceae as a distinct family within the Halymeniales. Despite strong support for its monophyly, the genera within the Grateloupiaceae display diverse morphological traits and share external features that prevent accurate generic identification without additional molecular analyses. This study conducted detailed morphological observations and assessed the phylogenetic relationships of a Grateloupia -like species found in Korea, which superficially resembles “G”. imbricata . We describe Pachymeniopsis shinchonai sp. nov., characterized by erect, compressed axes branching dichotomously to subdichotomously, maturing into a dome-shape thallus. This species is distinguished from related species by its densely arranged thallus, which forms a hemispherical shape, its abundant secondary attachments adhering to adjacent branches and the substratum, and its phylogenetic position in the rbc L tree. This species contributes to the biodiversity of the intertidal zone on Jeju Island, Korea. Our phylogenetic analysis confirms the monophyly of nine clades within the Grateloupiaceae and underscores the need for further studies to resolve the generic status of Pachymeniopsis, Prionitis, and Phyllymenia , which cannot be readily distinguished by morphological criteria alone. Due to the lack of support for several genera, comprehensive collections and multi-gene analyses are essential to accurately delineate the internal generic relationships within the family.

In this paper, the red macroalga Ceramium pallidum is reported and described for the first time from the Mediterranean Sea. Specimens of C. pallidum were collected in the lower intertidal zone from Jebha on the Mediterranean coast of Morocco. The material was examined in detail and compared with congeners. Descriptions of morphological and reproductive features with taxonomic remarks are provided, accompanied by photographs. Furthermore, a key for all the Mediterranean taxa of non-spinose Ceramium is presented. The total number of taxa at both specific and infraspecific levels accepted in the genus Ceramium for the Mediterranean Sea is 31.

This work conducted metabolic profiling on nine brown, one red, and two green algal species collected from different sampling sites of Kuwait’s coastal waters in the Arabian Gulf. Crude extracts of freeze-dried seaweed samples were prepared using solvents of different polarities by solvent extraction, namely, methanol and dichloromethane, and analysed by liquid chromatography-mass spectrometry for metabolite identification. The Principal Component Analysis scores scatter plot grouped the extracts of Codium papillatum , Chondria sp., Iyengaria stellata , Feldmannia indica , Padina boergesenii , Colpomenia sinuosa , Dictyota dichotoma , Sargassum aquifolium , S. asperifolium and S. ilicifolium together, suggesting their similar chemical profiles. However, S. ilicifolium var. acaraeocarpum and C. vagabunda were separated from the remainder of seaweed taxa by unique metabolite features. As expectable, species-specific differences in chemical profiles were observed in different seaweeds. Dereplication studies were employed to identify differential metabolites and to search for their previously reported bioactivities. The study led to the tentative identification of 22 metabolites using various annotation tools contained within the Global Natural Products Social Molecular Networking platform, most importantly MolNetEnhancer. The most prevalent chemical class annotations were “terpenoids” and “lipids and lipid-like molecules”. The potential modes of action of the metabolites in certain diseases were further studied using computational approaches such as molecular docking and ligand-based pharmacophore generation. This constitutes the first metabolomics study of seaweeds from the Arabian Gulf.