The pigment composition of Phaeocystis antarctica (Haptophyceae) under various conditions of light, temperature, salinity, and iron.

The pigment composition of Phaeocystis antarctica was monitored under various conditions of light, temperature, salinity, and iron. 19'-Hexanoyloxyfucoxanthin (Hex-fuco) always constituted the major light-harvesting pigment, with remarkably stable ratios of Hex-fuco-to-chl a under the various environmental conditions. Increased pigment-to-chl a ratios at low irradiance confirmed the light-harvesting function of Fucoxanthin (Fuco), 19'-Hexanoyloxy-4-ketofucoxanthin (Hex-kfuco), 19'-butanoyloxyfucoxanthin (But-fuco), and chl c2 and c3. Increased pigment-to-chl a ratios at high irradiance, low iron concentrations, and to a lesser extent at high salinity confirmed the photoprotective function of diadinoxanthin, diatoxanthin, and ß,ß-carotene. Pigment ratios were not always according to expectations. The consistent increase in But-fuco/chl at high temperature, high salinity, and low iron suggests a role in photoprotection rather than in light harvesting. Low Hex-kfuco/chl ratios at high salinity were consistent with a role as light harvester, but the high ratios at high temperature were not, leaving the function of Hex-kfuco enigmatic. Dedicated experiments were performed to test whether or not the light-harvesting pigment Fuco could be converted into its structural relative Hex-fuco, and vice versa, in response to exposure to light shifts. Rapid conversions could not be confirmed, but long-term conversions cannot be excluded. New pigment ratios are proposed for chemotaxonomic applications. The ratios will improve pigment-based diagnosis of algal species in waters dominated by P. antarctica.

Characterization of phytoplankton functional groups in a tropical shellfish harvesting estuary (Ashtamudi) and adjacent nearshore waters (southwest coast of India).

A pioneering study on phytoplankton marker pigments, by adopting the HPLC-CHEMTAX analytical approach, was carried out in one of the major shellfish harvesting estuaries (Ashtamudi estuary-AE) on the southwest coast of India and also its adjacent nearshore waters (< 20 m depth) to study the dynamics of phytoplankton functional groups (PFGs). The AE, in general, appeared to be warm (> 29 °C) during the non-monsoon seasons, along with the prevalence of higher salinity (> 25) and NH4-N (> 5 µM) levels. However, during the summer monsoon (SM), the prevailing substantial river influx converted the AE into a low salinity (< 10) dominated system, provided with enhanced levels of NO3-N (4.6-12.6 µM) and PO4-P (0.2-1.4 µM), specifically on its upper reaches. The dissolved inorganic nitrogen (DIN) in the AE was mainly comprised of ammonium (NH4-N), approximately up to ~ 81.8% of the DIN, regardless of seasons, which signifies the eutrophic state of the estuary, the upstream sampling locations, in particular. Concerning the phytoplankton community, a pronounced spatio-temporal variation in chlorophyll a biomass was discernible in the AE, with an exceptional increase (6.4-12.1 mg m-3) during the SIM period. The prevalence of a conspicuous increase in chlorophyll a (av. > 5 mg m-3) along with enhanced zeaxanthin (av. > 1.5 mg m-3) recorded in the AE during the non-monsoon (specifically SIM period) season apparently signified the characteristic governance of cyanobacterial community. During the SM period, the estuary sustained more or less similar concentrations of certain marker pigments, i.e. alloxanthin, zeaxanthin, fucoxanthin and chl b, which representing the co-occurrence of cryptophytes, cyanobacteria, diatoms and chlorophytes, respectively. In contrast, the nearshore waters, wherein enhanced nitrate (NO3-N) and phosphate (PO4-P) levels prevailed, irrespective of seasons, sustained dominance of fucoxanthin over other marker pigments, which indicated the numerical supremacy of diatoms. The CHEMTAX analysis, adopted for estimating the chlorophyll a equivalents of various PFGs, corroborated the supremacy of cyanobacterial derived chlorophyll a in the estuary, and it was conspicuous during the non-monsoonal seasonal periods. Even though the estuary has shown remarkable spatio-temporal hydrographic inconsistencies, that variability was not much operative in generating extreme changes in the nutrient components and subsequent phytoplankton community compositions. From the conspicuous increase in N:P and Si:P ratios, resulting mainly from the low levels of P, it can be concluded that the AE has been a P-limited system for phytoplankton growth (especially for large-sized phytoplankton, e.g. diatoms and dinoflagellates), mainly during the non-monsoonal seasonal periods. Perhaps, this P-limitation, along with the prevalence of warm water column and enhanced NH4-N levels, could be the potential causes of the preponderance of cyanobacterial populations in the AE.

A rapid fluorescence approach on differentiation of typical dinoflagellate of East China Sea.

Detecting the marine phytoplankton by the means of absorption or fluorescence spectra were successfully deployed in the past decades, however, the differentiation are mainly limited in levels of class, such as bacillariophytas, dinophytas, raphidophytes, chlorophytes, cyanobacteria, etc. which are characterized by their specific composition of photosynthetic pigments. To further differentiate the typical dinoflagellate Prorocentrum donghaiense, Amphidinium carterae, Scrippsiella trochoidea, Karenia mikimotoi out of the common diatom Skeletonema costatum and haptonema Phaeocystis globosa at East China Sea, a rapid 3D-fluorescence method equipped with CHEMTAX model were conducted. Initial fluorescence excitation spectra of each algal species (under variable environmental conditions) were captured by 3D-fluorometer first. Then fingerprints of each algae were characterized by ten-point discrete excitation spectrum with the excitation wavelengths of 405, 420, 435, 470, 490, 505, 535, 555, 570 and 590 nm, which closely reflecting the difference of photosynthetic pigments. By equipping with CHEMTAX model, the standard spectra and norm spectra were constructed for FS-CHEMTAX (Fluorescence spectra-CHEMTAX) model to further identify the algal species and estimate the cell density. The developed method performed a better way of identifying the toxic species Amphidinium carterae, Phaeocystis globosa, and Karenia mikimotoi out of the non-toxic ones, with the identification accuracy rates of 83.3%, 90% and 100%, in monocultures, and 77.8%, 90% and 100%, in the bi-mixed cultures, respectively. Meanwhile, the detection limits for the three toxic species were found as low as 250, 1,400 and 120 cells/mL. The concentrations estimated are in good agreement with the microscopic cell counts for all the algae groups (correlation coefficients (R2) exceed 0.8). The relative error of predict concentration was lowest for small cells, i.e., Phaeocystis globosa (10.0%) and Amphidinium carterae (21.1%), but the highest for big cells, i.e. Karenia mikimotoi (41.8%) when the target algae become the dominant species. The overall concentration detection error was no more than one order of magnitude, indicating that this method could provide an important technical support for monitoring the related harmful algal blooms.

On the use of chemotaxonomy, a phytoplankton identification and quantification method based on pigment for quick surveys of subtropical reservoirs.

Traditionally, composition and biomass of phytoplankton communities are determined by microscopy, but this method is time-consuming and so does not allow for high-frequency data acquisition across space and time. Pigment-based chemotaxonomy (CHEMTAX) is now widely applied to study of phytoplankton community structure on broader spatial and temporal scales of oceans, but the ability of this approach to provide estimates of phytoplankton assemblage in freshwater ecosystems is yet underdeveloped. To investigate the efficiency of the high-performance liquid chromatography (HPLC)-CHEMTAX in quantifying the different phytoplankton groups in inland freshwater, we present a comparison between phytoplankton pigment analyses by HPLC with CHEMTAX and microscopic counting of phytoplankton samples from four subtropical reservoirs in January and July 2014, respectively. The correlation between pigment and phytoplankton abundance detected by microscopy was stronger than that between pigment and phytoplankton biomass. The published marker pigments and their revised ratios can be used to describe phytoplankton abundances in a mixed community of freshwater phytoplankton, and pigment-based CHEMTAX can successfully describe the overall pattern of phytoplankton community dynamics during different seasons. The use of pigment-based CHEMTAX for quick surveys of phytoplankton communities can be recommended as a useful supplement or alternative tool to microscopy for freshwater ecosystem management.

Understanding optical absorption associated with phytoplanktonic groups in the marginal seas.

Marine phytoplankton absorption plays an important role in oceanic biological productivity and ecological environmental dynamics. Understanding the optical absorption variability associated with phytoplanktonic groups still remains a challenge. In this study, samples (n = 206) were collected for the marginal seas of the northwest Pacific Ocean from six cruise surveys that covered different seasons. Using in situ parameters, including phytoplankton absorption coefficients and concentrations of the phytoplanktonic groups derived from phytoplankton pigments collected with high-performance liquid chromatography (HPLC), we developed a Gaussian model to characterize the specific absorption spectra of eight phytoplanktonic groups, including diatoms, chlorophytes, cryptophytes, cyanobacteria, prymnesiophytes, prasinophytes, dinoflagellates, and chrysophytes, without the package effect. The model was established by accurately identifying for the numbers and locations of the Gaussian peaks and their corresponding half-wave widths. The proposed model produced promising results, and a leave-one-out cross validation generated R2 values exceeding 0.7 for the whole visible light range and above 0.85 (correspondingly MAPE <40%) for the simulated wave bands, excluding the range of 550-650 nm. Meanwhile, a comparison with several spectra observed in the lab showed a high degree of similarity, indicative of the superior performance of our model. Applying the documented specific absorption spectra to the investigated water bodies (whether water surface or profiles) enabled us to quantify the absorption coefficients from different phytoplanktonic groups and characterize their relative contributions to the total. The findings of this study support our understanding of the dynamics of phytoplankton community structure with optical data.

Domoic Acid and Pseudo-nitzschia spp. Connected to Coastal Upwelling along Coastal Inhambane Province, Mozambique: A New Area of Concern.

Harmful algal blooms (HABs) are increasing globally in frequency, persistence, and geographic extent, posing a threat to ecosystem and human health. To date, no occurrences of marine phycotoxins have been recorded in Mozambique, which may be due to absence of a monitoring program and general awareness of potential threats. This study is the first documentation of neurotoxin, domoic acid (DA), produced by the diatom Pseudo-nitzschia along the east coast of Africa. Coastal Inhambane Province is a biodiversity hotspot where year-round Rhincodon typus (whale shark) sightings are among the highest globally and support an emerging ecotourism industry. Links between primary productivity and biodiversity in this area have not previously been considered or reported. During a pilot study, from January 2017 to April 2018, DA was identified year-round, peaking during Austral winter. During an intense study between May and August 2018, our research focused on identifying environmental factors influencing coastal productivity and DA concentration. Phytoplankton assemblage was diatom-dominated, with high abundances of Pseudo-nitzschia spp. Data suggest the system was influenced by nutrient pulses resulting from coastal upwelling. Continued and comprehensive monitoring along southern Mozambique would provide critical information to assess ecosystem and human health threats from marine toxins under challenges posed by global change.

Characterization of phytoplankton community in a river ecosystem using pigment composition: a feasibility study.

CHEMTAX is a mathematical software for phytoplankton composition evaluation using pigment composition. Although this method has been previously applied in the ocean environment, we firstly utilized the combination of matrix factorization program CHEMTAX and high-performance liquid chromatography (HPLC) to characterize the phytoplankton community from a river system (western part of Weihe River Basin). The obtained results were compared with those from microscopic examination. Based on the comparison, it is suggested that after increasing the ratio of characteristic pigment to chlorophyll a of diatoms and euglena, the diatoms calculated by the CHEMTAX method accounted for 80% of the total biomass, and the results were consistent with microscopic examination, but diatoms obtained from F2, C1 and W5 sample sites were significantly overestimated 33%~60%. The comparison also showed that the model always underestimated cyanobacteria (sample sites F2, C1 were underestimated 25%) and euglena were overestimated (sample sites W3, Q1 were respectively overestimated 33%, 23%), but for chlorophytes, both overestimation and underestimation could occur. When the relevant results from previous applications in the ocean phytoplankton community evaluation were taken into consideration, it can be concluded that CHEMTAX-HPLC method was not accurate enough to characterize the phytoplankton communities in the freshwater (river/lake) ecosystem.

A comparative study of phytoplankton community structure and biomass determined by HPLC-CHEMTAX and microscopic methods during summer and autumn in the central Bohai Sea, China.

As the largest inland sea of China, the Bohai Sea has confronted significant environmental changes in recent decades, and a shift of phytoplankton community from diatoms to dinoflagellates was observed by microscopic method in previous studies. However, the counting of some small-sized non-diatoms (e.g., flagellates and cyanobacteria) have long been neglected due to the limitation of this method. In this study, we measured the phytoplankton community structure and abundance in the central Bohai Sea in summer and autumn of 2015 by employing both microscopic method and high-performance liquid chromatography (HPLC) pigments - CHEMTAX analysis. The results of microscopic counting showed that the phytoplankton community was characterized by diatoms, dinoflagellates, and chrysophytes, which contained a total of 107 species. Dinoflagellates and diatoms co-dominated in summer while the latter became the dominant group in autumn. Compared with microscopic counting, CHEMTAX analysis allowed identification of a larger number of phytoplankton groups (including 8 phyla). The results of CHEMTAX analysis showed that besides diatoms and dinoflagellates, the small-sized non-diatoms (i.e., flagellates and cyanobacteria) also played an important role. Diatoms and cyanobacteria dominated the total Chl a (contributing 32.5% and 17.1%, respectively), followed by cryptophytes, dinoflagellates, and prasinophytes in the summer. A short-term summer to autumn variability of phytoplankton abundance and community was observed. Temperature and nutrient availability affected the succession of the phytoplankton community from diatoms and non-diatoms co-dominance in the summer to absolute diatoms dominance in the autumn. A direct comparison of algal cell abundance and CHEMTAX biomass showed that a significant positive correlation was observed only for dinoflagellates (P < 0.01) in the autumn. Our work provides some basic information on the dynamics of small-sized flagellates and cyanobacteria in this area, and also suggests that a combination of both the methods is needed in future investigations to better understand the current status as well as the future changes of phytoplankton community.

Determining temporal and spatial distribution of autotrophic picoplankton community composition through HPLC-pigment method and flow cytometry in the central Bohai Sea (China).

The temporal-spatial distribution of marine autotrophic picoplankton (APP) in the central Bohai Sea was investigated in April (spring), June (early summer), August (summer), and October (autumn) in 2015 through a combination of HPLC-pigment method and flow cytometry. Flow cytometry results showed that APP was composed of Synechococcus (Syn) and pico-eukaryotes (PEUKs). The lowest average abundances of Syn and PEUKs was obtained in April. Afterward, the average APP density substantially increased, and Syn dominated the total cell abundances. Although generally outnumbered by Syn, PEUKs were the larger contributor to total APP carbon biomass (>52%) in all the cruises, except in August, when Syn bloomed. Compared with the cytometric method, HPLC-pigment CHEMTAX revealed a more sophisticated diversity of APP community. In April, diatoms were the main contributor to pico-Chl a, whereas prasinophytes became the main contributor in June and October. Syn bloom was evidenced by CHEMTAX, which revealed that it contributed 69.3% of Chl a in August. Redundancy analysis suggested that temperature was the main factor influencing the distribution of APP. Moreover, nutrients and their structures had some effects, which depended on different APP groups in the area. The accordance between CHEMTAX and cytometric method was evaluated through correlation analysis. A significantly positive correlation between cell abundance and CHEMTAX-derived Chl a was observed for Syn in August and PEUKs in June. Nevertheless, further study is needed owing to the observed discrepancies between the methods.

Parallel assessment of marine autotrophic picoplankton using flow cytometry and chemotaxonomy.

Autotrophic picoplankton (0.2-2µm) can be a significant contributor to primary production and hence play an important role in carbon flow. The phytoplankton community structure in the Baltic Sea is very region specific and the understanding of the composition and dynamics of pico-size phytoplankton is generally poor. The main objective of this study was to determine the contribution of picoeukaryotic algae and their taxonomic composition in late summer phytoplankton community of the West-Estonian Archipelago Sea. We found that about 20% of total chlorophyll a (Chl a) in this area belongs to autotrophic picoplankton. With increasing total Chl a, the Chl a of autotrophic picoplankton increased while its contribution in total Chl a decreased. Picoeukaryotes play an important role in the coastal area of the Baltic Sea where they constituted around 50% of the total autotrophic picoplankton biomass. The most abundant groups of picoeukaryotic algae were cryptophytes (16%), chlorophytes (13%) and diatoms (9%). Picocyanobacteria were clearly dominated by phycoerythrin containing Synechococcus. The parallel use of different assessment methods (CHEMTAX and flow cytometry) revealed the share of eukaryotic and prokaryotic part of autotrophic picoplankton.

Triclosan alterations of estuarine phytoplankton community structure.

Antimicrobial additives in pharmaceutical and personal care products are a major environmental concern due to their potential ecological impacts on aquatic ecosystems. Triclosan (TCS) has been used as an antiseptic, disinfectant, and preservative in various media. The sublethal and lethal effects of TCS on estuarine phytoplankton community composition were investigated using bioassays of natural phytoplankton communities to measure phytoplankton responses to different concentrations of TCS ranging from 1 to 200µgl-1. The EC50 (the concentration of an inhibitor where the growth is reduced by half) for phytoplankton groups (diatoms, chlorophytes, cryptophytes) examined in this ranged from 10.7 to 113.8µg TCS l-1. Exposures resulted in major shifts in phytoplankton community composition at concentrations as low as 1.0µg TCS l-1. This study demonstrates estuarine ecosystem sensitivity to TCS exposure and highlights potential alterations in phytoplankton community composition at what are typically environmental concentrations of TCS in urbanized estuaries.

The influence of salinity in the domoic acid effect on estuarine phytoplankton communities.

Toxic species of the diatom genus Pseudo-nitzschia, observed worldwide from coastal waters to the open ocean, produce the neurotoxin domoic acid (DA). DA is an important environmental and economic hazard due to shellfish contamination with subsequent effects on higher trophic levels. Previous research has demonstrated that, among other environmental factors, salinity influences the abundance and toxicity of Pseudo-nitzschia. In this study, the environmental factors driving the growth of Pseudo-nitzschia and the production of dissolved DA (dDA) in North Inlet estuary were examined. The effect of salinity on the growth inhibition of phytoplankton induced by the initial presence as well as by an addition of dDA was also assessed. Initially, the diatom abundance was negatively correlated with the abundance of Pseudo-nitzschia and with the concentration of dDA. With the addition of a concentrated solution of dDA, the percent inhibition of cryptophytes and diatoms was significantly correlated with salinity and suggested a higher sensitivity to dDA at extreme salinities. These results emphasize the importance of salinity in assessing the properties of DA and potentially of other phycotoxins on phytoplankton.

Determining in situ periphyton community responses to nutrient and atrazine gradients via pigment analysis.

Agrochemicals, including fertilizers and herbicides, are significant contributors of non-point source pollution to surface waters and have the potential to negatively affect periphyton. We characterized periphyton communities using pigment markers to assess the effects of nutrient enrichment and the herbicide atrazine with in situ experimental manipulations and by examining changes in community structure along existing agrochemical gradients. In 2008, the addition of nutrients (20 mg/L nitrate and 1.25 mg/L reactive phosphate), atrazine (20 µg/L) and a combination of both nutrients and atrazine had no significant effect on periphyton biomass or community structure in a stream periphytometer experiment. In 2009, similar experiments with higher concentrations of atrazine (200 µg/L) at two stream sites led to some minor effects. In contrast, at the watershed scale (2010) periphyton biomass (mg/m(2) chlorophyll a) increased significantly along correlated gradients of nitrate and atrazine but no direct effects of reactive phosphate were observed. Across the watershed, the average periphyton community was composed of Bacillariophyceae (60.9%), Chlorophyceae (28.1%), Cryptophyceae (6.9%) and Euglenophyceae (4.1%), with the Bacillariophyceae associated with high turbidity and the Chlorophyceae with nitrate enrichment. Overall, effects of nitrate on periphyton biomass and community structure superseded effects of reactive phosphate and atrazine.