Photosynthetic production of hydrogen peroxide by Ulva rigida C. Ag. (Chlorophyta)

Production of hydrogen peroxide has been found in Ulva rigida (Chlorophyta). The formation of H₂O₂ was light dependent with a production of 1.2 mol·g FW^–1·h^–1 in sea water (pH 8.2) at an irradiance of 700 mol photons m^–2·s^–1. The excretion was also pH dependent: in pH 6.5 the production was not detectable (< 5 nmol·g FW^–1·h^–1) but at pH 9.0 the production was 5.0 mol·g FW^–1·h^–1. The production of H₂O₂ was totally inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU). The ability of U. rigida growing in tanks (7501) under a natural light regime to excrete H₂O₂ was checked and found to be seven times higher at 08.00 hours than other times of the day. The H₂O₂ concentration in the cultivation tank (density: 2 g FW·l^–1) reached the highest value (3 M) at 11.00 hours. Photosynthesis was not influenced by H₂O₂ formation. The H₂O₂ is suggested to come from the Mehler reaction (pseudocyclic photophosphorylation). With an oxygen evolution of 120 mmol·g FW^–1·h^–1 at pH 8.2 and 90 mmol·g FW^–1·h^–1 at pH 9.0, 0.5% and 2.7% of the electrons were used for extracellular H₂O₂ production. The H₂O₂ production is sufficiently high to be of physiological and ecological significance, and is suggested to be a part of the defence against epi and endophytes.Abbreviations ACL artificial, continuous light - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - GNL greenhouse - LDC Luminol-dependent chemiluminescence - SOD Superoxide dismutase This investigation was supported by SAREC (Swedish Agency for Research Cooperation with Developing Countries), Hierta-Retzius Foundation, Marianne and Marcus Wallenberg Foundation, the Swedish Environmental Protection Board, and CICYT Spain.     

Utilization of seaweed Ulva sp. in Paracas Bay (Peru): experimenting with compost

In Paracas Bay (Peru), large quantities of Ulva sp. interfere with various important activities of the zone. In this context, the present study was undertaken to evaluate the effect of adding Ulva sp. in compost piles and the quality of the resulting composts. Six compost piles were prepared using, straw, green material mixture, cow manure and Ulva in different quantities (9, 17 and 28% of volume) and forms. Several variables were monitored during the process and the chemical characteristics of the final composts were determined. Aerial biomass achieved by maize plants was also evaluated for each compost at different compost/sand proportions. Results show that the compost pile made with Ulva powder registered the highest temperature and the longest thermophilic phase. Piles prepared with 28% washed Ulvapresented anoxic conditions at the beginning and had higher electrical conductivity values. Carbon/Nitrogen ratio diminished appropriately in all piles and there was no negative effect observed on the pH of the piles. Compost prepared with Ulva had lower contents of Total Kjeldahl Nitrogen, and produced maize plants aerial biomass.     

Gracilaria conferta and its epiphytes: (2) Interrelationship between the red seaweed and Ulva cf. lactuca

Ulva cf. lactuca has been a disturbing competitor of experimental Gracilaria conferta outdoor cultures in Israel. The effect of environmental conditions on the competitive ability of Ulva versus Gracilaria, and the main limiting factors for which these seaweeds compete, were studied here. Single and biculture experiments of both seaweeds showed that Ulva outgrew and damaged Gracilaria under all irradiance and temperature combinations. The higher competitive ability of Ulva cf. lactuca in bicultures was not a result of responses to shading or nitrogen shortage, but rather to a shortage of available inorganic carbon, an increase in pH and apparent excretions of Ulva which inhibited the growth of Gracilaria.     

Effect of grazing by isopods and amphipods on growth of Ulva spp. (Chlorophyta)

Eutrophication of shallow coastal waters often leads to blooms of macroalgae. Grazing by crustaceans, such as amphipods and isopods, can reduce macroalgal biomass accumulation. At the same time, growth of the macroalgae can be stimulated by epiphyte removal. The role of grazing by isopods and amphipods on Ulva spp. biomass development was investigated in the Veerse Meer, a brackish lagoon situated in the southwest Netherlands. Exclusion of grazing in the field did not stimulate Ulva spp. growth. In fact, growth rates were higher in exclosures that allowed grazers to enter. Edibility tests identified the amphipod Gammarus locusta, and the isopods Idotea chelipes and Sphaeroma hookeri as potential grazers on Ulva spp. However, when epiphytic diatoms were present on the Ulva spp. thalli, Gammarus and Sphaeroma grazed on ephiphytes and not on Ulva tissue. Only Idotea continued to graze on Ulva spp. A laboratory growth experiment revealed a positive effect of Gammarus presence on Ulva spp. growth, probably caused by preferential removal of epiphytic diatoms from the Ulva spp. thalli. The growth stimulation by epiphyte removing grazers such as Gammarus may explain the higher growth rates in the presence of grazers observed in the field. When determining the potential role of invertebrate grazers in controlling macroalgal biomass accumulation, it is important to include an assessment of the epiphyte abundance on the macroalgae, as preferential removal of epiphytes may stimulate growth and thus have the opposite effect.     

Inorganic-carbon uptake by the marine diatom Phaeodactylum tricornutum

Air-grown cells of the marine diatom Phaeodactylum tricornutum showed only 10% of the carbonic-anhydrase activity of air-grown Chlamydomonas reinhardtii. Measurement of carbonic-anhydrase activity using intact cells and cell extracts showed all activity was intracellular in Phaeodactylum. Photosynthetic oxygen evolution at constant inorganic-carbon concentration but varying pH showed that exogenous CO₂ was poorly utilized by the cells. Sodium ions increased the affinity of Phaeodactylum for HCO ₃ ^- and even at high HCO ₃ ^- concentrations sodium ions enhanced HCO ₃ ^- utilization. The internal inorganic-carbon pool (HCO ₃ ^- +CO₂] was measured using a silicone-oil-layer centrifugal filtering technique. The internal [HCO ₃ ^- +CO₂] concentration never exceeded 15% of the external [HCO ₃ ^- +CO₂] concentration even at the lowest external concentrations tested. It is concluded that an internal accumulation of inorganic carbon relative to the external medium does not occur in P. tricornutum.Abbreviation Hepes 4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid     

A simple method for mass isolation of protoplasts from species of Monostroma, Enteromorpha and Ulva (Chlorophyta, Ulvales)

A simple enzyme mixture containing 2% Cellulase Onozuka R–10 and1% Macerozyme R–10 prepared in deionised water supplemented with 3% NaCland 1 mM CaCl₂ was developed for isolating rapidlyprotoplasts from different species of Monostroma,Enteromorpha and Ulva. The yield fordifferent species of Monostroma ranged from 9.6 ×10⁶ to 10.2 × 10⁶ cells g^–1f. wt thallus, and forEnteromorpha from 3.48 × 10⁶ to 11.7× 10⁶ cells g^–1 f. wt and forUlva from 4.58 × 10⁶ to 26.8 ×10⁶ cells g^–1 f. wt. The overallregeneration rate of the protoplasts isolated was usually > 90% and showednormal morphogenesis. The method yields rapid mass production of viableprotoplasts with high regeneration rates.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Inorganic-carbon transport in some marine eukaryotic microalgae

Inorganic-carbon transport was investigated in the eukaryotic marine microalgaeStichococcus minor, Nannochloropsis oculata and aMonallantus sp. Photosynthetic O₂ evolution at constant inorganic-carbon concentration but varying pH showed thatS. minor had a greater capacity for CO₂ rather than HCO ₃ ^– utilization but forN. oculata andMonallantus HCO ₃ ^– was the preferred source of inorganic carbon. All three microalgae had a low affinity for CO₂ as shown by the measurement of inorganic-carbon-dependent photosynthetic O₂ evolution at pH 5.0. At pH 8.3, where HCO ₃ ^– is the predominant form of inorganic carbon, the concentration of inorganic carbon required for half-maximal rate of photosynthetic O₂ evolution [K _0.5 (CO₂)] was 53 M forMonallantus sp. and 125 M forN. oculata, values compatible with HCO ₃ ^– transport. Neither extra- nor intracellular carbonic anhydrase was detected in these three microalgal species. It is concluded that these microalgae lack a specific transport system for CO₂ but that HCO ₃ ^– transport occurs inN. oculata andMonallantus, and in the absence of intracellular carbonic anhydrase the conversion of HCO ₃ ^– to CO₂ may be facilitated by the internal pH of the cell.     

Non-photosynthetic enhancement of growth by high CO2 level in the nitrophilic seaweed Ulva rigida C. Agardh (Chlorophyta)

The effects of increased CO₂ levels (10,000 μl l⁻¹) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with CO₂ enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased. The internal C pool remained constant at high CO₂, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO₂ levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli, nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO₂ levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led to the production of new biomass in proportion to C. Growth enhancement by increased level of CO₂ was entirely dependent on the enhancement effect of CO₂ on N-assimilation rates. The increase in nitrate reductase activity at high CO₂ was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO₂ in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory mechanism maintaining the internal C:N balance in response to different CO₂ levels is discussed. Received: 27 March 2000 / Accepted: 9 October 2000     

Two components of onset and recovery during photoinhibition of Ulva rotundata

Short-term (up to 5 h) transfers of shade-adapted (100 mol · m^–2 · s^–1) clonal tissue of the marine macroalga Ulva rotundata Blid. (Chlorophyta) to higher irradiances (1700, 850, and 350 mol · m^–2 · s^–1) led to photoinhibition of room-temperature chlorophyll fluorescence and O₂ evolution. The ratio of variable to maximum (F_v/F_m) and variable (F_v) fluorescence, and quantum yield () declined with increasing irradiance and duration of exposure. This decline could be resolved into two components, consistent with the separation of photoinhibition into energy-dissipative processes (photoprotection) and damage to photosystem II (PSII) by excess excitation. The first component, a rapid decrease in F_v/F_m and in F_v, corresponds to an increase in initial (F_o) fluorescence and is highly sensitive to 1 mM chloramphenicol. This component is rapidly reversible under dim (40 mol · m^–2 · s^–1) light, but is less reversible with increasing duration of exposure, and may reflect damage to PSII. The second (after 1 h exposure) component, a slower decline in F_v/F_m and F_v with declining F_o, appears to be associated with the photoprotective interconversion of violaxanthin to zeaxanthin and is sensitive to dithiothreitol. The accumulation of zeaxanthin in U. rotundata is very slow, and may account for the predominance of increases in F_o at high irradiances.Abbreviations and Symbols CAP chloramphenicol - DTT dithiothreitol - F_o, F_m, F_v initial, maximum, and variable fluorescence - quantum yield - PFD photon flux density - PSII photosystem II To whom correspondence should be addressedWe are grateful to O. Björkman and S. Thayer, Carnegie Institution of Washington, Stanford, Cal., USA, for analysis of xanthophyll pigments reported here. This research was supported by National Science Foundation grant OCE-8812157 to C.B.O. and J.R. Support for G.L. was provided by a NSF-CNRS (Centre National de la Recherche Scientifique) exchange fellowship.     

Role of intracellular carbonic anhydrase in inorganic-carbon assimilation by Porphyridium purpureum

Air-grown cells of Porphyridium purpurem contain appreciable carbonic-anhydrase activity, comparable to that in air-grown Chlamydomonas reinhardtii, but activity is repressed in CO₂-grown cells. Assay of carbonic-anhydrase activity in intact cells and cell extracts shows all activity to be intracellular in Porphyridium. Measurement of inorganic-carbon-dependent photosynthetic O₂ evolution shows that sodium ions increase the affinity of Porphyridium cells for HCO ₃ ^- . Acetazolamide and ethoxyzolamide were potent inhibitors of carbonic anhydrase in cell extracts but at pH 5.0 both acetazolamide and ethoxyzolamide had little effect upon the concentration of inorganic carbon required for the half-maximal rate of photosynthetic O₂ evolution (K_0.5[CO₂]). At pH 8.0, where HCO ₃ ^- is the predominant species of inorganic carbon, the K_0.5 (CO₂) was increased from 50 M to 950 M in the presence of ethoxyzolamide. It is concluded that in air-grown cells of Porphyridium. HCO ₃ ^- is transported across the plasmalemma and intracellular carbonic anhydrase increases the steady-state flux of CO₂ from inside the plasmalemma to ribulose-1,5-bisphosphate carboxylase-oxygenase by catalysing the interconversion of HCO ₃ ^- and CO₂ within the cell.Abbreviations AZ acetazolamide - EZ ethoxyzolamide - K_0.5[CO₂] half-maximal rate of photosynthetic O₂ evolution     

Utilisation of Ulva rigida biomass in the Venice Lagoon (Italy): biotransformation in compost

In the Venice Lagoon (Italy), about 10⁶ t (wet weight) of Ulva rigida biomass are produced annually as one of the major results of eutrophication. Harvests have been initiated to reduce negative impacts of this biomass, however, due to the high costs of such effort, only 40 000 t yr^-1 are currently being collected. At the moment, biotransformation into compost seems to be the only feasible technology for utilising large quantities of Ulva biomass. We describe and discuss here a successful composting strategy together with the chemico-physical and microbiological characteristics of the resultant composts. Our composting experiments were conducted at a scale of 20 t. The composting technology utilises large proportions (70–90%) of Ulva biomass and results in a valuable, high-quality end product (compost and compost-based products). This process and the resulting products represents a relatively simple way of utilising the Ulva biomass produced annually in the Venice Lagoon.     

Changes in respiration,photosynthesis and protein composition during induced synchronous formation of gametes and zoospores in Ulva mutabilis Føyn

In the marine green alga Ulva mutabilis Føyn, large daily fluctuations in respiratory and photosynthetic rates are found after the induction of synchronous formation of gametes and zoospores. A sharp reduction in photosynthetic capacity preceeds the zooid-forming cell divisions. During the same period, samples for polyacrylamide electrophoresis show an initial increase followed by a decrease in the amount of ribulose-1,5-bisphosphate carboxylase. Some other transient protein changes were also noted. A new protein band with MW 51,400 appears in the 48-h sample and becomes a prominent constituent of gametes and zoospores; it may represent tubulin.Abbreviations PAGE polyacrylamide gel electrophoresis - SDS sodium dodecylsulphate To whom correspondence should be addressed     

Fluorescence quenching during photosynthesis and photoinhibition of Ulva rotundata blid.

The relationships between photoinhibition and photoprotection in high and low-light-grown Ulva were examined by a combination of chlorophyll-fluorescence-monitoring techniques. Tissues were exposed to a computer-controlled sequence of 5-min exposures to red light, followed by 5-min darkness, with stepwise increases in photon flux. Coefficients of chlorophyll fluorescence quenching (1?q_P and NPQ) were calculated following a saturating pulse of white light near the end of each 5-min light treatment. Dark-adapted chlorophyll fluorescence parameters (F₀ and F_V/F_M) were calculated from a saturating pulse at the end of each 5-min dark period. Low-light-grown Ulva showed consistently higher 1?q_P, i.e. higher reduction status of Q (high primary acceptor of photosystem II), and lower capacity for nonphotochemical quenching (NPQ) at saturating light than did high-light-grown plants. Consequently, low-light plants rapidly displayed photoinhibitory damage (increased F₀) at light saturation in seawater. Removal of dissolved inorganic carbon from seawater also led to photoinhibitory damage of high-light-grown Ulva at light saturation, and addition of saturating amounts of dissolved inorganic carbon protected low-light-grown plants against photoinhibitory damage. A large part of NPQ was abolished by treatment with 3 mM dithiothreitol and the processes so inhibited were evidently photoprotective, because dithiothreitol treatment accelerated photoinhibitory damage in both low- and high-light-grown Ulva. The extent of photoinhibitory damage in Ulva was exacerbated by treatment with chloramphenicol (1 mM) without much effect on chlorophyll-quenching parameters, evidently because this inhibitor of chloroplast protein synthesis reduced the rate of repair processes.     

Bicarbonate uptake in the marine macroalga Ulva sp. is inhibited by classical probes of anion exchange by red blood cells

We demonstrate in this work that HCO _inf3 ^sup– uptake in the marine macroalga Ulva sp. features functional resemblances to anion transport mediated by anion exchangers of mammalian cell membranes. The evidence is based on (i) competitive inhibition of photosynthesis by the classical red-blood-cell anion-exchange blockers 4,4-dinitrostilbene-2,2-disulfonate and 4-nitro-4-isothiocyanostilbene-2,2-disulfonate under conditions where HCO _inf3 ^sup– , but not CO₂, was the inorganic carbon form taken up; (ii) inhibition of HCO _inf3 ^– uptake by pyridoxal phospate, indicating the involvement of lysine residues in the binding/translocation of HCO _inf3 ^sup– ; and (iii) inhibition of HCO _inf3 ^sup– (but not of CO₂) uptake by exofacial trypsin treatments, indicating the functional involvement of a plasmalemma protein. It is suggested that HCO _inf3 ^sup– uptake mediated by such a putative anion transporter can be a fundamental step in providing inorganic carbon for the CO₂-concentrating system of marine marcoalgae in an environment where the HCO _inf3 ^sup– concentration is high, but the CO₂ concentration and rates of uncatalyzed HCO _inf3 ^sup– dehydration are low.Abbreviations CI ionorganic carbon - DIDS 4,4-diisothiocyanostilbene-2,2-disulfonate - DNDS 4,4-dinitrostilbene-2,2-disulfonate - NIDS 4-nitro-4-isothiocyanostilbene-2,2-disulfonate - PLP pyridoxal phosphate - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase     

Induction of fast-growing and morphologically different strains through intergeneric protoplast fusions of Ulva and Enteromorpha (Ulvales,Chlorophyta)

Isolated protoplasts of Ulva pertusa and Enteromorpha prolifera were electrically fused. Treatment of protoplasts in 1% protease for 15–20 min prior to fusion enhanced fusion ability. Protoplasts from each fusion partner were mixed together in 1:1 ratio in low conductivity electrofusion solution at a density of 1 × 10⁵ cells ml⁻¹ before subjecting them to electrofusion. The protoplasts were aligned in AC field (1MHz, 25 V for 10–15 s) and subsequently fused by a high intensity single DC pulse of 250 V for 25 μs duration. Fusion buffer supplemented with 1 mM calcium and 1 mM magnesium yielded optimum fusion frequencies (about 18–24%). Entrapment of fusion treated cells inside agarose/agar plate facilitated marking and regeneration of fusion products. The regeneration patterns of fused protoplasts were similar to normal (unfused) protoplast development. Most of the regenerated plants from fusion products had a thallus similar to either U. pertusa type or E. prolifera type. Although some of the plants of the former were morphologically similar to U. pertusa, but most had a higher growth rate (1.9 to 1.5 times) than U. pertusa. Furthermore the thallus of some plants had a characteristic irregular and dentate margin, which was never observed in the parental type.     

Absence of major differences between soluble proteins from haploid gametophytes and diploid sporophytes in the green alga Ulva mutabilis Føyn

Soluble proteins from haploid gametophytes and diploid sporophytes of the marine green alga Ulva mutabilis Føyn have been reexamined, using polyacrylamide gel electrophoresis and isoelectric focusing. A two-dimensional system resolved about 150 protein spots. In contrast to an earlier report (Hoxmark (1976) Planta 130, 327–332), no major differences could be detected between soluble proteins from the two generation types by any of the methods used.To whom correspondence should be addressed     

Role of carbonic anhydrase in photosynthesis and inorganic-carbon assimilation in the red alga Gracilaria tenuistipitata

The mechanism of inorganic-carbon (C_i) accumulation in the red seaweed Gracilaria tenuistipitata Zhang et Xia has been investigated. Extracellular and intracellular carbonic-anhydrase (CA) activities have been detected. Photosynthetic O₂ evolution in thalli and protoplasts of G. tenuistipitata were higher at pH 6.5 than at pH 8.6, where HCO ₃ ^– is the predominant form of C_i. Dextran-bound sulfonamide (DBS), a specific inhibitor of extracellular CA, reduced photosynthetic O₂ evolution at pH 8.6 and did not have any effect at pH 6.5. After inhibition with DBS, O₂ evolution was similar to the rate that could be supported by CO₂ from spontaneous dehydration of HCO ₃ ^– . The rate of photosynthetic alkalization of the surrounding medium by the algal thallus was dependent on the concentration of C_i and inhibited by DBS. We suggest that the general form of C_i that enters through the plasma membrane of G. tenuistipitata is CO₂. Bicarbonate is utilized mainly by an indirect mechanism after dehydration to CO₂, and this mechanism involves extracellular CA.Abbreviations C_i inorganic carbon (CO₂ + HCO ₃ ^– ) - CA carbonic anhydrase - DIC dissolved inorganic carbon (total) - DBS dextran-bound sulfonamide - EZ ethoxyzolamide - NSW natural seawater - PPFD photosynthetic photon flux density - REA relative enzyme activity - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase This research was supported by the Deutsche Forschungsgemeinschaft (Bonn) as a programme of the Sonderforschungsbereich 251 der Universität Würzburg and by the Fonds der Chemischen Industrie (Frankfurt). Joint work in Würzburg was possible thanks to travel grants from the Chancellor of the University of Würzburg, Professor R. Günther, from the Australian National University under the auspices of its Overseas Studies Programme, and from the New Zealand — Federal Republic of Germany Scientific and Technological Exchange Programme, which are gratefully acknowledged. We thank Dr. A. Meyer and Ms. E. Kilian for untiringly conducting part of the experimental work, Ms. G. Theumer and Ms. D. Faltenbacher-Werner for their valuable assistance, and Mr. H. Walz (Walz Company, Effeltrich, FRG) for his skilled help with the calibration of our gas-exchange system for measurements with helox. The Department of Conservation, New Zealand, is thanked for permission to collect lichens.     

The effect of localised eutrophication on competition between Ulva lactuca (Ulvaceae,Chlorophyta) and a commercial resource of Gracilaria verrucosa (Gracilariaceae,Rhodophyta)

In spring (August) 1993 a bloom of Ulva lactuca appeared for the first time in Saldanha Bay, South Africa, and persisted through summer. Ulva wash-ups contaminated the beach and part of the commercial Gracilaria beach-cast had to be discarded. The biomass and distribution of Gracilaria and Ulva are described in relation to the seasonal water chemistry of the bay. Gracilaria survives in deeper water in summer by the pulsing of nutrients on an approximately 6-day cycle of movement of the thermocline that separates nutrient-rich bottom water from warm oligotrophic surface water. Ammonium-rich fish-factory discharge into this surface layer in a sector of the bay provided localised conditions for Ulva to out-compete Gracilaria at depths of 2–5m, demonstrating the powerful disruptive effect of eutrophication in this strongly stratified system.     

Determination of the chemical composition of ulvan, a cell wall polysaccharide from Ulva spp. (Ulvales, Chlorophyta) by FT-IR and chemometrics

The water-soluble cell wall polysaccharides from green seaweeds of Ulva spp. (Ulvales, Chlorophyta), referred to as ulvan, demonstrate composition- and structure-related functional properties. Mid-infrared spectroscopy combined with chemometric techniques was investigated as a means to rapidly predict the chemical composition of ulvan extracts. A calibration was realized with 41 ulvan extracts from two Ulva species. The variables studied included the constituent sugars (rhamnose, xylose, glucose, galactose, glucuronic acid, iduronic acid), protein, and sulfate contents. The correlation between Fourier transform infrared and chemical data was developed using partial least squares (PLS) regression with full cross-validation (leave one out). The coefficients of determination in cross-validation () and the standard error in cross-validation were determined for each variable. The PLS model validation resulted in a coefficient of determination () and a standard error in prediction. Good predictions were obtained for rhamnose ( = 0.9244), xylose ( = 0.8758), glucuronic acid ( = 0.9415), and sulfate ( = 0.9218), which are the main ulvan constituents. However, minor components such as proteins, glucose, galactose, and iduronic acid were not correctly predicted. This study showed that mid-infrared spectroscopy combined with PLS regression is a reliable and fast method for the quantification of the main chemical constituents of ulvan extracts.