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.     

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.     

Possible influences of a macroalgal bloom in eelgrass beds on fish assemblages in the lower Knysna Estuary,South Africa

The occurrence of a macroalgal bloom at eelgrass (Zostera capensis) sampling sites in the summer of 2014/2015 provided an opportunity to use underwater video cameras to monitor the possible effects of environmental change on fish diversity and abundance in the lower reaches of the Knysna Estuary. A General Linear Model (GLM) showed that there was a significant difference in the abundance of fish before and after an invasion of the sampling sites by the macroalga Ulva lactuca. The eelgrass bed fish abundance was more affected by the macroalgal bloom than the bare substratum fish abundance, with the Ulva impacting negatively on the relative abundance of Mugilidae in the former habitat. The hypothesis that macroalgal invasions have a negative effect on fish diversity and abundance is therefore supported by this preliminary study.     

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.     

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.     

Tracing the origin of green macroalgal blooms based on the large scale spatio-temporal distribution of Ulva microscopic propagules and settled mature Ulva vegetative thalli in coastal regions of the Yellow Sea,China

From 2008 to 2016, massive floating green macroalgal blooms occurred annually during the summer months in the Yellow Sea. The original source of these blooms was traced based on the spatio-temporal distribution and species composition of Ulva microscopic propagules and settled Ulva vegetative thalli monthly from December 2012 to May 2013 in the Yellow Sea. High quantities of Ulva microscopic propagules in both the water column and sediments were found in the Pyropia aquaculture area along the Jiangsu coast before a green macroalgal bloom appeared in the Yellow Sea. The abundance of Ulva microscopic propagules was significantly lower in outer areas compared to in Pyropia aquaculture areas. A molecular phylogenetic analysis suggested that Ulva prolifera microscopic propagules were the dominant microscopic propagules present during the study period. The extremely low biomass of settled Ulva vegetative thalli along the coast indicated that somatic cells of settled Ulva vegetative thalli did not provide a propagule bank for the green macroalgal blooms in the Yellow Sea. The results of this study provide further supporting evidence that the floating green macroalgal blooms originate from green macroalgae attached to Pyropia aquaculture rafts along the Jiangsu coastline of the southern Yellow Sea.     

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.     

Spatial and temporal variability in macroalgal blooms in a eutrophied coastal estuary

All three macroalgal clades (Chlorophyta, Rhodophyta, and Phaeophyceae) contain bloom-forming species. Macroalgal blooms occur worldwide and have negative consequences for coastal habitats and economies. Narragansett Bay (NB), Rhode Island, USA, is a medium sized estuary that is heavily influenced by anthropogenic activities and has been plagued by macroalgal blooms for over a century. Over the past decade, significant investment has upgraded wastewater treatment from secondary treatment to water-quality based limits (i.e. tertiary treatment) in an effort to control coastal eutrophication in this system. The goal of this study was to improve the understanding of multi-year macroalgal bloom dynamics through intensive aerial and ground surveys conducted monthly to bi-monthly during low tides in May–October 2006–2013 in NB. Aerial surveys provided a rapid characterization of macroalgal densities across a large area, while ground surveys provided high resolution measurements of macroalgal identity, percent cover, and biomass.Macroalgal blooms in NB are dominated by Ulva and Gracilaria spp. regardless of year or month, although all three clades of macroalgae were documented. Chlorophyta cover and nutrient concentrations were highest in the middle and upper bay. Rhodophyta cover was highest in the middle and lower bay, while drifting Phaeophyceae cover was patchy. Macroalgal blooms of >1000 g fresh mass (gfm)/m² (max = 3510 gfm/m²) in the intertidal zone and >3000 gfm/m³ (max = 8555 gfm/m³) in the subtidal zone were observed within a heavily impacted embayment (Greenwich Bay). Macroalgal percent cover (intertidal), biomass (subtidal), and diversity varied significantly between year, month-group, site, and even within sites, with the highest species diversity at sites outside of Greenwich Bay. Total intertidal macroalgal percent cover, as well as subtidal Ulva biomass, were positively correlated with temperature. Dissolved inorganic nitrogen concentrations were correlated with the total biomass of macroalgae and the subtidal biomass of Gracilaria spp. but not the biomass of Ulva spp. Despite seasonal reductions in the nutrient output of wastewater treatment facilities emptying into upper Narragansett Bay in recent years, macroalgal blooms still persist. Continued long-term monitoring of water quality, macroalgal blooms, and ecological indicators is essential to understand the changes in macroalgal bloom dynamics that occur after nutrient reductions from management efforts.     

Genetic analysis of the Linnaean Ulva lactuca (Ulvales,Chlorophyta) holotype and related type specimens reveals name misapplications,unexpected origins,and new synonymies

Current usage of the name Ulva lactuca, the generitype of Ulva, remains uncertain. Genetic analyses were performed on the U. lactuca Linnaean holotype, the U. fasciata epitype, the U. fenestrata holotype, the U. lobata lectotype, and the U. stipitata lectotype. The U. lactuca holotype is nearly identical in rbcL sequence to the epitype of U. fasciata, a warm temperate to tropical species, rather than the cold temperate species to which the name U. lactuca has generally been applied. We hypothesize that the holotype specimen of U. lactuca came from the Indo‐Pacific rather than northern Europe. Our analyses indicate that U. fasciata and U. lobata are heterotypic synonyms of U. lactuca. Ulva fenestrata is the earliest name for northern hemisphere, cold temperate Atlantic and Pacific species, with U. stipitata a junior synonym. DNA sequencing of type specimens provides an unequivocal method for applying names to Ulva species.     

Coupling planktonic and benthic shifts during a bloom of Alexandrium catenella in southern Chile: Implications for bloom dynamics and recurrence

Cell abundances and distributions of Alexandrium catenella resting cysts in recent sediments were studied along time at two locations in the Chilean Inland Sea exposed to different oceanographic conditions: Low Bay, which is much more open to the ocean than the more interior and protected Ovalada Island. The bloom began in interior areas but maximum cyst concentrations were recorded in locations more open to the ocean, at the end of the Moraleda channel. Our results showed a time lapse of around 3 months from the bloom peak (planktonic population) until the number of resting cysts in the sediments reached a maximum. Three months later, less than 10% of the A. catenella cysts remained in the sediments. Maximum cyst numbers in the water column occurred one month after the planktonic peak, when no cells were present. The dinoflagellate assemblage at both study sites was dominated by heterotrophic cysts, except during the A. catenella bloom. CCA analyses of species composition and environmental factors indicated that the frequency of A. catenella blooms was associated with low temperatures, but not with salinity, chlorophyll a concentration, and predator presence (measured as clam biomass). However, resting cyst distribution was only related to cell abundance and location. The occurrence of A. catenella cysts was also associated with that of cysts from the toxic species Protoceratium reticulatum. By shedding light on the ecological requirements of A. catenella blooms, our observations support the relevance of encystment as a mechanism of bloom termination and show a very fast depletion of cysts from the sediments (<3 months), which suggest a small role for resting cyst deposits in the recurrence of A. catenella blooms in this area.     

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.     

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.     

Foliose Ulva Species Show Considerable Inter‐Specific Genetic Diversity,Low Intra‐Specific Genetic Variation,and the Rare Occurrence of Inter‐Specific Hybrids in the Wild

Foliose Ulva spp. have become increasingly important worldwide for their environmental and financial impacts. A large number of such Ulva species have rapid reproduction and proliferation habits, which explains why they are responsible for Ulva blooms, known as “green tides”, having dramatic negative effects on coastal ecosystems, but also making them attractive for aquaculture applications. Despite the increasing interest in the genus Ulva, particularly on the larger foliose species for aquaculture, their inter‐ and intra‐specific genetic diversity is still poorly described. We compared the cytoplasmic genome (chloroplast and mitochondrion) of 110 strains of large distromatic foliose Ulva from Ireland, Brittany (France), the Netherlands and Portugal. We found six different species, with high levels of inter‐specific genetic diversity, despite highly similar or overlapping morphologies. Genetic variation was as high as 82 SNPs/kb between Ulva pseudorotundata and U. laetevirens, indicating considerable genetic diversity. On the other hand, intra‐specific genetic diversity was relatively low, with only 36 variant sites (0.03 SNPs/kb) in the mitochondrial genome of the 29 Ulva rigida individuals found in this study, despite different geographical origins. The use of next‐generation sequencing allowed for the detection of a single inter‐species hybrid between two genetically closely related species, U. laetevirens, and U. rigida, among the 110 strains analyzed in this study. Altogether, this study represents an important advance in our understanding of Ulva biology and provides genetic information for genomic selection of large foliose strains in aquaculture.     

Effects of a macroalgal mat (Ulva lactuca) on estuarine sand flat copepods: an experimental study

The effects of a macroalgal mat (Ulva lactuca) on intertidal sand flat copepods were studied in Jamaica Bay, NY. In 1999, Ulva was removed from paired quadrats in the algal mat. Density and species richness were estimated from sediment cores over seven biweekly periods and compared with Ulva-removal quadrats and with an unvegetated reference site. In a separate analysis at the same site, species composition and density of all copepods within the algal mat were determined from replicated quadrat samples over seven dates. Emergence traps were deployed in all treatments in 1999 to quantify copepod movements from sediments into the water column during flooding tide. Dissolved oxygen (DO) was continuously monitored over several 96-h periods in and above the algal mat. In 2000, three biomass levels of Ulva (0, 100, 200 g DW per m²) were added to paired quadrats in the unvegetated zone. Density and species richness were estimated over eight time periods. Ulva removal resulted in significant increases in density and species richness, but levels remained lower than at the unvegetated site. Likewise, addition of Ulva biomass produced significant declines in copepod density. However, the differences between low- and high-Ulva-addition treatments were insignificant. Increases in phytal copepods after Ulva addition did not compensate for losses of epibenthic and infaunal species. The overall effect of the Ulva mat was a net loss of copepod density, including the loss of nearly all infaunal species. Anoxia in sediments and within the algal mat are correlated with declines in infaunal species and with escape by some infaunal species from the sediment into the water column.     

MOLECULAR ASSESSMENT OF ULVA SPP. (ULVOPHYCEAE,CHLOROPHYTA) IN THE HAWAIIAN ISLANDS1

Sequences of the nuclear internal transcribed spacer 1 (ITS1) region and the chloroplast rbcL gene were obtained from 86 specimens of Ulva (including “Enteromorpha”) from five of the main Hawaiian Islands. These 86 specimens were divided into 11 operational taxonomic units (OTUs) based on analyses of primary sequence data and comparisons of ITS1 secondary structure. Of the 11 OTUs, six have not previously been reported from anywhere in the world. Only three represented exact sequence matches to named species (Ulva lactuca L., syn. U. fasciata Delile; U. ohnoi Hiraoka et Shimada); two others represented exact sequence matches to unnamed species from Japan and New Zealand. Of the 12 species names currently in use for Hawaiian Ulva, only one, U. lactuca (as U. fasciata), was substantiated. General morphology of the specimens did not always correspond with molecular OTUs; for example, reticulate thallus morphology, previously considered diagnostic for the species U. reticulata Forssk., was expressed in thalli assigned to U. ohnoi and to one of the novel OTUs. This finding confirms a number of recent studies and provides further support for a molecular species concept for Ulva. These results suggest that Ulva populations in tropical and subtropical regions consist of species that are largely unique to these areas, for which the application of names based on types from temperate and boreal European and North American waters is inappropriate. Ulva ohnoi, a “green tide” species, is reported from Hawaii for the first time.     

GAMETOGENESIS AND GAMETE RELEASE OF ULVA MUTABILIS AND ULVA LACTUCA (CHLOROPHYTA): REGULATORY EFFECTS AND CHEMICAL CHARACTERIZATION OF THE “SWARMING INHIBITOR”1

Gametophytes of Ulva mutabilis Føyn and Ulva lactuca L. were artificially induced to form gametangia by removal of sporulation inhibitors. After this treatment, U. mutabilis gametes were ready for swarming on the third morning after induction, while U. lactuca gametangia needed 1–2 d longer for maturation. Release of gametes of U. lactuca was dependent solely upon exposure to the first light in the morning. Gametangia of U. mutabilis, however, also required sufficient dilution of the swarming inhibitor (SWI). SWI was excreted transiently by both Ulva species early during gametogenesis. While the SWI concentration in U. mutabilis medium remained above the inhibitory concentration until the gametangia were mature, the concentration of U. lactuca‐SWI dropped rapidly below this level. In the presence of sufficient SWI, mature gametes of U. mutabilis remained motionless within the gametangia despite light and open exit pores. However, using SEM, an additional seal was detected within these pores, which probably prevented premature swarming until dilution of SWI and exposure to light. Observations by time lapse microscopy and experiments with the myosin kinase inhibitor BDM suggest that the gametes may be either extruded by the gametangium or leave the exit pore by active gliding motion, driven by a myosin‐like motor protein. The SWIs were purified from both Ulva species, and mass spectral analysis showed their molecular masses (292 Da) were identical.     

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.     

Molecular phylogenetic analyses of the Japanese Ulva and Enteromorpha (Ulvales, Ulvophyceae), with special reference to the free-floating Ulva

In order to elucidate the species composition of free‐floating Ulva that cause green tide in several bays in Japan, and to clarify the generic status of Ulva and Enteromorpha (Ulvales, Ulvophyceae), the nuclear encoded internal transcribed spacer (ITS) region including the 5.8S gene and the plastid encoded large subunit of ribulose‐1, 5‐bisphosphate carboxylase/ oxgenase (rbcL) gene sequences for 15 species were determined. Both ITS and rbcL analyses indicate that free‐floating Ulva samples are divided into four different lineages that correspond to Ulva lactuca Linnaeus, U. pertusa Kjellman, U. armoricana Dion etal. and U. fasciata Delile. These four species are distinguished by cell morphology including the arrangement of cells, the shape and size of cells and the position of chloroplasts. Molecular data also indicated that Ulva and Enteromorpha are not separated as respective monophyletic groups within a large monophyletic clade and congeneric as shown by previous molecular studies using the ITS sequences alone. This strongly suggests that these genera are congeneric and Enteromorpha should be reduced to the synonym of Ulva.     

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.     

Differential toxic effects of Ulva lactuca (Chlorophyta) on the herbivorous gastropods,Littorina littorea and L. obtusata (Mollusca)

Members of the genus Ulva are widespread and abundant in intertidal and shallow subtidal areas but there are conflicting data regarding susceptibility to herbivory. While some studies have documented that Ulva spp. were favored by a diversity of marine herbivores, other work has revealed herbivore deterrence. We investigated grazing and growth rates of the littorinid species, Littorina littorea and L. obtusata, when offered Fucus vesiculosus, Ascophyllum nodosum, Ulva lactuca, and Chondrus crispus, highlighting distinctive vulnerabilities to toxic effects of U. lactuca. Ulva lactuca was the preferred food of L. littorea, while L. obtusata showed no grazing on this ephemeral algal species. In contrast, F. vesiculosus was highly preferred by L. obtusata. Although L. littorea demonstrated a grazing preference for U. lactuca, growth rate of this gastropod species was nearly 3× greater when fed F. vesiculosus, suggesting a non‐lethal, negative effect of U. lactuca on L. littorea with long‐term exposure. Mortality of L. obtusata ranged from 0% to 100% when held in the presence of various Ulva densities for 1 week, and Ulva exudate depressed herbivory of this gastropod. We conclude that the water‐soluble, toxic exudate produced by U. lactuca in response to herbivory had allelochemical properties, and may contain a cleavage product (acrylic acid) of dimethylsulfoniopropionate or reactive oxygen species (i.e., H₂O₂). Observed differences in susceptibility to Ulva toxicity by the littorinid species may be related to generalist versus specialist feeding and habitat strategies.