ABSTRACT Optimizing biomass yield and biochemical composition in sea-based cultivation of Ulva fenestrata requires balancing environmental conditions with cultivation timing. This study examined how outplant and harvest timing influence growth and biochemical traits in a temperate sea-based aquaculture system. Outplant timing had a pronounced effect on biomass yield, while biochemical composition was more strongly influenced by harvest timing and associated environmental factors. Seedlings deployed in autumn (September–November) achieved up to eight-fold higher biomass than those outplanted in late winter or spring (February–March). Despite low temperature and light during early winter, autumn outplants maintained slow but steady growth, indicating physiological resilience and effective nutrient utilization under suboptimal conditions. Biochemical composition – including crude protein, chlorophyll, carotenoids and total fatty acids – peaked during late winter to early spring harvests when ambient nitrate levels were highest. As temperature and light increased in spring, tissue nitrogen and polyunsaturated fatty acid contents declined, reflecting nitrogen limitation and temperature-driven lipid remodelling. This trade-off between maximizing biomass under warmer conditions and maintaining nutritional quality during cooler, nutrient-rich periods highlights the need for strategic cultivation management. We conclude that optimal production of U. fenestrata in temperate waters is achieved by autumn outplanting and harvest before the spring nutrient decline when aimed at food purposes. Continuous environmental monitoring, adaptive harvest timing and strain selection could further enhance both biomass yield and quality, supporting sustainable and high-value Ulva cultivation.

ABSTRACT This study evaluates the diversity and distribution of species of the genus Halosaccion along the Russian Pacific coast using morphological data and molecular analyses. Halosaccion minjaii was found to be genetically distant from other species in the genus; this and its unique morphological features – namely the development of tetrasporangia in elevated sori between long sterile filaments (which are much longer than tetrasporangia) and the mode of spermatangia formation – led to the proposal of a new genus, Nothohalosaccion, with a single species N. minjaii. Data on species distribution in the north-western Pacific were refined. Halosaccion americanum was recorded for the first time in the Okhotsk Sea. This extended the species range north-westward. In contrast, the distribution of Halosaccion microsporum was restricted to northern and western parts of the Okhotsk Sea, the eastern Kamchatka coast and western Bering Sea. The distribution patterns of species of the genera Halosaccion and Nothohalosaccion are discussed in relation to the oceanography of the region. Types of the names H. microsporum, Dumontia hydrophora (≡ Halosaccion hydrophorum) and Ulva glandiformis (≡ Halosaccion glandiforme) are designated to guarantee their unambiguous use and to stabilize the nomenclature.

ABSTRACT Since the late 19th century, studies of the genus Porphyra sensu lato (Bangiales, Rhodophyta) have revealed a broad spectrum of life history strategies and reproductive modes. These variations are often interpreted as adaptive responses to the selective pressures imposed by spatially and temporally heterogeneous environments. However, the dynamics and prevalence of sexual versus asexual reproduction in natural populations remain poorly understood and insufficiently documented. In this study, we investigated the spatio-temporal variation in reproductive strategies of Porphyra umbilicalis, an emerging target species for aquaculture in the Northeast Atlantic, across a broad European range. Through microscopic examination and tracking the germination of spores released from fertile individuals in multiple populations, four main patterns were identified: (1) clear geographic structuring of reproductive strategies, with asexual reproduction prevailing in the Southern Bight of the North Sea and English Channel, and sexual populations more common in the South European Atlantic Shelf and Celtic Seas; (2) persistent dominance of asexual reproduction in populations with mixed reproductive modes, with a seasonal increase in the frequency of sexually reproductive individuals during winter; (3) microhabitat partitioning within the high intertidal zone, with asexual individuals occupying uppermost elevations and sexual individuals concentrated below, indicating ecologically driven niche differentiation; and (4) no consistent link between thallus size and reproductive mode, although sexual individuals were significantly larger during winter and spring. Collectively, these findings illustrate how environmental gradients shape reproductive strategies in P. umbilicalis, and suggest that asexuality may confer adaptive advantages in marginal intertidal zones.

ABSTRACT Until recently, two species of the tribe Chondrieae were recorded from the Russian Pacific coast: Chondria dasyphylla and C. decipiens. In this study we re-examined these algae from the region using comparative morphological and molecular analyses. It was shown that both C. dasyphylla and C. decipiens do not occur in the studied region. Specimens previously identified as ‘C. decipiens’ are confirmed as Neochondria ammophila based on molecular and morphological analyses. Specimens from the Russian Pacific coast previously identified as C. ‘dasyphylla’, represent a complex of species, described here as a new genus Nothochondria, with N. dimorphica sp. nov., and two new species, C. epiphytica and C. pendula. Phylogenetic analysis based on COI, rbcL and SSU indicates that N. dimorphica forms a strongly supported clade separate from a diverse clade containing Chondria capillaris, the generitype of Chondria, as well as from the recently described genus, Neochondria. Based on its vegetative anatomy, Nothochondria is intermediate between Chondria and Neochondria. Similarly to Neochondria, it has adventitious cells among pericentral cells, while the distinctness of the axial and pericentral cells throughout the thallus makes it close to Chondria. Data on the distribution of these species along the Russian Pacific coast are provided.

ABSTRACT Ocean warming is driving poleward range shifts for many marine species. For foundation organisms that underpin the wider ecosystem, such as canopy-forming seaweeds, shifts in distributions or population demography can have widespread ecological consequences. The warm water kelp, Laminaria ochroleuca, is found towards its leading edge in Plymouth Sound (southwest England, UK), where it has proliferated in recent years, partially replacing the cool-water congeneric species, L. hyperborea, at some wave-sheltered locations. To determine how ecosystem dynamics have changed due to this substitution and to benchmark population structure, monthly surveys were conducted of L. ochroleuca populations at three sites over 10 months. Canopy-forming L. ochroleuca sporophytes were recorded in all months at all sites, in densities of up to ~8 individuals m‒2, indicating that this species is now a conspicuous space occupier within this ecosystem. Blade length, weight and fertility followed clear seasonal patterns peaking during late spring/early summer and rapidly declining in autumn/winter. Between-site variability was also observed, with greater densities, blade lengths/widths and standing stock biomass at the most wave-sheltered but tidally influenced site. The most abundant herbivore associated with L. ochroleuca was the blue rayed limpet, Patella pellucida, which was predominantly found in summer months and in greater abundance than reported values for other kelps in the region. Our survey wide estimates of carbon standing stock ranged from 408 ± 67 to 1006 ± 181 g C m‒2 across sites, with a regional mean of 615 g C m‒2, which was in line with previous estimates for the congeneric L. hyperborea at nearby sites. Overall, the most detailed demographic assessment of L. ochroleuca to date is provided, which allows for a greater understanding of its ecological role within the wider temperate ecosystem and serves as a robust baseline against which to detect future ecological changes.

ABSTRACT Marine algae, a rich source of bioactive substances, have long been utilized in biomedical and veterinary sciences. This study breaks new ground by assessing the antiviral therapeutic potential of water extracts from four algal species – Colaconema formosanum, Caulerpa microphysa, Gelidium amansii and Sarcodia suae – against vesicular stomatitis virus (VSV) infection. The standout among these was Sarcodia suae water extract (SSWE), which not only significantly repressed VSV replication and enhanced cell survival without cytotoxic effects, but also demonstrated its antiviral activity through interference with viral attachment, entry, RNA replication, and egress, and reduced VSV-induced autophagy in Mv1Lu cells during the late stages of infection. The EC50 of SSWE was 0.422 ± 0.14 mg ml‒1. The cytotoxicity assay confirmed the high biocompatibility of SSWE. This study identifies SSWE as a promising natural antiviral agent and elucidates its mechanisms of action, highlighting the need for further research to optimize its use in controlling VSV-related diseases.

ABSTRACT Rugulopteryx okamurae is an invasive non-indigenous species (NIS) of marine alga present in the benthic communities of the Strait of Gibraltar, where it has colonized most of the coast triggering ecological, economic and social consequences. The purple sea urchin Paracentrotus lividus is a generalist herbivore with potential to provide resistance to this NIS. Two experiments were carried out to determine if (i) P. lividus consumes R. okamurae under laboratory conditions, (ii) to assess its grazing preferences when this NIS is offered together with the native Ulva sp. and (iii) to find biochemical tissue markers related to R. okamurae ingestion. In the first experiment, sea urchins fed with R. okamurae, Ulva sp. or both diets were evaluated in groups for two months. Ingestion, food preference, growth and survival were assessed. In the second one, the same specimens from the R. okamurae and mixed diets were used to analyse their individual preferences, ingestion rates, growth and fatty acid profiles during another two months. Ingestion rates showed that sea urchins accepted the NIS R. okamurae as food under laboratory conditions, increasing its intake after a long exposure period. The electivity values for R. okamurae also increased when P. lividus was exposed to this alga for a long time. Regarding the fatty acids profile of tissues, the results showed that intestinal arachidonic acid (ARA, 20:4n-6) clearly differentiates sea urchins fed with R. okamurae from those fed with the mixed diet. ARA also appeared to be related to the feeding preferences, highlighting this fatty acid as a reliable marker of R. okamurae ingestion. Further research is needed in order to determine P. lividus feeding behaviour and its role as a biocontrol species in the areas invaded by R. okamurae.

ABSTRACT Chrysophytes are a diverse group of stramenopile protists comprising a variety of taxa with different cell organizations. Here, we morphologically and genetically characterize a novel chrysophyte genus isolated from three freshwater localities in the Czech Republic, described as Globulochrysis compacta gen. nov. sp. nov. The genus is well characterized by the frequent formation of closely packed cells, developing into large, spherical sporangia. This alga also forms solitary cells, mucilaginous colonies, amoebae, and teardrop-shaped zoids. We also investigated the morphologically similar genus Chrysotilos, isolated from its type locality in the Austrian Alps. In culture, Chrysotilos showed characteristic neustonic growth, which was, however, not observed in Globulochrysis. Phylogenetic analyses based on 18S rRNA and rbcL genes showed that these two algae belong to two distinct lineages. Whereas Chrysotilos was inferred within the clade Hibberdiales, Globulochrysis formed a completely new lineage within the order Hydrurales.

ABSTRACT Species identification in red algae poses significant challenges when relying solely on morphological characteristics. Consequently, the absence of molecular information often conceals misidentifications, cryptic diversity and introduced cryptic species. Within the genus Lophocladia, species have traditionally been delineated based on subtle morphological traits. Lophocladia trichoclados and Lophocladia lallemandii have been extensively documented in warm and temperate coastal regions, with the latter recognized as an invasive species in the Mediterranean. However, the molecular relationship between these species remains unexplored. To address this gap, a comprehensive taxonomic reevaluation of Lophocladia was conducted in the NE Atlantic, Mediterranean Sea and Red Sea. Through combined molecular and morphological analyses of 75 specimens, two distinct taxa of Lophocladia were identified within the study area. Sequences of the rbcL plastid gene unequivocally demonstrated that L. lallemandii and L. trichoclados are conspecific. Consequently, we propose the synonymization of L. lallemandii with L. trichoclados, which has nomenclatural priority. We report L. kuetzingii, a potentially introduced species from Australia, for the first time in the Macaronesian region of the North Atlantic. This finding underscores the importance of expanding red algal DNA datasets, as such efforts significantly enhance our ability to detect and discern introduced species. Additionally, this research highlights the existence of taxonomic uncertainties surrounding introduced species, even among those already classified as invasive.

ABSTRACT Although genome sequences of lichenized fungi are increasingly becoming available, genome sequences of microalgae involved in the lichen symbiosis are still scarce. For lichenized eukaryotic algae, genome sequencing has focused mostly on Trebouxia and Asterochloris, with little genomic data available for Stichococcus-like algae, such as Diplosphaera. The genus Diplosphaera is a common component of biological soil crusts, and often occurs associated with lichens of the family Verrucariaceae. It is characterized by cylindrical to spherical cells containing a plate-like chloroplast, and more specifically by a vegetative cell division that leads to the formation of typical two- to four-celled clusters. Here, we present a draft genome sequence for the algal partner of an Australian lichen specimen of Endocarpon pusillum. The genome was sequenced with Pac Bio long read and Illumina short read technologies, and transcriptome data were generated to inform the structural annotations. This algal strain is here identified as Diplosphaera chodatii based on nuSSU and ITS data. Compared with closely related lichenized and non-lichenized algae, the genome of D. chodatii stands out for its large size (85.6 Mb) and gene content (21,261 protein-encoding regions), as well as its high rate of duplicated genes (60% of the BUSCO genes are duplicated). These results suggest that whole genome duplication or large-scale segmental duplications may have occurred in the evolutionary history of this algal species. HIGHLIGHTS Little genome data are available for lichenized algae. We generated the first genome for a lichenized Diplosphaera chodatii. Results suggest a possible whole genome duplication in this species.