Diatom Skeletonema Costatum Research Articles

Comparative Transcriptomic Analysis Reveals Novel Insights into the Adaptive Response of Skeletonema costatum to Changing Ambient Phosphorus.

Phosphorus (P) is a limiting macronutrient for diatom growth and productivity in the ocean. Much effort has been devoted to the physiological response of marine diatoms to ambient P change, however, the whole-genome molecular mechanisms are poorly understood. Here, we utilized RNA-Seq to compare the global gene expression patterns of a marine diatom Skeletonema costatum grown in inorganic P-replete, P-deficient, and inorganic- and organic-P resupplied conditions. In total 34,942 unique genes were assembled and 20.8% of them altered significantly in abundance under different P conditions. Genes encoding key enzymes/proteins involved in P utilization, nucleotide metabolism, photosynthesis, glycolysis, and cell cycle regulation were significantly up-regulated in P-deficient cells. Genes participating in circadian rhythm regulation, such as circadian clock associated 1, were also up-regulated in P-deficient cells. The response of S. costatum to ambient P deficiency shows several similarities to the well-described responses of other marine diatom species, but also has its unique features. S. costatum has evolved the ability to re-program its circadian clock and intracellular biological processes in response to ambient P deficiency. This study provides new insights into the adaptive mechanisms to ambient P deficiency in marine diatoms.

Antialgal and antilarval activities of bioactive compounds extracted from the marine dinoflagellate Amphidinium carterae

With the global ban on the application of organotin-based marine coatings by the International Maritime Organization, the development of environmentally friendly, low-toxic and nontoxic antifouling compounds for marine industries has become an urgent need. Marine microorganisms have been considered as a potential source of natural antifoulants. In this study, the antifouling potential of marine dinoflagellate Amphidinium carterae, the toxic and red-tide microalgae, was investigated. We performed a series of operations to extract the bioactive substances from Amphidinium carterae and tested their antialgal and antilarval activities. The crude extract of Amphidinium carterae showed significant antialgal activity and the EC50 value against Skeletonema costatum was 55.4 μg mL−1. After purification, the isolated bioactive substances (the organic extract C) exhibited much higher antialgal and antilarval activities with EC50 of 12.9 μg mL−1 against Skeletonema costatum and LC50 of 15.1 μg mL−1 against Amphibalanus amphitrite larvae. Subsequently, IR, Q-TOFMS, and GC-MS were utilized for the structural elucidation of the bioactive compounds, and a series of unsaturated and saturated 16- to 22-carbon fatty acids were detected. The data suggested the bioactive compounds isolated from Amphidinium carterae exhibited a significant inhibiting effect against the diatom Skeletonema costatum and Amphibalanus amphitrite larvae, and could be substitutes for persistent, toxic antifouling compounds.

Growth and biochemical responses of Skeletonema costatum to petroleum contamination

Clonal populations of the diatom Skeletonema costatum isolated from Lake Pontchartrain (Louisiana, USA) near the 2010 Deepwater Horizon oil release were exposed to uncontaminated f/2 medium or light slop oil emulsified (O-E; 25, 50, 75, 100 % of initial levels) in f/2 during short- (10 day) and long-term (21 day) incubations. During 10-day incubations, inhibition of logarithmic growth slopes occurred in the most severely contaminated populations (75, 100 % O-E f/2). Growth in oil-contaminated populations was reduced during 21-day incubations, and growth rates for all populations converged by ca. day 12. Additionally, total cell lipid contents for populations exposed to uncontaminated and contaminated media differed, and mean values for control populations were ca. 2-fold greater than populations maintained in 100 % O-E f/2 medium. Saturated and unsaturated cellular lipids in uncontaminated populations were greater than in petroleum-contaminated populations. Relative cellular fatty acids abundances and RuBisCO RNA transcript copy numbers, proxies for food storage and cellular stress, and mRNA transcript regulation influencing photosynthesis, respectively, were altered half-way through the long-term incubation; C16:0 and C16:1 fatty acids were greater and less, respectively, and RuBisCO transcript copy numbers were greater within severely contaminated populations (compared to uncontaminated populations). Yet, fatty acid abundances and RuBisCO copy numbers were equivalent among culture populations by the end of the incubation. Oil contaminants within the culture medium were measured; C6–C12 hydrocarbons and arsenic coincided with (initial) growth inhibition and (later) altered cell physiologies, respectively. Relationships among assessed parameters were deemed useful determinants for evaluating phytoplankton inhibition in response to petroleum contamination.

Growth inhibition and oxidative stress induced by 1-octyl-3-methylimidazolium bromide on the marine diatom Skeletonema costatum

Marine diatom Skeletonema costatum is an important prey in the marine food web and is often used as a standard test organism in ecotoxicological studies. In this study, in vivo experiments were performed to analyze the effects of 1-octyl-3-methylimidazolium bromide ([C8mim]Br) on the growth, photosynthetic activity, and oxidative stress in S. costatum using 96h growth tests with a batch-culture system. The growth of S. costatum was significantly inhibited by [C8mim]Br with 48 and 96h-EC50 of 17.9 and 39.9mgL−1, respectively. The maximum quantum yield (Fv/Fm) and the light use efficiency (α) were inhibited by [C8mim]Br, which affected the growth of S. costatum. Subsequent biochemical assays in S. costatum revealed that [C8mim]Br induced changes of Chl a content, soluble protein content, and SOD activity, which had significant increases in low [C8mim]Br treatments (≤20mgL−1), but decreased in high [C8mim]Br exposures (≥40mgL−1). The increase of SOD activity at low concentrations (≤20mgL−1) may be considered as an active defense of S. costatum against [C8mim]Br stress by reactive oxygen species (ROS) quenching. In addition, [C8mim]Br increased ROS level and malondialdehyde (MDA) content in S. costatum, suggesting that the physiological effects of [C8mim]Br are resulted from ROS generation.

Floraciones algales nocivas durante el periodo 2008-2010 en el Golfo de Nicoya, Costa Rica

En este estudio se analizaron los eventos de floraciones algales nocivas (FAN) en cuatro estaciones de muestreo fijas en el Golfo de Nicoya durante el periodo de enero de 2008 a diciembre de 2010. Se recolectaron muestras de agua a 1 y 5 m de profundidad durante cada evento de FAN. Además, se midieron in situ los parámetros fisicoquímicos: profundidad del disco de Secchi, temperatura, salinidad, oxígeno disuelto y el porcentaje de saturación de oxígeno del agua. Los datos de radiación solar y precipitación fueron suministrados por el Instituto Meteorológico Nacional de Costa Rica. Se determinaron las concentraciones de las microalgas responsables y las especies asociadas. Se registraron 11 eventos, de los cuales el 72.7% se presentaron en la época lluviosa y un 27.3% en la época seca, la mayoría de éstos, durante el fenómeno atmosférico de La Niña. Las especies responsables fueron los dinoflagelados Alexandrium monilatum, Levanderina fissa, Cochlodinium polykrikoides y Prorocentrum minimum, la diatomea Skeletonema costatum y la cianobacteria Trichodesmium erythraeum. Las especies asociadas que se registraron con mayor frecuencia fueron los dinoflagelados Dinophysis caudata, Prorocentrum micans, Tripos fusus, Tripos furca y Protoperidinium conicum. Las FAN en el Golfo de Nicoya fueron más frecuentes durante la época lluviosa, probablemente debido a los aportes fluviales al sistema estuarino de los ríos Tempisque, Barranca y Grande de Tárcoles. Esa estacionalidad, en conjunto con las alteraciones provocadas por eventos atmosféricos globales como La Niña y El Niño, determinó la formación de FAN en el golfo durante el periodo de estudio.

Significance of different microalgal species for growth of moon jellyfish ephyrae, Aurelia sp.1

The scyphozoan Aurelia aurita (Linnaeus) sp. l., is a cosmopolitan species-complex which blooms seasonally in a variety of coastal and shelf sea environments around the world. The effects of different microalgal species on the growth of newly-released Aurelia sp.1 ephyrae were studied under laboratory conditions. We fed ephyrae with four different microalgal species (diatom, autotrophic dinoflagellate, heterotrophic dinoflagellate, and chlorophyta) plus Artemia nauplii for 12-24 d at 18°C. Results showed that the growth rate diverged significantly for Artemia nauplii compared to other food types. In addition, there was no significant variation between the growth rates for Skeletonema costatum and Prorocentrum donghaiense, and no significant variation was found in the growth rates for N. scintillans and P. subcordiformis. Artemia nauplii could support the energy requirement for the newly-released ephyrae to develop to meduase, and the ephyrae with Artemia nauplii showed a significant average growth rate of 25.85% d−1. Newly-released ephyrae could grow slightly with some species of microalgae in the earliest development stage. Chain diatom Skeletonema costatum and autotrophic dinoflagellate Prorocentrum donghaiense, could not support the growth of the ephyrae, while heterotrophic dinoflagellate Noctiluca scintillans and chlorophyta Platymonas subcordiformis could support the growth of the ephyrae. However, none of the ephyrae fed with the tested phytoplankton could mature to medusae.

Toxicity of CeO2 nanoparticles – The effect of nanoparticle properties

Conflicting reports on the toxicity of CeO2 nanomaterials have been published in recent years, with some studies finding CeO2 nanoparticles to be toxic, while others found it to have protective effects against oxidative stress. To investigate the possible reasons for this, we have performed a comprehensive study on the physical and chemical properties of nanosized CeO2 from three different suppliers as well as CeO2 synthesized by us, and tested their toxicity. For toxicity tests, we have studied the effects of CeO2 nanoparticles on a Gram-negative bacterium Escherichia coli in the dark, under ambient and UV illuminations. We have also performed toxicity tests on the marine diatom Skeletonema costatum under ambient and UV illuminations. We found that the CeO2 nanoparticle samples exhibited significantly different toxicity, which could likely be attributed to the differences in interactions with cells, and possibly to differences in nanoparticle compositions. Our results also suggest that toxicity tests on bacteria may not be suitable for predicting the ecotoxicity of nanomaterials. The relationship between the toxicity and physicochemical properties of the nanoparticles is explicitly discussed in the light of the current results.

Photochemical responses of the diatom Skeletonema costatum grown under elevated CO2 concentrations to short-term changes in pH

Variability in pH is a common occurrence in many aquatic environments, due to physical, chem- ical and biological processes. In coastal waters, la- goons, estuaries and inland waters, pH can change very rapidly (within seconds or hours) in addition to daily and seasonal changes. At the same time, pro- gressive ocean acidification caused by anthropogenic CO2 emissions is superimposed on these spatial and temporal pH changes. Photosynthetic organisms are therefore unavoidably subject to significant pH varia- tions at the cell surface. Whether this will affect their response to long-term ocean acidification is still un- known, nor is it known whether the short-term sensi- tivity to pH change is affected by the pCO2 to which the cells are acclimated. We posed the latter open question as our experimental hypothesis: Does accli- mation to seawater acidification affect the response of phytoplankton to acute pH variations? The diatom Skeletonema costatum, commonly found in coastal and estuarine waters where short-term acute changes in pH frequently occur, was selected to test the hypo thesis. Diatoms were grown at both 390 (pH 8.2, low CO2; LC) and 1000 (pH 7.9, high CO2; HC) µatm CO2 for at least 20 generations, and photosynthetic re- sponses to short-term and acute changes in pH (be- tween 8.2 and 7.6) were investigated. The effective quantum yield of LC-grown cells decreased by ca. 70% only when exposed to pH 7.6; this was not ob- served when exposed to pH 7.9 or 8.2. HC-grown cells did not show significant responses in any pH treat- ment. Non-photochemical quenching showed opposite trends. In general, our results indicate that while LC- grown cells are rather sensitive to acidification, HC- grown cells are relatively unresponsive in terms of photochemical performance.

Ecotoxicological effects of ballast water effluent teated by an electrolytic method on marine environment

Ballast water effluent treated by an electrolytic method contains reactive chlorine species and disinfection by-products (DBPs). In this study, we conducted whole effluent toxicity (WET) testing and ecological risk assessment (ERA) to investigate its ecotoxicological effects on marine environment. WET testing was carried out for three marine pelagic organisms, i.e., diatom Skeletonema costatum, rotifer Brachionus plicatilis and fish Paralichthys olivaceus. The biological toxicity test revealed that S. costatum was the only organism that showed apparent toxicity to the effluent; it showed no observed effect concentration (NOEC), lowest observable effect concentration (LOEC) and effect concentration of 50% (EC50) values of 12.5%, 25.0% and 83.3%, respectively, at brackish water condition. In contrast, it showed insignificant toxicity at seawater condition. B. plicatilis and P. olivaceus also showed no toxicities to the effluent at the both salinity conditions. Meanwhile, chemical analysis revealed that the ballast water effluent contained total residual oxidants (TROs) below 0.03 μg/L and a total of 20 DBPs including bromate, volatile halogenated organic compounds (VOCs), halogenated acetonitriles (HANs), halogenated acetic acids (HAAs) and chloropicrin. Based on ERA, the 20 DBPs were not considered to have persistency, bioaccumulation and toxicity (PBT) properties. Except monobromoacetic acid, the ratio of predicted environmental concentration (PEC) to predicted no effect concentration (PNEC) of the other 19 DBPs did not exceed 1. Thus, our results of WET testing and ERA indicated that the ballast water effluent treated by electrolysis and subsequently neutralization was considered to have no adverse impacts on marine environment.

Degradation kinetics of a potent antifouling agent, butenolide, under various environmental conditions

Here, we investigated the degradation kinetics of butenolide, a promising antifouling compound, under various environmental conditions. The active ingredient of the commercial antifoulant SeaNine 211, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), was used as positive control. The results showed that the degradation rate increased with increasing temperature. Half-lives of butenolide at 4°C, 25°C and 40°C were>64d, 30.5d and 3.9d, respectively. Similar half-lives were recorded for DCOIT: >64d at 4°C, 27.9d at 25°C and 4.5d at 40°C. Exposure to sunlight accelerated the degradation of both butenolide and DCOIT. The photolysis half-lives of butenolide and DCOIT were 5.7d and 6.8d, respectively, compared with 9.7d and 14.4d for the dark control. Biodegradation led to the fastest rate of butenolide removal from natural seawater, with a half-life of 0.5d, while no obvious degradation was observed for DCOIT after incubation for 4d. The biodegradative ability of natural seawater for butenolide was attributed mainly to marine bacteria. During the degradation of butenolide and DCOIT, a gradual decrease in antifouling activity was observed, as indicated by the increased settlement percentage of cypris larvae from barnacle Balanus amphitrite. Besides, increased cell growth of marine diatom Skeletonema costatum demonstrated that the toxicity of seawater decreased gradually without generation of more toxic by-products. Overall, rapid degradation of butenolide in natural seawater supported its claim as a promising candidate for commercial antifouling industry.

Effect of silicate and inorganic carbon availability on the growth and competition of a diatom and two red tide dinoflagellates

:The influence of silicate and inorganic carbon availability on the growth of three common algal species, namely, the diatom Skeletonema costatum (Coscinodiscophyceae) and the dinoflagellates Prorocentrum minimum and Alexandrium tamarense (Dinophyceae), was studied. Competition experiments using these three species were performed under different conditions to determine the dominance of red tide algal species in certain marine environments. Skeletonema costatum outgrew the two dinoflagellates in the silicate-replete medium as a result of its high growth rate. However, the cell density of S. costatum decreased with reduced silicate and changed inorganic carbon availabilities. Skeletonema costatum stopped growing when the inorganic carbon concentration was doubled at a constant pH of 7.7, which may have resulted from the enhanced growth of the two dinoflagellates. Prorocentrum minimum and A. tamarense became dominant at constant pH 7.7 conditions. As a component of the CO2 concentrating mechanism (CCM), extracellular carbonic anhydrase (eCA) showed significantly lower activities in S. costatum under low-silicate and constant pH 7.7 conditions; whereas, the P. minimum eCA activity remained almost unaffected. Different eCA responses to reduced silicate and varied carbon sources suggested that the species differed in inorganic carbon acquisition. The results suggested that patterns of species dominance of bloom-forming microalgae may be related to silicate and inorganic carbon availabilities.

Growth and competition for different forms of organic phosphorus by the dinoflagellate Prorocentrum donghaiense with the dinoflagellate Alexandrium catenella and the diatom Skeletonema costatum s.l.

Growth and competition between the dinoflagellates Prorocentrum donghaiense and Alexandrium catenella and the diatom Skeletonema costatum sensu lato in response to different forms of phosphorus were investigated in mixed cultures. The results indicated that S. costatum s.l. outcompeted P. donghaiense to become dominant owing to high growth rates, irrespective of the KH2PO4 content or any dissolved organic phosphorus (DOP) substrate. However, P. donghaiense densities in the DOP substrates, particularly lecithin, grew to 2–4 times higher than those in KH2PO4. The growth rates of P. donghaiense and A. catenella were comparable. A. catenella densities decreased when the phosphorus substrate was changed from inorganic to organic, and P. donghaiense outcompeted A. catenella only when lecithin was added. Abundant alkaline phosphatase (AP) was expressed when the external phosphate was lower than 0.1 μmol l−1. The highest bulk AP activities in the lecithin treatments suggested that lecithin might be more difficult to hydrolyze by these algae compared with glucose-6-phosphate and ribonucleic acid. We suggested that the advantage which P. donghaiense was shown to have in utilizing DOP for growth is what allowed it to become abundant or even dominant in natural communities when phosphate was depleted.

Variation of bioaccumulation ability of 2,2′,4,4′-tetrabromodiphenyl ether by marine diatom Skeletonema costatum under different N:P ratios

The growth, biochemical content and bioaccumulation quantity of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) in Skeletonema costatum were studied under different N:P ratios (1, 4, 16, 64 and 128). All cellular biochemical contents of S. costatum presented decreasing trend over cultivation time. At early stage of cultivation, the cellular protein, carbohydrate and lipid in S. costatum presented higher values in treatments of N:P=4 and 16. However, they were lower in these treatments at the late stage, but higher in treatments N:P=1 and 128. Similarly, BDE-47 levels per cell of S. costatum were higher in treatments of N:P=4 and 16 at early stage of cultivation, which were 3.8 and 3.7 ng (106 cells)−1, respectively. At the middle stage of cultivation, the BDE-47 level per S. costatum cell lowered; and it further reduced in the treatments of N:P=4 and 16 at the late stage with the values 0.6 and 0.5 ng (106 cells)−1, respectively. However, it rose in N:P=128, reaching up to 2.3 ng (106 cells)−1. Compared with BDE-47 per cell, BDE-47 per algal volume under different N:P ratios did not present obvious difference. The quantity BDE-47 accumulated per cell of S. costatum was positively correlated with protein, carbohydrate and lipid per cell; meanwhile, the BDE-47 per volume had a positive correlation with biochemical content per volume. The variation of bioaccumulation ability of BDE-47 in S. costatum can be explained by biochemical changes due to N:P ratios.

Effects of solar UV radiation on photosynthetic performance of the diatom Skeletonema costatum grown under nitrate limited condition

National Natural Science Foundation [40930846, 41120164007, 41206132]; Program for Changjiang Scholars and Innovative Research Team [IRT_13R51]; China-Japan collaboration project from MOST [S2012GR0290]; Special Research Fund for the National Non-profit Institutes [2008M15]; MEL Visiting Fellowship Program [MELRS1006]

Temperature-dependent toxicities of nano zinc oxide to marine diatom, amphipod and fish in relation to its aggregation size and ion dissolution

This study, for the first time, concurrently investigated the influence of seawater temperature, exposure concentration and time on the aggregation size and ion dissolution of nano zinc oxides (nZnO) in seawater, and the interacting effect of temperature and waterborne exposure of nZnO to the marine diatom Skeletonema costatum, amphipod Melita longidactyla and fish Oryzias melastigma, respectively. Our results showed that aggregate size was jointly affected by seawater temperature, nZnO concentration and exposure time. Among the three factors, the concentration of nZnO was the most important and followed by exposure time, whereas temperature was less important as reflected by their F values in the three-way analysis of variance (concentration: F3, 300 = 247.305; time: F2, 300 = 20.923 and temperature: F4, 300 = 4.107; All p values <0.001). The aggregate size generally increased with increasing nZnO concentration and exposure time. The release of Zn ions from nZnO was significantly influenced by seawater temperature and exposure time; the ion dissolution rate generally increased with decreasing temperature and increasing exposure time. Growth inhibition of diatoms increased with increasing temperature, while temperature and nZnO had an interactional effect on their photosynthesis. For the amphipod, mortality was positively correlated with temperature. Fish larvae growth rate was only affected by temperature but not nZnO, while the two factors interactively modulated the expression of heat shock and metallothionein proteins. Evidently, temperature can influence aggregate size and ion dissolution and thus toxicity of nZnO to the marine organisms in a species-specific manner.

Monitoring and trends in harmful algal blooms and red tides in Korean coastal waters, with emphasis on Cochlodinium polykrikoides

Red tides have a long history in Korea with the first record in AD 161, and a total of 38 red tide events reported from AD 161 to 1820. Since the 1980s, the frequency of red tide events has increased and the red tide area has expanded. From 1972 to 2001, 1330 red tide events occurred, and 273 (20.5%) were caused by fish killing dinoflagellates, mostly since the mid 1990s. Overall, the diatom Skeletonema costatum and the dinoflagellate Karenia mikimotoi were dominant HAB species in the 1970s and 1980s. However, the dominant red tide species changed to the dinoflagellates Cochlodinium polykrikoides and Ceratium spp. and the raphidophytes Chattonella spp. in the 1990s and 2000s. In addition, the dinoflagellate Akashiwo sanguinea and Heterosigma akashiwo have been major components during red tides the past four decades. After 1995, when a massive C. polykrikoides bloom occurred, the National Fisheries Research and Development Institute (NFRDI) and local governments began monitoring red tides nationwide. Along with the NFRDI, more than 30 fisheries extension service stations under local governments monitor red tides. The National Maritime Police Agency monitors the movement of red tides using aerial surveillance with helicopters. Paralytic shellfish poisoning events are also monitored by the red tide monitoring network system of NFRDI and local governments. We reviewed here historical records of red tides in Korea, red tide monitoring systems, trends in frequency of occurrence of red tide events, and red tide causative species in Korean waters. Red tide dynamics and physical–environmental factors potentially related to C. polykrikoides red tides are also discussed; red tides caused by C. polykrikoides along Korean coasts have decreased sharply starting from 2008 after achieving a high density bloom annually from 1995 to 2007.

An optimality model of photoadaptation in contrasting aquatic light regimes

To investigate photoacclimation of phytoplankton adapted to different aquatic light regimes, a physiologically explicit phytoplankton optimality model was applied in two contrasting environments: constant irradiance vs. dynamic irradiance associated with oceanic mixed layers. Nitrogen was assumed to be partitioned between cellular components associated with light harvesting, carbon fixation, biosynthesis, and photoprotection. The model was used to predict how resources are (re)distributed to optimize growth in the different environments. Optimal intracellular nitrogen allocation in dynamic environments was associated with constitutive investment in Calvin cycle enzymes; in contrast, in the static environment Calvin cycle allocation was reduced at low light. Furthermore, reduced allocation to components associated with photoprotection in static environments led to heavily inhibited photosynthesis‐irradiance response consistent with that of Prochlorococcus adapted to relatively stable oligotrophic gyres. In contrast, photosynthetic response in the diatom Skeletonema costatum was better explained by maintenance of photoprotection components across a range of integrated light doses. Limited range of chlorophyll : C in Thalassiosira pseudonana was consistent with optimization of resource allocation to light‐harvesting components in dynamic environments, in contrast to the relatively wide range in allocation to light harvesting predicted by the model in static environments and chlorophyll cell−1 observed in high‐light‐adapted Prochlorococcus. The model was used to explain variability of the photosynthesis‐irradiance response of samples from the Celtic and Irish Seas. Photoacclimation state is a consequence of optimization of resource allocation to the set of environmental parameters (e.g., surface irradiance, depth of mixing, and light attenuation) that influence light variability.

Characterization of exudates released by the marine diatom Skeletonema costatum exposed to copper stress: a 3D-fluorescence spectroscopy approach

In a laboratory study, metal contamination experiments were conducted to investigate the effects of two free copper concentrations (10(-9) and 10(-8) M) on cell growth and on dissolved organic matter exudation by a marine diatom Skeletonema costatum. Throughout incubation, the growth kinetics and exudation of extracellular molecules (i.e. dissolved organic carbon (DOC) and the fluorescent organic matter) were determined. Results revealed an inhibition of S. costatum growth when the free copper level increased (from 10(-9) to 10(-8)). Furthermore, DOC release was more significant in cultures contaminated by 10(-9) M Cu(2+) than in control, suggesting a coping mechanism developed by this species. In this study, samples were daily analysed by 3D-fluorescence and PARAFAC algorithm, in order to compare the fluorescent material produced during growth under different contaminations. PARAFAC treatment revealed two main contributions: one related to the biological activity (C1), the other linked to the marine organic matter (C2). The third component C3 was typically protein-like. This fluorophore was considered as a tryptophan-like fluorophore, whereas the C1 and the C2 components were associated to marine production such as humic matter.

A dynamic model of the cellular carbon to chlorophyll ratio applied to a batch culture and a continental shelf ecosystem

A novel parameterization of the dynamical relationship between cellular carbon (C) and chlorophyll (Chl) is developed using a Chl synthesis term that includes the physiological status of the cell and the effect of packaging of pigments within cells. The geometric derivation highlights the non‐linear relationship between Chl content and absorption due to the package effect. When parameterized for a generic 3 µm radius phytoplankton cell, the model reproduces the magnitude and daily variations of C : Chl and C : nitrogen ratios of the diatom Skeletonema costatum in published laboratory experiments. The parameterization is then applied in a three‐dimensional biogeochemical model containing three phytoplankton classes in the coastal waters off southeast Tasmania, Australia, which demonstrates the behavior of the dynamic Chl parameterization over a range of light‐ and nutrient‐limiting environments for phytoplankton of different sizes and growth rates. The model produces C : Chl ratios of ∼ 12–20 (weight : weight) and ∼ 60–80 for phytoplankton communities dominated by fast‐growing small and fast‐growing large cells, respectively, close to the ratios of 17 and 76 observed at two sampling stations during periods with diatom‐ and flagellate‐dominated communities. Throughout the simulation, community C : Chl ratios generally vary between 12 and 200, which is similar to the range observed globally. In the new parameterization, C : Chl ratios are most influenced by the package effect for light‐limited, slow‐growing large microalgae, with physiological processes becoming important for smaller, nutrient‐limited, fast‐growing microalgae.

Influence of bio-optical parameter variability on the reflectance peak position in the red band of algal bloom waters

On the basis of field measurements, the quantitatively different relationships of peak position in the red band of the remote sensing reflectance vs. Chl concentration are found in the bloom waters of the diatom Skeletonema costatum and the dinoflagellate Prorocentrum donghaiense in coastal areas of the East China Sea. Model simulations of remote sensing reflectance, Rrs, accounting for the influence of variations in the bio-optical parameters such as chlorophyll fluorescence quantum efficiency, Φ, and specific absorption coefficient, aph⁎, are carried out to analyze the characteristics of this spectral peak. The strong effect of fluorescence on the magnitude of Rrs results in the inhibition of the shift of the peak to longer wavelengths, increasing Φ enhances this effect. Increasing aph⁎, specifically in the red-wavelength band, causes a sharper shift in the red peak position by decreasing the effect of the fluorescence. The dominant parameter governing the slope of the shift is aph⁎. The analysis indicates that the higher aph⁎ of S. costatum in the red region is primarily responsible for the much higher slope of the peak shift than for that of P. donghaiense. We show that the relationship between the peak position and Chl concentration may be useful for discriminating S. costatum blooms from those due to P. donghaiense, although information about chlorophyll fluorescence quantum efficiency should be included. Finally, we show that using the band ratio Rrs(708nm)/Rrs(665nm) instead of Chl in the relationship with peak position can be useful for the practical identification of S. costatum blooms from hyperspectral measurements of remote sensing reflectance.