SEASONAL FLUCTUATIONS IN TISSUE NITROGEN,PHOSPHORUS, AND N:P FOR FIVE MACROALGAL SPECIES COMMON TO THE PACIFIC NORTHWEST COAST1

Variations in tissue nitrogen (N) and phosphorus (P) were examined over a complete seasonal cycle for five macroalgae common in Oregon coastal water. Tissue N ranged from 2.0 to 5.5% dry weight (dry wt) in leafy macroalgae (Enteromorpha intestinalis (Linnaeus) Link. Ulva fenestrata Postels et Ruprecht, and Porphyra sp.) and from 0.9 to 2.6% drt wt in branched macroalgae (Codium fragile (Suringar) Hariot and Pelvetiopsis limitata Setchell). Tissue P ranged from 0.32 to 0.86% dry wt in leafy macroalgae and from 0.27 to 0.50% dry wt in branched macroalgae, Ulva fenestrata, C. fragile, and P. limitata appeared to be N limited during part of the year based on tissue N levels. Variations in N:P showed a more distinct seasonal pattern than either tissue N and tissue P. All macroalgae examined appeared to be N limited at least part of the year based on N:P composition, and P limitation occurred for all macroalgae examined except C. fragile. Our results suggest that tissue N:P ratio for macroalgae may be a good index for evaluating in situ nutrient status.     

PHOTOACCLIMATION AND GROWTH RATE RESPONSES OF ULVA ROTUNDATA (CHLOROPHYTA) TO INTRADAY VARIATIONS IN GROWTH IRRADIANCE1

A vegetative clone of the chlorophyte macroalga Ulva rotundata was maintained in an outdoor continuous flow system under nutrient sufficient conditions and various light regimes. Step changes between 9 and 100% incident irradiance (I^o) were employed to simulate cloud passage. Temporary (1–4 h) midday (I^o)perturbations evoked net changes in growth rate (μ) and chlorophyll (chl) content. Under I_o alternating at various periodicities from 15 min to 7 h, net μ was the average of the μ under steady state 9 and 100% I^o, regardless of periodicity. However, the μ in alternating light was considerably less than μ under steady state 55% I^o(? 9%+ 100%/2), as expected based on the nonlinear shape of the μ-I relationship. Unlike μ, chl content depended primarily on the total daily irradiance, probably clue to the slower response of chl compared to photosynthetic rate. On time scales ≥ one day, chl was linearly correlated with light-regulated daily μ under both steady state and intraday fluctuating irradiance, consistent with photosynthetic feedback regulation of chl concentration.     

Cell wall structure of the agarophytes Gracilaria tikvahiae and G. cornea (Rhodophyta) and penetration by the epiphyte Ulva lactuca (Chlorophyta)

Use of light, transmission, and scanning electronmicroscopes revealed that the epidermal cell wall ofthe red algal agarophytes Gracilaria tikvahiaeMcLachlan and G. cornea J. Agardh consists of adecklamelle and outer and inner wall layers. The twospecies differed, with G. cornea having asignificantly thicker outer wall and a more diffusedecklamelle. After induction, the zooids of Ulvalactuca would attach to glass slides and the twospecies of Gracilaria via an adhesion pad. Within a few days, 3–5 celled germlings penetrated thedecklamelle and outer wall layer of both basiphytes. By the time the epiphyte germlings reached the 15celled stage, they had penetrated the inner walllayer. The differences in epidermal cell wallconstruction between the two basiphytes may play arole in the ability of zooids of U. lactuca toattach in nature where epiphytization of G.cornea is infrequent.     

Effects of Ulva spp. and seasonal disturbances on the recovery of a temperate rocky intertidal community

The inhibitory effects of ulvoid algae and their seasonality on the recovery and succession of an intertidal algal community were investigated under field conditions using a two‐factorial design. The experiment was conducted in the mid‐low intertidal zone on the Southern coast of Korea. In spring and fall, each of the ten 50 × 50 cm plots was disturbed artificially, and Ulva spp. were continuously excluded from five plots of the seasonal plots. The succession of spring plots was nearly twice as fast as that of the fall plots (spring, 4–6 months; fall, 10–15 months), indicating that the seasonal effects contributed significantly to the speed of the succession. The inhibition by Ulva species delayed the succession; however, the strength of this delay was limited largely by the duration and persistence of Ulva mass, which was also highly seasonal. The presence of Ulva spp. did not alter the final assemblage at the climax stage; instead, it caused a delay in community resilience. This study provides a few analytical factors for community‐wise comparison during the evaluation of the status of successional stages.     

绿色荧光蛋白(ZsGreen)基因在长石莼细胞中的表达

主要研究绿色荧光蛋白(ZsGreen)基因在长石莼(缘管浒苔)细胞中的表述.应用绿色荧光蛋白基因、抗除草剂bar基因、CMV 35S启动子和SV40双启动子构建了质粒载体PSV-bar-ZsGeen,采用改进的PEG法将质粒载体PSV-bar-Zs-Geen导入到缘管浒苔原生质体中,经过细胞培养发育再生藻株,通过除草剂筛选出阳性藻株,且转化率达38.58％,进一步PCR分子检测和显微荧光检测表明,绿色荧光蛋白基因在转基因植株中得到表达,为今后转基因浒苔研究奠定基础.     

Composition,uniqueness and variability of the epiphytic bacterial community of the green alga Ulva australis

Green Ulvacean marine macroalgae are distributed worldwide in coastal tidal and subtidal ecosystems. As for many living surfaces in the marine environment, little is known concerning the epiphytic bacterial biofilm communities that inhabit algal surfaces. This study reports on the largest published libraries of near full-length 16S rRNA genes from a marine algal surface (5293 sequences from six samples) allowing for an in-depth assessment of the diversity and phylogenetic profile of the bacterial community on a green Ulvacean alga. Large 16S rRNA gene libraries of surrounding seawater were also used to determine the uniqueness of this bacterial community. The surface of Ulva australis is dominated by sequences of Alphaproteobacteria and the Bacteroidetes, especially within the Rhodobacteriaceae, Sphingomonadaceae, Flavobacteriaceae and Sapropiraceae families. Seawater libraries were also dominated by Alphaproteobacteria and Bacteroidetes sequences, but were shown to be clearly distinct from U. australis libraries through the clustering of sequences into operational taxonomic units and Bray–Curtis similarity analysis. Almost no similarity was observed between these two environments at the species level, and only minor similarity was observed at levels of sequence clustering representing clades of bacteria within family and genus taxonomic groups. Variability between libraries of U. australis was relatively high, and a consistent sub-population of bacterial species was not detected. The competitive lottery model, originally derived to explain diversity in coral reef fishes, may explain the pattern of colonization of this algal surface.     

Effect of bacterial biofilms formed on fouling-release coatings from natural seawater and Cobetia marina,on the adhesion of two marine algae

Previous studies have shown that bacterial biofilms formed from natural seawater (NSW) enhance the settlement of spores of the green alga Ulva linza, while single-species biofilms may enhance or reduce settlement, or have no effect at all. However, the effect of biofilms on the adhesion strength of algae, and how that may be influenced by coating/surface properties, is not known. In this study, the effect of biofilms formed from natural seawater and the marine bacterium Cobetia marina, on the settlement and the adhesion strength of spores and sporelings of the macroalga U. linza and the diatom Navicula incerta, was evaluated on Intersleek® 700, Intersleek® 900, poly(dimethylsiloxane) and glass. The settlement and adhesion strength of these algae were strongly influenced by biofilms and their nature. Biofilms formed from NSW enhanced the settlement (attachment) of both algae on all the surfaces while the effect of biofilms formed from C. marina varied with the coating type. The adhesion strength of spores and sporelings of U. linza and diatoms was reduced on all the surfaces biofilmed with C. marina, while adhesion strength on biofilms formed from NSW was dependent on the alga (and on its stage of development in the case of U. linza), and coating type. The results illustrate the complexity of the relationships between fouling algae and bacterial biofilms and suggest the need for caution to avoid over-generalisation.     

Antifouling potential of Subtilisin A immobilized onto maleic anhydride copolymer thin films

The proteinaceous nature of the adhesives used by most fouling organisms to attach to surfaces suggests that coatings incorporating proteolytic enzymes may provide a technology for the control of biofouling. In the present article, the antifouling (AF) and fouling release potential of model coatings incorporating the surface-immobilized protease, Subtilisin A, have been investigated. The enzyme was covalently attached to maleic anhydride copolymer thin films; the characteristics of the bioactive coatings obtained were adjusted through variation of the type of copolymer and the concentration of the enzyme solution used for immobilization. The bioactive coatings were tested for their effect on the settlement and adhesion strength of two major fouling species: the green alga Ulva linza and the diatom Navicula perminuta. The results show that the immobilized enzyme effectively reduced the settlement and adhesion strength of zoospores of Ulva and the adhesion strength of Navicula cells. The AF efficacy of the bioactive coatings increased with increasing enzyme surface concentration and activity, and was found to be superior to the equivalent amount of enzyme in solution. The results provide a rigorous analysis of one approach to the use of immobilized proteases to reduce the adhesion of marine fouling organisms and are of interest to those investigating enzyme-containing coating technologies for practical biofouling control.     

A model that predicts the attachment behavior of Ulva linza zoospores on surface topography

A predictive model for the attachment of spores of the green alga Ulva on patterned topographical surfaces was developed using a constant refinement approach. This ‘attachment model’ incorporated two historical data sets and a modified version of the previously-described Engineered Roughness Index. Two sets of newly-designed surfaces were used to evaluate the effect of two components of the model on spore settlement. Spores attached in fewer numbers when the area fraction of feature tops increased or when the number of distinct features in the design increased, as predicted by the model. The model correctly predicted the spore attachment density on three previously-untested surfaces relative to a smooth surface. The two historical data sets and two new data sets showed high correlation (R ² = 0.88) with the model. This model may be useful for designing new antifouling topographies.     

Free-floating Ulva in the southwest Netherlands: species or morphotypes? a morphological,molecular and ecological comparison

Free-floating Ulva L. biomass in the eutrophic brackish ‘Veerse Meer’ lagoon (southwest Netherlands) consists of four morphologically identified species: U. curvata (Kützing) De Toni, U. lactuca L., U. rigida C. Agardh and U. scandinavica Bliding. U. curvata could be recognized easily because of the characteristic central cavity in the holdfast of the attached plants, the arrangement of cells in rows and the single pyrenoid in each cell. U. rigida was distinguished by the thick thallus and the large number of pyrenoids. The Veerse Meer isolate, however, was slightly different from the isolate from the Oosterschelde estuary (the Netherlands). U. lactuca and U. scandinavica showed a high degree of overlap in thallus thickness and cell size, but U. scandinavica usually possessed more pyrenoids. However, doubts have frequently been expressed about the use of some morphological characters in Ulva taxonomy. To determine the validity of such characters in the identification of Ulva species, the morphological variation within and between morphological species was recorded and a molecular data set generated. To detect possible ecophysiological differences between species, optimum temperatures and salinities for growth were determined experimentally. The sequences of the nuclear ribosomal DNA internal transcribed spacer 2 (ITS2) and flanking regions of U. lactuca, U. rigida and U. scandinavica from the Veerse Meer were all identical, but differed from that of U. rigida from the Oosterschelde estuary. Ulva species from the Veerse Meer were most closely related to U. armoricana and U. rigida from Brittany (2.9% and 3.5% divergence respectively); the difference between U. rigida from the Veerse Meer and from the Oosterschelde estuary was 7.5%. Rooted trees, based on a comparison of these sequences with sequences of other Ulva and Enteromorpha species obtained from the literature, using Monostroma arcticum as outgroup, suggested that Ulva is paraphyletic with respect to Enteromorpha. The optimum temperature for growth of U. curvata was 25?°C; for all other species it was 10?°C. The optimum salinity for growth was 30?°C for all isolates. It is concluded that U. lactuca, U rigida and U. scandinavica from the Veerse Meer are all members of one highly polymorphic species.