Seasonal variations in salt-marsh macroalgae photosynthesis. I. Ascophyllum nodosum ecad scorpioides

Photosynthesis in whole plants of the intertidal alga Ascophyllum nodosum ecad scorpiodes was evaluated by measuring ¹⁴C-uptake under a variety of light intensities and approximately monthly intervals during a 15 month study. Photosynthetic rates were determined in terms of dry weight, pigment content and uptake into ethanolsoluble and insoluble fractions. The specimens, naturally acclimated to in situ light intensities and temperatures, exhibited photosynthetic responses to light intensity which differed with time of year. Maximum photosynthetic potential occurred during the spring months and minimum potential occurred during late summer and winter months. Variations in photosynthetic potential were closely related to seasonal changes in field biomass. Both photosynthetic potential and biomass were inversely related to growth patterns of the salt-marsh phanerogam Spartina alternilora.This research was supported by Research Grant AG-375 from the National Science Foundation and, in part, by the State University of New York Research Foundation and the Energy Research and Development Administration (ERDA).     

Photosynthesis and respiration of exposed salt-marsh fucoids

Photosynthesis and respiration of the salt-marsh fucoids Ascophyllum nodosum ecad scorpioides and Fucus vesiculosus were investigated using an infrared CO₂ gas analyzer under a variety of light intensities, temperatures, and levels of desiccation while the algae were exposed to the atmosphere. Results indicated that net photosynthesis (0.5 to 2.0 mg C/g dry weight/h) saturated rapidly at light intensities (0.1 to 0.2 g cal/cm²/min) which were approximately 10 to 50% of the daily summer maximum intensities for algae found under phanerogam (Spartina alterniflora) canopies. Desiccation exhibited the most pronounced effect on photosynthesis, which increases slightly between 0 and 25% water loss, levels off, and decreases sharply at water losses greater than 50%. Dark respiration (0.1 to 0.3 mg C/g dry weight/h) is also inhibited by desiccation. Both species of algae appear to be broadly adapted to all three parameters investigated.This research was supported by research grants AG-375 and BO 38018 from the National Science Foundation and, in part, by the State University of New York Research Foundation and the Energy Research and Development Administration (ERDA).Communicated by M.R. Tripp, Newark     

Survival,metabolism and growth of Ulva lactuca under winter conditions: a laboratory study of bottlenecks in the life cycle

Photosynthesis and growth in low light and survival under simulated winter conditions were studied in the freefloating green alga Ulva lactuca L., collected in Roskilde Fjord, Denmark during late autumn and maintained in stock in natural water. It adapts efficiently to low light by increasing chlorophyll concentration and light absorption and continues to grow at the lowest irradiance tested, 0.6 E m^-2 s^-1. This irradiance corresponds to minimum light requirements of deep-living marine macroalgae and phytoplankton growing under ice. The photosynthetic efficiency per unit of incident light is five-fold higher for U. lactuca grown at 1.7 E PAR m^-2 s^-1 as compared with 56.3 E m^-2 s^-1, and the efficiency per unit of light absorbed is twice as high. The maximum photosynthetic efficiency (0.051 mol C E^-1 absorbed) is similar to values for shade-adapted marine phytoplankton. U. lactuca is able to survive for two months in the dark and to resume growth immediately when transferred to light. Exposure to anoxia and sulphide gradually reduces vitality, but does not affect survival over two months. Rigorous deep freezing is detrimental to survival of U. lactuca, while field samples show that more gradual, natural freezing is not. U. lactuca is not easily fitted into one of the traditional strategy concepts. U. lactuca is a very plastic species that combines rapid growth during favourable periods (opportunism) with high survival capacity in the same type of tissue during stress periods (persistence). U. lactuca occupies a niche as a free-floating form in sedimentary coastal areas that are devoid of attached algae.     

Kinetic evidence for common photosynthetic step in diverse seaweeds

The turnover time of photosynthetic oxygen production was the same, near 0.5 msec, for the seaweeds Ulva lactuca, Codium fragile, Porphyryaumbilicalis, Chondrus crispus, Champia parvula and Fucus vesiculosis. This turnover time did not change for sun- and shade-adapted U. lactuca and P. umbilicalis. The similarity of these turnover times to those of other algae, higher plants, and cyanobacteria is strong evidence for similarity in the kinetics, and thus for a universal mechanism of photosynthesis. Evolution in the light-gathering apparatus responsible for the color of seaweeds has occurred without variation in the mechanism of photosynthesis. The size of the Emerson-Arnold photosynthetic unit (the ratio of chlorophyll to oxygen formed in a single tumover light flash) in the green seaweeds is about the same as that in algae, i.e., 2000. It is about half this number for the red and brown seaweeds. The different accessory pigments in the latter two groups compensate for the smaller amount of chlorophyll. The size of the unit was independent of sun- and shade-adaptation in U. lactuca, but did increase in shade-adapted P. umbilicalis.     

Photosynthesis and carbon storage between tides in a brown alga, Fucus vesiculosus

Intertidal macroalgae may spend a significant part of their lives in air. During photosynthesis in air, they encounter much lower concentrations of inorganic carbon than in seawater. Because they accumulate inorganic carbon from seawater, we investigated whether they similarly accumulate it from air. We measured photosynthesis in the intertidal species Fucus vesiculosus L. during 1990 and 1991 with a gas-phase O₂ electrode or CO₂-exchange apparatus in air and with a liquid-phase O₂ electrode in seawater. Maximum rates were rapid and similar in air and seawater regardless of the method. Tissue from seawater could carry on photosynthesis in CO₂-free air, indicating that carbon was stored in the tissue. After 2 h, this store was depleted and photosynthesis ceased. Supplying CO₂ in air replenished the store. Under identical conditions, terrestrial C₃ and C₄ species showed no evidence of this store, but a CAM (crassulacean acid metabolism) species did. However, in contrast to the CAM behavior, F. vesiculosus did not store CO₂ significantly in the dark. We found a small acid-releasable pool of carbon in the tissue that disappeared as photosynthesis depleted the carbon store. However, the pool was too small to account for the total carbon stored. While CO₂ was being acquired or released from the store in the light, photosynthesis was not inhibited by 21% O₂. These results indicate that there are two parallel paths for the supply of CO₂ to photosynthesis. The first depends on inorganic carbon in seawater or in air and supports rapid photosynthesis. The second involves CO₂ slowly released from an organic intermediate. The release protects CO₂ fixation from the inhibitory effects of 21% O₂. Photosynthesis in F. vesiculosus thus appears to be C₃-like in its rapid fixation of CO₂ from a small inorganic pool into phosphoglycerate. However, it is C₄-like in its pre-fixation of carbon in an organic pool in the light, and is CAM-like in its ability to slowly use this pool as a sole source of CO₂. The organic pool may serve to protect photosynthetic CO₂ fixation against the inhibitory effects of O₂ in air and in the boundary layer in seawater. Received: 6 March 1998 / Accepted: 16 October 1998     

Distribution and maximum growth depth of Fucus vesiculosus along the Gulf of Finland

 A survey of the distribution and maximum depth of a continuous Fucus vesiculosus belt was carried out in the Gulf of Finland in 1991. F. vesiculosus is widely distributed throughout the Gulf of Finland, including the vicinity of Vyborg Bay, Russia in the east. The maximum growth depth of F. vesiculosus in the Gulf of Finland reflects two different patterns according to the exposure to wave action. The most robust and continuous F. vesiculosus belt is observed on exposed shores, where the maximum growth depth is 5 to 6 m, with the optimum at 2 to 3 m. On moderately exposed shores the maximum growth depth is 3 m, with an optimum growth depth of <2 m. The maximum growth depth also varies geographically, with a decreasing trend towards the east. Maximum growth depth of F. vesiculosus correlates with light intensity. The compensation point for F. vesiculosus photosynthesis is about 25 μmol m⁻² s⁻¹, and photosynthesis is saturated at a light intensity of 300 μmol m⁻² s⁻¹. Vertical irradiance attenuation measurements in situ in summer revealed that for F. vesiculosus photosynthesis the quantity of light is optimal (200 to 300 μmol m⁻² s⁻¹) at <3 m depth. At depths >5 m the quantity of light is near or below the photosynthesis compensation point and insufficient for growth. These depth limits of light penetration coincide with measured growth depths of F. vesiculosus in the Gulf of Finland. Received: 7 May 1999 / Accepted: 18 November 1999     

Effect of freezing on photosynthesis of intertidal macroalgae: relative tolerance of Chondrus crispus and Mastocarpus stellatus (Rhodophyta)

The effect of freezing on photosynthetic metabolism was studied in the red algae, Chondrus crispus and Mastocarpus stellatus. Plants of both species were collected from the intertidal at Chamberlain or Kresge Point, Maine, USA (43°56N, 69°54W) between February and March 1987. Photosynthetic rates were measured immediately after freezing at-20°C and following recovery periods in seawater. Photosynthesis in C. crispus declined rapidly following freezing, falling to 70% of control values within 1 h and 30% after 3 h exposure. Minimum photosynthetic rates (7 to 9% of controls) occurred following freezing exposures of 12 h or more. Full photosynthetic recovery in C. crispus after 3 h at-20°C required 48 h. Photosynthesis in C. crispus did not fully recover in plants frozen for 6 h or more. In contrast, photosynthesis in M. stellatus was relatively unaffected by freezing exposures of <12 h. Twelve hours or more at-20°C reduced photosynthesis to 55% of controls. Photosynthesis in M. stellatus fully recovered from 24 h at-20°C within 24 h. In both species the reduction of photosynthesis by freezing was associated with damage to the plasma membrane and reduced efficiency of energy transfer from phycobilisomes to chlorophyll a, but did not appear to involve ribulose-1,5-bisphosphate carboxylase oxygenase activity. The freezing tolerance of C. crispus and M. stellatus positively correlates with their respective intertidal distributions, suggesting that freezing may be involved in controlling the distributions of these species on the shore.     

Kinetic measurements of metal accumulation in two marine macroalgae

 We measured the uptake kinetics of four metals (Cd, Cr, Se and Zn) in two marine macroalgae (the green alga Ulva lactuca and the red alga Gracilaria blodgettii). Metal uptake generally displayed a linear pattern with increasing exposure time. With the exception of Cr, which exhibited comparable uptake rate constants at different concentrations, uptake rate constants of Cd, Se and Zn decreased with increasing metal concentration, indicating that the seaweeds had a higher relative uptake at lower metal concentration. Uptake of Cd and Zn was higher in U. lactuca than in G. blodgettii, whereas uptake of Cr and Se was comparable between the two species. Only Cd and Zn uptake in U. lactuca was significantly inhibited by dark exposure. A decrease in salinity from 28 to 10‰ enhanced the uptake of Cd, Cr, Se and Zn in U. lactuca 1.9-, 3.0-, 3.6-, and 1.9-fold, respectively. In G. blodgettii, Cd uptake increased twofold when salinity was decreased from 28 to 10‰, whereas uptake of Cr and Zn was not significantly affected by salinity change. The calculated depuration rate constants of metals in U. lactuca were 0.01 d⁻¹ for Cd, 0.05 to 0.08 d⁻¹ for Cr, 0.14 to 0.16 d⁻¹ for Se, and 0.12 to 0.15 d⁻¹ for Zn, and were relatively independent of the metal body burden in the algae. The predicted bioconcentration factor was 3 × 10⁴ for Cd, 2 × 10³ for Cr, 40 to 150 for Se, and 1 to 2 × 10⁴ for Zn in U. lactuca. Our kinetic study suggested that U. lactuca would be a good biomonitor of Cr and Zn contamination in coastal waters. Received: 14 September 1998 / Accepted: 29 May 1999     

Light quality in relation to growth,photosynthetic rates and carbon metabolism in two species of marine plankton algae

The effect of light quality on growth, photosynthesis and carbon metabolism in two species of marine algae,Cyclotella nana (Hustedt) andDunaliella tertiolecta (Butcher), was examined. Relative growth constants forC. nana were 0.37, 0.29 and 0.25 in blue, white and green light, respectively. Corresponding constants were 0.41, 0.31 and 0.29 forD. tertiolecta. Photosynthetic rates in both species were higher in blue light and lower in green light compared with white light of the same intensity. More than 60% of¹⁴C assimilated byC. nana orD. tertiolecta grown in blue or green light was incorporated into the ethanol-insoluble fraction, compared with 10 to 30% in this fraction in white light. The relative importance of the various components within this fraction was independent of light quality. Although less¹⁴C was assimilated into the ethanol-soluble fraction in blue or green light, there was a relative increase in some amino acids and organic acids in this fraction and a decrease in sugars and sugar phosphates relative to white light of the same intensity. These differences were independent of light intensity, photosynthetic rate and cell density in the cultures.     

Biosorption of Direct Yellow 12 from aqueous solution using green alga Ulva lactuca

The potential of commonly available green alga Ulva lactuca was investigated as viable biomaterials for removal of synthetic azo dye (Direct Yellow 12, DY-12) from aqueous solution. The results obtained from the batch experiments revealed that the ability of the U. lactuca to remove DY-12 from its aqueous solution was dependent on the dye concentration, pH, and algal biomass but less dependent on the particle size of the U. lactuca. The equilibrium conditions and kinetics of adsorption were investigated, and the adsorption kinetic was consistent with the pseudo-second-order model (R ²=1). The adsorption isotherm followed only the Freundlich model with a correlation coefficient R ²=0.99. This study demonstrated that the U. lactuca could be used as an effective biosorbent for the removal of DY-12 from its aqueous solution.     

Nitrate reductase and glutamine synthetase activity,internal N pools,and growth of<Emphasis Type="Italic"> Ulva lactuca</Emphasis>: responses to long and short-term N supply

Fast-growing macroalgae, including Ulva lactuca Linnaeus, respond rapidly to changes in nutrient conditions, particularly to short-term N supply. This ability to rapidly take up and assimilate N contributes to the increasing occurrence of macroalgal blooms in heavily N loaded coastal ecosystems. To determine whether long-term nutrient histories affect short-term responses in activity of N-assimilating enzymes, including nitrate reductase (NRA) and glutamine synthetase activity (GSA), internal N storage, and macroalgal growth, we conducted an in situ nitrate fertilization experiment between 7 and 22 July 2004, with fronds of U. lactuca collected from estuaries with high and low N loads in Waquoit Bay, Cape Cod, Massachusetts, USA (N 41° and W 70°). Initial NRA, GSA, % N, δ¹⁵N, and growth of U. lactuca fronds were higher in the site where nitrate was in high supply. Differences in NRA persisted even after short-term experimental enrichment. Differences in internal N pools, δ¹⁵N, and growth, in contrast, mirrored the changes of nutrient supply. The rate of turnover of the internal N content of U. lactuca was quite short (<2 d), and turnover of enzyme activity may have been even shorter. N isotopic fractionation by U. lactuca appeared to be of small magnitude, unlike the case of phytoplankton, and similar to that of vascular plants. δ¹⁵N was a better indicator of short-term response to external and internal nutrient supplies in U. lactuca than enzyme activity or N content, and may reliably detect rapid changes in N availability, source, and uptake and assimilation processes.     

Photoadaptation of photosynthesis in Gonyaulax polyedra

Gonyaulax polyedra Stein exhibited a combination of photoadaptive strategies of photosynthesis when only a single environmental variable, the light intensity during growth, was altered. Which of several biochemical/physiological adjustments to the light environment were employed depended on the level of growth irradiance. The photoadaptive strategies employed over any small range of light levels appeared to be those best suited for optimizing photosynthetic performance and not photosynthetic capacity. (Photosynthetic performance, P _i, is defined as the rate of photosynthesis occurring at the level of growth irradiance.) Among all photosynthetic parameters examined, only photosynthetic performance showed a consistent correspondence to growth rates of G. polyedra. Above 3500 to 4000 W cm^-2, where photosynthetic performance was equal to photosynthetic capacity, cells were not considered light-limited in either photosynthesis or growth. At these higher light levels, photosynthetic perfomance, cell volume, growth rates and respiration rates remained maximal; photosynthetic pigment content varied only slightly, while the photosynthetic capacity of the cells declined. At intermediate light levels (3000 to 1500 W cm^-2), photosynthesis, not growth, was light-limited, and photoadaptive strategies were induced which enhance absorption capabilities and energy transfer efficiencies of chlorophyll a to the reaction centers of G. polyedra. Photosynthetic capacity remained constant at about 280 mol O₂ cm^-3 h^-1, while photosynthetic performance ranged from 100 to 130 mol O₂ cm^-3 h^-1. Major increases in photosynthetic pigments, especially peridinin-chlorophyll a-proteins and an unidentified chlorophyll c component, accompanied photoadaptation to low irradiances. Maximal growth rates of 0.3 divisions day^-1 were maintained, as were respiration rates of about-80 mol O₂ cm^-3 h^-1 and cell volumes of about 5.4×10^-8 cm^-3 cell^-1. Below about 1250 W cm^-2, photosynthesis in G. polyedra was so light-limited that photosynthetic performance was unable to support maximal growth rates. Under these conditions, G. polyedra displayed photostress responses rather than photoadaptive strategies. Photostress was manifested as reduced cell volumes, slower growth, and drastic reductions in pigmentation, photosynthetic capacity, and rates of dark respiration.     

Adaptation of light-harvesting pigments to downwelling light and the consequent photosynthetic performance of the eulittoral rockweeds Ascophyllum nodosum and Fucus vesiculosus

We compared the effect of habitat and water depth on the light-harvesting pigment content for Ascophyllum nodosum and Fucus vesiculosus at two near-shore stations in Long Island Sound (USA). Excised pieces of seaweeds were attached at depth intervals to a vertically buoyed line, and left in situ for 7 days. For comparison, fronds were collected from sun and shade habitats in the littoral zone. The three major antenna (light-harvesting) pigments increased in concentration with depth or shade. Chlorophyll c to a ratios remained stable at about 0.2. Fucoxanthin to chlorophyll a ratios decreased by 20 to 30% with depth or shade. Although pigment composition for the two rockweed species was equivalent, the maximum photosynthetic performance of F. vesiculosus exceeded that of A. nodosum by a factor of 2, while the compensation depths for 4 m-adapted A. nodosum and F. vesiculosus under natural limiting light conditions were equivalent. Plants held at 4 m had higher photosynthetic rates compared with plants held at 0 m, no matter the depth of measurement. Indirect evidence indicates that the enhanced photosynthesis of 4 m-adapted plants is due not only to higher concentrations of antenna pigments but to other physiological factors as well. We conclude that the clearly delineated vertical distribution of these two canopy species, the F. vesiculosus zone over the A. nodosum zone, is not determined by light quantity or quality, but by biotic factors as evidenced by the experiments of Menge which are cited herein.     

Spatial variation in dimethylsulfoniopropionate (DMSP) production in <Emphasis Type="Italic">Ulva lactuca</Emphasis> (Chlorophyta) from the Northeast Pacific

Although dimethylsulfoniopropionate (DMSP) has a variety of functions in marine macroalgae including that of a cryoprotectant, an osmolyte, a way to remove excess sulfur and energy, an antioxidant, and an allelopathic precursor, the latter two functions are believed to be the most important in Ulva lactuca L. (=U. fenestrata) in intertidal populations on the coast of Washington state, USA. The present study found significant variation in DMSP concentrations among U. lactuca collected in May 2005 from six sites ranging from 47°54.45′N (Possession Point, Whidbey Island, WA, USA) to 48°30.55′N (Shannon Point Beach, Anacortes, WA, USA), and also among individuals within sites, and among tissues (basal tissues near the holdfast, middle of the blades, and tips). Concentrations ranged from 37 to 224 μmol g⁻¹ fresh mass (FM). In several 10-day experiments between July 2001 and August 2004 with U. lactuca collected from several places on the coast of Washington, the effects of nutrient level (DIN), light intensity and wavelength, and grazing by the herbivorous gastropod Lacuna vincta, were examined. None of these manipulations resulted in DMSP concentrations that differed significantly from controls, and variance in DMSP concentrations within each experiment was very low. Although DMSP concentrations in U. lactuca may be affected by factors not tested in these experiments, it is also possible that the observed spatial differences reflect constitutive genotypic or phenotypic differences among geographically separated U. lactuca populations or among cryptic Ulva species. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Effects of O2, pH and DIC on photosynthetic net-O2 evolution by marine macroalgae

Net photosynthetic O₂ evolution by five marine macroalgae:Ulva lactuca L.,Enteromorpha sp.,Ceramium strictum Harvey,Fucus serratus L., andF. vesiculosus L., collected from Danish waters in the summer of 1983 was followed at increasing O₂ and with pH either fixed close to pH 7, 8 or 9, or drifting upwards during photosynthesis in a closed chamber to determine the effects of changing O₂, pH and DIC (dissolved inorganic carbon) on photosynthesis. Increasing O₂, increasing pH and decreasing DIC together limited O₂ evolution. Raising the O₂ concentration with pH and DIC held constant resulted in less inhibition of net-O₂ evolution than when all three factors acted together. The O₂ inhibition of photosynthesis was similar to the reported O₂ inhibition of ribulose 1,5-bisphosphate carboxylase isolated from lower and higher plants. Net-O₂ evolution as a function of the molar ratio of O₂ to HCO^– ₃ + CO₂ in solution provided a general, linear relationship (r ² = 0.72 to 0.84), predicting inhibition of photosynthesis based on O₂ pH and DIC changing together. Slopes of this relationship, representing competition between O₂ and carbon based on external concentrations, were similar for the five taxonomically different algae, suggesting that similar processes act to reduce net-O₂ evolution.     

Photosynthesis in whole plants of Chondrus crispus

Photosynthesis in whole plants of Chondrus crispus Stackhouse was measured by ¹⁴C uptake under various light intensities and temperature regimes. In plants collected from waters of 6° to 7°C, photosynthesis did not increase with light intensity over a range of 200 to 2400 foot candles (ft-c). However, in plants collected from waters of 10° to 12°C, the rate of photosynthesis was lower over the range 200 to 1400 ft-c but, at 2000 ft-c, increased to a level similar to that of the 6° to 7°C plants. Ethanol-soluble and insoluble fractions showed similar patterns.     

Tolerance of estuarine benthic diatoms to high concentrations of ammonia,nitrite ion,nitrate ion and orthophosphate

A carbon-14 assimilation method was used to determine action spectra and photosynthesis versus irradiance (P versus I) curves of natural populations of phytoplankton and zooxanthellae from a coral reef fringing Lizard Island in the Australian Barrier Reef. The action spectra were related to the phytoplankton species composition. The curves showed shade adaptation in phytoplankton from deeper waters and in the zooxanthellae. Rates of photosynthesis of zooxanthellae were shown to be highly but variably dependent on their host organisms. Photosynthetic production by zooxanthellae was about 0.9 gC m^-2 day^-1, which is about three times higher than phytoplankton production in the waters close to the reef.     

Nutrients uptake and growth of Ulva lactuca (Linnaeus, 1753) in grey mullet (Mugil cephalus) wastewater versus natural estuarine water

This study investigates the capability of Ulva lactuca to grow in an integrated system, aiming to optimise the needing of resources and to decrease the ecological impact of wastewater. The nutrients uptake and the growth of U. lactuca in Mugil cephalus wastewater (WW) were evaluated and compared with U. lactuca cultivated in estuarine water (EW). Fresh thalli of U. lactuca were cultivated for 10 days in 5?L cylindrical tanks, 3 replicates per treatment. The uptake of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP), as well as the biomass yield and specific growth rate of U. lactuca, were assessed every two days. At the end of the experiment, U. lactuca resulted in a higher assimilation of DIN in EW (95.7?±?0.3%, mean?±?SE) than in wastewater (68.7?±?1.0%) (p?80%), as well as in the biomass yield and specific growth rate. This study demonstrates the efficiency of U. lactuca in the assimilation of DIN and DIP from M. cephalus WW, contributing to reduce the release of dissolved inorganic nutrients in the natural environment.     

Ecotypic differentiation in the marine diatom Skeletonema costatum: influence of light intensity on the photosynthetic apparatus

Three genetically distinct clones of Skeletonema costatum (Grev.) Cleve were grown at 20°C under high (274 E m^-2 s^-1) and low (27 E m^-2 s^-1) light conditions and their photoadaptive photosynthetic responses compared. When all three clones were grown under low light, pigment analyses and fluorescence excitation spectra demonstrated that the accessory pigments, chlorophyll c and fucoxanthin, became more important in light-harvesting compared to chlorophyll a. Photosynthetic unit sizes increased for Photosystems I and II in low light, but photosynthesis vs irradiance characteristics were not reliable predictors of photosynthetic unit features. Fluorescence excitation spectra and photosynthesis vs irradiance (P-I) relationships indicated that changes in energy transfer occurred independent of changes in pigment content. Large increases in accessory pigment content were not accompanied by large increases in excitation from these pigments. Changes in energy transfer properties were as important as changes in PSU size in governing the photoadaptive responses of S. costatum. When the three clones were grown under identical conditions, each had a separate and distinct pattern of photoadaptation. Significant differences among clones were found for pigment ratios, photosynthetic unit sizes for Photosystems I and II and efficiency of energy transfer between pigments. These strikingly different photoadaptive strategies among clones may partially account for the great ecological success of the diatom species. This is the first quantitative investigation of the importance of both chlorophyll c and fucoxanthin to the adaptive responses of diatoms to light intensity, and represents the most complete characterization of the photoadaptive responses of a single species of marine phytoplankter to differences in light environment.     

Growth rate and carbon affinity ofUlva lactuca under controlled levels of carbon,pH and oxygen

We examined the growth rate (µ) ofUlva lactuca L. (collected from Roskilde Fjord, Denmark in 1987) at different levels of dissolved inorganic carbon (DIC), pH and oxygen in two culture facilities. Growth was faster in Facility A (µ _max ca 0.3 d^–1) than in B (µ _max ca 0.2 d^–1), probably because of more efficient stirring and higher light intensity. The growth-DIC response curve exhibited low half-saturation constant (K _1/2) values (0.35 mM DIC in A, 0.55 mM in B) and growth rates close toµ _max at natural seawater concentration of 2 mM DIC. Growth rate showed a low sensitivity to oxygen over a wide range of DIC and oxygen concentrations. Collectively, the results demonstrated an efficient mechanism for DIC use, unaffected by acclimatization to DIC concentrations between 0.2 and 3 mM. The growth rate decreased little between pH 7.5 and 9 at 2 mM DIC, but steeply above pH 9 approaching zero just above pH 10. The decline of growth at high pH may result from direct pH effects on cell pH, reduced HCO ₃ ^- availability and impaired operation of the carbon uptake process. The growth responses ofU. lactuca to DIC, pH and oxygen resembled those observed in previous short-term photosynthetic experiments. This similarity is probably due to the fast growth ofU. lactuca which means that photosynthetic products are rapidly converted into cell growth. Based on the culture experiments we argue that field plants ofU. lactuca not exposed to stagnant water and DIC depletion are likely to be limited in growth by environmental factors other than DIC (e.g. light and nutrients). Dense mats ofU. lactuca, however, may show reduced growth as a result of DIC depletion, high pH and self-shading.