Dominate Phytoplankton Communities Research Articles

Reservoir regulation-induced variations in water level impacts cyanobacterial bloom by the changing physiochemical conditions

Gaining insight into the impact of reservoir regulation on algal blooms is essential for comprehending the dynamic changes and response mechanisms in the reservoir ecosystem. In this study, we conducted a comprehensive field investigation linking physiochemical parameters, and phytoplankton community to different water regimes in the Three Gorges Reservoir. Our aim was to explore the effects of reservoir regulation on the extinction of cyanobacterial blooms. The results showed that during the four regulatory events, the water levels decreased by 2.02–4.33 m, and the average water velocity increased 68 % compared to before. The average total phosphorus and total nitrogen concentrations reduced by up to 20 %, and the cyanobacterial biomass correspondingly declined dramatically, between 66.94 % and 75.17 %. As the change of water level decline increasing, there was a significant increase of algal diversity and a notable decrease of algal cell density. Additionally, a shift in the dominant phytoplankton community from Cyanobacteria to Chlorophyceae was observed. Our analysis indicated that water level fluctuations had a pronounced effect on cyanobacterial extinction, with hydrodynamic changes resulting in a reduction of cyanobacterial biomass. This research underlined the potential for employing hydrodynamic management as a viable strategy to mitigate the adverse ecological impacts of cyanobacterial blooms, providing a solution for reservoir's eco-environmental management.

Clams on stilts: a phytoplankton bioassay investigating effects of wastewater effluent amendments and Corbicula fluminea grazing

Shallow-water habitats are being restored in the Sacramento-San Joaquin River Delta with the goal of enhancing phytoplankton production and food availability for higher trophic levels. However, elevated grazing pressure from the non-native freshwater clam Corbicula fluminea and localized depletions of dissolved inorganic nitrogen may limit phytoplankton biomass accumulation in restored habitats. To evaluate interactions between nutrients and grazing on phytoplankton productivity and biomass accumulation, Sacramento River water high or low in phytoplankton biomass was amended with wastewater effluent, presence of C. fluminea, or both, in 48 h in situ incubations. We measured changes in chl a concentration, phytoplankton community composition, and photosynthetic efficiency as well as carbon and nitrogen uptake rates as indicators of phytoplankton responses. Diatoms dominated phytoplankton communities before and after incubation. Chl a concentrations increased 0.7 and 7.4 times in the high and low phytoplankton biomass controls, respectively, and 4.5 and 14 times in the high and low phytoplankton biomass effluent-added treatments, respectively. In the clam treatments, chl a accumulation was suppressed to near zero regardless of effluent additions or initial phytoplankton biomass. In treatments with clams and effluent combined, phytoplankton photosynthetic efficiency was nearly 50% lower than in the effluent-only treatments, suggesting phytoplankton were stressed in the presence of clams. This experiment demonstrated that the presence of clams can prevent the accumulation of phytoplankton biomass, both directly by clam filtering and indirectly by depressing phytoplankton photosynthetic efficiency and rate of growth. We recommend that future wetland restoration projects promoting increased phytoplankton biomass assess clam settlement likelihood as well as nutrient availability.

Algal population growth and dynamics of Asan Wetland

A one year study of the phytoplankton community composition was carried out in the Asan wetland, a reservoir fed by River Yamuna in Uttarakhand India. In terms of bio-volume, phytoplankton community was generally dominated by Bacillariophyceae. Mean phytoplankton standing crops were highest in the wetland. The frequency and severity of algal blooms was increased significantly. To control their expansion, it was essential to identify the factors responsible for blooming of waters. Nutrient enrichment (mainly due to anthropogenic activities) and environmental factors (including the climate change) were considered the major catalyst for onset, proliferation and development of blooms. The phytoplankton of the Asan wetland was studied for one year with physical and chemical variables in relation to a pollution gradient. Analysis of the physical and chemical variables and phytoplankton density indicated that the wetland is experiencing heavy pressure of pollution due to anthropogenic activities. The dominant phytoplankton community mainly comprises of family, Chlorophyceae, Bacillariophyceae and Myxophyceae. Physical factors, though vital, had an indirect effect in facilitating the interaction among various available nutrients. In terms of phytoplankton density and diversity common genera observed include Chlorella, Chlaymydomonas, Spirogyra, Ulothrix, Hydrodictyon, Cladophora, Cosmarium, Chlorococcum, Oedogonium, Microspora, Desmidium, Chara, Zygenema, Syndesmus, Volvox, Ceratoneis, Amphora, Caloneis, Fragilaria, Navicula, Synedra, Diatoms, Gomphonema, Pinnularia, Melosira, Tabellaria, Denticula, Cymbella, Cyclotella, Nostoc, Anabaena, Oscillatoria, Rivularia, Coccochloris and Phormidium. Several genera were found most prominent during the study period having no seasonal impact on their abundance and variation. The spatial and temporal patterns observed in some of these dominant species were attributable to patterns in key environmental variables including temperature, flow, pH, dissolved oxygen and nutrient concentrations.

Application of modified clay in intensive mariculture pond: Impacts on nutrients and phytoplankton

Nutrients and phytoplankton associated with mariculture development are important concerns globally, as they can significantly impact water quality and aquaculture yield. Currently, there is still insufficient information regarding the variations in nutrients and phytoplankton community of intensive mariculture systems, and effective treatment is lacking. Here, based on consecutive daily monitoring of two Litopenaeus vannamei ponds from July to October, the dynamic variations in nutrients and phytoplankton were elucidated. In addition, modified clay (MC) method was adopted to regulate the nutrients and phytoplankton community. The temporal variations in organic and inorganic nutrients presented fluctuating upward trends. Notably, organic nutrients were the dominant species, with average proportions of TON/P in TN/P were as high as 75.29% and 87.36%, respectively. Furthermore, a marked increase in the ratios of dinoflagellates to diatoms abundance were also observed in the control pond, concurrently with dominant organic nutrients, ascending N/P ratio and decreasing Si/N and Si/P ratios. In the MC-regulated pond, MC reduced the contents of both organic and inorganic nutrients. Furthermore, a distinct change pattern of dominant phytoplankton community occurred, with green algae becoming the most abundant phytoplankton in the MC-regulated pond. This study can provide new insights into an effective treatment for managing water quality and maintaining sustainable mariculture development.

Phosphorus deficiency stimulates dominance of Cylindrospermopsis through facilitating cylindrospermopsin-induced alkaline phosphatase secretion: Integrating field and laboratory-based evidences

Potentially toxic Cylindrospermopsis raciborskii blooms are of emerging concerns, as its scale is spreading from tropical regions to high latitudes, increasing the risk of aquatic biota being exposed to cylindrospermopsin (CYN). So far, CYN-producing C. raciborskii strains have only been reported in tropical waters which are commonly phosphorus (P)-deficient, where they can dominate phytoplankton communities. However, the influence of CYN on phytoplankton communities under different P status remains unclear. In this study, we first analyzed the summer observations of 120 tropical reservoirs in Guangdong Province. The proportion of potential CYN-producers was significantly higher in P-deficient and CYN-present reservoirs than that in P-sufficient or CYN-absent ones. This suggested that in P-deficient condition, the potential CYN producers might gain more advantages by the help of CYN. Then, in laboratory experiments we found that upon P deprivation, CYN did not inhibit the cell growth of other algal cells, but significantly stimulates them to secret more alkaline phosphatase (ALP) than in P-sufficient condition. Through transcriptomics, we further revealed that under such P-deficient condition, CYN remarkably induced intracellular nitrogen allocation and protein export system by activating the PIK3/Akt-cGMP/PKG signaling pathways in Scenedesmus bijugatus, thus enhancing its ALP secretion. Our study implies that CYN-induced ALP secretion is facilitated upon P deficiency, thus supporting the dominance of its producers C. raciborskii.

Effects of phytoplankton community composition and productivity on sea surface pCO2 variations in the Southern Ocean

The Southern Ocean is a vast net sink for atmospheric carbon dioxide (CO2), with marine phytoplankton playing a crucial role in CO2 fixation. We assessed how changes in the dominant phytoplankton community and net primary productivity (NPP) affected variations in the partial pressure of CO2 in surface water (pCO2sw) in the Indian sector of the Southern Ocean during austral summer. pCO2sw was negatively correlated with total phytoplankton and diatom abundances, as estimated from pigment signatures, in the zone south of the Antarctic Circumpolar Current; however, pCO2sw was not correlated with haptophyte abundance. Additionally, a stronger correlation was found between pCO2sw and total phytoplankton NPP than between chlorophyll a concentration and pCO2sw. We reconstructed pCO2sw at inter-annual scale using satellite data and assessed the inter-annual variability of air-sea CO2 flux. Over the period from 1997 to 2007, the integrated CO2 fluxes over the study region showed very large variations from a small source to a strong sink. Variations in the integrated CO2 fluxes were also correlated with changes in satellite-derived phytoplankton community in the Indian sector of the Southern Ocean and changes in the dominant phytoplankton community may control CO2 dynamics in the marginal ice zone.

Ecological characteristics of dominant phytoplankton community in Lake Nanhai (Baotou) during freezing-thawing period

为了探究包头南海湖浮游植物群落特征和物种与生境之间的关系，于2018年11月和2019年1月、3月分别对南海湖浮游植物群落结构进行调查分析，得出南海湖冻融期浮游植物群落结构为绿藻-硅藻-蓝藻型.使用改进的Levins公式和Petraitis指数测定了南海湖冻融期优势种的生态位量度.结果显示：在不同生境条件下，物种生态位宽度存在季节性变化，同样，生态位重叠也随季节变化而变化.随着湖面冰冻，多数浮游植物生态位宽度有所下降；结冰期生态位重叠程度最高，融冰期生态位重叠程度最低.综合冻融过程优势藻种生态特征，绿藻门的四尾栅藻（Scenedesmus quadricauda）是冻融过程中最主要优势种，优势度、密度、生态位量度均优于其他优势藻种，能充分利用环境资源，更具竞争力.优势种与环境因子的灰关联分析显示，pH是影响浮游植物优势种数量的主要相关因子.;This study investigated the phytoplankton community structure and their relationship with habitats in Lake Nanhai of Baotou city, based on the data from November 2018 and January and March 2019 respectively. It found that the phytoplankton community comprised of Chlorophyta-Bacillariophyta-Cyanophyta in the freezing-thawing period. The niche traits of the dominant species in the freezing-thawing period were determined by using the improved Levins Niche Breadth Index and Petraitis Index. Results showed that there were seasonal changes in the niche breadth of the species under different habitats. Similarly, the niche overlap also changed with the seasons, with highest values during the icing period and lowest during the ice-melting period. Scenedesmus quadricauda was the most dominant species in the process of freezing and thawing. It's dominance degree, density, niche breadth and niche overlap are superior to other dominant phytoplankton species, and it can make full use of environmental resources, and be more competitive. Grey correlation analysis between dominant species and environmental factors showed that pH was the main factor affecting the density of dominant species of phytoplankton.

Comparison of Phytoplankton Communities Between Melt Ponds and Open Water in the Central Arctic Ocean

Climate warming has a significant impact on the sea ice and ecosystem of the Arctic Ocean. Under the increasing numbers of melt ponds in Arctic sea ice, the phytoplankton communities associated with the ice system are changing. During the 7th Chinese National Arctic Research Expedition cruise in summer 2016, photosynthesis pigments and nutrients were analyzed, revealing differences in phytoplankton communities between melt ponds and open water in the central Arctic. Photo synthetic pigment analysis suggested that Fuco (5-91 μg m-3 and Diadino (4-21 μg m-3) were the main pigments in the open water. However, the melt ponds had high concentrations of Viola (7-30 μg m-3), Lut (4-59 μg m-3) and Chl b (11-38 μg m-3), suggesting that green algae dominated phytoplankton communities in the melt ponds. The significant differences in phytoplankton communities between melt ponds and open water might be due to the salinity difference. Moreover, green algae may play a more important role in Arctic sea ice ecosystems with the expected growing number of melt ponds in the central Arctic Ocean.

Seasonal dynamics of phytoplankton morphological characters and driving factors in tropical reservoirs: A case study from Gaozhou Reservoir

体积、比表面积和最大轴性长度是浮游植物主要的形态性状，反映浮游植物资源竞争和反牧食能力.群落中物种的性状分布会随着环境条件的季节改变而变化，热带水库环境条件的季节性变化小，可能导致群落形态性状变化不显著.本文以热带大型水库——高州水库为研究对象，分析浮游植物形态性状季节动态及关键影响因子.高州水库浮游植物以丝状和单细胞藻类为主，群落水平的平均细胞体积在108.52~753.25 μm³之间，平均比表面积在0.93~2.08 μm^-1之间，平均最大轴性长度在5.21~17.44 μm之间，均有明显的季节特征.浮游植物群落平均细胞体积、最大轴性长度与总氮浓度呈负相关，与水温呈正相关；平均比表面积与硝态氮浓度呈负相关.粘质长孢藻（Dolichospermum mucosa）和光角星鼓藻（Staurastrum muticum）是高州水库浮游植物优势种，其形态性状均具有明显的时空差异，表现出明显的形态可塑性.粘质长孢藻的平均细胞体积、最大轴性长度与总氮浓度呈正相关，与水温呈负相关；平均比表面积与总氮浓度呈负相关，与水温呈正相关.光角星鼓藻的平均细胞体积、最大轴性长度与正磷酸盐浓度呈正相关.总体上高州水库浮游植物在群落和种群水平形态性状均有明显的季节差异，夏季以大细胞为主，其他季节以小细胞种类为主，水温、氮和磷的可利用性是导致浮游植物形态性状季节差异的关键因子.;Volume, specific surface area and the longest axial linear dimension are main morphological characters of phytoplankton. These characters reflect the ability of phytoplankton in competing for resources and resisting grazing. The morphological characters of cells change with the seasonal environmental conditions. It was assumed that limited seasonal changes occurred on phytoplankton cells morphological characters in community, due to the small seasonal variation of environmental conditions in tropical reservoirs. To test this assumption, the seasonal dynamic of phytoplankton morphological characters and the affecting factors in large tropical reservoir (Gaozhou Reservoir)were analyzed. The phytoplankton community was dominated by filamentous species and unicellular algae in Gaozhou Reservoir. In community level, the average cell volume was 108.52-753.25 μm³, the average cell specific surface area was 0.93-2.08 μm^-1, the average cell longest axial linear dimension was 5.21-17.44 μm, and the three morphological characters all showed seasonal dynamics. The average cell volume and the average cell longest axial linear dimension were correlated negatively with total nitrogen, and positively with temperature, the average cell specific surface area was correlated negatively with nitrate nitrogen. Dolichospermum mucosa and Staurastrum muticum were the dominant phytoplankton species in Gaozhou Reservoir, and they both showed morphological plasticity and seasonal dynamics in the morphological characters. The average cell volume and the average cell longest axial linear dimension of D. mucosa were correlated positively with total nitrogen, and negatively with temperature. The average cell specific surface area of D. mucosa was correlated negatively with total nitrogen, and positively with temperature. The average cell volume and the average cell longest axial linear dimension of S. muticum were correlated positively with soluble reactive phosphate. In conclusion, the morphological characters of phytoplankton in community and species were different with seasonal dynamics in Gaozhou Reservoir. The large cells dominated phytoplankton community in summer, but small cells in other season. Temperature, the availability of nitrogen and phosphorus were the primary factors to explain the morphological variation of phytoplankton.

Bacterial Epibiotic Communities of Ubiquitous and Abundant Marine Diatoms Are Distinct in Short- and Long-Term Associations.

Interactions between phytoplankton and bacteria play a central role in mediating biogeochemical cycling and food web structure in the ocean. The cosmopolitan diatoms Thalassiosira and Chaetoceros often dominate phytoplankton communities in marine systems. Past studies of diatom-bacterial associations have employed community-level methods and culture-based or natural diatom populations. Although bacterial assemblages attached to individual diatoms represents tight associations little is known on their makeup or interactions. Here, we examined the epibiotic bacteria of 436 Thalassiosira and 329 Chaetoceros single cells isolated from natural samples and collection cultures, regarded here as short- and long-term associations, respectively. Epibiotic microbiota of single diatom hosts was analyzed by cultivation and by cloning-sequencing of 16S rRNA genes obtained from whole-genome amplification products. The prevalence of epibiotic bacteria was higher in cultures and dependent of the host species. Culture approaches demonstrated that both diatoms carry distinct bacterial communities in short- and long-term associations. Bacterial epibonts, commonly associated with phytoplankton, were repeatedly isolated from cells of diatom collection cultures but were not recovered from environmental cells. Our results suggest that in controlled laboratory culture conditions bacterial–diatom and bacterial–bacterial interactions select for a simplified, but specific, epibiotic microbiota shaped and adapted for long-term associations.

The influence of cyanobacteria blooms on the attenuation of nitrogen throughputs in a Baltic coastal lagoon

We combined a mass balance approach with measurements of air–water and sediment–water nitrogen (N) exchange to better understand the mechanisms attenuating N throughputs in a eutrophic coastal lagoon. We were particularly interested in how seasonal shifts in external versus internal N fluxes and the transition from diatom- to cyanobacteria- dominated phytoplankton communities influence N storage and loss to the atmosphere. We found that on an annual basis almost all of the N removed by the lagoon was due to sediment storage following the spring diatom bloom. This period was characterized by high riverine inputs of dissolved inorganic nitrogen, high rates of assimilatory conversion to particulate nitrogen (PN), and net accrual of N in sediments. By contrast, the larger summer bloom was associated with low sediment N storage, which we attribute in part to the presence of positively-buoyant cyanobacteria. Low settling rates during cyanobacteria blooms favored export of PN to the Baltic Sea over sediment accrual in the lagoon. In addition, summer dinitrogen (N2) fixation by cyanobacteria largely offset annual N2 losses via denitrification. These findings show that cyanobacteria blooms diminish N attenuation within the lagoon by altering the balance of N exchange with the atmosphere and by promoting export of particulate N over sediment burial.

Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii

Diatoms, as important contributors to aquatic primary production, are critical to the global carbon cycle. They tend to dominate phytoplankton communities experiencing rapid changes of underwater light. However, little is known regarding how climate change impacts diatoms’ capacity in coping with variable light environments. Here we grew a globally abundant diatom T. weissflogii, under two levels of temperature (18, 24°C) and pCO2 (400, 1000μatm), and then treated it with a light challenge to understand the combined effects of ocean warming and acidification on its exploitation of variable light environments. The higher temperature increased the photoinactivation rate at 400μatm pCO2 and the higher pCO2 alleviated the negative effect of the higher temperature on PSII photoinactivation. Temperature did not affect the PsbA removal rate, but higher pCO2 stimulated PsbA removal. Photoinactivation outran repair, leading to decreased maximum photochemical yield in PSII. The higher pCO2 induced high sustained phase of nonphotochemical quenching when cells were less photoinhibited. The high light exposure induced the activity of both superoxide dismutase (SOD) and catalase (CAT) and the higher temperature stimulated them further, with insignificant effect of pCO2. Our findings suggest that ocean warming, ocean acidification and high light exposure would interact on PSII function and protection, and combination of these three environmental factors would lead to a reduced PSII activity in T. weissflogii. This study provides helpful insight into how climate change variables combined with local stressor impact diatoms’ photosynthetic physiology.

CO2 induced growth response in a diatom dominated phytoplankton community from SW Bay of Bengal coastal water

The ongoing increase in surface seawater CO2 level could potentially impact phytoplankton primary production in coastal waters; however, CO2 sensitivity studies on tropical coastal phytoplankton assemblages are rare. The present study investigated the interactive impacts of variable CO2 level, light and zinc (Zn) addition on the diatom dominated phytoplankton assemblages from the western coastal Bay of Bengal. Increased CO2 supply enhanced particulate organic matter (POC) production; a concomitant depletion in δ13CPOM values at elevated CO2 suggested increased CO2 diffusive influx inside the cell. Trace amount of Zn added under low CO2 level accelerated growth probably by accelerating Zn-Carbonic Anhydrase activity which helps in converting bicarbonate ion to CO2. Almost identical values of δ13CPOM in the low CO2 treated cells grown with and without Zn indicated a low discrimination between 13C and 12C probably due to bicarbonate uptake. These evidences collectively indicated the existence of the carbon concentration mechanisms (CCMs) at low CO2. A minimum growth rate was observed at low CO2 and light limited condition indicating light dependence of CCMs activity. Upon the increase of light and CO2 level, growth response was maximum. The cells grown in the low CO2 levels showed higher light stress (higher values of both diatoxanthin index and the ratio of photo-protective to light-harvesting pigments) that was alleviated by both increasing CO2 supply and Zn addition (probably by efficient light energy utilization in presence of adequate CO2). This is likely that the diatom dominated phytoplankton communities benefited from the increasing CO2 supply and thus may enhance primary production in response to any further increase in coastal water CO2 levels and can have large biogeochemical consequences in the study area.

Effect of algal blooms on retention of N, Si and P in Europe's largest coastal lagoon

Nutrient fluxes from land to sea are regulated by climatic factors governing hydrologic loading rates (e.g., storm events, snowmelt) and by internal processes within estuaries that affect nutrient transformation and retention. We compared monthly input and output fluxes of N, Si, and P at the entrance and exit of the hypereutrophic Curonian Lagoon to better understand how seasonal changes in the stoichiometry of nutrient inputs and the occurrence of algal blooms affected nutrient retention within the lagoon. Nutrient ratios were indicative of increasing Si and N limitation during the growing season, and these were associated with a shift from a diatom-based to a cyanobacteria dominated phytoplankton community. The estuary was a net sink for dissolved nutrients, but we observed large interannual difference in the overall retention of N and P. The occurrence of a large cyanobacteria bloom in 2012 was associated with increased export of particulate matter to the Baltic Sea resulting in a net surplus of P export. Bloom conditions mobilized P from sediments and resulted in a shift from net retention to net export for the lagoon. The findings of our study illustrate how changes in nutrient loading ratios influence phytoplankton community composition, which in turn alters the source-sink status of the estuary.

Distributions of phytoplankton in a coastal lagoon of Mahin, Ondo, Western Nigeria

Distributions of phytoplankton were investigated in Mahin Lagoon within Transgressive mud coast of Ondo, Western Nigeria. Collections and analyses of samples of phytoplankton and surface waters (for some physico-chemical parameters) were done at fifteen stations along the stretch of the lagoon in October 2013 and 2014 as well as March 2014 and 2015. Higher salinity levels were recorded at stations close the mouth of the Atlantic Ocean than those further upstream. Biochemical oxygen demand was high (7.7±2.3-10.6±1.8 mg/L) at stations with high levels of anthropogenic activities. Division Bacillariophyta (diatoms) dominated phytoplankton community in term of species diversity. Most species recorded during rainy season had relatively even spatial distributions. During March 2014 and 2015, high brackish water species such as Chaetoceros affinis , Asterionela japonica and Fragilaria construens were recorded only close to the Atlantic Ocean while stations further upstream had freshwater species such as Aulacoseira granulata , Synedra acus and Eudorina cylindrical . Stations close to high human population and anthropogenic activities had low phytoplankton abundance and diversity. Pollution indicator species, such as Microcystis aeruginosa and Oscillatoria borneti were recorded with relatively high abundance across fifteen stations. Implications of the anthropogenic activities on phytoplankton distributions and sustainable management of the lagoon are discussed. Keywords: Algae, species diversity, brackish waters, seasonality, anthropogenic activities

Chytrid parasitism facilitates trophic transfer between bloom-forming cyanobacteria and zooplankton (Daphnia).

Parasites are rarely included in food web studies, although they can strongly alter trophic interactions. In aquatic ecosystems, poorly grazed cyanobacteria often dominate phytoplankton communities, leading to the decoupling of primary and secondary production. Here, we addressed the interface between predator-prey and host-parasite interactions by conducting a life-table experiment, in which four Daphnia galeata genotypes were maintained on quantitatively comparable diets consisting of healthy cyanobacteria or cyanobacteria infected by a fungal (chytrid) parasite. In four out of five fitness parameters, at least one Daphnia genotype performed better on parasitised cyanobacteria than in the absence of infection. Further treatments consisting of purified chytrid zoospores and heterotrophic bacteria suspensions established the causes of improved fitness. First, Daphnia feed on chytrid zoospores which trophically upgrade cyanobacterial carbon. Second, an increase in heterotrophic bacterial biomass, promoted by cyanobacterial decay, provides an additional food source for Daphnia. In addition, chytrid infection induces fragmentation of cyanobacterial filaments, which could render cyanobacteria more edible. Our results demonstrate that chytrid parasitism can sustain zooplankton under cyanobacterial bloom conditions, and exemplify the potential of parasites to alter interactions between trophic levels.

Effect of nitrate enrichment and diatoms on the bioavailability of Fe(III) oxyhydroxide colloids in seawater

The photoconversion of colloidal iron oxyhydroxides was a significant source of bioavailable iron in coastal systems. Diatoms dominate phytoplankton communities in coastal and upwelling regions. Diatoms are often exposed to eutrophication. We investigated the effects of different species of diatom, cell density, illumination period, and nitrate additions on the bioavailability of Fe(III) oxy-hydroxide colloids in seawaters. With the increase of illumination period from 1 to 4 h, the ratios of concentrations of total dissolved Fe (DFe) to colloidal iron oxyhydroxides and Fe(II) to DFe increased up to 24.3% and 23.9% for seawater without coastal diatoms, 45.6% and 30.2% for Skeletonema costatum, 44.3% and 29.7% for Thalassiosira weissflogii, respectively. The photochemical activity of coastal diatoms themselves (excluding the dissolved organic matter secreted by algae) on the species transformation of iron in seawater (including the light-induced dissolution of Fe(III) oxyhydroxide colloids and the photo-reduction of Fe(III) into Fe(II)) was confirmed for the first time. There was no significant difference of the ability of S. costatum and Thalassiosira weissflogii on the photoconversion of colloidal iron oxyhydroxides. The photoproduction of dissolved Fe(II) and DFe in the seawater with or without diatoms could be depressed by the nitrate addition.

Patterning and predicting phytoplankton assemblages in a large subtropical river

Through time-series sampling during the whole of 2009, phytoplankton patterns and prediction models were built up with a self-organizing map (SOM) and Linear Discriminant Analysis (LDA) within the downstream region of a large subtropical river, the Pearl River (China). The excessive nutrient conditions resulted in a diatom dominant phytoplankton community. While green algae contributed more only in species diversity, as they were mainly dependent on inoculations from external resources, and their abundance remained low under fast and turbid flow conditions. The time periods of phytoplankton samples were classified into four clusters using a self-organiz- ing map (SOM) based on species similarities. These clusters were clearly different with respect to species richness, biomass and indicators. The LDA predicting model indicated that these clusters of species assemblages could easily be differentiated by physical factors such as water temperature, discharge and precipitation. As for nutrients, only phosphate could have an occasional impact on phytoplankton assemblages. By using the environmental variables, the global score for predicting the assemblages was 64.2 %, with the predicting performance rates for clusters I, IIa, IIb1 and IIb2 at 50, 48, 62 and 74 %, respectively. Cluster I benefited from a combination of higher temperatures and low discharge, and had the highest species richness and biomass. Cluster IIb1 benefited from high discharge and diverse species inoculations, but interruptions in increases of biomass. Cluster IIb2 showed that low tempera- tures resulted in both low species richness and biomass. Cluster IIa, characterized by phosphate, indicated that phytoplankton assemblages were occasionally P-limited in the studied section. In conclusion, the annual patterns of the downstream phytoplankton assemblages in the Pearl River were mainly regulated by physical factors but occasionally limited by nutrients.

Analysis of Effects of Berberine on the Photosynthesis of Microcystis aeruginosa at Gene Transcriptional Level

AbstractMicrocystis aeruginosa has great competition advantages to survive, grow, and dominate phytoplankton communities for its high photosynthetic activity in unsuitable conditions. Berberine was the allelochemical capable of inhibiting M. aeruginosa growth. To better understand the allelopathic mechanism involved, RNA‐sequencing technology was used to investigate the berberine‐induced changes in photosynthesis gene expression of M. aeruginosa. Using the next‐generation sequencing platform Illumina/Solexa, a total of 13 099 868 and 13 870 448 90‐bp pair‐end reads for “no berberine” and “berberine” libraries were obtained, respectively. Among these genes, 10 324 794 (no berberine) and 8 944 254 (berberine) reads mapped multiply in the genome, while 9 988 318 (no berberine) and 8 316 668 (berberine) mapped to unique targets, respectively. It was indicated that berberine significantly repressed the expression of 869 genes and induced the expression of 1419 genes. Those berberine‐affected genes belonged to different functional categories, especially enriched in various photosynthesis‐relevant metabolic pathways based on the analysis of gene ontology, clusters of orthologous group terms, and Kyoto Encyclopedia of Genes and Genomes. The results suggested that berberine‐induced disturbance in the algal photosynthesis process via repressing the expression of key photosynthesis genes, such as psbD, psaA, psaB, might be one of the main mechanisms involved in inhibitory allelopathic activity of berberine.

한강유역 조류경보제에 남조류 우점 예측인자 도입에 관한 연구

The chlorophyll-a concentration in algae bloom warning system of Hangang basin did not predict the cyanobacteria dominance. In this study, suggest the predicting indicator of cyanobacteria dominance through analyzing the environmental factors affecting on the cell count of cyanobacteria. Firstly, the dominance of algae was analyzed with seasonal variation during Jan. 2012~Sep. 2013. The diatom dominated phytoplankton communities during the period of January~April. In the May~June, the green algae dominated. And, the dominance of algae was changed to cyanobacteria in the July~August. Also, the environmental factors affecting to cyanobacteria blooms ; nutrients (TN, TP), temperature, precipitation, dam-discharge were evaluated during the study period. Rather than temperature factor, relatively low dam discharge causes cyanobacteria to grow rapidly and create a blooms. The low dam-discharge may increase the water retention time. Finally, it is proved that a low ratio of TN to TP (