An unusual bloom of Gyrodinium cf. aureolum in the Argentine sea: community structure and conditioning factors

In October 1988 a bloom of Gyrodinium cf. aureolum was recordedalong a transect across the continental shelf reaching celldensities of 1300 ml^–1 and chlorophyll a concentrationsup to 16 µg 1^–1. The bloom was restricted to a nutrient-richthin surface layer of 10 m depth at the beginning of seasonalpycnocline. Hydrological conditions showed a particular salinitydistribution. The phytoplankton community was dominated by G.cf. aureolum but the coexisting flora presented a great diversity.UV-absorbing pigments were recorded in the community.     

Green mass aggregations of Gyrodinium cf. aureolum Hulburt in the Ria of Pontevedra (north-west Spain)

In this paper we report a bloom of Gyrodinium cf. aureolum occurringin an estuary of the north-west coast of Spain. It was sampledin late August 1989, in shallow waters 2 m deep in the Ria ofPontevedra. Its temperature was 19.5°C and salinity 35     

Studies on the growth and nitrogen assimilation of the bloom dinoflagellate Gyrodinium aureolum Hulburt

Growth experiments were carried out with laboratory culturesof Gyrodinium aureolum. Physiological studies on CO₂ fixationand nitrogen nutrition were undertaken with a natural populationdominated by the same organism. These studies suggested thatthe population was in a late stage of bloom development andsuffering from a degree of nitrogen limitation. The relevanceof the ammonium enhancement of dark CO₂ fixation as a techniquefor determining the nitrogen status of phytoplankton is discussedas are the difficulties involved in extrapolating results fromlaboratory studies to field situations.     

Irradiance and daylength effects on growth and chemical composition of Gyrodinium aureolum Hulburt in culture

For Gyrodinium aureolum significant irradiance and daylengtheffects were found on the division rate and on the growth-relevantChla-normalized photosynthetic rate (^gP^B). Optimum conditionsof irradiance and daylength were found at 230 µmol m^–2s^–1 and 14 h for the division rate, and at >260 µmolm^–2 s^–1 and <6 h for ^gP^B.^gP^B showed no photoinhibition,while the division rate decreased markedly at irradiances abovesaturation. This difference and the difference in optimum irradiancebetween the division rate and ^gP^B are explained by a decreasein cellular Chla/carbon ratio with increasing irradiance. Thecellular content of carbon and nitrogen decreased significantlywith increasing irradiance. Total phosphorus was independentof irradiance and daylength. Below the saturation irradiancefor ^gP^B the daily Chla-normalized carbon yield may be describedas an exponential function of the daily irradiance (irradiancex daylength).     

Temperature and salinity effect on growth and chemical composition of Gyrodinium aureolum Hulburt in culture

A factorial experiment shows highly significant effects of temperature(12 5–22.5°C) and salinity (17.8–34 S) on thegrowth rate of Gyrodinium aureolum, with a significant temperature-salinityinteraction. The maximum growth rate of G aureolum is measuredto 0.61 div. day^–1 at 20°C and 22.3 S. Gyrodiniumaureolum does not grow at temperatures :10 °C or 25°Cand at salinities 12 S. The cellular content of carbon (C) andnitrogen (N) and the elemental ratios N/C, P/C and N/P are significantlyaffected by the temperature The cellular content of phosphorus(P) and the elemental ratios P/C and N/P vary significantlywith salinity Significant temperature-salinity interactionsare found for the cellular content of carbon, nitrogen and phosphorus.Variations in the N/P ratio indicate that G.aureolum has a largestorage capacity for phosphorus It is suggested that temperatureis one important limiting factor in the initiation of bloomsof G.aureolum in north European waters.     

Genetic differentiation and phenotypic plasticity in Plantago major ssp major. I. The effect of differences in level of irradiance on growth, photosynthesis, respiration and chlorophyll content

Growth, root respiration, photosynthesis, dark respiration, chlorophyll content and chlorophyll alb ratio were followed in two genotypes of Plantago major L. ssp major L., originating from an exposed and a shaded habitat, respectively, at two levels of irradiance. In addition, responses of these processes to a transfer of plants from one light condition to the other were studied. Genetic differentiation between the two genotypes was reflected in growth rate, photosynthetic activity, dark respiration and chlorophyll content. Individuals of the genotype originating from a shaded habitat were less inhibited by low irradiance: growth was less depressed at low irradiance, while the genotype of the exposed habitat seemed to be more restricted to exposed conditions. The adaptive plastic response of growth and physiological parameters upon an alteration in irradiance was very small. The shoot to root ratio was a stable plant characteristic in these experiments. Plants of both genotypes were probably damaged after a transfer from the low to the high level of irradiance; the growth of these plants was not stimulated by high irradiance, and the photosynthetic activity was even decreased. Plants, which were transferred to the low level of irradiance, showed an immediate effect of the change and no adaptive response was observed. Obviously, the ability to perform adaptive plastic responses, which was demonstrated in the non-transferred plants after pretreatment, had been lost during the experiment and was confined to the seedling stage of individuals of the two genotypes.     

The influence of phosphate deficiency on photosynthesis, respiration and adenine nucleotide pool in bean leaves

The decrease in inorganic phosphate (Pi) content of 10-d-old Phaseolus vulgaris L. plants did not affect rates of photosynthesis (PN) and respiration (RD), leaf growth, and adenylate concentration. Two weeks of phosphate starvation influenced the ATP content and leaf growth more than PN and RD. The ATP concentration in the leaves of 15- and 18-d-old phosphate deficient (-P) plants after a light or dark period was at least half of that in phosphate sufficient (+P, control) plants. Similar differences were found in fresh and dry matter of leaves. However, PN declined to 50 % of control in 18-d-old plants only. Though the RD of -P plants (determined as both CO2 evolution and O2 uptake) did not change, an increased resistance of respiration to KCN and higher inhibition by SHAM (salicylhydroxamic acid) suggested a higher engagement of alternative pathway in respiration and a lower ATP production. The lower demand for ATP connected with inhibition of leaf growth may influence the ATP producing processes and ATP concentration. Thus, the ATP concentration in the leaves depends stronger on Pi content than on PN and RD.     

The effects of irradiance on growth, respiration and nitrate reductase activity of Terminalia ivorensis and Terminalia superba

Controlled-environment experiments were conducted to determine the effect of three irradiance levels obtained by artificial shading (40%, 65% and 100% light) on the growth, distribution of photosynthate, relative growth rate, net assimilation rate, respiration and nitrate reductase activities in the leaves of seedlings of Terminalia ivorensis and Terminalis superba, two important tropical tree species. Total dry weights of both species increased with increasing irradiance level during growth. Shading affected the percentage dry matter in the roots and number of leaves of both species. Relative growth rate, net assimilation rate, respiration and nitrate reductase in the leaves of both species increased with increases in irradiance level during growth. Significant differences between the species were observed in most of the parameters studied.     

Temporal and spatial distribution of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in the St Lawrence, Canada

The occurrence of the potentially ichthyotoxic dinoflagellateGyrodinium aureolum Hulburt is reported for the first time inthe Lower Estuary and Gulf of St Lawrence. Taxonomic identificationusing an iramunochemical tagging method suggests a close taxonomicproximity between the species found in the St Lawrence and G.aureolumpresent in European waters. In 1993, G.aureolum was observedalong the entire coast of Quebec and in offshore waters of theGulf of St Lawrence. At the coastal stations, G.aureolum showedlarge week-to-week variations, but higher densities were observedduring late August and early September. Bloom concentrations(10⁶ cells 1^–1) were only observed in the GaspéCurrent at Mont-Louis, on the north coast of the Gaspd peninsula.In the central part of the Gulf, G.aureolum was concentratedin the upper 5 m of the stations directly influenced by thefreshwater run-off of the St Lawrence Estuary. Results fromprincipal component analysis indicate that G.aureolum favorsenvironments with high nitrogen recycling activity.     

Effects of organic carbon sources on growth, photosynthesis, and respiration of Phaeodactylum tricornutum

The growth, photosynthesis, and respiration of the marine diatom Phaeodactylum tricornutum were examined under photoautotrophic and mixotrophic conditions. 100 mM glycerol, acetate, and glucose significantly increased specific growth rate, and mixotrophic growth achieved higher biomass concentrations. Under mixotrophic conditions, respiration rate (R _d) and light compensation irradiance (I _c) were significantly higher, but net maximum photosynthetic O₂ evolution rate (P _m) and saturation irradiance (I _k) were depressed. Organic carbon sources decreased the cell photosynthetic pigment content and chlorophyll a to c ratio, but with a higher carotenoid to chlorophyll a ratio. Ratios of variable to maximum chlorophyll fluorescence (F _v/F _m) and 77 K fluorescence spectra of mixotrophic cells indicated a reduced photochemical efficiency of photosystem II. The results were accompanied by lower electron transport rate. Therefore, organic carbon sources reduced the photosynthesis efficiency, and the enhancement of biomass of P. tricornutum implied that organic carbon sources had more pronounced effects on respiration than on photosynthesis.     

Observations on pigments and morphology of Gyrodinium aureolum Hulburt, a marine dinoflagellate containing 19' -hexanoyloxyfucoxanthin as the main carotenoid

Gyrodinium aureolum, a common "red tide" dinoflagellate in Europeanwaters often associated with fish mortality, was isolated fromthe Oslofjord, Norway, and analysed for chlorophylls and carotenoids.Besides chlorophyll a and c the following carotenoids were characterizedby thin-layer chromatography, visible light spectrophotometryand mass spectrometry: ß,-carotene, ß,ß-carotene,djatoxanthin, diadinoxanthin, 19'-hexanoyloxyfucoxanthin and3 xanthophylls which could not be correlated with hitherto structurallyknown carotenoids from dinoflagellates. G. aureolum deviatesfrom most dinoflagellates by the lack of peridinin, but showsaffinity with Gyrodinium sp.-A by the possession of 19'-hexanoyloxyfucoxanthin. Preliminary light microscopical observations on the internalstructure indicate that G. aureolum is uni-nucleate with a typicaldinokaryotic nucleus containing continually condensed chromosomes.The chloroplasts seem to possess an internal pyrenoid like someother dinoflagellates with deviating carotenoid pigmentation.The similarity in carotenoid pigmentation and chloroplast structureof Emiliania huxleyi (Prymnesiophyceae) and Gyrodinium sp.-Aand G.aureolum (Dinophyceae) is pointed out. The potential chemotaxonomicvalue of the carotenoid composition in establishing identitywith morphologically similar and ichthyotoxic dinoflagellatesis briefly discussed.     

The influence of irradiance,photoperiod and temperature on the growth kinetics of three planktonic diatoms

The influence of irradiance, photoperiod and temperature was determined for the growth kinetics of the diatoms Aulacoseira subarctica, Stephanodiscus astraea and Stephanodiscus hantzschii and the results compared with those of cyanobacteria. Irradiance and photoperiod relationships were qualitatively similar to those for cyanobacteria in that: (1) growth rate (K) was proportionally greater under short photoperiods, with ratios of K under continuous light to K under 3:21 light:dark (LD) cycles of 1·50, 1·80 and 2·96 for A. subarctica, S. astraea and S. hantzschii respectively; (2) at subsaturating irradiances, K was proportional to irradiance and independent of temperature with a negligible predicted maintenance growth rate requirement. Apparent growth efficiencies (GE) at subsaturating irradiances were 0·26±0·03, 0·42±0·03 and 0·50±0·03 divisions mol^-1m² for A. subarctica, S. astraea and S. hantzschii with the values for Stephanodiscus species comparable to values for Oscillatoria species. Under a 3:21 LD cycle at 4 °C, light-saturated growth rates were 0·066±0·004, 0·197±0·033 and 0·285±0·018 divisions day^-1 for A. subarctica, S. astraea and S. hantzschii. S. hantzschii growth rate at 4 °C exceeded maximum Oscillatoria growth rates at 23 °C and the S. astraea growth rate at 4 °C was equivalent to O. agardhii growth rate at 20 °C. Temperature increases above 4 °C gave Q₁₀ values between 4 °C and 12 °C of 3·68, 2·39 and 1·92 for A. subarctica, S. astraea and S. hantzschii, but higher temperatures resulted in minor increases in K. S. astraea growth rate peaked at 16 °C, declining sharply at higher temperatures. February to March in situ growth rates in Lough Neagh, mean temperature 4·3 °C, showed that the A. subarctica in situ K of 0·058 divisions day^-1 was close to the laboratory K at 4 °C, but that S. astraea in situ K of 0·101 divisions day^-1 was lower than the laboratory K at 4 °C.     

The effect of salinity on growth,photosynthesis and respiration in the estuarine red algaBostrychia radicans mont

The estuarine red alga,Bostrychia radicans, was subjected to osmotic stresses ranging from hypo-osmotic (9.9‰) to hyperosmotic conditions (37.4‰). The growth rate decreased with increasing salinities and showed a maximum in a mesohaline medium, while the photosynthetic rate and the chlorophyll a content increased under hyper-osmotic conditions. The rate of respiration remained constant over the salinity range tested.B. radicans revealed typical characteristics of “shade plants” having a low light compensation point at 3–4 μE m⁻² s⁻¹ correlated with a low photon flux density of 70–100 μE m⁻² s⁻¹ for saturation of photosynthesis. These physiological properties may explain the success ofB. radicans in estuarine habitats.     

Immuno-flow cytometric identification and enumeration of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in artificially mixed algal populations

Flow cytometric identification and enumeration of Gyrodiniumaureolum Hulburt (Dinophyceae) were performed in artiticiallymixed algal populations using direct immunofluorescence. Calibrationof the flow cytometer, performed with a mixed algal populationspiked with immuno-fluorescently labelled G.aureolum cells,showed that selection of target cells after analysis on greenand orange fluorescence can be done with a recovery of 91.8%[coefficient of variation (CV) = 0.09]. Other selection methodswere less good, with 67.4% (CV = 0.16) and 58.4% (CV = 0.43)recovery based on green and red fluorescence or green fluorescenceand perpendicular light scattering. For mixed algal populationsspiked with unlabelled G.aureolum cells, the quantificationof target cells was quite good (recovery of 76.7%; CV = 0.20).The percentage of total cell loss was high (58.0–92.0%),but this was caused mostly by loss of species smaller in sizethan G.aureolum. Estimates of the relative contribution of G.aureolumin labelled samples were therefore often far too high, but detectionand quantification were not affected. The methodological underestimation(23.3%) was partly caused by gating on green and orange fluorescence(inaccuracy 8.2%).     

Effects of temperature, salinity, irradiance and diurnal periodicity on growth and photosynthesis in the diatom Nitzschia americana: light-limited growth

The effects of variations in temperature (10, 15, 20, 25, 30C)and salinity (8, 15, 20, 26, 32 p.p.t.) on cell size and ratesof photosynthesis and population growth were evaluated in axenic,light-limited (30 µE m^–2 s^–1) cultures ofan estuarine clone of the diatom ^{Nitzschia americana}. Experimentalconditions were chosen to reflect the range of natural conditionswhich occur in the clone's native environment, the Cape FearRiver Estuary, Nqrth Carolina. Rates of light-limited grossphotosynthesis; or photosynthetic efficiency (PSE), were determinedfrom short-term (1 h) ¹⁴C incubations. Diurnal variation inPSE was analyzed using ¹⁴C samples taken during times of estimatedmaximum and minimum rates of diurnal photosynthesis. The salinity-dependenttemperature response of PSE is characterized by a gradual increasein rates up to a temperature optimum at –25C, beyondwhich rates rapidly decline to zero at an upper lethal limit(30–40C). A similar pattern was observed in populationgrowth rates as a function of salinity and temperature. Independentof temperature, optimum salinity for growth was 26 p.p.t. Amaximum growth rate of 2.4 div d^–1 was measured at 25Cand 26 p.p.t. The effect of non-optimum salinity is a reductionin growth rates relative to a predicted temperature-dependentmaximum. Salinity-dependent patterns of variation in cell volume,in general, mirrored the response of population growth suchthat cultures with relatively high growth rates were dominatedby small cells. Significant diurnal variation was observed inPSE; maximum diurnal rates were generally 1.5–3.5 timesgreater than minimum diurnal rates.     

Effects of phosphorus and chilling under low irradiance on photosynthesis and growth of tomato plants

To determine the effects of phosphorus nutrition on chilling tolerance of photosynthetic apparatus, tomato (Lycopersicon esculentum Mill. cv. Kenfengxin 2002) plants were raised under different P contents and subjected to 7 d of chilling at 9/7 °C. After chilling (2 h or 7 d) plant growth, P content in tissue, gas exchange and chlorophyll fluorescence were measured. Decreasing P concentration [P] in the nutrient solution markedly reduced plant growth and the chilled plants exhibiting higher optimum [P] than the unchilled plants. Decreasing [P] significantly decreased light saturated net photosynthetic rate (P_Nsat), maximum carboxylation velocity of Rubisco (V_cmax), maximum potential rate of electron transport contributed to Rubisco regeneration (J_max), quantum efficiency of photosystem (PS) 2 (ΠPS2) and O₂ sensitivity of P_Nsat (PS_O2) and this trend was especially apparent in chilled plants.     

The influence of environmental factors on apparent photosynthesis and respiration of the submersed macrophyte Elodea canadensis

Abstract Oxygen effects on apparent photosynthetic and dark respiratory O₂ exchange rates of detached leaves of Elodea canadensis Michx. (Hydrocharitaceae) were determined over a range of conditions which the submersed plant is likely to experience in shallow water. Apparent photosynthesis is inhibited by O₂ under all the experimental regimes of light, temperature, CO₂ concentration and pH. This inhibition is not caused solely by an accelerated rate of dark respiration, and the observed variations in O₂ inhibition are comparable to O₂ effects on photosynthesis and photorespiration of terrestrial C₃ plants. Percentage inhibition of apparent photosynthesis is enhanced by high O₂ and also by low CO₂. These results indicate that high O₂, high pH and low CO₂ conditions could cause major losses in photosynthetic activity under field conditions. This may account for some of the losses in biomass that are observed under still water conditions.     

The influence of summer/winter conditions of temperature and irradiance on diel oscillations in photosynthesis by Fragilaria crotonensis

SUMMARY. 1. The common pennate diatom (Bacillaryiophyta) Fragilaria crotonensis Kitton showed strong periodicity in its photosynthesis -irradiance (P—I) relationship under summer conditions of high irradiance and temperature which damped progressively throughout the growth phase. Under winter conditions of low irradiance and temperature, weak periodicity was observed.
2. The amplitude of diel oscillations in photosynthesis as a function of irradiance under winter conditions showed only slight variation throughout the growth phase. Under summer conditions, however, amplitudes for both α and P_max were highest in the early exponential phase, declining progressively during growth.
3. These results indicate that the occurrence of periodicity is dependent, in part, on the growth phase of the cells and, in part, on environmental parameters of irradiance and temperature variations under simulated summer and winter conditions.     

Effects of irradiance on growth,photosynthesis, and water use efficiency of seedlings of the chaparral shrub,Ceanothus megacarpus

Summary The effects of irradiance during growth on biomass allocation, growth rates, leaf chlorophyll and protein contents, and on gas exchange responses to irradiance and CO₂ partial pressures of the evergreen, sclerophyllous, chaparral shrub, Ceanothus megacarpus were determined. Plants were grown at 4 irradiances for the growth experiments, 8, 17, 25, 41 nE cm^-2 sec^-1, and at 2 irradiances, 9 and 50 nE cm^-2 sec^-1, for the other comparisons.At higher irradiances root/shoot ratios were somewhat greater and specific leaf weights were much greater, while leaf area ratios were much lower and leaf weight ratios were slightly lower than at lower irradiances. Relative growth rates increased with increasing irradiance up to 25 nE cm^-2 sec^-1 and then leveled off, while unit leaf area rates increased steeply and unit leaf weight rates increased more gradually up to the highest growth irradiance.Leaves grown at 9 nE cm^-2 sec^-1 had less total chlorophyll per unit leaf area and more per unit leaf weight than those grown at 50 nE cm^-2 sec^-1. In a reverse of what is commonly found, low irradiance grown leaves had significantly higher chlorophyll a/b than high irradiance grown leaves. High irradiance grown leaves had much more total soluble protein per unit leaf area and per unit dry weight, and they had much higher soluble protein/chlorophyll than low irradiance grown leaves.High irradiance grown leaves had higher rates of respiration in very dim light, required higher irradiances for photosynthetic saturation and had higher irradiance saturated rates of photosynthesis than low irradiance grown leaves. CO₂ compensation irradiances for leaves of both treatments were very low, <5 nE cm^-2 sec^-1. Leaves grown under low and those grown under high irradiances reached 95% of their saturated photosynthetic rates at 65 and 85 nE cm^-2 sec^-1, respectively. Irradiance saturated rates of photosynthesis were high compared to other chaparral shrubs, 1.3 for low and 1.9 nmol CO₂ cm^-2 sec^-1 for high irradiance grown leaves. A very unusual finding was that leaf conductances to H₂O were significantly lower in the high irradiance grown leaves than in the low irradiance grown leaves. This, plus the differences in photosynthetic rates, resulted in higher water use efficiencies by the high irradiance grown leaves. High irradiance grown leaves had higher rates of photosynthesis at any particular intercellular CO₂ partial pressure and also responded more steeply to increasing CO₂ partial pressure than did low irradiance grown leaves. Leaves from both treatments showed reduced photosynthetic capability after being subjected to low CO₂ partial pressures (100 bars) under high irradiances. This treatment was more detrimental to leaves grown under low irradiances.The ecological implications of these findings are discussed in terms of chaparral shrub community structure. We suggest that light availability may be an important determinant of chaparral community structure through its effects on water use efficiencies rather than on net carbon gain.