POLYMORPHIC BEHAVIOR OF ULVA LACTUCA (CHLOROPHYTA) IN AXENIC CULTURE. I. OCCURRENCE OF ENTEROMORPHA-LIKE PLANTS IN HAPLOID CLONES1

An isolate of Ulva lactuca L. was brought into axenic culture in both defined synthetic medium and enriched seawater. Haploid clones were established and followed through several generations in both media. Plants possessing distromatic, partially distromatic or completely tubular blades in cross sections, as well as individuals that were completely distromatic in one area of the blade and tubular in another all developed from the same swarmer population. Variations in basal area morphology also occurred. Progeny from swarmers of any of these morphological types showed a similar mixture of morphological variation, indicating non-mutational variability in phenotypic expression of the blade and basal areas. A mechanism by which such variation may occur without mutation is discussed.     

Photosynthesis of Ulva fasciata. IV. pH, carbonic anhydrase and inorganic carbon conversions in the unstirred layer

Abstract. The common marine macroalga Ulva was found to have a surface pH of about 10 during photosynthesis. Under such a condition, the equilibrium CO₂ concentration within the unstirred layer would be below reported CO₂ compensation points, and dehydration of HCO₃ could not occur. Even at a compensation point approaching zero, uncatalysed rates of HCO₃ to CO₂ conversion within the unstirred layer volume could not support photosynthetic rates as measured under stirred conditions in the presence of a carbonic anhydrase inhibitor. Based on this, it is concluded that Ulva takes up HCO₃. It is likely that HCO₃ uptake leads to high internal CO₂ levels which, in turn, suppress photorespiration and thus cause this plant's efficient gas exchange features. Carbonic anhydrase activity was measurable only in plant extracts. However, inhibitor studies suggest the presence of a surface enzyme. The possible functions of extracellular carbonic anhydrase in Ulva are assessed in terms of CO₂ hydration during emergence and a possible HCO₃, transport system.     

Adsorbents for Apheresis Prepared from Polysaccharides of Algae that Threaten Ecosystem Services

In this work, we investigated whether materials isolated from algae that threaten ecosystems can be used for human benefit. We converted acidic polysaccharides (ulvan) from the alga Ulva pertusa into soft hydrogel materials. In addition to ulvan, the hydrogels also contained alginate in a polyion complex with chitosan. Cross‐linking the hydrogel with glutaraldehyde reduced polysaccharide elution from the polyion complex gel. We also found that both ulvan? chitosan and alginate? chitosan gels were able to remove urea and heavy metals from aqueous solution. This is clinically significant, since during apheresis, toxic compounds such as urea have to be removed from the bloodstream of patients. Importantly, albumin was not removed by the hydrogels, implying that this vital protein can be returned to the bloodstream following dialysis.     

Comparative Studies on the Allelopathic Effects of Ulva pertusa Kjellml, Corllina pilulifera Postl et Ruprl, and Sargassum thunbergii mertl O. Kuntze on Skeletonema costatum （Grev.）Cleve

In the present study, we evaluated the allelopathic effects of three macroalgae, namely Ulva pertusa Kjellml, Corallina pilufifera Postl et Ruprl, and Sargassum thunbergii Mertl O. Kuntze, on the growth of the microalga Skeletonema costaturn （Grev.） Creve using culture systems in which the algae coexisted. The effects of the macroalgal culture medium filtrate on S. costatum were also investigated. Moreover, isolated co-culture systems were built to confirm the existence of allelochemicals and preclude growth inhibition by direct contact. The coexistence assay data demonstrated that the growth of S. costaturn was strongly inhibited when fresh tissues, dry powder and aqueous extracts were used; the allelochemicals were lethal to S. costatum at relatively higher concentrations. The effects of the macroalgal culture medium filtrate on the microalga showed both species specificity and complexity. The inhibitory effect of fresh macroalgal tissue and culture medium filtrate on the microalga was due to the alleochemicals released by the macroalgae. The results of the present study show that the allelopathic effects of macroalgae on the microalga are complex. The present study could shed light onto the basis of the interaction between macro- and microalgae.     

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.     

Seasonal and interannual variation of sterols in macrophytes from the Pacific coast of Baja California Peninsula (Mexico)

The seasonal and interannual proximate and sterol composition were assessed in two red (Gelidium robustum, Gelidiaceae and Gracilariopsis sjoestedtii, Gracilariaceae), two brown (Ecklonia arborea, Lessoniaceae and Macrocystis pyrifera, Laminariaceae), and two green (Ulva lactuca and Ulva clathrata, Ulvaceae) macroalgae species and the seagrass Phyllospadix torreyi (Zosteraceae) sampled over 3 years in a subtropical climate in Baja California Sur, Mexico. Each macroalga had a particular sterol composition that was typical of their taxonomic group. The red algae had cholesterol as the major sterol; 92% on average in G. robustum and 90% in G. sjoestedtii, followed by t‐dehydrosterol and brassicasterol. In the brown algae the major sterol was fucosterol, which accounted for approx. 90% and 92% of total sterols for M. pyrifera and E. arborea, respectively, followed by campesterol (7% and 5%) and isofucosterol (1.5% and 1.3%). The green algae had isofucosterol as the major sterol, with 92% on average for U. lactuca and 87% for U. clathrata, followed by cholesterol, fucosterol, and brassicasterol or norcholesterol. The seagrass P. torreyi had β‐sitosterol as the major sterol (39 to 89%, depending on the season), followed by campesterol (4 to 7%), stigmasterol (3 to 6%), and isofucosterol (1.7 to 3.5%). Four (cholesterol, campesterol, fucosterol, and isofucosterol) of the 14 sterols identified in macroalgae and the seagrass could be used to differentiate between classes (Florideophyceae – red, Phaeophyceae – brown, Ulvophyceae – green, and Monocots – seagrass) both seasonally and interannually. The seasonal and interannual sterol composition of macroalgae and seagrass was quite stable, with the exception of red G. sjoestedtii sampled in August and green macroalga U. lactuca and seagrass P. torreyi both sampled in May 2002. Seasonal and interannual variations of proximate and sterol composition are discussed in relation to their reproductive state and environmental parameters.     

Effect of background colour on growth and adhesion strength of Ulva sporelings

This study examined the effects of a range of black, grey and white substrata on the growth and attachment strength of Ulva sporelings on glass and polydimethylsiloxane (Silastic®-T2) surfaces. The rate of development of sporelings was strongly influenced by the colour of the substratum on which they grew. On black backgrounds, sporelings grew slowly and germination was delayed. Laboratory screening methods for antifouling and fouling-release coatings that rely on the growth of Ulva sporelings can be compromised if samples are of different colours. Hydrodynamic removal of sporelings from coatings may also be affected by substratum colour, since smaller plants generate lower hydrodynamic forces making them more difficult to remove.     

Fluorine-free mixed amphiphilic polymers based on PDMS and PEG side chains for fouling release applications

Fluorine-free mixed amphiphilic block copolymers with mixtures of short side groups of polydimethyl siloxane (PDMS) and polyethylene glycol (PEG) were synthesized and studied for their ability to influence the surface properties and control the adhesion of marine organisms to coated surfaces. The settlement (attachment) and strength of adhesion of two different marine algae, the green seaweed Ulva and the diatom Navicula, were evaluated against the surfaces. It is known that hydrophobic coatings based on polydimethyl siloxane elastomers (PDMSe) are prone to protein adsorption and accumulation of strongly adherent diatom slimes, in contrast to PEG-based hydrophilic surfaces that inhibit protein adsorption and moderate only weak adhesion of diatoms. By incorporating both PDMS and PEG side chains into the polymers, the effect of incorporating both polar and non-polar groups on fouling-release could be studied. The dry surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The ability of these mixed amphiphilic polymers to reconstruct in water was examined using underwater bubble contact angle and dynamic water contact angle experiments. To understand more about surface reconstruction behavior, protein adsorption experiments were carried out with fluorescein isothiocyanate-labeled bovine serum albumin (BSA-FITC) on both dry and pre-soaked surfaces.     

Short-term testing of antifouling surfaces: the importance of colour

Abstract

Data from short-term biofouling assays are frequently used to evaluate the performance of antifouling (AF) coatings. There are a large number of factors, however, that may influence community development. One such factor is colour. The hypothesis was that differences in colour may impact the short-term development of a biofouling community and therefore bias the results. An experiment was designed to investigate the effect of black and white substrata on settlement of fouling organisms in the field. Both Ulva sp. and Spirorbis sp. had significantly higher settlement on black surfaces. This result emphasises the importance of considering colour and other factors when undertaking short-term testing of AF coatings.