Green Macroalga Ulva Rigida Research Articles

Photoprotection by photoinhibitory and PSII-reaction centre quenching controls growth of Ulva rigida (Chlorophyta) and is a pre-requisite for green tide formation

Main ConclusionThe combined photoinhibitory and PSII-reaction centre quenching against light stress is an important mechanism that allows the green macroalga Ulva rigida to proliferate and form green tides in coastal ecosystems.Eutrophication of coastal ecosystems often stimulates massive and uncontrolled growth of green macroalgae, causing serious ecological problems. These green tides are frequently exposed to light intensities that can reduce their growth via the production of reactive oxygen species (ROS). To understand the physiological and biochemical mechanisms leading to the formation and maintenance of green tides, the interaction between inorganic nitrogen (Ni) and light was studied. In a bi-factorial physiological experiment simulating eutrophication under different light levels, the bloom-forming green macroalga Ulva rigida was exposed to a combination of ecologically relevant nitrate concentrations (3.8–44.7 µM) and light intensities (50–1100 µmol photons m−2 s−1) over three days. Although artificial eutrophication (≥ 21.7 µM) stimulated nitrate reductase activity, which regulated both nitrate uptake and vacuolar storage by a feedback mechanism, nitrogen assimilation remained constant. Growth was solely controlled by the light intensity because U. rigida was Ni-replete under oligotrophic conditions (3.8 µM), which requires an effective photoprotective mechanism. Fast declining Fv/Fm and non-photochemical quenching (NPQ) under excess light indicate that the combined photoinhibitory and PSII-reaction centre quenching avoided ROS production effectively. Thus, these mechanisms seem to be key to maintaining high photosynthetic activities and growth rates without producing ROS. Nevertheless, these photoprotective mechanisms allowed U. rigida to thrive under the contrasting experimental conditions with high daily growth rates (12–20%). This study helps understand the physiological mechanisms facilitating the formation and persistence of ecologically problematic green tides in coastal areas.

Green Macroalgae Hydrolysate for Biofuel Production: Potential of Ulva rigida

In this study, the green macroalgae Ulva rigida, which contains 34.9% carbohydrates, underwent treatment with commercial hydrolytic enzymes. This treatment yielded a hydrolysate that contained 23 ± 0.6 g·L−1 of glucose, which was subsequently fermented with Saccharomyces cerevisiae. The fermentation process resulted in an ethanol concentration of 9.55 ± 0.20 g·L−1. The optimal conditions for ethanol production by S. cerevisiae were identified as follows: non-sterilized conditions, an absence of enrichment, and using an inoculum size of 118 mg·L−1. Under these conditions, the fermentation of the green macroalgal hydrolysate achieved a remarkable conversion efficiency of 80.78%. The ethanol o/t ratio, namely the ratios of the experimental to theoretical ethanol produced, for Scheffersomyces stipitis, Candida guilliermondii, Kluyveromyces marxianus, and S. cerevisiae after 48 h of fermentation were 52.25, 63.20, 70.49, and 82.87%, respectively. Furthermore, S. cerevisiae exhibited the best outcomes in terms of ethanol production (9.35 g·L−1) and conversion efficiency (80.78%) after 24 h (optimal time) of fermentation.

Valuable Nutrients from Ulva rigida: Modulation by Seasonal and Cultivation Factors

Ulva macroalgae species are recognized to be an underexploited source of key nutrients, including proteins, fibers and minerals. The present work evaluated the nutritional value protein, ash, mineral composition, fat, fatty acid profile and dietary fiber of the green macroalgae Ulva rigida produced in an open land-based integrated multi-trophic aquaculture (IMTA) system, over four seasons. Overall, protein and fat content of the farmed algae ranged between 7.6 and 25.8% DW and between 0.2 and 1.3% DW, respectively, reaching the highest levels during autumn/winter seasons. In turn, total dietary fiber and ashes showed a contrary seasonal tendency, reaching maximum levels in spring (40.9–58.3% DW and 25.5–38.8% DW, respectively). Notably, the latter were particularly characterized by their richness in potassium, magnesium and iron, and a sodium/potassium ratio bellow 1.7. Variable cultivation conditions of stocking density (Sd) and flow rate (Fr) were also tested, allowing to confirm that manipulation of cultivation conditions in an IMTA system may help to improve the nutritional value of this macroalga and to boost its market value through its use as a functional food ingredient.

Valuing Bioactive Lipids from Green, Red and Brown Macroalgae from Aquaculture, to Foster Functionality and Biotechnological Applications.

Marine edible macroalgae have functional proprieties that might improve human health and wellbeing. Lipids represent a minor fraction of macroalgae, yet with major interest as main carriers of omega 3 polyunsaturated fatty acids and intrinsic bioactive properties. In this study, we used lipid extracts from the green macroalgae Ulva rigida and Codium tomentosum; the red Gracilaria gracilis, Palmaria palmata and Porphyra dioica; and the brown Fucus vesiculosus, produced in a land-based integrated multitrophic aquaculture (IMTA) system. We determined the lipid quality indices based on their fatty acid profiles and their bioactivities as putative antioxidant, anti-inflammatory and antiproliferative agents. The results reveal to be species-specific, namely U. rigida displayed the lowest atherogenicity and thrombogenicity indices. Palmaria palmata and F. vesiculosus lipid extracts displayed the lowest inhibitory concentration in the free radical scavenging antioxidant assays. Ulva rigida, C. tomentosum, P. palmata and P. dioica inhibited COX-2 activity by up to 80%, while P. dioica and P. palmata extracts showed the highest cytotoxic potential in the MDA-MB-231 breast cancer cells. This work enhances the valorization of macroalgae as functional foods and promising ingredients for sustainable and healthy diets and fosters new applications of high-valued algal biomass, in a species-specific context.

Catalytic transformation of the marine polysaccharide ulvan into rare sugars, tartaric and succinic acids

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 °C renders a high percentage of rhamnose (78–79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 °C affords moderate amounts of tartaric acid (24–26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.

Anticoagulant Activity of Sulfated Ulvan Isolated from the Green Macroalga Ulva rigida.

(1) Background: Brown and red algal sulfated polysaccharides have been widely described as anticoagulant agents. However, data on green algae, especially on the Ulva genus, are limited. This study aimed at isolating ulvan from the green macroalga Ulva rigida using an acid- and solvent-free procedure, and investigating the effect of sulfate content on the anticoagulant activity of this polysaccharide. (2) Methods: The obtained ulvan fraction was chemically sulfated, leading to a doubling of the polysaccharide sulfate content in a second ulvan fraction. The potential anticoagulant activity of both ulvan fractions was then assessed using different assays, targeting the intrinsic and/or common (activated partial thromboplastin time), extrinsic (prothrombin time), and common (thrombin time) pathways, and the specific antithrombin-dependent pathway (anti-Xa and anti-IIa), of the coagulation cascade. Furthermore, their anticoagulant properties were compared to those of commercial anticoagulants: heparin and Lovenox®. (3) Results: The anticoagulant activity of the chemically-sulfated ulvan fraction was stronger than that of Lovenox® against both the intrinsic and extrinsic coagulation pathways. (4) Conclusion: The chemically-sulfated ulvan fraction could be a very interesting alternative to heparins, with different targets and a high anticoagulant activity.

Lipidomic signature of the green macroalgae Ulva rigida farmed in a sustainable integrated multi-trophic aquaculture

Ulva species, green macroalgae, are widely distributed across the globe, being one of the most heavily traded edible seaweeds. Nonetheless, although this genus has been largely used in scientific studies, its lipidome remains rather unexplored. The present study sheds light over the lipid profile of Ulva rigida produced in a land-based integrated multi-trophic aquaculture (IMTA) system using liquid chromatography coupled to high-resolution mass spectrometry for molecular lipid species identification. The lipidome of U. rigida revealed the presence of distinct beneficial n-3 fatty acids for human health, namely alpha-linoleic acid (ALA) and docosapentaenoic acid (DPA). A total of 87 molecular species of glycolipids, 58 molecular species of betaine lipids, and 57 molecular species of phospholipids were identified in the lipidome of U. rigida including some species bearing PUFA and with described bioactive properties. Overall, the present study contributes to the valorization and quality validation of sustainably farmed U. rigida.

Interaction strength between different grazers and macroalgae mediated by ocean acidification over warming gradients

Since the past century, rising CO2 levels have led to global changes (ocean warming and acidification) with subsequent effects on marine ecosystems and organisms. Macroalgae-herbivore interactions have a main role in the regulation of marine community structure (top-down control). Gradients of warming prompt complex non-linear effects on organism metabolism, cascading into altered trophic interactions and community dynamics. However, not much is known on how will acidification and grazer assemblage composition shape these effects. Within this context, we aimed to assess the combined effects of warming gradients and acidification on macroalgae-herbivore interactions, using three cosmopolitan species, abundant in the Iberian Peninsula and closely associated in nature: the amphipod Melita palmata, the gastropod Gibbula umbilicalis, and the green macroalga Ulva rigida. Under two CO2 treatments (ΔCO2 ≃ 450 μatm) across a temperature gradient (13.5, 16.6, 19.9 and 22.1 °C), two mesocosm experiments were performed to assess grazer consumption rates and macroalgae-herbivore interaction, respectively. Warming (Experiment I and II) and acidification (Experiment II) prompted negative effects in grazer's survival and species-specific differences in consumption rates. M. palmata was shown to be the stronger grazer per biomass (but not per capita), and also the most affected by climate stressors. Macroalgae-herbivore interaction strength was markedly shaped by the temperature gradient, while simultaneous acidification lowered thermal optimal threshold. In the near future, warming and acidification are likely to strengthen top-down control, but further increases in disturbances may lead to bottom-up regulated communities. Finally, our results suggest that grazer assemblage composition may modulate future macroalgae-herbivore interactions.

Anaerobic co-digestion of Tunisian green macroalgae Ulva rigida with sugar industry wastewater for biogas and methane production enhancement

Ulva rigida is a green macroalgae, abundantly available in the Mediterranean which offers a promising source for the production of valuable biomaterials, including methane. In this study, anaerobic digestion assays in a batch mode was performed to investigate the effects of various inocula as a mixture of fresh algae, bacteria, fungi and sediment collected from the coast of Sfax, on biogas production from Ulva rigida. The results revealed that the best inoculum to produce biogas and feed an anaerobic reactor is obtained through mixing decomposed macroalgae with anaerobic sludge and water, yielding into 408mL of biogas. The process was then investigated in a sequencing batch reactor (SBR) which led to an overall biogas production of 375mL with 40% of methane. Further co-digestion studies were performed in an anaerobic up-flow bioreactor using sugar wastewater as a co-substrate. A high biogas production yield of 114mL g−1 VSadded was obtained with 75% of methane. The co-digestion proposed in this work allowed the recovery of natural methane, providing a promising alternative to conventional anaerobic microbial fermentation using Tunisian green macroalgae. Finally, in order to identify the microbial diversity present in the reactor during anaerobic digestion of Ulva rigida, the prokaryotic diversity was investigated in this bioreactor by the denaturing gradient gel electrophoresis (DGGE) method targeting the 16S rRNA gene.

Production and characterization of enzymatic cocktail produced by Aspergillus niger using green macroalgae as nitrogen source and its application in the pre-treatment for biogas production from Ulva rigida

Marine macroalgae are gaining more and more importance as a renewable feedstock for durable bioenergy production, but polysaccharides of this macroalgae are structurally complex in its chemical composition. The use of enzymatic hydrolysis may provide new pathways in the conversion of complex polysaccharides to fermentable sugars. In this study, an enzymatic cocktail with high specificity was first isolated from Aspergillus niger using the green macroalgae Ulva rigida as nitrogen source. The cocktail is rich on β-glucosidase, pectinase and carboxy-methyl-cellulase (CMCase). The highest activity was obtained with β-glucosidase (109IUmL−1) and pectinase (76IUmL−1), while CMCase present the lowest activity 4.6IUmL−1. The U. rigida pre-treatment with this enzymatic cocktail showed high rate of reduced sugar release, and could bring promising prospects for enzymatic pre-treatment of the biogas production from U. rigida biomass which reached 1175mLgCODint−1.

Ocean acidification and warming gradients modulate interaction strength between different mesograzers and macroalgae

Event Abstract Back to Event Ocean acidification and warming gradients modulate interaction strength between different mesograzers and macroalgae Eduardo Sampaio1, 2*, Ivan F. Rodil1, Fatima Vaz-Pinto1, Angela Fernandez1 and Francisco Arenas1 1 Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), Portugal 2 Marine and Environmental Sciences Centre (MARE), Portugal In the future, continuous rise in the levels of atmospheric CO2, along with concomitant increases in temperatures, will lead to alterations in global climate with consequent effects on marine ecosystems. By regulating top-down in a critical trophic level, macroalgae-herbivore interactions play a key role in shaping marine community structures. Taking into account previous studies, gradients of ocean warming and acidification may have cumulative effects on organism metabolism, which can induce great variations on the strength of such interactions. Within this context, we aimed to assess the effects of warming and acidification on macroalgae-herbivore interaction strength, using different mesograzers. For this purpose, three cosmopolitan and closely associated rocky intertidal species were chosen: the herbivores Melita palmata and Gibbula umbilicalis, and the green macroalga Ulva rigida. Two consecutive mesocosm experiments consisting of a two-day consumption trial and a seven-day macroalgae-herbivore interaction trial were performed under crossed treatments of pH (two levels: ambient and acidification) and temperature (four levels: 13.5 ºC, 16.1 ºC, 19.9 ºC and 22.1ºC). Grazer identity differences were obvious, as warming and acidification produced notorious differences in each grazer’s survival and consumption rates. M. palmata was shown to be the most affected by climate stressors, while also being the most voracious grazer. Macroalgae-herbivore interaction strength was strongly altered over gradients of temperature depending on pH levels. In short, acidification appears to accelerate the interaction strength profile effects stemmed from increasing gradients of temperature. In the near future, slight warming and acidification increases may lead to stronger top-down control. However if extreme conditions are reached, herbivorous pressure may lessen, allowing seaweeds to thrive. Keywords: warming, acidification, macroalgae, herbivore, interaction strength. Conference: XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016. Presentation Type: Poster Presentation Topic: 2. GLOBAL CHANGES, INVASIVE SPECIES AND CONSERVATION Citation: Sampaio E, Rodil IF, Vaz-Pinto F, Fernandez A and Arenas F (2016). Ocean acidification and warming gradients modulate interaction strength between different mesograzers and macroalgae. Front. Mar. Sci. Conference Abstract: XIX Iberian Symposium on Marine Biology Studies. doi: 10.3389/conf.FMARS.2016.05.00180 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 May 2016; Published Online: 03 Sep 2016. * Correspondence: Mr. Eduardo Sampaio, Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), Porto, Porto, 4050-123, Portugal, edusilvasampaio@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Eduardo Sampaio Ivan F Rodil Fatima Vaz-Pinto Angela Fernandez Francisco Arenas Google Eduardo Sampaio Ivan F Rodil Fatima Vaz-Pinto Angela Fernandez Francisco Arenas Google Scholar Eduardo Sampaio Ivan F Rodil Fatima Vaz-Pinto Angela Fernandez Francisco Arenas PubMed Eduardo Sampaio Ivan F Rodil Fatima Vaz-Pinto Angela Fernandez Francisco Arenas Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Characterisation of estuarine intertidal macroalgae by laser-induced fluorescence

The article reports the application of laser-induced fluorescence (LIF) for the assessment of macroalgae communities of estuarine intertidal areas. The method was applied for the characterisation of fifteen intertidal macroalgae species of the Tagus estuary, Portugal, and adjacent coastal area. Three bands characterised the LIF spectra of red macroalgae with emission maxima in the ranges 577–583 nm, 621–642 nm and 705–731 nm. Green and brown macroalgae showed one emission maximum in the red region (687–690 nm) and/or one in the far-red region (726–732 nm). Characteristics of LIF emission spectra were determined by differences in the main fluorescing pigments: phycoerythrin, phycocyanin and chlorophyll a (Chl a). In the green and brown macroalgae groups, the relative significance of the two emission maxima seems to be related to the thickness of the photosynthetic layer. In thick macroalgae, like Codium tomentosum or Fucus vesiculosus, the contribution of the far-red emission fluorescence peak was more significant, most probably due to re-absorption of the emitted red Chl a fluorescence within the dense photosynthetic layer. Similarly, an increase in the number of layers of the thin-blade green macroalgae Ulva rigida caused a shift to longer wavelengths of the red emission maximum and the development of a fluorescence peak at the far-red region. Water loss from Ulva's algal tissue also led to a decrease in the red/far-red Chl fluorescence ratio (F685/F735), indicating an increase in the density of chloroplasts in the shrinking macroalgal tissue during low tide exposure.

Uptake of PCBs contained in marine sediments by the green macroalga Ulva rigida

The uptake of PCBs contained in marine sediments by the green macroalga Ulva rigida was investigated in both laboratory and field experiments. Under laboratory conditions, total PCBs (tPCBs) uptake was significantly greater in live vs dead plants. The concentration of tPCB taken up in live plants was greatest in the first 24h (1580μgkg−1 dry weight), and then increased at a lower rate from day 2 to 14. Dead plants had a significantly lower tPCB concentration after 24h (609μgkg−1 dry weight) and lower uptake rate through day 14. Lesser chlorinated PCB congeners (below 123) made up the majority of PCBs taken up. Congener composition in both laboratory and field experiments was correlated to congener logKow value and sediment content. Field experiments showed that Ulva plants could concentrate PCBs to 3.9mgkg−1 in 24h. Thus, U. rigida is capable of removing PCBs in sediments at a rapid rate.

The Turkish Mezzes Formulated with Protein-Rich Green Sea Vegetable (Chlorophyta), Ulva rigida, Cultured in Onshore Tank System

Eating macroalgae (seaweeds) is considered an unusual activity in Turkey, although macroalgae have been known and prized for their nutritional purposes for many years in the Orient. The present study examines the addition of macroalgae to Turkish daily diets. Most Turkish meals begin with mezze, which is literally “a pleasant taste” and is probably derived from the Arabic word mezaq, which means “the taste, the savor of a thing.” The green macroalga Ulva rigida Agardh 1824 (Chlorophyta) was used to develop alternative protein-rich Turkish mezzes, using otherwise traditional recipes.U. rigida was reared in tanks. The yield of U. rigida in an onshore tank system demonstrated the potential of U. rigida to produce marine biomass. The U. rigidas were used in macroalga-based mezzes. The macroalga substituted grape leaves, spinach, lamb’s lettuce, salicornia, or lettuce and resulted in higher protein content than those vegetables.The prepared Ulva mezzes were tested in regard to taste, smell, color, texture, and general appearance and scored “pretty good” and “perfect.” The results suggest that Ulva can be produced and utilized for protein rich mezzes in Turkey.

Chemical Study and Biological Activity Evaluation of Two Azorean Macroalgae: Ulva rigida and Gelidium microdon

The green macroalga Ulva rigida C. Agardh (Chlorophyta) and the red macroalga Gelidium microdon Kutzing (Rhodophyta), collected from the Azorean archipelago, were investigated for their secondary metabolites and their in vitro growth inhibitory effect on three human tumor cell lines: MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer) and A375-C5 (melanoma), as well as for their antifungal and antibacterial activities. The methanol extract of U. rigida furnished isofucosterol (1), 7(E)-3β-hydroxy-5α,6α-epoxymegastigmane (2) and (+)-dehydrovomifoliol (3) while the methanol extract of G. microdon yielded cholesterol (4) and lumichrome (5). The crude extracts of both macroalgae were found to be moderately active against the three cell lines whereas compound 1 showed a weak effect and compound 2 was inactive. The crude extracts of the two macroalgae were found to be moderately active against some fungi and bacteria while compounds 1 and 2 were inactive against all microorganisms tested.

Reduction of land based fish-farming impact by phytotreatment pond system in a marginal lagoon area

Intensive land-based fish farming facilities discharged wastewaters into an inlet of the Orbetello lagoon (Southern Tuscany, Italian West Coast), producing large blooms of the green macroalga Ulva rigida C. Ag., accompanied by dystrophic crises. Enclosing a part of this critical inlet resulted in a new pond for phytotreatment of the fish-farming effluents. Between June 1998 and May 1999 a trial study was carried out, during the daylight, in order to: a) define the changes in the wastewater physico-chemical parameters after discharge through the phytotreatment, b) quantify the removal of nitrogen and phosphorus, c) estimate the efficiency of U. rigida biomass produced within the pond in reducing wastewater nutrient loads. During the test period the water physico-chemical parameters were recorded; water dissolved nitrogen (N) and phosphorus (P), Ulva thalli total N and P (UTN, UTP) and macroalga biomass were determined. The results indicated that: 1) the phytotreatment system affected greatly pH and DO values and it reduced thermal impact on the lagoon; 2) the wastewater inorganic nutrient loads were reduced significantly while dissolved organic components (DON and DOP) were not meaningfully lowered; 3) the diurnal nutrients removal was not directly due to U. rigida uptake because the biomass produced annually stored only 1.63% and 0.91% of the dissolved inorganic N (DIN) and P (SRP) inflow values, respectively. Inefficiency of phytotreatment action was probably due to the drop of U. rigida nutrient uptake owing to high macroalgae density inside the pond. Therefore, other processes must be taken into account to explain N and P abatements, such as ammonia volatilization and nitrification/denitrification for N, and the precipitation of insoluble compounds for P.

Effects of CO 2 and nitrogen supply on the biochemical composition of Ulva rigida with especial emphasis on lipid class analysis

Summary Lipid class composition was analysed in the green macroalga Ulva rigida grown under normal (350 ppm) and high (10,000 ppm) CO2 levels, and in nitrate saturated and nitrogen limited conditions. A new protocol for the extraction of lipids has been defined. Culture conditions altered the fate of assimilated carbon, and significant changes were observed in protein and total lipid content in particular. A CO2-enriched atmosphere conditioned the effects of nitrogen limitation on lipid class composition, revealing deep qualitative changes in carbon metabolism. Triglycerides accumulated at high CO2 and under nitrogen limitation, while chloroplast-related lipids showed an inverse response. Changes in phospholipids could be related to carbon availability as they did not respond to nitrogen limitation. The ratio sterols/acetone-mobile polar lipids followed a negative linear relation with the optimum quantum yield for photosynthetic electron transport (Fv/Fm), and was considered as an index of the «light status» of the cell. The specificity of the response of lipid classes to growth conditions in U. rigida emphasizes the potential role of lipid class analyses as a diagnostic tool for environmental stress.

Feeding selectivity of the herbivorous fish Scartichthys viridis:effects on macroalgal community structure in a temperate rocky intertidal coastal zone

The ecological importance of fish herbivory was examined in a temperate rocky intertidal zone along the central Chilean coast. In this system, the blenny Scartichthys viridis is the most abundant and only herbivorous fish. We describe its diet, determine its field food selectivity (gut contents vs macroalgal field availability comparison) and report on its laboratory dietary preferences in a multiple-choice feeding experiment. Finally, we evaluate the relative effects of fish herbivory and grazing invertebrates on macroalgal abundance, distribution and diversity patterns in the field, using replicated exclusion cages to manipulate grazing intensity. S. viridis was found to be a selective grazer; its diet was dominated by 2 macroalgae: the green Ulva and the red Gelidium, representing 32.6 and 41.4% of its total gut content biomass, respectively Ulva was consumed much above its field availability while Gelidium was selected only during fall-winter. In the laboratory, S. viridis selected the green macroalgae Ulva rigida and Codium dimorphum and avoided Gelidium chilense. We suggest that Gelidium may be included in its diet due to the limited availability of Ulva in the field. Experimental exclusion of this fish from rocky surfaces resulted in increased abundance of green foliose macroalgae (U. rigida and Enteromorpha linza), and, to a much lesser extent, of the red foliose macroalgae G. chilense, Porphyra columbina, and Mazzaella Iaminarioides, and of the brown macroalgae Colpomenia phaeodactyla and Petalonia fascia, as well as an extension of the distribution of P. columbina from the high intertidal to the mid intertidal zone, where it normally does not occur. Exclusion of grazing invertebrates resulted in a decrease in foliose macroalgal species richness, but had no effect on biomass. To our knowledge, this is the first experimental demonstration of the effect of an herbivorous fish on macroalgal community structure in a temperate rocky intertidal area. The selective feeding displayed by S. viridis, its high numerical abundance, and the results of the herbivore exclusion experiment suggest its importance in maintaining the low abundance of foliose macroalgae and the high relative cover of brown and red crustose macroalgae, characteristic of many low to mid rocky intertidal areas along the coast of central Chile.

Blue Light Induction of in situ Nitrate Reductase Activity in the Marine Green Alga Ulva rigida

The regulation by light (especially blue light) and NO3- of the nitrate reductase (NR) activity was studied in the marine green macroalga Ulva rigida C. Agardh. NR activity was measured in situ as no available in vitro method exists for Ulva rigida. The effectiveness spectrum of NR-enhancement by light was determined. Blue light was clearly the most effective wavelength, being more effective than white or red light. Blue light enhancement of NR was strictly dependent on photosynthesis since it was inhibited by 95% in presence of 5 × 10-5 M DCMU. The time course of NR enhancement by blue light was hyperbolic in shape, the semimaximal level of increase was reached in 24 min in N-sufficient algae. Blue light activation of NR is dependent upon photo flux density in a sigmoidal manner; 95% of the maximum increase was reached at 137 μmol m-2 s-1. Blue light enhancement of NR is linearly dependent on the amount of KNO3 available in the medium at the beginning of the experiment. Increase in NO3- by itself, in dark or without a concomitant increase in photon flux density, only increases NR activity by 12% (darkness) or 25% (white light, 4 μmol m-2 s-1) with respect to a blue light control. The blue light enhancement of NR was inhibited by actinomycin D (33%), rifampicin (32%) and cycloheximide (88%). Therefore, in Ulva rigida the blue light enhancement of NR occurs mainly by induction of de novo synthesis.