Seasonal variation of dominant free-floating and attached Ulva species in Rudong coastal area,China

In this paper, species compositions and seasonal variations of attached Ulva species on Porphyra aquaculture rafts and free floating Ulva species at Rudong coastal area, Jiangsu Province of China were investigated during 2010–2011. Based on the sequences analysis of nuclear-encoded ITS (including 5.8S rDNA regions) and 5S rDNA spacer regions, dominant species of both attached and free-floating Ulva samples were identified as Ulva compressa, Ulva linza, Ulva prolifera and Ulva flexuosa. Phylogenetic tree based on sequences of ITS and 5S rDNA spacer regions for attached and free-floating Ulva species was constructed, respectively. Species compositions of the Ulva population attached on aquaculture rafts varied with seasons, and U. prolifera was only found on aquaculture rafts in March 2011 during the 2010–2011 Porphyra yezoensis cultivation season, which had the same sequences of ITS and 5S rDNA spacer regions as that of the dominant species bloomed in the Yellow Sea of China in 2008. Dominant species of the free-floating Ulva population at the early stage of the green tide were U. compressa, U. flexuosa, and U. linza. Free-floating U. prolifera appeared in the middle of May, 2011. ITS sequence similarity rates of U. compressa and U. flexuosa between the attached and free-floating species were 100%. And ITS and 5S rDNA spacer sequences of the attached and the free-floating U. prolifera population also showed no differences. Further study showed that there were two types of free-floating U. prolifera population (Type 5S-A and Type 5S-B) based on 5S rDNA spacer sequences. The present study would provide some useful information for clarifying the outbreak mechanism of green tides occurred in the Yellow Sea, China.     

Cryptic diversity of Ulva (Ulvales,Chlorophyta) in the Great Bay Estuarine System (Atlantic USA): introduced and indigenous distromatic species

Distromatic foliose blades of the algal genus Ulva are notoriously difficult to identify due to their simple morphologies and few diagnostic characteristics that often exhibit intraspecific variation and interspecific overlap. Hence, species differentiation is difficult and diversity estimates are often inaccurate. Two major goals of this study were to assess the diversity of distromatic Ulva spp. in the Great Bay Estuarine System (GBES) of New Hampshire and Maine, USA, and to compare historical and present day records of these species. Molecular analysis (using ITS sequences) of field-collected specimens revealed four distinct taxa: Ulva lactuca, U. rigida, U. compressa, and U. pertusa. Prior to molecular screening, Ulva lactuca was the only distromatic Ulva species reported for the GBES. Ulva pertusa and the foliose form of U. compressa are newly recorded for the Northwest Atlantic, and the range of U. rigida has been extended. Molecular analysis of historical herbarium voucher specimens indicates that U. rigida, U. pertusa, and the foliose form of U. compressa have been present in the GBES since at least 1966, 1967, and 1972, respectively. The distromatic morphotype of U. compressa is found only in low salinity areas, which suggests that salinity may influence its morphological development. Molecular and morphological evaluations are critical if we are to distinguish between cryptic taxa, accurately assess biodiversity, and effectively monitor the spread of non-indigenous macroalgae.     

Examination of Ulva bloom species richness and relative abundance reveals two cryptically co-occurring bloom species in Narragansett Bay,Rhode Island

Blooms caused by the green macroalga Ulva pose a serious threat to coastal ecosystems around the world. Despite numerous studies of the causes and consequences of these blooms, we still have a limited understanding of Ulva bloom species richness and abundance due to difficulties in identifying Ulva species using morphological features. Along the northeastern U.S. coastline, all blooms of distromatic Ulva blades were previously identified as Ulva lactuca. Recent molecular sequencing, however, discovered the presence of additional distromatic Ulva species. Therefore, in order to determine the relative abundance of Ulva species within blooms, we conducted monthly surveys at four Narragansett Bay, RI, sites representing a gradient of bloom severity. We found that the biomass of Ulva within blooms was a mix of Ulva compressa and Ulva rigida, not U. lactuca as previously reported. In contrast, sites not impacted by blooms that were located near the mouth of Narragansett Bay were dominated by U. lactuca. We also observed spatial and temporal differences in Ulva and total macroalgal diversity between bloom-impacted sites, indicating that Ulva bloom composition can be radically different between similar sites within close proximity. We discuss our results in the context of Ulva blooms worldwide, highlighting the need to definitively determine bloom species composition in order to fully understand bloom dynamics.     

Systematics of green algae resembling Ulva conglobata,with a description of Ulva adhaerens sp. nov. (Ulvales,Ulvophyceae)

A phylogenetic and morphological study of green algae resembling Ulva conglobata from Japan was undertaken, along with morphological observations of the original material of U. conglobata Kjellman. The samples resembling U. conglobata included five genetically distinct species: U. fasciata, U. pertusa, U. tanneri, Ulva sp. 1 and Ulva sp. 2. The discovery of marginal denticulations in some of the original material of U. conglobata, made it possible to distinguish those species without denticulations: U. pertusa, U. tanneri and Ulva sp. 2. The morphological characteristics of Ulva sp. 1 matched those of U. conglobata, but Ulva sp. 1 was not clearly identified as U. conglobata owing to the lack of DNA sequence data of the original material. Ulva sp. 2 had lobes adhering to each other by rhizoids. This morphological feature is stable in Ulva sp. 2 and unique among Ulva species. In conjunction with the molecular data, Ulva sp. 2 was described as a new species, U. adhaerens sp. nov. This species features rhizoidal extensions in regions other than the base and an elaborate arrangement of the extensions used for adhesion. It thereby expands our knowledge of the morphogenesis of the morphologically simple genus Ulva.     

Conspecificity of the model organism Ulva mutabilis and Ulva compressa (Ulvophyceae,Chlorophyta)

As one of the most abundant and ubiquitous representatives of marine and brackish coastal macrophytobenthos communities, the genus Ulva is not only an important primary producer but also of ecological and morphogenetic interest to many scientists. Ulva mutabilis became an important model organism to study morphogenesis and mutualistic interactions of macroalgae and microorganisms. Here, we report that our collections of Ulva compressa Linnaeus (1753) from Germany are conspecific with the type strains of the model organism U. mutabilis Føyn (1958), which were originally collected at Olhão on the south coast of Portugal and have from that time on been maintained in culture as gametophytic and parthenogenetic lab strains. Different approaches were used to test conspecificity: (i) comparisons of vegetative and reproductive features of cultured material of U. mutabilis and German U. compressa demonstrated a shared morphological pattern; (ii) gametes of U. compressa and U. mutabilis successfully mated and developed into fertile sporophytic first‐generation offspring; (iii) molecular phylogenetics and species delimitation analyses based on the Generalized Mixed Yule‐Coalescent method showed that U. mutabilis isolates (sl‐G[mt+]) and (wt‐G[mt‐]) and U. compressa belong to a unique Molecular Operational Taxonomic Unit. According to these findings, there is sufficient evidence that U. mutabilis and U. compressa should be regarded as conspecific.     

Molecular phylogenetic analyses of Ulva (Chlorophyta, Ulvophyceae) mats in the Xiangshan Bay of China using high-resolution DNA markers

Intertidal Ulva mats occur annually in winter and spring in the Xiangshan Bay (29°26′–29°34′ N, 121°27′–121°50′ E) of China. Thousands of tons of Ulva biomass have been harvested as edible seaweeds for human consumption for several decades in this region. This investigation was designed to quantify Ulva microscopic propagules associated with the mat, identify species composition, and to analyze intra-species relationships using three molecular markers. Phylogenetic analysis based on the nuclear encoded rDNA internal transcribed spacer region, the plastid encoded large subunit of the ribulose 1,5-bisphosphate carboxylase gene, and the 5S rDNA spacer region showed that the mat was principally composed of Ulva prolifera and Ulva flexuosa. Their propagules were detected in both the water column and sediment. Based on phylogenetic analyses of the 5S rDNA spacer region, mat samples of U. prolifera and U. flexuosa were genetically distinct from the green tide samples in the Yellow Sea and U. flexuosa samples from Jiangsu coasts, respectively, revealing that isolated geographical position of the Xiangshan Bay might result in the maintenance of a distinct Ulva population. The results demonstrate that high-resolution DNA markers have great potential in identification and discrimination at and below the species level.     

Morphological and molecular characterization of free-floating and attached green macroalgae Ulva spp. in the Yellow Sea of China

During the summer of 2008 and 2009, massive algal blooms repeatedly broke out in the Yellow Sea of China. These were undoubtedly caused by the accumulations of one or more species in the macroalgal genus Ulva. In previous reports, morphological observation indicated that the species involved in this phenomenon is Ulva prolifera but molecular analyses indicated that the species belongs to an Ulva linza–procera–prolifera (LPP) clade. Correct identification of the bloom species is required to understand and manage the blooms, but the taxonomic status of the bloom species remains unclear. In the current study, the taxonomic status of 22 selected specimens from the Yellow Sea was assessed by using both morphological and molecular (ITS and rbcL sequences) data. In addition, 5S rDNA analyses were performed for those samples clustering in the LPP clade, and phylogenetic tree and ribotype analyses were constructed for determining the possible origin of the bloom. Three free-floating and two attached Ulva species were distinguished and described: Ulva compressa Linnaeus and Ulva pertusa Kjellman were found in free-floating samples; U. linza Linnaeus was found on rocks; and U. prolifera O.F. Müller was found in both habitats. Diversity in free-floating Ulva of the Yellow Sea appears to be greater than previously thought. The dominant free-floating Ulva species, U. prolifera, was not closely related to local populations attached to rocks but was closely related to populations from Japan.     

Discrimination of the common macroalgae (Ulva and Blidingia) in coastal waters of Yellow Sea,northern China,based on restriction fragment-length polymorphism (RFLP) analysis

Since 2007, reoccurring large-scale green algae blooms have caused deleterious effects to the estuarine ecosystem of Yellow Sea, northern China and subsequent economical losses. Previous surveys indicated the green tides were initiated in the coastal water of southern Jiangsu province where Porphyra farming was intensively conducted; however, the main ‘seed source’ of floating green algae is still under debate. Ulva prolifera was confirmed to be the major causative species of green tides. The multiple sympatric ulvoid species in the natural environment has complicated species identification in both field surveys and laboratory studies due to their morphological plasticity. Thus, we developed a genetic identification key based on restriction fragment length polymorphism (RFLP) analysis of the ITS nuclear marker to discriminate the common Ulva and Blidingia species in the Yellow Sea. Ten genetic lineages (1 in Blidingia, 9 in Ulva) were detected along the coast of China through phylogenetic analysis of ITS sequences. They can be separated by virtual restriction digestion using the four selected restriction enzymes (BspT107 I, EcoO109 I, Hin1 I and VpaK11B I). With additional PCR amplification of the 5S spacer region, we were able to discriminate U. prolifera from Ulva linza. Using this genetic key, we screened macroalgal samples collected from the coast of the Yellow Sea, and the results indicated 6 common lineages (U. prolifera, U. linza, Ulva compressa, Ulva pertusa, Clade 6 and Blidingia sp.) in this region, which could be explicitly distinguished by a single enzyme (BspT107 I) coupled with 5S spacer polymorphism. U. prolifera was confirmed to be present on the Porphyra aquaculture rafts with seasonal variation in the species composition. This genetic key will facilitate our long-term field surveys to investigate the origin of the floating U. prolifera and furthermore to explore its bloom dynamics along the coast of the Yellow Sea. It also provided a framework for the future inclusion of more Ulva species, which will expand the usage of this key.     

DNA content of Ulva compressa (Ulvales, Chlorophyta) nuclei determined with laser scanning cytometry

The green macroalgal genus Ulva (incl. Entemmorpha) contains economically valuable species, is of relevance for coastal management (green tides), and certain taxa serve as experimental organisms for fundamental research in green algae. The nuclear genome size of Ulva (Entemmorpha) compressa Linnaeus was measured in propidium iodide stained nuclei using laser scanning cytometry. Nuclei of fixed gametes yielded reproducible values, whereas nuclei extracted from multicellular gametophytes were unsuitable. With nuclei of Arabidopsis thaliana (L.) Heynh and Saccharomyces cerevisiae Hansen as references, the haploid nuclear genome size of U. compressa was calculated as 135 ± 7 Mbp. This is the smallest genome so far known from any species of Ulva.     

Ploidy Distribution of the Harmful Bloom Forming Macroalgae Ulva spp. in Narragansett Bay,Rhode Island,USA, Using Flow Cytometry Methods

Macroalgal blooms occur worldwide and have the potential to cause severe ecological and economic damage. Narragansett Bay, RI is a eutrophic system that experiences summer macroalgal blooms composed mostly of Ulva compressa and Ulva rigida, which have biphasic life cycles with separate haploid and diploid phases. In this study, we used flow cytometry to assess ploidy levels of U. compressa and U. rigida populations from five sites in Narragansett Bay, RI, USA, to assess the relative contribution of both phases to bloom formation. Both haploid gametophytes and diploid sporophytes were present for both species. Sites ranged from a relative overabundance of gametophytes to a relative overabundance of sporophytes, compared to the null model prediction of √2 gametophytes: 1 sporophyte. We found significant differences in cell area between ploidy levels for each species, with sporophyte cells significantly larger than gametophyte cells in U. compressa and U. rigida. We found no differences in relative growth rate between ploidy levels for each species. Our results indicate the presence of both phases of each of the two dominant bloom forming species throughout the bloom season, and represent one of the first studies of in situ Ulva life cycle dynamics.     

Spatial and temporal variability of biomass and composition of green tides in Ireland

Although nutrient enrichment of estuarine and coastal waters is considered a key factor for the development of green tides, the extent, distribution, and species composition of blooms vary among systems of similar nutrient loading, which compromises our ability to predict these events based on information about nutrient status alone. Additional factors may play a role in the control and development of macroalgal blooms. The identification of relevant scales of variation is a necessary prerequisite before explanatory models can be proposed and tested. In this study spatial and temporal patterns of biomass distribution were assessed for two Ulva morphologies in two Irish estuaries heavily affected by green tides (wet biomass >1 kg m⁻² during the peak bloom). Moreover, using genetic markers, the species composition of these green tides was assessed. Results revealed that these blooms were multi-specific, with Ulva prolifera, U. compressa and U.rigida the most frequent species. The species U. prolifera and U. compressa usually showed a tubular morphology, while U. rigida was mainly laminar. A seasonal succession common to both estuaries was also identified, with the bloom dominated by tubular species during spring and early summer, and co-dominated by tubular and laminar morphologies during late summer and autumn. Moreover, tubular and laminar morphologies exhibited different distribution patterns, with tubular morphologies varying at bigger spatial scales and higher biomass than the laminar. As tubular and laminar morphologies exhibited different distribution patterns, varying tubular morphologies along bigger spatial scales with higher biomass levels than the laminar. Considering that tubular morphologies were usually anchored to the sediment, while laminar Ulva were usually observed free-floating, these differences could explain a differential influence by water motion. An important annual and decadal variability in biomass levels of Ulva was observed, in the case of the Tolka estuary a noticeable increase over the last two decades. These findings should be considered for the development of management and monitoring strategies since the different habitat of laminar and tubular morphologies (anchored vs. free-floating) may play an important role in the balance of nutrients and biomass in the estuary, or determine the response to pollutant exposure. Furthermore, the presence of different species with different ecological requirements could favour the duration and extension of the bloom though temporal and spatial successions.     

Molecular and morphological diversity of Narragansett Bay (RI,USA) Ulva (Ulvales,Chlorophyta) populations

Macroalgal bloom‐forming species occur in coastal systems worldwide. However, due to overlapping morphologies in some taxa, accurate taxonomic assessment and classification of these species can be quite challenging. We investigated the molecular and morphological characteristics of 153 specimens of bloom‐forming Ulva located in and around Narragansett Bay, RI, USA. We analyzed sequences of the nuclear internal transcribed spacer 1 region (ITS1) and the chloroplast‐encoded rbcL; based on the ITS1 data, we grouped the specimens into nine operational taxonomic units (OTUs). Eight of these OTUs have been previously reported to exist, while one is novel. Of the eight OTUs, all shared sequence identity with previously published sequences or differed by less than 1.5% sequence divergence for two molecular markers. Previously, 10 species names were reported for Ulva in Rhode Island (one blade and nine tube‐forming species) based upon morphological classification alone. Of our nine OTUs, three contained blade‐forming specimens (U. lactuca, U. compressa, U. rigida), one OTU had a blade with a tubular stipe, and six contained unbranched and/or branched tubular morphologies (one of these six, U. compressa, had both a blade and a tube morphology). While the three blade‐forming OTUs in Narragansett Bay can frequently be distinguished by careful observations of morphological characteristics, and spatial/temporal distribution, it is much more difficult to distinguish among the tube‐forming specimens based upon morphology or distribution alone. Our data support the molecular species concept for Ulva, and indicate that molecular‐based classifications of Ulva species are critical for proper species identification, and subsequent ecological assessment or mitigation of Ulva blooms.     

Resolving the identity of commercially cultivated Ulva (Ulvaceae,Chlorophyta) in integrated seaweed-abalone aquaculture farms in South Africa

Species of Ulva have a wide range of commercial applications and are increasingly being recognized as promising candidates for integrated aquaculture. In South Africa, Ulva has been commercially cultivated in integrated seaweed-abalone aquaculture farms since 2002, with more than 2000 tonnes of biomass cultivated per annum in land-based paddle raceways. However, the identity of the species of Ulva grown on these farms remains uncertain. We therefore characterized samples of Ulva cultivated in five integrated multi-trophic aquaculture farms (IMTA) across a wide geographical range and compared them with foliose Ulva specimens from neighboring seashores. The molecular markers employed for this study were the chloroplast-encoded Ribulose-1,5-bisphosphate carboxylase oxygenase (rbcL), the Internal Transcribed Spacer (ITS) of the nuclear, and the chloroplast elongation factor tufA. All currently cultivated specimens of Ulva were molecularly resolved as a single species, U. lacinulata. The same species has been cultivated for over a decade, although a few specimens of two other species were also present in early South African IMTA systems. The name Ulva uncialis is adopted for the Ulva “Species A” by Fort et al. (2021), Molecular Ecology Resources, 22, 86) significantly extending the distribution range for this species. A comparison with wild Ulva on seashores close to the farms resulted in five new distribution records for South Africa (U. lacinulata, U. ohnoi, U. australis, U. stenophylloides, and U. aragoënsis), the first report of a foliose form of U. compressa in the region, and one new distribution record for Namibia (U. australis). This study reiterates the need for DNA confirmation, especially when identifying morphologically simple macroalgae with potential commercial applications.     

Identification by SDS PAGE of green seaweeds ( Ulva and Enteromorpha) used in the food industry

SDS PAGE was tested as an analytical tool for the identification of fourgreen algae (Ulva rigida, U. rotundata, Enteromorphaintestinalis, E. compressa) used as food ingredients. A referencepattern composed of the bands present all year long was performed foreach species. The pattern for Ulva rotundata consists of 7 bandslocated between 69.9 and 15.5 kDa with the presence of triplicate bandsat 29.5, 26.3 and 22.9 kDa. The pattern for Ulva rigida is consistsof three bands with apparent molecular weights of 68.5, 56.4 and 44.7kDa. The Enteromorpha compressa pattern is characterised by sixbands located between 65.8 and 19.8 kDa. A double band withmolecular weights of 23.1 and 23.9 distinguished this pattern from theothers. Six bands situated between 66.4 and 19.4 kDa with a specifictriplicate band of 25.9, 23.9 and 22.5 kDa constituted the specific patternof Enteromorpha intestinalis. SDS PAGE appears to be suitable forthe identification of green seaweed foods.     

Comparative study on mitogenomes of green tide algae

Since 2007, the annual green tide disaster in the Yellow Sea has brought serious economic losses to China. There is no research on the genetic similarities of four constituent species of green tide algae at the genomic level. We previously determined the mitochondrial genomes of Ulva prolifera, Ulva linza and Ulva flexuosa. In the present work, the mitochondrial genome of another green tide (Ulva compressa) was sequenced and analyzed. With the length of 62,311 bp, it contained 29 encoding genes, 26 tRNAs and 10 open reading frames. By comparing these four mitochondrial genomes, we found that U. compressa was quite different from the other three types of Ulva species. However, there were similarities between U. prolifera and U. linza in the number, distribution and homology of open reading frames, evolutionary and codon variation of tRNA, evolutionary relationship and selection pressure of coding genes. Repetitive sequence analysis of simple sequence repeats, tandem repeat and forward repeats further supposed that they have evolved from the same origin. In addition, we directly analyzed gene homologies and translocation of four green tide algae by Mauve alignment. There were gene order rearrangements among them. With fast-evolving genomes, these four green algal mitochondria have both conservatism and variation, thus opening another window for the understanding of origin and evolution of Ulva.     

Two bloom-forming species of Ulva (Chlorophyta) show different responses to seawater temperature and no antagonistic interaction

The generalized use of molecular identification tools indicated that multispecific green tides are more common than previously thought. Temporal successions between bloom-forming species on a seasonal basis were also revealed in different cold temperate estuaries, suggesting a key role of photoperiod and temperature controlling bloom development and composition. According to the Intergovernmental Panel on Climate Change, water temperatures are predicted to increase around 4°C by 2100 in Ireland, especially during late spring coinciding with early green tide development. Considering current and predicted temperatures, and photoperiods during bloom development, different eco-physiological experiments were developed. These experiments indicated that the growth of Ulva lacinulata was controlled by temperature, while U. compressa was unresponsive to the photoperiod and temperatures assayed. Considering a scenario of global warming for Irish waters, an earlier development of bloom is expected in the case of U. lacinulata. This could have significant consequences for biomass balance in Irish estuaries and the maximum accumulated biomass during peak bloom. The observed seasonal patterns and experiments also indicated that U. compressa may facilitate U. lacinulata development. When both species were co-cultivated, the culture performance showed intermediate responses to experimental treatments in comparison with monospecific cultures of both species.     

Ulva: An emerging green seaweed model for systems biology

Green seaweeds exhibit a wide range of morphologies and occupy various ecological niches, spanning from freshwater to marine and terrestrial habitats. These organisms, which predominantly belong to the class Ulvophyceae, showcase a remarkable instance of parallel evolution toward complex multicellularity and macroscopic thalli in the Viridiplantae lineage. Within the green seaweeds, several Ulva species (“sea lettuce”) are model organisms for studying carbon assimilation, interactions with bacteria, life cycle progression, and morphogenesis. Ulva species are also notorious for their fast growth and capacity to dominate nutrient-rich, anthropogenically disturbed coastal ecosystems during “green tide” blooms. From an economic perspective, Ulva has garnered increasing attention as a promising feedstock for the production of food, feed, and biobased products, also as a means of removing excess nutrients from the environment. We propose that Ulva is poised to further develop as a model in green seaweed research. In this perspective, we focus explicitly on Ulva mutabilis/compressa as a model species and highlight the molecular data and tools that are currently available or in development. We discuss several areas that will benefit from future research or where exciting new developments have been reported in other Ulva species.     

Protein content, amino acid composition and nitrogen-to-protein conversion factors of Ulva rigida and Ulva capensis from natural populations and Ulva lactuca from an aquaculture system, in South Africa

The South African abalone aquaculture industry is expanding and there is a lack of information on the nutritional profiles of the seaweeds that are used as feed. The current study quantified the protein contents of Ulva rigida and Ulva capensis from natural populations and Ulva lactuca from a commercial, integrated seaweed/abalone aquaculture system. Three methods of protein quantification were used: the Bradford method, crude protein, and specific nitrogen to protein (N-Prot) conversion factors, and results were compared to each other. The results showed that values obtained with the “traditional” conversion factor of 6.25 were on average higher than Bradford values by factors of 64.1 % in U. capensis, 77.1 % in U. rigida and 58.9 % in U. lactuca. This pattern is in line with other published work on seaweed and microalgae. Analyses of amino acid composition showed that aspartic acid was the most abundant amino acid and that these species were also rich in glycine and alanine but poor in histidine, methionine and cysteine. N-Prot factors were as follows: U. capensis, 5.58; U. rigida, 5.12 and U. lactuca, 5.65. An average N-Prot factor of 5.45 provides a more accurate estimate of the protein content of the Ulva species studied than the “traditional” factor of N?×?6.25.     

Influence of abiotic factors on the content of fatty acids of Ulva Intestinalis

The composition of fatty acids (FAs) of a green alga (Ulva intestinalis) inhabiting small rivers of the Elton Lake basin has been investigated. It has been established that long-chain FAs with 16 and 18 carbon atoms are essential. We have investigated the composition variability of FAs of lipids of U. intestinalis depending on environmental factors: the level of mineralization, temperature, oxygen saturation, and acidity. It has been revealed that FA nonsaturation increases with an increase in mineralization. We assume that ω-6 and ω-3 desaturases participate in the adaptation of U. intestinalis to this factor.