The names published by Linnaeus in Species Plantarum represent the foundation of modern plant taxonomy. Despite their systematic value, very few of Linnaeus's original type specimens have been analyzed using current DNA sequencing technologies. Here, we performed high-throughput sequencing on Linnean and other type specimens of Ulva, a genus of ecological and commercial importance. Chloroplast and mitochondrial genomes were assembled for Linnaeus's U. compressa, U. intestinalis, U. lanceolata, and U. linza as well as Kützing's Phycoseris smaragdina type specimens. Phylogenetic analyses of these data showed that the names U. compressa and U. intestinalis were correctly applied, but U. linza and U. lanceolata were misapplied. Ulva linza is the earliest available name for the European species currently called U. pseudocurvata. The correct name for the globally distributed species previously known as U. "linza" is Ulva smaragdina (Kützing) comb. nov. The names Ulva lanceolata, U. crispata, and Phycoseris olivacea do not represent distinct species, instead being heterotypic synonyms of U. compressa, and P. planifolia is a heterotypic synonym of U. intestinalis. These results demonstrate that genetic characterization of type material can unequivocally resolve longstanding taxonomic debates over scientific names.

Despite increasing awareness of invasive non‐native species (INNS) and enhanced biosecurity controls in many countries, INNS are still arriving and establishing in new destinations, remaining a globally acknowledged threat to native biodiversity. Preventing the introduction of INNS, as opposed to controlling them once they have arrived, is recognised as the most effective approach to their management. Horizon scanning represents one of the key tools to identify high‐risk INNS that have yet to arrive within a region and has been applied in many contexts around the world, but to date there have been no studies that systematically assess the effectiveness of this approach. Here, we revisit the horizon scan for Great Britain conducted in 2013 that assessed the likelihood of high‐risk INNS arriving within the next 10 years, establishing and having an impact on biodiversity and ecosystems. We evaluated the success of this exercise in predicting arrival of these species within the subsequent 10 years. Ninety‐two species were shortlisted in the 2013 horizon scan. In total, 31 of the 92 species identified in the 2013 horizon scan had arrived by 2023. We found that 12 of the top 20 species had arrived within 10 years. In predicting arrival, there was a significant effect of species having arrived previously to Great Britain, and the number of countries in Western Europe and Baltic countries in which an INNS was found prior to 2013. Policy implications : We conclude that horizon scanning provides a rapid, affordable and successful mechanism to predict the arrival of high‐risk INNS. We highlight the importance of citizen science, including biological recording, and of local expertise for detecting and documenting arrival of INNS. We discuss knowledge gaps that could help inform and improve future horizon scanning. In addition, we recommend regularly repeating horizon scanning exercises to support biosecurity and awareness raising for INNS.

Macroalgae are seen as a sustainable resource for industries including agriculture, food, and nutraceuticals. Aquaculture is the dominant form of global seaweed biomass production, yet wild-harvesting remains important in Europe. Fucoid species such as Fucus vesiculosus commonly colonise intertidal shores and artificial structures, including oyster farms in Ireland, where they represent a largely unexploited biomass resource. However, the amount of biomass produced annually on oyster farms is unknown, making it unclear whether this resource could be harvested sustainably and potentially provide a new opportunity for shellfish farmers. Hence, this study investigated the potential for sustainable harvesting by management of F. vesiculosus fouling on an oyster aquaculture site, quantifying post-harvest seaweed biomass yield and regeneration. F. vesiculosus thalli were harvested under three treatments, a control (no cut), a longer cut to ~6 cm (Cut L) and a shorter cut to ~3.5 cm (Cut S) and regrowth was quantified over a 12-month period from April 2025 to 2026. The harvested F. vesiculosus thalli regenerated up to 87% of pre-harvest lengths within 12 months. The thalli showed non-linear seasonal growth patterns, with thallus lengths increasing over time. The Cut S treatment resulted in a higher relative growth rate among treatments and a greater initial biomass yield of 0.54 kg per m of trestle. Having determined the total number of oyster trestles in a 1 km stretch of shoreline, we estimated that ~11 tonnes of biomass could be harvested using the Cut S treatment. Our results suggest that low intensity partial harvesting of settled F. vesiculosus on oyster farms could be sustainable, and our results provide proof-of-concept for future co-location of Fucus crops and oysters within a shellfish aquaculture site.

Abstract The red seaweed genus Ahnfeltia is an ancient lineage that has persisted for over 500 million years with remarkably limited diversification despite a global distribution in cold-temperate intertidal habitats. Compared to the highly diverse sister lineage, Rhodymeniophycidae, Ahnfeltia provides a unique system for investigating long-term evolutionary persistence in marine macroalgae. Here, we generated chromosome-scale genomes from five populations across three species and combined population genomics with paleogeographic niche modelling. Our results reveal remarkable genomic conservation, strong geographic isolation with limited gene flow, high homozygosity, and evidence of purifying selection. Niche projections indicate long-term stability and spatial connectivity of suitable cold-temperate habitats. These findings suggest that Ahnfeltia ’s persistence and limited diversification are linked to genomic constraints and stable ecological niches over geological timescales. This study provides new insights into the genomic basis of evolutionary stasis in ancient marine lineages and highlights potential vulnerability to ongoing climate change affecting cold-water coastal ecosystems.

The systematic status of the newly proposed genus Stirkia Barros-Barreto & Maggs and its relationship to the currently accepted name Ceramothamnion H.Richards remain uncertain because no authentic specimens of the generitype C. codii H.Richards from the type locality in Bermuda have been sequenced. To clarify the taxonomy of C. codii, we performed high-throughput sequencing on a topotype, a 1912 Phycotheca Boreali-Americana (P.B.-A.) specimen collected by F.S. Collins. The rbcL, COI-5P and LSU genetic markers from the P.B.-A. specimen were assembled and used to infer gene and multi-gene phylogenies to determine its phylogenetic history. In all analyses, the topotype of C. codii was closely allied with C. fujianum Barros-Barreto & Maggs, the generitype of Stirkia, as well as with other species of Ceramothamnion from the southwestern Atlantic and Pacific Oceans. These data support the relegation of the genus Stirkia to Ceramothamnion and indicate that the only previously published DNA sequences of C. codii, from Hawai'i, represent a different, presumably undescribed species of Ceramothamnion. They also highlight the power of whole genome sequencing and the need to analyse type, topotype, or historically authentic herbarium specimens to ensure the accurate application of algal binomials.

The rhodophyte Palmaria palmata (L.) Weber & Mohr is one of the target species of a growing European seaweed industry due to its high content of protein and essential amino acids which makes it suitable for human food, dietary supplements, and as salmon feed. However, the lack of a published nuclear genome limits phylogenetics analyses and gene function investigations which could help the development of a breeding programme. We present the first draft genome of P. palmata that was obtained with PacBio HiFi long read sequencing with average coverage of 10x, consisting of an assembly of 1.05 Gb, N50 = 2.75 Mb and BUSCO completeness of 72.1 %. This is the third largest genome in the Rhodophyta so far, characterized by the highest percentage of repeat elements, 91.3 %. The number of protein coding genes, 9641, two thirds of which are single-exon, is similar to that of other Florideophyceae. This number is far below land plants (ca 25-30,000), and lost protein-coding genes span all biological functions, with the exception of nucleotide metabolism. Reproduction and organogenesis were the most affected, with 98 and 97 % missing genes, respectively. Additionally, a population study on the whole genome of 33 P. palmata individuals from across the Northern East Atlantic area found three main clusters largely consistent with their geographic distribution. These results represent a fundamental step towards breeding and genetic studies to further explore the vastly unexploited economic potential of Palmaria palmata.

Concrete coastal structures, at the interface of land and sea, are increasing in response to population pressure and rising sea levels. Maximizing biodiversity on these artificial structures is being approached using various eco-engineering methods, as an opportunity for bioreceptivity, but less attention has been given to how their biotic colonization will affect human users. Biotic composition and succession have an impact on the human use of the structures, as algae have varying levels of slipperiness, hence danger for users, and also influence degradation of concrete. The ecological engineering study reported in this article determined variation in biotic colonization among different concrete designs. Experimental blocks were deployed for 1 year in the intertidal zone to test differences in colonization among (i) a range of concrete mixes: manufactured with ordinary Portland cement (OPC); rapid hardening Portland cement (RHPC); OPC with microsilica (MS); and OPC with ground granulated blast furnace slag (GGBS) and (ii) different surface texture: surface obtained with controlled permeability formwork (CPF); trowel finished surface; surface obtained with wooden formwork; and patterned finish. Differences in algal colonization among different concrete mixes persisted for 9 of 12 months, with microsilica concrete having consistently higher algal coverage than other types of concretes. Surface finishes had a greater effect: in particular on CPF blocks, low algal growth and high grazer activity left the surface clear after 1 year of deployment, whereas trowel, formwork and patterned finishes had increasingly rapid colonization. Understanding the significance of concrete engineering techniques for ecological processes of an increasingly man-made coastline interfaces engineering with biology and applies to coastal ecosystems worldwide. Our study has shown through the integration of ecology and concrete engineering technology that techniques such as using CPF can greatly influence the resulting assemblages and hence affect attributes such as slipperiness (for users) and the speed of concrete erosion.

This study details a comprehensive biochemical and structural characterization of exiguolysin, a novel thermolysin-like, caseinolytic peptidase secreted by a marine isolate of Exiguobacterium oxidotolerans strain BW26. Exiguolysin demonstrated optimal proteolytic activity at 37 °C and pH 3, retaining 85% activity at 50 °C, highlighting its potential stability under broad reaction conditions. SDS-PAGE and LC-MS analysis identified the enzyme as a 32 kDa M4-family metalloprotease. Exiguolysin activity was inhibited by 1,10-phenanthroline, confirming its dependence on metal ions for activity. Zymographic analysis and substrate specificity assays revealed selective hydrolysis of matrix metalloproteinase (MMP) substrates but no activity against elastase substrates. Analysis of the predicted gene sequence and structural predictions using AlphaFold identified the presence and position of HEXXH and Glu-Xaa-Xaa-Xaa-Asp motifs, crucial for zinc binding and catalytic activity, characteristic of ‘Glu-zincins’ and members of the M4 peptidase family. High-throughput screening of a 20 × 20 N-alpha mercaptoamide dipeptide inhibitor library against exiguolysin identified SH-CH2-CO-Met-Tyr-NH2 as the most potent inhibitor, with a Ki of 1.95 μM. Notably, exiguolysin selectively inhibited thrombin-induced PAR-1 activation in PC-3 cells, potentially indicating a potential mechanism of virulence in modulating PAR-1 signalling during infection by disarming PARs. This is the first detailed characterization of a peptidase of the M4 (thermolysin) family in the genus Exiguobacterium which may have industrial application potential and relevance as a putative virulence factor.

Seaweed aquaculture is becoming increasingly important as the global seaweed market is set to exceed £20 billion by 2030, leaving natural populations at risk of overexploitation. Fucoids, such as Fucus serratus, are intertidal seaweeds hand-harvested for their use in agricultural, pharmaceutical, and biomedical industries. Despite many aspects of the biology of fucoids being well researched, there have been very few studies on their aquaculture. In this study, we grew F. serratus biomass from gamete life stages in the Queen’s University Marine Laboratory for 8 months and monitored their growth, amino acid and phenolic contents in a subtidal field trial. Gametes of F. serratus were successfully fertilized in vitro and attached to substrata: Tiles (mesocosm) and Dyneema Twine (subtidal). The growth of F. serratus on each substrate was monitored for 6 months in the laboratory facility with juveniles reaching 2–4 mm in length. The juveniles on twine were then deployed at the Strangford Lough test site and growth was compared against the juveniles on tiles after an additional two months. Prior to field deployment, individuals grown on tiles were significantly longer (~17%) than those on twine growing to ~3 cm, however, after the two-month deployment, the twine thalli grew significantly longer than those on the tiles (~33%) reaching ~6 cm in length. Subtidal F. serratus grown on twine had significantly higher amino acid content, whereas the phenolic content was significantly lower (~62 mg PGE g−1) than seaweed grown on the tiles (~128 mgPGE g−1). Growing F. serratus successfully in subtidal areas is highly important for providing sustainably sourced biomass to reduce reliance on wild harvesting. Further, cultivating in the subtidal zone will help to avoid competition for space from other aquaculture industries operating in the intertidal zone.

Green tides are unattached blooms of green macroalgae (seaweeds) that occur globally and can attain vast proportions. The main components of the blooms are species of the sea lettuce genus Ulva, a sheet-like green seaweed, which can form unusual morphs under these conditions (Blomster et al., 2002). In estuaries and shallow coastal embayments drifting or cast-up macroalgae can reach quantities of up to 27 kg wet weight m-2. Green tides have been researched extensively since Fletcher's (1996) review highlighted their importance, but they came to wide public attention at the time of the 2008 Qingdao Summer Olympics when the Yellow Sea blooms endangered the sailing events. In May–July 2008, prior to the Olympics, the Yellow Sea coastline experienced the world’s largest green tide with 1 million tonnes of drifting biomass covering 13,000–30,000 km2 (Leliaert et al., 2008). Enormous quantities were washed into shallow water and onto the beaches. News reports from the time show volunteers working to remove the biomass and save the events. Green tides have increased in frequency and extent globally over the last few decades, with the most significant blooms continuing to be those in the Yellow Sea

The 2007 flora "Green Seaweeds of Britain and Ireland" did not present the molecular data underpinning the Ulvaceae treatment, mostly ITS sequences. Subsequently, names have changed as type material of Ulva species is sequenced and intensive sampling with DNA barcoding adds new European species. To update the Ulvaceae, we systematically sampled from 2007 to 2021, identifying specimens using various molecular markers alongside DNA from type material of four species. We show here that Ulva gigantea, based on rbcL, tufA and ITS sequences of its holotype, is assigned to Ulva compressa, as is the lectotype of Ulva curvata. Ulva gigantea sensu GenBank and Ulva pseudocurvata are conspecific. The correct name is U. pseudocurvata based on rbcL sequences of the lectotype. Two species of monostromatic Ulvaceae were included in the 2007 flora, but we show that both of them and all earlier British monostromatic collections represent Ulvaria splendens, a species originally described from Alaska. Analysis of two rbcL amplicons of the Ulva sordida lectotype shows that it is conspecific with Ulvaria splendens. Our first genuine collections of Ulvaria obscura from SW England and SW Wales correspond to topotype material from the Bay of Biscay, recent samples from Galicia and unpublished tufA sequences from Britanny.

Journal of PhycologyVolume 60, Issue 1 p. 46-48 ALGAE HIGHLIGHT On the track of unknown algae Christine Maggs, Corresponding Author Christine Maggs [email protected] Search for more papers by this author Christine Maggs, Corresponding Author Christine Maggs [email protected] Search for more papers by this author First published: 16 February 2024 https://doi.org/10.1111/jpy.13428Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. REFERENCES Bickford, D., Lohman, D. 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AbstractThe rhodophytePalmaria palmata(L.) Weber & Mohr is one of the target species of a growing European seaweed industry due to its high content of protein and essential amino acids which makes it suitable for human food, dietary supplements, and as salmon feed. However, the lack of a published nuclear genome limits phylogenetics analyses and gene function investigations which could help the development of a breeding programme.We present the first draft genome ofP. palmatathat was obtained with PacBio HiFi long read sequencing with average coverage of 10×, consisting of an assembly of 1.05 Gb, N50=2.75Mb and BUSCO completeness of 72.1%. Additionally, a population study on the whole genome of 33P. palmataindividuals from across the Northern East Atlantic area found three main clusters consistent with their geographic distribution: (1) Denmark and Norway, (2) France and western Ireland, (3) Faroe Islands. All individuals from Northern Ireland share ancestry with western Ireland and Denmark, and some individuals from the Faroe Islands show admixture from Faroe, western Ireland and Northern Ireland. These results represent a fundamental step towards breeding and genetic studies to further explore the vastly unexploited economic potential ofPalmaria palmata.Highlights- We report the first draft genome ofPalmaria palmata, from PacBio HiFi long reads.- The size of the genome, 1.05 Gb, is among the largest so far among the Rhodophyta.- Busco completeness of 72.1% and contig N50 of 2.75 Mb indicate good quality.- The genomes of 33 more individuals from North Atlantic Europe have been sequenced.- Phylogenetic analysis found three clusters consistent with geographic distribution.

Brown seaweeds are a rich source of carotenoids, particularly fucoxanthin, which has a wide range of potential health applications. Fucoxanthin fluctuates within and among seaweeds over time, frustrating efforts to utilise this resource. Thus, we require comprehensive analyses of long- and short-term concentrations across species in field conditions. Here, we used High Performance Liquid Chromatography to compare fucoxanthin content in four brown macroalgae, Ascophyllum nodosum, Fucus serratus , Fucus vesiculosus and Saccharina latissima , monthly for 1 year. F. serratus and F. vesiculosus had significantly higher fucoxanthin content (mg/g), which was highest in Spring (0.39 ± 0.04) and Autumn (0.45 ± 0.04) [mean (± SE)]. Two species, A. nodosum and F. serratus , were collected monthly at the same location for a further two non-consecutive years. For both A. nodosum and F. serratus , a significant interaction effect of seasons and years was identified, highlighting that there is variation in fucoxanthin content among and within species over time. We also show that fucoxanthin content differs significantly among months even within seasons. Therefore, it is not sufficient to assess fucoxanthin in single months to represent seasonality. We discuss how weather, nutrients and reproduction may have driven the seasonal variation, and reveal patterns of fucoxanthin concentration that can provide information concerning its availability for many important medical functions.

Molecular analyses, in combination with morphological studies, provide invaluable tools for delineating red algal taxa. However, molecular datasets are incomplete and taxonomic revisions are often required once additional species or populations are sequenced. The small red alga Conferva parasitica was described from the British Isles in 1762 and then reported from other parts of Europe. Conferva parasitica was traditionally included in the genus Pterosiphonia (type species P. cloiophylla in Schmitz and Falkenberg 1897), based on its morphological characters, and later transferred to Symphyocladia and finally to Symphyocladiella using molecular data from an Iberian specimen. However, although morphological differences have been observed between specimens of Symphyocladiella parasitica from northern and southern Europe they have yet to be investigated in a phylogenetic context. In this study, we collected specimens from both regions, studied their morphology and analyzed rbcL and cox1 DNA sequences. We determined the phylogenetic position of a British specimen using a phylogenomic approach based on mitochondrial and plastid genomes. Northern and southern European populations attributed to S. parasitica represent different species. Symphyocladiella arecina sp. nov. is proposed for specimens from southern Europe, but British specimens were resolved as a distant sister lineage to the morphologically distinctive Amplisiphonia, so we propose the new genus Deltalsia for this species. Our study highlights the relevance of using materials collected close to the type localities for taxonomic reassessments, and showcases the utility of genome-based phylogenies for resolving classification issues in the red algae.

Effective monitoring of non-indigenous seaweeds and combatting their effects relies on a solid confirmation of the non-indigenous status of the respective species. We critically analysed the status of presumed non-indigenous seaweed species reported from the Mediterranean Sea, the Northeast Atlantic Ocean and Macaronesia, resulting in a list of 140 species whose non-indigenous nature is undisputed. For an additional 87 species it is unclear if they are native or non-indigenous (cryptogenic species) or their identity requires confirmation (data deficient species). We discuss the factors underlying both taxonomic and biogeographic uncertainties and outline recommendations to reduce uncertainty about the non-indigenous status of seaweeds. Our dataset consisted of over 19,000 distribution records, half of which can be attributed to only five species (Sargassum muticum, Bonnemaisonia hamifera, Asparagopsis armata, Caulerpa cylindracea and Colpomenia peregrina), while 56 species (40%) are recorded no more than once or twice. In addition, our analyses revealed considerable variation in the diversity of non-indigenous species between the geographic regions. The Eastern Mediterranean Sea is home to the largest fraction of non-indigenous seaweed species, the majority of which have a Red Sea or Indo-Pacific origin and have entered the Mediterranean Sea mostly via the Suez Canal. Non-indigenous seaweeds with native ranges situated in the Northwest Pacific make up a large fraction of the total in the Western Mediterranean Sea, Lusitania and Northern Europe, followed by non-indigenous species with a presumed Australasian origin. Uncertainty remains, however, regarding the native range of a substantial fraction of non-indigenous seaweeds in the study area. In so far as analyses of first detections can serve as a proxy for the introduction rate of non-indigenous seaweeds, these do not reveal a decrease in the introduction rate, indicating that the current measures and policies are insufficient to battle the introduction and spread of non-indigenous species in the study area.

AimGlobal warming is affecting the distribution of species worldwide, but the level of adaptation of edge populations to warmer temperatures remains an open question. Here, we assess the thermal tolerance of populations of two habitat-forming seaweeds along their latitudinal range, using thermal niche unfilling to assess their resilience to global warming. LocationEuropean Atlantic coastline. TaxonAscophyllum nodosum (Linnaeus) Le Jolis (Phaeophyceae) and Chondrus crispus Stackhouse (Rhodophyta). MethodsWe studied the ecotypic variation in upper survival temperatures (USTs) by measuring survival and growth of adults representing populations under a gradient of seawater temperature (12-30 degrees C). Comparing the USTs with maximum seawater temperatures obtained from satellites, we investigated safety margins and niche unfilling states, both in recent history and under future climate scenarios. ResultsUSTs (approximate to 24 degrees C) did not differ significantly between populations, except for higher values (27.9 degrees C) for the northernmost populations (cold edge) of A. nodosum. Populations of both species had thermal safety margins over the last few decades (from 1982 to 2021). However, projections based on USTs showed that in several years these margins have been eliminated and will completely disappear in the Bay of Biscay under RCP4.5 and RCP6.0 2090-2100 IPCC scenarios for C. crispus and under RCP8.5 for both species, threatening the populations there. Main ConclusionsSouthern marginal populations were not better adapted to global warming than populations elsewhere. Both seaweed species tolerated higher temperatures than the ambient maxima, suggesting a thermal niche unfilling state with thermal safety margins in their recent history. However, those are being depleted by ongoing climate change and this trend is predicted to increase. Marine heat waves are important threats to these habitat-forming species, transiently reducing or even eliminating safety margins in the hottest parts of the European Atlantic coastline, contributing to explaining the distributional gap there.

Despite the importance of morphological characters for classification, molecular data are now more widely used than morphology in phylogenetic reconstructions, particularly in studies of algae. The tribe Ceramieae C.Agardh ex Greville (Ceramiaceae) is a widespread, speciose, and morphologically diverse group of valuable red algae with many identified bioactives. We aimed to elucidate phylogenetic relationships in the tribe to delimit genera and provide a new classification. Generic delimitation is currently based on morphological characters, and there has been no overall reassessment of generic circumscriptions and evolutionary relationships using molecular data. We used three molecular markers (mitochondrial COI-5P, plastid rbcL and nuclear LSU). Within the Ceramieae, several clades are recovered, although the relationships among major clades are not supported. These clades are here recognized as genera, with new circumscriptions for Ceramium Roth, Carpoblepharis Kutzing, Herpochondria F.Schmitz & Falkenberg, Campylaephora J.Agardh and Celeceras Kutzing, and the proposal of Pseudoceramium Barros-Barreto & Maggs, gen. nov., Yoneshiguea Barros-Barreto, Maggs & M.A.Jaramillo, gen. nov. and Stirkia Barros-Barreto & Maggs, gen. nov. The Ceramieae show a high degree of morphological homoplasy among species as well as extreme phenotypic plasticity within species. Genera lack unique synapomorphies and multiple morphological characters are required to define most of them. Molecular data are critical for understanding systematics in this group.

The IUCN Red List of Threatened Species is an authoritative tool in biodiversity conservation. Whilst IUCN criteria have been applied successfully to groups such as birds and mammals, a Red List assessment of British seaweeds in 2021 revealed that the categories to which seaweed species were assigned were dependent on how the criteria were applied. Here, this seaweed assessment is used as a case study with which to evaluate the IUCN methodology for use with ‘non-standard’ groups of organisms. A data-driven assessment of red (Rhodophyta), green (Chlorophyta) and brown (Phaeophyceae) seaweeds, which applied three (A, B and D) of the five IUCN criteria (A–E), categorized 13% of 617 British species as threatened. Following peer review, only 7% of species were categorized as threatened (1% Critically Endangered—CR, 3% Endangered—EN, 3% Vulnerable—VU), and 55% as Data Deficient. This reduction in species categorized as threatened suggests that strict application of the IUCN criteria may, at least for the seaweeds, over-estimate threat. As a result of this assessment, recommendations include the need for a more unified monitoring system and a review of the suitability for/application of the IUCN assessment criteria to some types of organisms. For example, in clonal populations, it is not possible to count individuals, and complex life histories cause additional complications. IUCN criteria must be applicable to a wide range of organisms, including seaweeds.

The green seaweed Ulva is important from ecological and economic perspectives, but the identification of species is often problematic. Here we assessed and discussed different perspectives to establish a stable taxonomic framework for Ulva , which will benefit both ecological and applied research. We evaluated (1) the performance of commonly used DNA-barcode markers (ITS rDNA, rbc L, and tuf A) using species delimitation methods (PTP and GMYC), (2) the usage of species names in the literature, and (3) the geographic coverage of genetic data to identify poorly sampled regions. Species delimitation employing the tuf A gene was the most consistent across methods. Not surprisingly, DNA-based species delimitation was often in disagreement with traditional morphology-based species definitions. Biological species concepts, where tested, proved to be generally narrower than DNA-based species delimitation. Although the use of molecular markers has greatly improved our view of Ulva diversity, the names associated with DNA sequences in public databases are often unreliable, complicating species identification. Recently, sequencing type materials has considerably reduced the gap between DNA sequence data and Linnaean names, but our knowledge on Ulva diversity remains inadequate, especially in tropical regions. Perspectives for Ulva taxonomy include the consistent use of multiple DNA-barcode markers assisted by species delimitation methods, applications of genomic data, and crossing experiments. To arrive at a stable nomenclature, we outline the benefits and shortcomings of adhering to the rules and practices of the International Code of Nomenclature for algae, fungi, and plants, for example, by sequencing name-bearing types and discuss alternative approaches.