ULTRAVIOLET ABSORBING SUBSTANCES FROM AGARUM FIMBRIATUM (PHAEOPHYCEAE) PROTECT GRIFFITHSIA PACIFICA FROM UV RADIATION

Patterns of recruitment and abundance of Ulva pertusa and Enteromorpha linza in the three locations on the south coast of Korea where green tide frequently occurred were investigated with respect to the substrate profile, temporal and spatial variations, and their persistence. Artificial substrates (10 to 20 cm) were made of a mixture of a piece of granite rock and cement on ceramic tiles. These setting plates, representing different surface texture, were placed horizontally and vertically along the rocky shoreline, and replaced every 1 to 2 months. Both populations showed highly seasonal blooms, with peaks in October, 1998 to February, 1999 and another slight peak was observed in the fall of 1999 only for Ulva. However, the winter peak of 1998 did not appeared in the following year, indicating that a significant year-to-year variation existed. Regarding their settlement onto artificial plates with different roughness, Ulva preferred to settle on the rough surface both in the upper and lower intertidal zone; however, this pattern only appeared in the upper zone for Enteromorpha. Vertical distribution of the two populations was well separated; Enteromorpha was more abundant in the upper zone and Ulva in the lower zone. Their seasonal blooms were concomitant with ammonia levels, but occurrence was not well correlated with nitrate and phosphate. The ability of the populations to persist, once blooms occurred, was also distinct; Ulva persisted ca. twice as long as Enteromorpha , having a greater impact in the presence of green tide in this geographical area.     

PRELIMINARY STUDIES OF SEASONALITY,ECOLOGY, AND SPECIES COMPOSITION OF ULVOID ALGAL BLOOMS IN WASHINGTON STATE

Blooms of green macroalgae can devastate important finfish and shellfish habitats. Ulvaria obscura, a relatively unstudied green alga, is a major contributor to these blooms in the San Juan Islands, Washington State, USA. The biomass and productivity of this and other ulvoid algae were measured seasonally for two years. Experiments comparing the growth rates, responses to desiccation, photoacclimation, and grazer preference of U. obscura and Ulva fenestrata were conducted. Ulvaria blooms tended to occur in the subtidal while Ulva blooms were often intertidal. Both genera bloomed between late June and September. Despite their superficial similarity, Ulvaria and Ulva display markedly different physiological and ecological responses. Ulva was capable of faster growth, had higher rates of photosynthesis, and was more desiccation tolerant than Ulvaria. Ulvaria, however, appears to be more resistant to grazing than Ulva.     

Variation in nuclear DNA base composition (mol % G + C) in three orders of marine green algae

Estimates of nuclear DNA base pair composition by determination of thermal denaturation temperatures (T_m) indicated guanine + cytosine (G + C) levels of 35–56% for 17 species of marine green algae. T_m values were found to be reproducible with coefficients of variation among samples and replicates of generally less than 1 percent. G + C % values in four species of Enteromorpha varied within a narrow range of 53–56%, whereas values for three species of Ulva showed substantially greater variation, ranging from 35–55%. Ulva fasciata collections from two geographically separate North Carolina sites had mean G + C composition of 44.8 and 35.6 respectively, suggesting that these populations may be genetically distinct. Enteromorpha linza, which has been treated as a species of Ulva, had a G + C composition of 53.2, typical of the Enteromorpha species investigated. Nuclear DNA base pair composition data for species of Cladophorales and Caulerpales are given as well.Center for Marine Science Research, UNC-W contribution No. 009.     

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 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.     

BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY1

During the last decade, the Palmones River estuary has undergone severe eutrophication followed by a green tide episode; two species of Ulva, rotundata Blid. and Ulva curvata (Kütz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P)of Ulva species, as well as some physicochemical variables in the estuary. Maximum biomass (up to 375 g dry wt·m^?2 in some spots, corresponding to a thallus area index of nearly 17 m²Ulva·m^?2 sediment) were observed in June and December. However, the biomass varied among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates observed. Growth rates were estimated directly in the field. The rates were generally higher in Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The difference between both estimates was used to quantify the importance of the processes causing loss of biomass, which were attributable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme self-shading. Maximum chlorophyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water. However, the absolute concentrations of tissue N and P were always higher than the critical levels for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estuary. In addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass.     

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.     

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.     

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.     

SEASONAL VARIATION OF PHOTOSYNTHETIC PERFORMANCE AND LIGHT ATTENUATION IN ULVA CANOPIES FROM PALMONES RIVER ESTUARY1

The primary production of Ulva populations relies on their photosynthetic performance, which is dependent on the light availability under natural conditions. This study concerns the light attenuation characteristics in Ulva canopies and the seasonal photosynthetic performance of two different species (Ulva rotundata Blid., Ulva curvata (Kütz.) De Toni) blooming in the Palmones river estuary. Light within canopies differed from that reaching the surface. Light availability was reduced through the water column (at high tide) and Ulva canopies. In addition, light was spectrally filtered. As a result, the photosynthetically usable radiation (PUR) was further attenuated through Ulva canopies, increasing the photosynthetically active radiation/PUR ratio. The muddy sediment deposited on and between the Ulva thalli also drastically restricted the light availability. Thick Ulva mats are frequently found covering the intertidal mudflats, and therefore, thalli within these mats may be subjected to steep light gradients. As a consequence, individual Ulva growth rates cannot be extrapolated to estimate the primary production of Ulva canopies. Interspecific differences were observed for light-saturated photosynthetic rates (P_max) and light compensation points (L_CP), with Ulva curvata generally displaying higher values than did U. rotundata. For both species, maxima were recorded in winter for P_max, quantum yield, chlorophyll content, and absorptance, whereas minima were found in summer. Dark respiration (R_d) was not seasonally affected, and a maximum L_CP was found in summer. To extrapolate these data to field situations, the temperature dependence of photosynthesis should be considered. The Q₁₀ values were 2.44 for R_d and 1.79 for P_max, whereas the photosynthesis rate at subsaturating light levels was unaffected. The Q₁₀ values showed an enhanced respiratory rate in summer and a minimum in winter, whereas the seasonal differences on P_max were damped.     

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.     

Green tide formed by free-floating Ulva spp. at Yatsu tidal flat, Japan

Green tides at Yatsu tidal flat, Tokyo Bay, Japan, were first reported in 1995 and formed by a bloom only of free-floating Ulva species. On the tidal flat, the bloom area in well-developed periods increased after 1995 and covered 27.1 ha in May 2002. Based on vertical aerial photographs, green tide remaining in winter during 1996–2007 covered 4.7 ha when first observed in 1999 and increased to 17.5 ha in January 2002 thereafter. We found that the expansion of green tide was related to such factors as an increase in Kira’s Warmth Index, a decrease in annual cumulative hourly air temperatures below 7°C in December, an increase in salinity, and unintentional introduction of Ulva ohnoi. We also found that green tide at Yatsu tidal flat occurred in the course of the improvement of water quality.     

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.     

Grazing on green algae by the periwinkleLittorina littorea in the Wadden Sea

On sedimentary tidal flats in the Wadden Sea near the Island of Sylt, the periwinkleLittorina littorea occurred preferentially on clusters and beds of mussels and on shell beds (100 to 350 m⁻²), achieved moderate densities on green algal patches or mats (20 to 50 m⁻²), and remained rare on bare sediments (<5 m⁻²). Green algae covering>10% of sediment surface appeared in summer on approximately one third of the tidal zone, mainly in the upper and sheltered parts and almost never on mussel and shell beds. In feeding experiments,L. littorea ingested more of the dominant alge,Enteromorpha, than ofUlva, irrespective of whether or not algae were fresh or decaying. The tough thalli ofChaetomorpha were hardly consumed. Snails feeding onEnteromorpha produced fecal pellets from which new growth ofEnteromorpha started. In the absence of periwinkles,Enteromorpha developed on mussels and the attached fucoids. Experimentally increased snail densities on sediments prevented green algal development, but the snails were unable to graze down established algal mats. It is concluded that natural densities ofL. littorea hardly affect the ephemeral mass development of green algae on sediments. However, where the snails occur at high densities, i.e. on mussel beds, green algal development may be prevented.     

SEASONAL VARIABILITY OF PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF ULVAN IN TWO ULVA SPECIES (CHLOROPHYTA) FROM THE BRITTANY COAST1

The seasonal variability in the extraction yield, physicochemical characteristics, and rheological properties of ulvan from two Ulva species contributing to Brittany “green tides” has been studied. These seaweeds were collected in the water column for Ulva armoricana Dion, de Reviers et Coat and on hard substrata for Ulva rotundata Bliding. The maximum ulvan extraction efficiency was not related to the maximum ulvan content in the seaweeds, but with the active growth period of the seaweeds. Ulvan chemical structure, macromolecular characteristics, and rheological properties were affected by both species and seasons. The proportion of high‐molecular‐weight ulvan was the major factor positively correlated with the gelling properties. Characteristics of ulvan from U. rotundata subjected to tides were more affected by seasons than ulvan from U. armoricana living in a more constant environment. These results point to several useful recommendations concerning Ulva sp. biomass collected with regard to ulvan characteristics and uses.     

Abundance and distribution of Ulva microscopic propagules associated with a green tide in the southern coast of the Yellow Sea

The presence of Ulva microscopic propagules may play an important role in the rapid development of high-biomass blooms of green algae in the Yellow Sea. Six cruises were conducted, to determine the abundance and distribution of Ulva microscopic propagules associated with a green tide that developed in the southern coastal waters of the Yellow Sea from April to August, 2012. Results indicated that Ulva microscopic propagules were widespread in these waters, with the highest density being up to 4800 ind. L⁻¹, prior to the appearance of the green tide in April. High densities were also widely distributed along the coast during May and June, after the appearance of the floating green tide. The quantity of Ulva microscopic propagules significantly decreased when the floating green tide declined in July, reaching densities of up to 162 ind. L⁻¹, following the disappearance of the floating green tide in August. Quantitative studies on the distribution patterns of Ulva microscopic propagules along the southern coast of the Yellow Sea indicated a significant correlation between density and salinity, turbidity and nutrient concentrations. Temporal and geographical distribution patterns of Ulva microscopic propagules were also significantly affected by the presence of a large biomass of attached, or floating, Ulva species algae.     

Does the abundance of girellids and kyphosids correlate with cover of the palatable green algae,Ulva spp.? A test on temperate rocky intertidal reefs

This study assessed whether the abundance of girellids and kyphosids was related to cover of the palatable green algae, Ulva australis and Ulva compressa, on rocky intertidal reefs in Jervis Bay, New South Wales, Australia. No relationship was found between Ulva spp. cover and abundance of Girella tricuspidata, Girella elevata and Kyphosus sydneyanus during a period of relatively low Ulva spp. cover (i.e. February 2011 to March 2011), but during a period of significantly higher Ulva spp. cover (i.e. October 2011 to November 2011) there was a strong correlation between Ulva spp. cover and G. tricuspidata abundance. Spatial analysis indicated that the abundance of G. tricuspidata was consistent across time, suggesting G. tricuspidata were not moving between reefs in response to variation in Ulva spp. cover between periods but rather that large schools of G. tricuspidata resided on reefs that had relatively higher Ulva spp. cover at certain times of the year.     

The effect of pH upon the photosynthesis of littoral marine algae

Summary The photosynthetic rates of a number of littoral marine algae were determined over a pH range from 8.1 to 10.3, employing the Winkler technique to measure evolved oxygen. In a large number of red, brown and green algae, the rate fell to a low value, or to complete inhibition, at pH 9.5 and higher. This indicates, in conformity with general permeability theory, that the HCO₃ ^}-ion cannot readily penetrate the cells, and is hence not available for photosynthesis.However, in two genera of coralline red algae (Bossea andCorallina) photosynthesis persists up to pH 10 or higher (though at a considerably reduced rate). This can be interpreted as due to utilization of the HCO₃ ^}-ion (though probably not the CO₃=ion). But several other non-coralline red algae (Centroceras, Botryocladia andGastroclonium), as well as the brown algaPelvetia (and possiblyFucus), and the green algaeUlva andEnteromorpha display this same ability.Thus the utilization of HCO₃ ^}-ion cannot alone be ascribed as the cause of calcium carbonate deposition, since several other non-calcareous algae have this same power. The utilization of HCO₃ ^}-at least permits calcification, however. The question might be reversed, to ask whyUlva, Enteromorpha. Pelvetia and several red algae are not calcified. Some cell wall property may be involved.     

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.     

In vitro recruitment of Ulva sp. and Enteromorpha sp. on gametophytic and tetrasporophytic thalli of four populations of Chondracanthuschamissoi from Chile

Chondracanthus chamissoi is a red alga which is acquiring an increasing economic importance in Chile and becoming a target species for cultivation. Because epiphytism is a major problem in the mariculture of seaweeds, the recruitment of Ulva sp. and Enteromorpha sp. on gametophytic (cystocarpic) and tetrasporophytic thalli of C. chamissoi was tested in vitro on four populations from different locations in Chile. For Ulva sp., the density, cover and length of the recruits varied between the reproductive phases of the host and among the studied populations of C. chamissoi. In most experiments, a larger number of epiphytic thalli was observed on gametophytic plants of C. chamissoi; populations from Calderilla and Lechagua had a higher resistance to epiphytism. For Enteromorpha sp., its ability to grow epiphytically on both phases of the host showed a greater variability, but was inferior to that of Ulva sp. The differential resistance to epiphytism in both reproductive phases and in plant origin indicates the possibility of obtaining selected strains of C. chamissoi with lower susceptibility to epiphytism that could be utilized in planning maricultural programs.