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Aquatic Photosynthesis
... This should increase overall lightlimitation of cells as at any given time as only a small proportion of the plume is within the euphotic zone. This has significant implications for regulating the acclimation and overall productivity of the phytoplankton (Falkowski and Raven, 2007). The relative importance of mixing on light availability within buoyant plume of the Hudson River is difficult to assess due to complex spatial dynamics making it difficult to sample using traditional sampling strategies. ...
... In the aged plume and coastal jets, the light levels and mixing were higher, but production appeared to be limited by nutrients as suggested by the low in situ nutrient concentrations and quantum yields. Phytoplankton will photoacclimate to maximize the light absorption and photosynthesis whenever possible (Prézelin et al., 1991; Falkowski and Raven, 2007). This is accomplished by the many cellular processes that " tune " E k to match the in situ irradiance (Dubinsky and Schofield, 2009). ...
... Phytoplankton biomass increases rapidly as the Hudson River plume enters the ocean with populations photosynthesizing at near the theoretical maximum within the re-circulating bulge. The associated high turbidity resulted in light-limited phytoplankton; however mixing rates were sufficiently rapid that the phytoplankton did not induce photoacclimation processes to overcome their overall light limitation (Prézelin et al., 1991, Falkowski and Raven, 2007; Dubinsky and Schofield, 2009). Using the draw down of nitrate as an integrated proxy for total phytoplankton productivity, the integrated daily productivity would be approximated to be close to 400 mg C d −1 . ...
... Do conservation conditions and imposed time-lags (due to the number of analyses to be performed) between sample collection and fluorescence measurements have potential cumulative effects? Phytoplankton photosynthesis is well known to be modulated by natural factors such as temperature (Raven and Geider, 1988; Davison, 1991), as temperature variations can dramatically disturb the fluorescence characteristics of organisms (Krause and Weis, 1991; Falkowski and Raven, 2007) well below the threshold at which high temperature irreversibly inhibits photosynthesis (Pastenes and Horton, 1996). Temperature variations result in changes in photosynthetic electron transport activity and other processes related to photosynthesis, and will further modify the fluorescence characteristics of algae (Falkowski and Raven, 2007). ...
... Phytoplankton photosynthesis is well known to be modulated by natural factors such as temperature (Raven and Geider, 1988; Davison, 1991), as temperature variations can dramatically disturb the fluorescence characteristics of organisms (Krause and Weis, 1991; Falkowski and Raven, 2007) well below the threshold at which high temperature irreversibly inhibits photosynthesis (Pastenes and Horton, 1996). Temperature variations result in changes in photosynthetic electron transport activity and other processes related to photosynthesis, and will further modify the fluorescence characteristics of algae (Falkowski and Raven, 2007). For temperate communities, strong reductions of the maximum rate of photosynthesis have been documented when temperature exceeds 30 1C (Morris and Kromkamp, 2003), although with optimal values that depend on species-of-interest (Claquin et al., 2008). ...
... oceanica ( Thayer and Björkman , 1990 ; Demmig - Adams and Adams , 1992 ) , which is characteristic of sun - adapted plants with a high investment in photoprotection ( Demmig - Adams and Adams , 1996 ; Ralph et al . , 2002 ; Falkowski and Raven , 2007 ) . ...
... Chl b : a molar ratio ) observed in P . oceanica saline - stressed leaves has been suggested to represent a degrada - tive process associated to ion toxicity in seagrasses ( McMillan and Moseley , 1967 ; Ralph , 1998 , 1999 ) , but can also be interpreted as a compensatory mechanism to reduce the light harvesting capac - ity of stressed leaves ( Kirk , 1994 ; Falkowski and Raven , 2007 ) , as it diminishes the excitation pressure over the PSII reaction centres , and thus the probability of photoinhibition ( e . g . ...
In the present study, we investigated the capacity for non-radiative energy dissipation operated by thexanthophyll cycle pigments of the Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa,under normal and increased salinity conditions. After being chronically stressed by hypersalinity duringseveral months in a mesocosm system, the efficiency of PSII photochemistry and non-photochemicalquenching (NPQ) kinetics and the leaf content in pigments (including xanthophylls) were analysed inunstressed and stressed plants under two approximations: (i) along a daily cycle in the mesocosm undermoderate light levels; and (ii) exposing leaf segments to direct high light and allowed latterly to recoverunder low light conditions. C. nodosa leaves exhibited not only a greater pool of xanthophyll cycle com-pounds but also a higher xanthophyll de-epoxidation state compared to P. oceanica leaves, which isindicative of a greater capacity for thermal energy dissipation. These differences in the photoprotectivecapacity of both seagrasses reflect the different light climates that naturally exist inside both meadowsdue to the stronger self-shading produced by P. oceanica canopies. Under direct high light, both speciesenhanced photoprotective down-regulation of photosystem II (PSII), and although they both finally exhib-ited signs of photodamage, this was mainly in P. oceanica, which also showed pigment degradation dueto sudden exposure to harmful irradiances. Chronic hypersaline stress did not alter the functioning ofthe xanthophyll-cycle-photoprotection of both species; nonetheless in combination with high light, itpredisposes P. oceanica leaves to photoinhibition, most likely through a reduction in the capacity forreparation damaged PSII reaction centres.
... The discovery of picoplankton and its importance in the food web of oceans changed the view on the structure and function of pelagic ecosystems (Johnson and Sieburth, 1979, 1982; Waterbury et al., 1979). Globally, picophytoplankton contributes at least 10% of net primary production, accounting for at least 3 Pg C fixed per year (Fogg, 1986; Falkowski and Raven, 1997). Several studies have shown that nano-(<20 µm and >2 µm) and pico-(<2 µm) phytoplankton quantitatively prevail in the Southern Ocean (Weber and El-Sayed, 1987; Ning et al., 1996). ...
... The reaction catalysed by Rubisco is not the only carboxylation reaction in autotrophic cells; -carboxylation reactions catalysed by phosphoenolpyruvate carboxylase (PEPC), phosphoenolpyruvate carboxykinase (PEPCK) or pyruvate carboxylase (PYRC) also fix inorganic C using organic components as cosubstrates from the Calvin–Benson cycle or from outside the cell (Appleby et al., 1980; Glover, 1989; Falkowski and Raven, 1997). The interest in -carboxylation reactions is to account for the marked incorporation of inorganic carbon into amino acids and intermediates of the tricarboxylic acid cycle (Mortain-Bertrand, 1988), which is coupled with incorporation of nitrate and ammonium (Yentsch, 1977). ...
During the ANTARES 3 cruise in the Indian sector of the Southern Ocean in October–November 1995, the surface waters of Kerguelen Islands plume, and the surface and deeper waters (30–60 m) along a transect on 62°E from 48°36′S to the ice edge (58°50′S), were sampled. The phytoplankton community was size-fractionated (2 μm) and cell numbers, chlorophyll biomass and carbon assimilation, through Rubisco and β-carboxylase activities, were characterized. The highest contribution of <2 μm cells to total biomass and total Rubisco activity was reported in the waters of the Permanent Open Ocean Zone (POOZ) located between 52°S and 55°S along 62°E. In this zone, the picophytoplankton contributed from 26 to 50% of the total chlorophyll (a + b + c) with an average of 0.09 ± 0.02 μg Chl l–1 for <2 μm cells. Picophytoplankton also contributed 36 to 64% of the total Rubisco activity, with an average of 0.80 ± 0.30 mg C mg Chl a–1 h–1 for <2 μm cells. The picophytoplankton cells had a higher β-carboxylase activity than larger cells >2 μm. The mixotrophic capacity of these small cells is proposed. From sampling stations of the Kerguelen plume, a relationship was observed between the Rubisco activity per picophytoplankton cell and apparent cell size, which varied with the sampled water masses. Moreover, a depth-dependent photoperiodicity of Rubisco activity per cell for <2 μm phytoplankton was observed during the day/night cycle in the POOZ. In the near ice zone, a physiological change in picophytoplankton cells favouring phosphoenolpyruvate carboxykinase (PEPCK) activity was reported. A species succession, or an adaptation to unfavourable environmental conditions such as low temperature and/or available irradiance levels, may have provoked this change. The high contribution of picophytoplankton to the total biomass, and its high CO2 fixation capacity via autotrophy and mixotrophy, emphasize the strong regeneration of organic materials in the euphotic layer in the Southern Ocean.
... Our results indicate that the biomass productivities obtained from C. malina are comparable with the biomass productivities of mesophilic and other polar and cold-adapted microalgae [9,16,44]. It is noteworthy that the metabolic rates (measured here as biomass productivity) of polar and cold-adapted microalgae were not reduced due to low temperatures, as suggested by several studies [57][58][59]. This statement probably is only applicable to mesophilic microalgae that cannot grow below thermal optimum temperature [16]. ...
Polar microalgae that are highly productive in cold climates can produce large amounts of biomass and poly-unsaturated fatty acids (PUFA). The polar Chlamydomonas malina RCC2488, grows at low temperatures and produces high amounts of lipids, which are mainly composed of PUFA. However, not much is known about its phylogenetic relationship with other strains within the order Chlamydomonadales and the optimum growth conditions for maximum biomass productivity have not yet been identified. In this study, a phylogenetic analysis was performed to determine the closest relatives of C. malina within the Chlamydomonadales order. To select the best growth conditions for maximum biomass productivities in cultivations performed at 8°C, different salinities (0-80) and light intensities (70-500 μmol photons m −2 s −1) were tested, using bubble column and flat-panel photobioreactors. The effect of nitrogen limitation was tested to determine if C. malina can accumulate energy reserve metabolites (carbohydrates and lipids). Phylogenetic analysis confirmed that C. malina, which belongs to the Chlamydomonales order, is closely related to the psychrophilics Chlamydomonas sp. UWO 241 and Chlamydomonas sp. SAG 75.94, as well as to the mesophilic C. parkeae MBIC 10599. The highest biomass (527 mg L −1 day −1), lipid (161.3 mg L −1 day −1) and polyunsaturated fatty acids (PUFA; 85.4 mg L −1 day −1) productivities were obtained at a salinity of 17.5, light intensity of 250 μmol photons m −2 s −1 and nitrogen replete conditions. Strikingly, the marine C. malina can grow even in fresh water, but the biomass productivity was reduced. While the intracellular lipid content remained unchanged under nitrogen deprivation, the carbohydrate content increased (up to 49.5% w/w), and the protein content decreased. The algal lipids were mainly comprised of neutral lipids, which were primarily composed of PUFA. Chlamydomonas malina RCC2488 is a polar marine microalga suitable for high biomass, carbohydrate, lipid and PUFA productivities at low temperatures.
... Detritus is split into two pools: a large one that sinks fast, and a small one that sinks slowly, i.e., that behaves similar to dissolved organic matter. The model considers a dynamic phytoplankton chlorophyll-to-carbon ratio (θ) which mimics photoacclimation in phytoplankton (Falkowski and Raven, 1997). The chlorophyll-to-carbon ratio depends on irradiance, nutrient availability and temperature following the model of Geider et al. (1997). ...
Upwelling-favorable winds have increased in most Eastern Boundary Upwelling Systems (EBUS) in the last decades, and it is likely that they increase further in response to global climate change. Here, we explore the response of biological production and air–sea CO2 fluxes to upwelling intensification in two of the four major EBUS, namely the California Current System (California CS) and Canary Current System (Canary CS). To this end, we use eddy-resolving regional ocean models on the basis of the Regional Oceanic Modeling System (ROMS) to which we have coupled a NPZD-type ecosystem model and a biogeochemistry module describing the carbon cycle and subject these model configurations to an idealized increase in the wind stress. We find that a doubling of the wind-stress doubles net primary production (NPP) in the southern California CS and central and northern Canary CS, while it leads to an increase of less than 50% in the central and northern California CS as well as in the southern Canary CS. This differential response is a result of i) different nutrient limitation states with higher sensitivity to upwelling intensification in regions where nutrient limitation is stronger and ii) more efficient nutrient assimilation by biology in the Canary CS relative to the California CS because of a faster nutrient-replete growth rate and longer nearshore water residence times. In the regions where production increases commensurably with upwelling intensification, the enhanced net biological uptake of CO2 compensates the increase in upwelling driven CO2 outgassing, resulting in only a small change in the biological pump efficiency and hence in a small sensitivity of air–sea CO2 fluxes to upwelling intensification. In contrast, in the central California CS as well as in the southern Canary CS around Cape Blanc, the reduced biological efficiency enhances the CO2 outgassing and leads to a substantial sensitivity of the air–sea CO2 fluxes to upwelling intensification.
... The climate equilibrium is influenced by the global carbon cycle in the biosphere. Oceans play a major role in this process: phytoplankton is responsible for about 40% of the global carbon fixation, commonly indicated as primary productivity [Falkowski and Raven, 1997]. Climatic conditions , nutrient availability and physical forcings are functions of space and time. ...
A lidar fluorosensor was developed in the framework of the Italian Antarctic Research Pro- gram. This system and some ancillary instruments were installed in the research vessel Italica during three oceanographic campaigns in the Southern Ocean and collected data on biochemi- cal parameters of the seawaters crossed. In particular, thematic maps of chlorophyll-a and chromophoric dissolved organic matter have been released, thus providing information on phytoplankton dynamics. Moreover, the chlorophyll-a measurements have been used for cali- brating the satellite imagery.
... Temperature changes elicit algal physiological responses (Raven and Geider, 1988; Falkowski and Raven, 1997) and can affect species composition. Kirk (Kirk, 1994) suggested that low temperature is an important limiting factor of photosynthesis in lakes. ...
... When an electron is relaxed from a higher energy level to a lower energy level, there is a radiative emission of energy. Light is remitted when the relaxation to a lower energy state does not cause a change in the spin direction of the electron, or fluorescence is produced (Falkowski et al, 2007). The goal of this project was to analyze the average growth rates of the diatom Chaeotoceros muelleri under various light perturbation programs to help us better understand how these organisms maximize the use of solar energy. ...
The understanding of marine microalgae is important due to their significant contributions to the global environment. The standard balanced growth rates of two strains Trichodesmium sp. and Chaetoceros muelleri were found by exposing replicates of the strains to a standard "12 hour light, 12 hour dark" sinusoidal light treatment over a series of days. The growth was measured by fluorescence using an XE-PAM fluorometer. The standard growth is the typical growth of these two strains under optimal light circumstances. The next step was to expose the more successful algal strain to various fluctuating light regimes. Twelve replicates of Chaetoceros muelleri underwent four different light treatments (Figure 3): the basic 12 light, 12 dark sinusoidal light curve(light bank 2), step-function light program of 12 hours of exposed light with high and low light fluctuations every hour (light bank 3), step-function light program of 12 hours of exposed light with light fluctuations every 15 minutes (light bank 5), and a step-function light program of 12 hours of exposed light with fluctuations every 3 minutes (light bank 6). The variability of these light programs was to simulate the ocean's dynamic light environment. Three dilutions of all of the samples took place over the course of the experiment, and the average growth rate was calculated every day using the growth formula Nt=Noe µt . The grand growth rate mean (in relative units) across
... ) is tightly related to phytoplankton physiological parameters, the maximum photosynthetic rate (P max ) and the initial slope of the production versus irradiance (a) (e.g., Kirk, 1994; Falkowski and Raven, 1997). More recently, Huot et al. (2007) performed a stepwise regression analysis to examine which environmental parameter had more impact on P max and a estimates. ...
The chlorophyll a specific absorption coefficient of phytoplankton, a4 *(l) is an important parameter to determine for primary production models and for the estimation of phytoplankton physiological condition. Knowledge of this parameter at high latitudes where nutrient rich cold water submitted to low incident light is a common environment is almost nonexistent. To address this issue, we investigated the light absorption properties of phytoplankton as a function of irradiance, temperature, and nutrients using a large data set in the southern Beaufort Sea during the open water to ice cover transition period. The a4 *(l) tended to increase from autumn when open water still existed to early winter when sea ice cover was formed, resulting from a biological selection of smaller-size phytoplankton more efficient to absorb light. There was no significant correlation between a4 *(l) and irradiance or temperature for both seasons. However, a4 *(l) showed a significant positive correlation with NO3 þ NO2. Implications of the results for phytoplankton community adaptation to changing light levels are discussed.
... µmol·L –1 would also be limiting for most taxa (including some relatively efficient marine species) of 80% or less of maximum rates. Utilization of the more abundant NO 3 – could be additionally impeded by the effect of the lower mean irradiance in May on NO 3 – reductase activity (Falkowski and Raven 2007) and through competitive inhibition by NH 4 + (Dortch 1990). The situation in May, in comparison with June and September, could often be a state of temperature, light, and N colimitation , in which the elevated need for N cannot quite be met despite fairly high available N concentrations. ...
Variable fluorescence of chlorophyll a was measured by pulse amplitude modulated fluorometry to determine its relationship with measures of nutrient status and phytoplankton community structure in Lake Erie. In 2005, nitrogen (N) deficiency was most common in May, phosphorus (P) deficiency was most common in June, and neither were common in September. The maximum quantum yield (Fv/Fm) measured by pulse amplitude modulated fluorometry was lower in May and June than in September. The observed range of Fv/Fm included many values lower than previously reported in the lower Laurentian Great Lakes, while Fv/Fm values showed strong inverse correlations with indicators of N and (or) P deficiency. Community structure was also associated with nutrient status. Cyanobacteria were common at sites displaying N deficiency, while flagellates dominated P-deficient sites in all basins. N deficiency is surprising in a lake with generally high nitrate levels, but was supported by N debt, particulate C:N ratios and depressed Fv/Fm. Further work to characterize and compare results obtained with different variable fluorescence methodologies is desirable, but the present results support the belief that Fv/Fm can characterize nutrient deficiency of phytoplankton community in this large lake.
... Pigments are widely used to characterize phytoplankton physiological state, species identity and biomass in marine and freshwater environments (Falkowski and Raven, 1997). Variations in the relative proportions of accessory pigments also alter the shape of the absorption spectrum of phytoplankton (a ph (l)) (Bricaud et al., 2004). ...
A phytoplankton bloom was detected in the Southern California Current System, off the Baja California Peninsula (Mexico) on June 2003 with chlorophyll-a concentration (TChla) of 10.13 mg m−3. Two stations (D1 and D2) were sampled on June 24, and D2 was resampled 6 days later; chlorophyll-a concentration had decreased by about one half. LAC MODIS-Chla images were obtained and showed the spread of the bloom on the day after sampling. The phytoplankton community consisted primarily of dinoflagellate temporary cysts, mainly at the surface and at 5 m in station D1. Two Pseudo-nitzschia species (P. australis, P. seriata) were also very abundant. Samples from the bloom had a specific phytoplankton absorption coefficient (View the MathML source) lower than the rest of the samples. Values varied from 0.0186 to 0.0455 m2 mg−1 for View the MathML source(440) and from 0.0092 to 0.0294 m2 mg−1 for View the MathML source(675), with ratios View the MathML source(440): View the MathML source(675) ranging from 0.99 to 2.20. These low ratios were associated with the combined effect of packaging, and with the relatively high ratios of fucoxanthin, peridinin, diadinoxanthin and chlorophyll-c2 to TChla. Samples from the surface and 5 m depth at station D1 had higher ratios of Perid:TChla (0.12–0.32) than the rest of the samples, suggesting that cysts have similar Perid:TChla as free-living dinoflagellates. An unusual absorption spectrum with a broad maximum around 480–500 nm was associated with the high proportion of cysts and diatoms. The slope of the spectra between 443 and 488 nm was a good index to differentiate bloom samples containing high proportions of dinoflagellate temporary cysts. Further investigation of the absorption properties of dinoflagellate cysts is needed in order to detect these waters by remote sensing. Although much work is still necessary to understand and explain the bio-optical properties of a bloom, the present study is the first assessment off the Baja California coast to simultaneously consider aspects such as absorption properties, pigment composition and to include a spatial evaluation of the extension of a bloom with satellite images.
Using biochar to improve chromium-contaminated soil is a promising method. In this study, the Enteromorpha prolifera biochar was prepared at different temperatures (300 °C 700 °C), and rye pot experiment was conducted to examine the improvement effect of Enteromorpha prolifera biochar on the chromium-contaminated soils. The results showed that biochar could obviously promote the growth of rye in the chromium-contaminated soil. Compared with the control group, plant height, root length and biomass were increased, with the maximum increases of 38.9 %, 32.1 % and 34.7 %. The chlorophyll content was increased to 2.2 - 4.6 times, and the proline and peroxidase (POD) contents were significantly decreased, with maximum decreases of 72.8 % and 93.2 %. The Enteromorpha prolifera biochar prepared at 400 °C had a best effect on improvement of chromium-contaminated soil at the dose of 30 g·kg ⁻¹ . The biochar effectively alleviated the stress from Cr (VI), and promoted the growth and metabolism of rye.
Although open outdoor pond systems are the most economically viable option for mass cultivation of algae as a biofuel source, such systems face a number of limitations. Open ponds experience environmental fluctuations (i.e., light levels, nutrient ratios, and temperature), invasion pressure by undesired algal species, pathogen infections, and herbivory by invading zooplankton, all of which may negatively influence the system's overall harvestable yield. Using ecological principles to address the limitations of open-pond cultivation is a promising direction in algal biofuel research. This review surveys the growing body of work on these topics and offers a mechanistic framework for optimizing algal biofuel production while minimizing the negative effects of invasion, infection, and herbivory. High levels of productivity (in terms of biomass and lipids) are crucial for viable biofuel production and can be achieved by increasing algal diversity and assembling communities based on species' eco-physiological traits. Herbivory can be significantly reduced by choosing algal species resistant to grazing or by introducing biotic controls on herbivores. Diverse assemblages of algal species can be constructed to fill in the available ecological niche space, leading not only to high productivity but also reduced invasibility by undesired strains and potentially reduced susceptibility to algal diseases. Optimization of the mass cultivation of algae requires an interdisciplinary approach that includes using ecological principles for designing productive, resistant, and resilient algal communities.
High rates of primary production support the great animal biodiversity of the Gulf of California. One of the main limitations to estimate total (PT) and new (PNEW) primary production by 14C and 15N bottle incubations, respectively, is the small number of point samples generated for a particular area, and with very poor time coverage. Satellite ocean color sensors offer an alternative to estimate phytoplankton production rates in the oceans with an ample spatial-temporal variability that is not possible to cover with research vessels. With ocean color sensors in orbit, scientific expectations remain to improve ocean primary production models. Parameters used by these algorithms fall into three categories: environmental, ecological, and physiological. A review is given on studies that have generated information on these parameters for Gulf of California waters, and opportunities for new research are highlighted. Satellite surface pigment (Chls) and irradiance data (PARsat) need to be associated to vertical profiles (Chlz and PARz) generated with a Gaussian distribution function and Lambert-Beer's law, respectively. A detailed description is given of the parameters that characterize this Gaussian function and a vertical attenuation coefficient of PAR variable with z, for different seasons and regions within the Gulf of California. The weakest part of modeling primary production are the photosynthesis-ir-radiance (P-E) curve parameters: the initial slope, assimilation number, and quantum efficiency, and these give us an opportunity for new research. Summer data to characterize all the set of parameters needed for modeling primary production based on satellite data are the scarcest.
Four wave-propelled autonomous vehicles (Wave Gliders) instrumented with a variety of oceanographic and meteorological sensors were launched from San Francisco, CA in November 2011 for a trans-Pacific (Pac-X) voyage to test platform endurance. Two arrived in Australia, one in Dec 2012 and one in February 2013, while the two destined for Japan both ran into technical difficulties and did not arrive at their destination. The gliders were all equipped with sensors to measure temperature, salinity, turbidity, oxygen, and both chlorophyll and oil fluorescence. Here we conduct an initial assessment of the data set, noting necessary quality control steps and instrument utility. We conduct a validation of the Pac-X dataset by comparing the glider data to equivalent, or near-equivalent, satellite measurements. Sea surface temperature and salinity compared well to satellite measurements. Chl fluorescence from the gliders was more poorly correlated, with substantial between glider variability. Both turbidity and oil CDOM sensors were compromised to some degree by interfering processes. The well-known diel cycle in chlorophyll fluorescence was observed suggesting that mapping physiological data over large scales is possible. The gliders captured the Pacific Ocean's major oceanographic features including the increased chlorophyll biomass of the California Current and equatorial upwelling. A comparison of satellite sea surface salinity (Aquarius) and glider-measured salinity revealed thin low salinity lenses in the southwestern Pacific Ocean. One glider survived a direct passage through a tropical cyclone. Two gliders traversed an open ocean phytoplankton bloom; extensive spiking in the chlorophyll fluorescence data is consistent with aggregation and highlights another potential future use for the gliders. On long missions, redundant instrumentation would aid in interpreting unusual data streams, as well as a means to periodically image the sensor heads. Instrument placement is critical to minimize bubble-related problems in the data.
The partitioning of organic matter (OM) between dissolved and particulate phases is an important factor in determining the fate of organic carbon in the ocean. Dissolved organic matter (DOM) release by phytoplankton is a ubiquitous process, resulting in 2–50% of the carbon fixed by photosynthesis leaving the cell. This loss can be divided into two components: passive leakage by diffusion across the cell membrane and the active exudation of DOM into the surrounding environment. At present there is no method to distinguish whether DOM is released via leakage or exudation. Most explanations for exudation remain hypothetical; as while DOM release has been measured extensively, there has been relatively little work to determine why DOM is released. Further research is needed to determine the composition of the DOM released by phytoplankton and to link composition to phytoplankton physiological status and environmental conditions. For example, the causes and physiology of phytoplankton cell death are poorly understood, though cell death increases membrane permeability and presumably DOM release. Recent work has shown that phytoplankton interactions with bacteria are important in determining both the amount and composition of the DOM released. In response to increasing CO2 in the atmosphere, climate change is creating increasingly stressful conditions for phytoplankton in the surface ocean, including relatively warm water, low pH, low nutrient supply and high light. As ocean physics and chemistry change, it is hypothesized that a greater proportion of primary production will be released directly by phytoplankton into the water as DOM. Changes in the partitioning of primary production between the dissolved and particulate phases will have bottom-up effects on ecosystem structure and function. There is a need for research to determine how these changes affect the fate of organic matter in the ocean, particularly the efficiency of the biological carbon pump.
Phytoplankton, such as diatoms, experience great variations of photon flux density (PFD) and light spectrum along the marine water column. Diatoms have developed some rapidly-regulated photoprotective mechanisms, such as the xanthophyll cycle activation (XC) and the non-photochemical chlorophyll fluorescence quenching (NPQ), to protect themselves from photooxidative damages caused by excess PFD. In this study, we investigate the role of blue fluence rate in combination with red radiation in shaping photoacclimative and protective responses in the coastal diatom Pseudo-nitzschia multistriata. This diatom was acclimated to four spectral light conditions (blue, red, blue-red, blue-red-green), each of them provided with low and high PFD. Our results reveal that the increase in the XC pool size and the amplitude of NPQ is determined by the blue fluence rate experienced by cells, while cells require sensing red radiation to allow the development of these processes. Variations in the light spectrum and in the blue versus red radiation modulate either the photoprotective capacity, such as the activation of the diadinoxanthin-diatoxanthin xanthophyll cycle, the diadinoxanthin de-epoxidation rate and the capacity of non-photochemical quenching, or the pigment composition of this diatom. We propose that spectral composition of light has a key role on the ability of diatoms to finely balance light harvesting and photoprotective capacity.
Interpretation of remote sensing reflectance from coastal waters at different wavelengths of light yields valuable information about water column constituents, which in turn, gives information on a variety of processes occurring in coastal waters, such as primary production, biogeochemical cycles, sediment transport, coastal erosion, and harmful algal blooms. The Hyperspectral Infrared Imager (HyspIRI) is well suited to produce global, seasonal maps and specialized observations of coastal ecosystems and to improve our understanding of how phytoplankton communities are spatially distributed and structured, and how they function in coastal and inland waters. This paper draws from previously published studies on high-resolution, hyperspectral remote sensing of coastal and inland waters and provides an overview of how the HyspIRI mission could enable the retrieval of new aquatic biophysical products or improve the retrieval accuracy of existing satellite-derived products (e.g., inherent optical properties, phytoplankton functional types, pigment composition, chlorophyll-a concentration, etc.). The intent of this paper is to introduce the development of the HyspIRI mission to the coastal and inland remote sensing community and to provide information regarding several potential data products that were not originally part of the HyspIRI mission objectives but could be applicable to research related to coastal and inland waters. Further work toward quantitatively determining the extent and quality of these products, given the instrument and mission characteristics, is recommended.
Oxygenic photosynthesis evolved over 2.4 billion years ago under conditions
where maximum efficiency was not a major selection pressure. Today, the most
efficient photosynthetic organisms under natural conditions are the land plants.
Algae and cyanobacteria, living under light-limited conditions and reliant on
high stirring rates for maximum carbon fixation rates, are generally less efficient
but offer possibilities in the future: perhaps upwards of 5% efficiency after
molecular improvement. Solar photovoltaic panels and solar thermal collectors,
however, offer an improved means of collecting solar energy compared
with the maximum 1–2% efficiency of plants, algae and cyanobacteria at the
present time. Nevertheless, in a world where petroleum products become
scarce, natural photosynthesis will become increasingly used for the production
of biofuels and organic products, but it seems unlikely that algae and cyanobacteria
will be used as a source of bioenergy. In the longer-term, photobiohydrogen
production and artificial photosynthesis offer much greater hope
for very efficient conversion of solar energy.
Fossil fuel depletion and attempts of global warmin
g mitigation have motivated the development of
biofuels. Several feedstock and transformation path
ways into biofuel have been proposed as an
alternative to usual fuels. Recently, microalgae ha
ve attracted a lot of attention because of the
promise of reduced competition with food crop and l
owered environmental impacts. Over the last
years, several Life Cycle Assessments have been rea
lised to evaluate the energetic benefit and Global
Warming Potential reduction of biofuel and bioenerg
y produced from microalgae. This chapter
presents a bibliographic review of fifteen LCA of m
icroalgae production and/or transformation into
biofuel. These studies differ often by the perimete
r of the study, the functional unit and the
production technologies or characteristics. Methods
for the environmental impacts assessment and
the energy balance computation also diverge. This r
eview aims at identifying the main options and
variations between LCAs and concludes by some recom
mendations and guidelines to improve the
contribution of an LCA and to facilitate the compar
ison between studies.
The rise of land plants during the early Palaeozoic had profound effects upon subsequent Earth history and evolution. The sequestration of standing biomass and carbon burial caused a primary shift in the distribution of active carbon within the biosphere and surficial Earth systems. This manifested itself in a dynamic decline in pCO 2 during Silurian-Devonian time, affecting both terrestrial and marine ecosystems. We examined first-order correlations between terrestrialization and pCO 2 by comparing the GEOCARB III data with time-constrained fossil events in the early evolution of land plants. We compared the same GEOCARB III data with the species/genus richness of lower Palaeozoic acritarchs. The correlation between the rise of woody plants and pCO 2 is built into the GEOCARB model for the Late Devonian and later, but pCO 2 begins to decline in the Cambrian long before the origin of woody trees (lignophytes). The influence of early phases in plant evolution may be seen in a two-stage pCO 2 decline corresponding to fossil evidence for the origin of thalloid bryophytes in the Middle Cambrian and the origin of tracheophytes near the Ordovician-Silurian boundary. The decline of the acritarchs shows a highly correlated lag of about 10 Ma with respect to the pCO 2 decline. The relation between pCO 2 and acritarch species richness suggests a tight coupling between the evolution of the marine phytoplankton and atmospheric CO 2, supporting previous suggestions that pCO 2 was a significant causal factor in the near extinction of acritarchs by the end of the Devonian.
Despite many advances in research on photosynthetic carbon fixation in marine diatoms, the biophysical and biochemical mechanisms of extracellular polysaccharide production remain significant challenges to be resolved at the molecular scale in order to proceed toward an understanding of their functions at the cellular level, as well as their interactions and fate in the ocean. This review covers studies of diatom extracellular polysaccharides using atomic force microscopy (AFM) imaging and the quantification of physical forces. Following a brief summary of the basic principle of the AFM experiment and the first AFM studies of diatom extracellular polymeric substance (EPS), we focus on the detection of supramolecular structures in polysaccharide systems produced by marine diatoms. Extracellular polysaccharide fibrils, attached to the diatom cell wall or released into the surrounding seawater, form distinct supramolecular assemblies best described as gel networks. AFM makes characterization of the diatom polysaccharide networks at the micro and nanometric scales and a clear distinction between the self-assembly and self-organization of these complex systems in marine environments possible.
Increasing trends in global warming already evident, the likelihood of further rise continuing, and their impacts give urgency to addressing carbon sequestration technologies more coherently and effectively. Carbon dioxide (CO2) is responsible for over half the warming potential of all greenhouse gases (GHG), due to the dependence of world economies on fossil fuels. The processes involving CO2 capture and storage (CCS) are gaining attention as an alternative for reducing CO2 concentration in the ambient air. However, these technologies are considered as short-term solutions, as there are still concerns about the environmental sustainability of these processes. A promising technology could be the biological capture of CO2 using microalgae due to its unmatched advantages over higher plants and ocean fertilization. Microalgae are phototrophic microorganisms with simple nutritional requirements, and comprising the major primary producers on this planet. Specific pathways include autotrophic production via both open pond or closed photobioreactor (PBR) systems. Photosynthetic efficiency of microalgae ranged from 10–20 % in comparison with 1–2 % of most terrestrial plants. Some algal species, during their exponential growth, can double their biomass in periods as short as 3.5 hours. Moreover, advantage of being tolerant of high concentration of CO2 (flue gas), low light intensity requirements, environmentally sustainable, and co-producing added value products put these as the favoured organisms. Advantages of microalgae in comparison with other sequestration methodologies are discussed, which includes the cultivation systems, the key process parameters, wastewater treatment, harvesting and the novel bio-products produced by microalgal biomass.
Marine primary production is a fundamental measure of the ocean's capacity to convert carbon dioxide to particulate organic carbon for the marine foodweb, and as such is an essential variable used in ecosystem and biogeochemical models to assess trophic dynamics and carbon cycling. The Sub-Antarctic Zone (SAZ) is a major sink for atmospheric carbon and exhibits large gradients in ocean conditions on both temporal and spatial scales. In this dynamic system, an understanding of small-scale temporal changes is critical for modelling primary production at larger scales. Thus, we investigated diel effects on maximum quantum yield of PSII (FV/FM), photosynthetic pigment pools and primary productivity in the western (Diel 1) and eastern SAZ region (Diel 3) south of Tasmania, Australia, and compared this to a station at the polar front (Diel 2). Phytoplankton in the eastern SAZ had the greatest diel response, with cells showing decreased FV/FM and increased biosynthesis and transformation of xanthophyll and other photoprotective pigments during the day, but only in the surface waters (0 and 10 m). Diel responses diminished by 30 m. Cells in the western SAZ had similar responses across the depths sampled, increasing their FV/FM during the night and increasing their xanthophyll pigment content during the day. Phytoplankton at the polar front (Diel 2) showed intermediate diel-related variations in photophysiology, with xanthophyll conversion and increases in photoprotective pigments during the day but constant FV/FM. These diel changes at all sampling stations had little impact on carbon fixation rates, although cells sampled from the deep chlorophyll maximum at the polar front had significantly lower maximum carbon fixation and minimum saturating irradiance (Ek) compared to the other depths and stations. Considering the oceanographic context, cells at Diel 1 and 2 received less light and were more deeply mixed than cells at Diel 3, causing a dampening of the diel response. These results highlight that phytoplankton in the SAZ is regulated by the physical processes of mixing and light provision, but short-term diel effects on maximum quantum yield of PSII and photoprotective pigments may not propagate to changes in carbon fixation, particularly when cells are nutrient replete. If however, the more stratified eastern SAZ (which had the greatest diel responses) is indicative of how the SAZ region might respond to climate change, then diel effects may become more prominent in the future.
Kelps of the genus Laminaria accumulate iodine at high concentrations, but the iodine retaining capacity can be affected by emersion and physiological stress. In this study, I2 emission into the atmosphere from Laminaria digitata and Laminaria hyperborea was compared under controlled low irradiances and temperatures. The two species exhibited different I2 emission rates as blades of L. digitata emitted I2 at rates five times higher than those from newly-grown blades (current growth season) of L. hyperborea. I2 emission was not detectable from old blades (previous growth season) of L. hyperborea. Additionally, effects of irradiance and temperature on both I2 emission into air and net I(-) release into seawater where assessed for L. digitata while monitoring photo-physiological parameters as stress indicators. Irradiances between 30 and 120 μmol photons m(-2) s(-1) had only marginal effects on both I2 emission and I(-) release rates, but physiological stress, indicated by photoinhibition, was observed. The results suggest that the irradiances applied here were not stressful enough to impact on the iodine release. By contrast, at elevated temperatures (20 °C), photoinhibition was accompanied by an increase in I2 emission rates, but net I(-) release rates remained similar at 10-20 °C. High I2 emission rates into air and I(-) release into seawater observed from L. digitata underpin the fundamental function of this kelp as mediator of coastal iodine fluxes.
Phytoplankton is acknowledged to be a very diverse source of bioactive molecules. These compounds play physiological roles that allow cells to deal with changes of the environmental constrains. For example, the diversity of light harvesting pigments allows efficient photosynthesis at different depths in the seawater column. Identically, lipid composition of cell membranes can vary according to environmental factors. This, together with the heterogenous evolutionary origin of taxa, makes the chemical diversity of phytoplankton compounds much larger than in terrestrial plants. This contribution is dedicated to pigments and lipids synthesized within or from plastids/photosynthetic membranes. It starts with a short review of cyanobacteria and microalgae phylogeny. Then the bioactivity of pigments and lipids (anti-oxidant, anti-inflammatory, anti-mutagenic, anti-cancer, anti-obesity, anti-allergic activities, and cardio- neuro-, hepato- and photoprotective effects), alone or in combination, is detailed. To increase the cellular production of bioactive compounds, specific culture conditions may be applied (e.g., high light intensity, nitrogen starvation). Regardless of the progress made in blue biotechnologies, the production of bioactive compounds is still limited. However, some examples of large scale production are given, and perspectives are suggested in the final section.
The natural leaf provides a superior template for engineering the artificial leaf in order to perform light energy conversion. To adapt to the aquatic environments, the aquatic plant leaves usually are thin and soft with excellent mass transportation and light-harvesting capability. In this report, the aquatic leaf is directly employed as a template to construct bioinspired hierarchical photocatalyst while mesoporous directing agent act as a second template. The dual templates consequently ensure the obtained TiO2 with optimal light harvesting structure, high surface area and excellent mass transportation, which contribute to improve photocatalytic capability. Specially, SiO2 is also introduced to form TiO2–SiO2 composite in the final hierarchical replica in order to improve the stability of mesostructures, perfect replication of leaves' fine structures and the dye adsorption capability for facilitating photodegradation. Consequently, the photocatalytic activity of the as-synthesized leaf replicas in the photodegradation of methylene blue is ca. 3 times higher than that of P25, and one order of magnitude higher than that of common nanocrystalline TiO2, under commercial black lamp irradiation.
In this study, we presented the most commonly employed net photosynthetic light-response curves (P
N/I curves) fitted by the Solver function of Microsoft Excel. Excel is attractive not only due to its wide availability as a part of the Microsoft Office suite but also due to the increased level of familiarity of undergraduate students with this tool as opposed to other statistical packages. In this study, we explored the use of Excel as a didactic tool which was built upon a previously published paper presenting an Excel Solver tool for calculation of a net photosynthetic/chloroplastic CO2-response curve. Using the Excel spreadsheets accompanying this paper, researchers and students can quickly and easily choose the best fitted P
N/I curve, selecting it by the minimal value of the sum of the squares of the errors. We also criticized the misuse of the asymptotic estimate of the maximum gross photosynthetic rate, the light saturation point estimated at a specific percentile of maximum net photosynthetic rate, and the quantum yield at zero photosynthetic photon flux density and we proposed the replacement of these variables by others more directly linked to plant ecophysiology.
This chapter describes the basics of ocean color remote sensing. It includes a description to obtain and use SeaWiFS data within NASA's freely available ocean color remote sensing software. Differences in methodology and some of the more recent developments in the optical remote sensing field are described. By exploring how light penetrates the water column and how the optical constituents affects the light as it travels through the water, the basic understanding of the value and limitations of ocean color data is provided. Remote sensing provides a tool that can provide information over time/space scales not possible using traditional sampling approaches from ships. SeaWiFS data can be acquired from NASA's Distributed Active Archive Center [DAAC], and can be ordered online. SeaWiFS is a commercial instrument flying on Orbimage's Orbview-2 spacecraft. Apart from the other image processing packages available, the chapter describes SeaDAS, as it is free and can be used with a currently operational satellite sensor (SeaWiFS). There are many other ocean color satellites being planned (and one that has just been launched), but the data streams are not currently available.
We suggest a way to estimate phytoplankton respiration separately from heterotrophic respiration. The analysis is based on three findings: (1) that carbon loss in the plankton overnight is mostly phytoplankton respiration; (2) that uptake of 14C estimates net primary production; and (3) that phytoplankton respiration occurs during the day at the same rate as at night. Based on these three findings, we propose that phytoplankton respiration can be estimated as twice the overnight loss of organic carbon. Heterotrophic respiration is then the difference between phytoplankton and total community respiration.
It is speculated that differences in coral bleaching susceptibility may be influenced by the genotype of in hospite Symbiodinium and their differential responses to bleaching stressors. Photoinhibition of photosystem II (PSII), damage to the D1 (psbA)
PSII reaction centre protein and production of reactive oxygen species by in hospite Symbiodinium are likely precursors of coral bleaching. In order to assess whether photorepair rates of in hospite Symbiodinium underlie the bleaching susceptibility of their hosts, photoinhibition (net and gross), photoprotection and photorepair rates
were assessed in a bleaching-‘tolerant’ coral (P. astreoides) and a bleaching-‘sensitive’ coral (M. faveolata) using non-invasive fluorometric techniques and by blocking de novo synthesis of psbA. Previous studies using such techniques
have demonstrated that in vitro Symbiodinium types ‘sensitive’ to bleaching stressors had reduced rates of photorepair relative to ‘tolerant’ Symbiodinum types. Our measurements demonstrated that Symbiodinium in the more bleaching tolerant P. astreoides had higher photorepair rates than Symbiodinium in M. faveolata. Higher repair rates in P. astreoides resulted in lower net photoinhibition relative to M. faveolata, where both corals exhibited similar susceptibility to photodamage (gross photoinhibition). Photoprotective mechanisms were
observed in both corals; M. faveolata exhibited higher antennae-bed quenching than P. astreoides at low-light intensities, but at and above light-saturating intensities, which are different for each coral species, P. astreoides displayed more efficient non-photochemical quenching (Stern–Volmer quenching) of chlorophyll fluorescence than M. faveolata. Increased NPQ by P. astreoides at E/E
k ≥ 1 was not driven by antennae-bed quenching. The ability of in hospite Symbiodinium in P. astreoides to mitigate the effects of photoinhibition under high light conditions compared with Symbiodinium in M. faveolata, and their high repair capacity following photoinhibition, may be a key factor to consider in future bleaching studies and
may underlie the relative bleaching tolerance of P. astreoides compared to M. faveolata.
Iron is the quantitatively most important trace metal involved in thylakoid reactions of all oxygenic organisms since linear (= non-cyclic) electron flow from H2O to NADP+ involves PS II (2–3 Fe), cytochrome b6-f (5 Fe), PS I (12 Fe), and ferredoxin (2 Fe); (replaceable by metal-free flavodoxin in certain cyanobacteria and algae under iron deficiency). Cytochrome c6 (1 Fe) is the only redox catalyst linking the cytochrome b6-f complex to PS I in most algae; in many cyanobacteria and Chlorophyta cytochrome c6 and the copper-containing plastocyanin are alternatives, with the availability of iron and copper regulating their relative expression, while higher plants only have plastocyanin. Iron, copper and zinc occur in enzymes that remove active oxygen species and that are in part bound to the thylakoid membrane. These enzymes are ascorbate peroxidase (Fe) and iron-(cyanobacteria, and most al gae) and copper-zinc- (some algae; higher plants) superoxide dismutase. Iron-containing NAD(P)H-PQ oxidoreductase in thylakoids of cyanobacteria and many eukaryotes may be involved in cyclic electron transport around PS I and in chlororespiration. Manganese is second to iron in its quantitative role in the thylakoids, with four Mn (and 1 Ca) per PS II involved in O2 evolution. The roles of the transition metals in redox catalysts can in broad terms be related to their redox chemistry and to their availability to organisms at the time when the pathways evolved. The quantitative roles of these trace metals varies genotypically (e.g. the greater need for iron in thylakoid reactions of cyanobacteria and rhodophytes than in other O2-evolvers as a result of their lower PS II:PS I ratio) and phenotypically (e.g. as a result of variations in PS II:PS I ratio with the spectral quality of incident radiation).
A comparison of photosynthesis-irradiance response curves (P–E response curves) obtained through fast repetition rate (FRR) fluorometry and radiocarbon (14C) tracer method was made in the chlorophyte, Dunaliella tertiolecta, grown under different irradiance conditions. In FRR-based P–E response curve experiments, actinic light provided by white light-emitting diodes (LEDs) was increased gradually from 0 to
1500 μmol quanta m−2 s−1 and the rate of photosynthetic electron transport was determined at each light level. Short-term experiments (20 min) of
14C-based P–E response curve were carried out with an improved photosynthetron, which contains white LEDs as the light source. Irrespective
of growth irradiance, the ratios of FRR to 14C-based initial slopes were almost uniform. The ratios of FRR- to 14C-based maximum rates were 25–36% higher than those of FRR- to 14C-based initial slopes. The relationship between electron transport and carbon assimilation was non-linear with increasing
discrepancy towards high actinic light. This non-linear relationship between FRR- and 14C-based estimates is primarily due to the effect of physiological processes stimulated at high levels of light, such as cyclic
electron flow and the Mehler reaction. The results of this study indicate that the FRR fluorometry can be used as a good indicator
of photosynthetic rates from low to middle light levels, but becomes increasingly questionable as the maximum photosynthetic
rate is approached. The degree to which this relationship is further affected by nutrient-status warrants investigation.
Seagrasses are considered important indicators of decline in water quality resulting in increased light attenuation that negatively influences their growth and survival. Chronic light-limitation interspersed with unpredictable acute attenuation events have had poorly understood effects on seagrass recovery dynamics. Zostera marina (eelgrass) and Halodule wrightii (shoalgrass) were subject to a matrix of light-deprivation events followed by recovery periods to mimic repeated acute shading events. Plant survival, morphology, biomass, chlorophyll content, and Fv/Fm were assessed over time to determine recovery. At the end of the experiment, all plants were harvested and species-specific treatment effects were determined. Significant differences due to treatments were noted in all parameters measured. In general, responses were similar for both life-stages and between species, suggesting similar physiological tolerance to repeated acute light-attenuation events. Only plants in treatments where light-deprivation was followed by a recovery interval of at least the same duration showed signs of long-term survival. Chlorophyll fluorescence (Fv/Fm) was an important metric for assessing recovery, but it failed to detect the onset of mortality in many plants. Other metrics of plant condition need to be assessed and coupled with chlorophyll fluorescence data to assess seagrass “health”. This is of particular importance in field studies, where the history of the plants is largely unknown.
The Coorong, Lower Lakes (Lake Alexandrina and Lake Albert) and Murray Mouth, is one of Australia’s largest estuaries, at the terminal end of Australia’s two longest rivers. This unique area of the Murray basin also has significant value in terms of indigenous heritage, commercial and recreational fishing, water sports and tourism. There is a paucity of data on primary productivity and nutrient cycles in the Coorong and Murray Mouth. This study was undertaken to map seasonal variations in primary production along a salinity gradient in the Coorong and the Murray Mouth. Very low values were obtained for phytoplankton productivity using the dissolved oxygen technique during the first two sampling times (September and November 2007). An underestimation of gross productivity is suspected resulting from sensitivity issues with the oxygen-based technique in low productivity conditions, coupled with significant community respiration occurring. Consequently, in April 2007, both the 14C technique and dissolved oxygen technique were used to measure phytoplankton productivity. Comparison of phytoplankton productivity indicated that measurements made using the 14C technique were approximately ten times higher than gross productivity using the dissolved oxygen technique at the three study sites. In April 2008, comparisons of phytoplankton productivity measurements using the 14C technique with net phytobenthic productivity indicated that phytoplankton productivity could be significant at Jack Point. However, this needs to be verified further with more sites and sampling times using the 14C technique.
Phytoplankton productivity in April 2008 ranged from 0.7 (Mundoo Channel) to 7.4 mgC m 2 h-1 (Jack Point). On the other hand, net phytobenthic productivity ranged from 7.67 ± 0.70 mgC m-2 h-1 (mean SE; Mundoo Channel; September 2007) to 24.86 ± 1.06 mgC m-2 h-1 (Noonameena; April 2008). Phytobenthic community respiration ranged from 12.76 ± 1.43 mgC m-2 h-1 (Jack Point; September 2007) to 33.48 ± 11.70 mgC m-2 h-1 (Mundoo Channel; September 2007). There was significant interaction between sampling times and sites for phytobenthic productivity and for phytobenthic respiration, significant differences were found for sites. While it is evident from the present study that the phytobenthic component is dominant, it is also hypothesized that there is heterotrophic productivity in the water column and sediments, which could also be a significant driver of the ecosystem processes in the Coorong and the Murray Mouth.
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Net primary productivity (NPP) fields, derived from satellite observations of ocean color, are commonly published without relevant information on uncertainties. In this study, we assessed the uncertainty in NPP estimates of the Vertically Generalized Productivity Model using a Monte Carlo approach. We did not consider the uncertainty stemming from the basic model formulation, but restricted the uncertainty analysis to input terms, which were generated by, or related to, remote sensing. The study was based on global monthly remote sensing data from 2005. We found that the typical distribution of uncertainty around the model output could be approximated by a lognormal probability density function. On average, NPP value in a grid cell was overestimated by 6%, relative to the mean of the corresponding uncertainty distribution. The random component of uncertainty in NPP, expressed as the coefficient of variation, amounted to an average of 108%. The systematic positive errors in individual grid cells built up to an overestimate of 2.5Pg C in the annual global NPP of 46.1Pg C. The largest individual contributor to the random uncertainty in NPP was the input term that describes the physiological state of phytoplankton. However, the biggest contribution to the systematic uncertainty in the model output came from the parameter that represents changes in the rate of chlorophyll-normalized photosynthesis with depth. Therefore, improvements in the accuracy of these two terms would have the largest potential to decrease the input-related uncertainty in the model NPP estimates.
The limited knowledge we have about red algal genomes comes from the highly specialized extremophiles, Cyanidiophyceae. Here, we describe the first genome sequence from a mesophilic, unicellular red alga, Porphyridium purpureum. The 8,355 predicted genes in P. purpureum, hundreds of which are likely to be implicated in a history of horizontal gene transfer, reside in a genome of 19.7 Mbp with 235 spliceosomal introns. Analysis of light-harvesting complex proteins reveals a nuclear-encoded phycobiliprotein in the alga. We uncover a complex set of carbohydrate-active enzymes, identify the genes required for the methylerythritol phosphate pathway of isoprenoid biosynthesis, and find evidence of sexual reproduction. Analysis of the compact, function-rich genome of P. purpureum suggests that ancestral lineages of red algae acted as mediators of horizontal gene transfer between prokaryotes and photosynthetic eukaryotes, thereby significantly enriching genomes across the tree of photosynthetic life.
Marine organisms in the pelagic realm regulate the fluxes of many important ma jor elements between the atmosphere and the upper ocean, and between the upper ocean and the deep ocean. In this chapter, we review the main components of the pelagic ecosystem and how they relate to biogeochemical cycles, including some aspects of the nitrogen cycle, dimethylsulfide production, and more particularly the carbon cycle. Scientific approaches and tools developed to determine the abun dance and distribution of planktonic organisms and to assess their contribution to biogeochemical processes are also presented through related parts of the chapter.
Marine diatoms are important primary producers that thrive in diverse and dynamic environments. They do so, in theory, by sensing changing conditions and adapting their physiology accordingly. Using the model species Thalassiosira pseudonana, we conducted a detailed physiological and transcriptomic survey to measure the recurrent transcriptional changes that characterize typical diatom growth in batch culture. Roughly 40% of the transcriptome varied significantly and recurrently, reflecting large, reproducible cell-state transitions between four principal states: (i) "dawn," following 12 h of darkness; (ii) "dusk," following 12 h of light; (iii) exponential growth and nutrient repletion; and (iv) stationary phase and nutrient depletion. Increases in expression of thousands of genes at the end of the reoccurring dark periods (dawn), including those involved in photosynthesis (e.g., ribulose-1,5-bisphosphate carboxylase oxygenase genes rbcS and rbcL), imply large-scale anticipatory circadian mechanisms at the level of gene regulation. Repeated shifts in the transcript levels of hundreds of genes encoding sensory, signaling, and regulatory functions accompanied the four cell-state transitions, providing a preliminary map of the highly coordinated gene regulatory program under varying conditions. Several putative light sensing and signaling proteins were associated with recurrent diel transitions, suggesting that these genes may be involved in light-sensitive and circadian regulation of cell state. These results begin to explain, in comprehensive detail, how the diatom gene regulatory program operates under varying environmental conditions. Detailed knowledge of this dynamic molecular process will be invaluable for new hypothesis generation and the interpretation of genetic, environmental, and metatranscriptomic data from field studies.
We present a mathematical model based on differential equations describing the dynamics of nitrogen (NH4+, NO2-, NO3- and organic nitrogen in phytoplankton) in ponds of white shrimp (Litopenaeus vannamei), with low salinity and zero turnovers, from planting to harvest. The model predicts the results of commercial production in three ponds. We show that this culture system, without replacement, retains the nitrogen and shrimp produced a lower feed conversion in comparison with systems with replacement. The model can be used to define strategies for improved performance.
Instrumentation measuring hyperspectral particle attenuation and absorption was used to assess particle concentration and size, chlorophyll, and spectral characteristics as a function of depth in four temperate lakes of different trophy. Partitioning the absorption coefficient permitted us to analyze properties of phytoplankton absorption as a function of ambient illumination and hydrographic conditions. Stratification was found to be a controlling factor in the size distribution and concentration of particles. Bloom cycles (chlorophyll > 10 mg m−3) were observed to evolve over several weeks but on occasion did change rapidly. Total chlorophyll concentration revealed the majority of the lakes did not follow the typical seasonal succession of biomass associated with temperate waters. Particle and chlorophyll concentration maxima did not always coincide, cautioning the use of chlorophyll a as a surrogate for algal biomass. Phytoplankton near the base of the euphotic zone, including a deep chlorophyll maximum in an oligotrophic system, were found to exhibit significant chromatic adaptation. Unique absorption peaks identified the ubiquitous presence of cyanobacteria in all four lakes. Finally, particle resuspension and possible nepheloid layers were observed in the two smallest lakes.
Marine phytoplankton, the photosynthetic microorganisms drifting in the illuminated waters of our planet, are extremely diverse, being distributed across major eukaryotic lineages. About 5000 eukaryotic species have been described with traditional morphological methods, but recent environmental molecular surveys are unveiling an ever-increasing diversity, including entirely new lineages with no described representatives. Eukaryotic marine phytoplankton are significant contributors to major global processes (such as oxygen production, carbon fixation and CO 2 sequestration, nutrient recycling), thereby sustaining the life of most other aquatic organisms. In modern oceans, the most diverse and ecologically significant eukaryotic phytoplankton taxa are the diatoms, the dinoflagellates, the haptophytes and the small prasinophytes, some of which periodically form massive blooms visible in satellite images. Evidence is now accumulating that many phytoplankton taxa are actually mixotrophs, exhibiting alternate feeding strategies depending on environmental conditions (e.g. grazing on prey or containing symbiotic organisms), thus blurring the boundary between autotrophs and heterotrophs in the ocean.
In January 1999, unialgal cultures of the diatom Thalassiosira sp., solate from natural phyto-plankton assemblages from Potter Cove, Antarctica, were exposed to solar ultraviolet radiation (UVR, 280-400 nm) in order to study the long-term acclimation of this species. Ultraviolet radiation B (UVBR, 280-315 nm) inhibited the growth rate during the first and second days of exposure. No UVBR inhibition was observed on the third day. The initial content of α-tocopherol (13 pmol (10 4 cell) -1) showed a marked decrease during the exponential growth phase (4 pmol (10 4 cell -1) by day 3). The initial content of β-carotene (3 pmol (10 4 cell) -1) did not show significant differences over time in cells exposed to UVBR. Two mycosporine-like amino acids (MAAs) were identified: porphyra-334 and shinorine. Cellular concentrations of MAAs increased significantly on days 2 and 3, and exposure of the algae to UVBR significantly enhanced this value. The relative importance of MAAs concentration was significant (P < 0.05) in relation to the α-tocopherol content. A positive correlation was shown between cellular MAAs concentration and growth rate. Our results suggest that photoprotection against UV-induced damage is characterized by short-term consumption of α-tocopherol and longer-term synthesis of MAAs. The UVBR damage/repair ratio during long-term exposure involves the combined action of several endogenous factors within the cell, with MAAs synthesis being the most effective factor related to photoprotection.
Preface to the third edition Part I. The Underwater Light Field: 1. Concepts of hydrologic optics 2. Incident solar radiation 3. Absorption of light within the aquatic medium 4. Scattering of light within the aquatic medium 5. Characterizing the underwater light field 6. The nature of the underwater light field 7. Remote sensing of the aquatic environment Part II. Photosynthesis in the Aquatic Environment: 8. The photosynthetic apparatus of aquatic plants 9. Light capture by aquatic plants 10. Photosynthesis as a function of the incident light 11. Photosynthesis in the aquatic environment 12. Ecological strategies References and author index Index to symbols Index to organisms Index to water bodies Subject index.
Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography. © Cambridge University Press 2006 and 2009. All rights reserved.