Variations In Phytoplankton Community Structure Research Articles

Seasonal variability of phytoplankton community structure in a coastal station of the Argentine continental shelf based on a chemotaxonomic approach

Seasonal variability of phytoplankton community structure in a coastal station of the Argentine continental shelf based on a chemotaxonomic approach

Spatial-temporal distributions of phytoplankton shifting, chlorophyll-a, and their influencing factors in shallow lakes using remote sensing

Understanding phytoplankton dynamics is crucial for assessing water ecosystem health. However, traditional in-situ investigations often fall short of capturing the spatial-temporal variations of phytoplankton community structure and biomass on large scales. This study introduces a novel approach that harnesses the power of machine learning models coupled with Sentinel-2 satellite data to predict phytoplankton shifting and chlorophyll-a (Chla) in three large shallow lakes in central China from 2016 to 2021. We employed an array of machine learning algorithms, including the extreme gradient boosting method (XGBoost), random forest (RF), support vector machine (SVM), and K-nearest neighbor (KNN) to retrieve Chla and phytoplankton groups clustered by hierarchical cluster analysis based on the Bray-Curtis similarity index (HCA). The influences of environmental factors, including meteorology and nutrients, on phytoplankton dynamics were then explored. Our results identified four distinct phytoplankton groups, each exhibiting unique structural characteristics according to the HCA. The RF and XGBoost, utilizing top-of-atmosphere reflectance, provided the most accurate estimations of phytoplankton shifting and Chla, respectively. The red edge-red ratio emerged as a key variable in both models, underlining the significance of red edge bands in phytoplankton monitoring. We mapped spatial-temporal patterns of phytoplankton group occurrence and average Chla concentration across the three lakes. Our findings indicated that eutrophication extended periods of cyanobacteria domination and algal blooms, particularly in bays and nearshore areas. Redundancy analysis and classification and regression tree model highlighted temperature as a significant driver of phytoplankton shifting, while nutrient levels exhibited stronger influences on Chla. Our study underscores the potential of integrating machine learning models with Sentinel-2 data to enhance the monitoring and prediction of phytoplankton dynamics in shallow lakes. This approach offers valuable insights for the early detection of algal blooms and informed management strategies, contributing to the preservation and sustainable management of aquatic ecosystems.

Environmental controls on the interannual variability in chlorophyll and phytoplankton community structure within the seasonal sub surface chlorophyll maximum in the western English channel

The subsurface chlorophyll maximum (SCM) is increasingly recognised as an important but understudied locus of primary production particularly in shelf seas. Here we report the results of a 4 year, repeat station, summer sampling programme (2013–2016) of a seasonally recurrent SCM in the Western English Channel. Interannual variability in phytoplankton community structure and chlorophyll distribution and intensity was strongly related to water column stability at the depth interval of the SCM and also to water temperature. The phytoplankton community was statistically distinct in each year. High stability, as evidenced by large Richardson numbers and a well-developed strong thermocline appeared to favour the growth of larger dinoflagellates (autotrophs or mixotrophs) and diatoms. Such conditions led to development of the most intense SCMs and these were sometimes dominated by a single or a few key species most prominently in 2015 with near monospecific concentrations of the dinoflagellate Tripos fusus with average peak SCM chlorophyll concentrations of 7.3 ± 4.4 μg l−1. By contrast, in years with low water column stability and intermittent turbulence at the thermocline (2014, 2016) there was greater chlorophyll dispersal and less intense SCM. In these low stability conditions, red fluorescent nano-phytoplankton, such as naked dinoflagellates, chlorophytes and prymnesiophytes, made a greater contribution to the community, possibly as a result of the advantages that motility and enhanced light utilisation efficiency confer within an SCM exposed to turbulence. It is also likely that turbulence disrupted the stability required by the larger dinoflagellates and diatoms. Several of the key SCM taxa were absent from surface waters including the dinoflagellates Tripos fusus, Tripos lineatus, and most of the Rhizosolenia/Proboscia diatoms, consistent with adaptations more suited to survival at depth in stratified waters. These traits include luxury nutrient uptake and storage and survival in low light (both groups) and mixotrophy (dinoflagellates). On the other hand, in 2013, diatoms including Pseudo-nitzschia spp. were abundant in both surface, SCM and bottom waters. The relatively cooler waters (11.6–12.1 °C on average in 2013 and 2016) were characterised by smaller diatoms (Chaetoceros spp. and Pseudo-nitzschia spp.) whereas the warmer waters (13.1 °C on average in 2014) contained larger diatoms (large Rhizosolenia spp., Lauderia annulata and Leptocylindrus danicus). There did not appear to be continuity of key species between years, other than for the dinoflagellate Tripos lineatus, which was significant in both 2013 and 2014 and present in 2015. In any given year, there was no correspondence between the key spring bloom phytoplankton species as monitored in the nearby Western Channel Observatory L4 station and the key SCM taxa.

Critical factors driving spatiotemporal variability in the phytoplankton community structure of the coral habitat in Dongshan Bay, China.

This study investigated the spatiotemporal distribution of the phytoplankton in the coral habitat of Dongshan Bay (China), along with critical factors affecting the distribution, during June, August, and December 2022. Phytoplankton abundance in Dongshan Bay exhibited considerably temporal variation, peaking in June 2022, gradually decreasing thereafter, and reaching its lowest point in December 2022. The abundance of bottom-layer phytoplankton consistently exceeded that of the surface layer throughout all seasons. The average phytoplankton abundance in the coral habitat of Dongshan Bay was lower than that in non-coral habitat areas. Fluctuations in the Zhangjiang River and coastal upwelling influenced the diversity and community structure of the phytoplankton. Critical factors causing spatiotemporal variability in phytoplankton community structure included nutrient concentrations and seawater temperature. Nutrients played key roles in influencing various phytoplankton groups. Dominant diatom species, such as Thalassionema nitzschioides and Thalassiosira diporocyclus, were positively correlated with ammonia nitrogen, seawater salinity, coral cover, and the number of coral species present. In winter, Calanus sinicus exhibited a negative correlation with harmful algal bloom species. Additionally, it was found that both in the coral habitat and surrounding open sea, currents, nutrients, and zooplankton may play crucial roles in determining the spatiotemporal variability in the phytoplankton community structure.

Characteristics of Phytoplankton Communities and Key Impact Factors in Three Types of Lakes in Wuhan

To reveal the characteristics and key impact factors of phytoplankton communities in different types of lakes, sampling surveys for phytoplankton and water quality parameters were conducted at 174 sampling sites in a total of 24 lakes covering urban, countryside, and ecological conservation areas of Wuhan in spring, summer, autumn, and winter 2018. The results showed that a total of 365 species of phytoplankton from nine phyla and 159 genera were identified in the three types of lakes. The main species were green algae, cyanobacteria, and diatoms, accounting for 55.34%, 15.89%, and 15.07% of the total number of species, respectively. The phytoplankton cell density varied from 3.60×106-421.99×106 cell·L-1, chlorophyll-a content varied from 15.60-240.50 μg·L-1, biomass varied from 27.71-379.79 mg·L-1, and the Shannon-Wiener diversity index varied from 0.29-2.86. In the three lake types, cell density, Chla, and biomass were lower in EL and UL, whereas the opposite was true for the Shannon-Wiener diversity index. NMDS and ANOSIM analysis showed differences in phytoplankton community structure (Stress=0.13, R=0.048, P=0.2298). In addition, the phytoplankton community structure of the three lake types had significant seasonal characteristics, with chlorophyll-a content and biomass being significantly higher in summer than in winter (P<0.05). Spearman correlation analysis showed that phytoplankton biomass decreased with increasing N:P in UL and CL, whereas the opposite was true for EL. Redundancy analysis (RDA) showed that WT, pH, NO3-, EC, and N:P were the key factors that significantly affected the variability in phytoplankton community structure in the three types of lakes in Wuhan (P<0.05).

Spatio-temporal variation in phytoplankton community structure in backwaters of the Ketar River, central Ethiopia

This study assessed the spatio-temporal dynamics of the phytoplankton community in backwaters of the Ketar River, central Ethiopia, in relation to water quality and macrophyte coverage. Phytoplankton samples and physicochemical information were collected at six sites along the river over 1 year (December 2017 to November 2018). Phytoplankton was collected using a 15-μm mesh net. A total of 56 species belonging to three algal phyla were identified; the most diverse phylum was Bacillariophyta (35 species), followed by Chlorophyta (13 species) and Euglenophyta (eight species). Bacillariophyta had the highest abundance and contributed 80.08% of the total phytoplankton abundance. Site 6 in the downstream portion had the highest abundance and greatest diversity of phytoplankton species. The algal phyla present showed significant differences in species diversity and abundance both spatially and temporally. Redundancy analysis results revealed that the spatial distribution of phytoplankton in the river positively correlated with pH, electrical conductivity, dissolved oxygen and nitrate-nitrogen, while water temperature and total suspended solids correlated negatively. Some indicators of organic pollution suggest that the water quality of the river is progressively declining, meriting close monitoring.

Advances in phytoplankton population ecology in the Pearl river estuary

Phytoplankton is an important primary producer of the estuarine ecosystem, which is essential for the biogeochemical cycle of water elements and nutrient transfer. The Pearl River estuary (PRE) is a dynamically complex estuary, and the environment of PRE is significantly impacted by anthropogenic activities, variation of phytoplankton community structure in the PRE are complex. This review aims to compare phytoplankton species, species diversity, and abundance variation characteristics from the 1980s and 2020s, evaluate the overall trend of phytoplankton in the PRE, and discuss the main environmental factors affecting phytoplankton growth in the PRE. The data from the past 40 years in PRE showed that the number of phytoplankton species significantly decreased (p &amp;lt; 0.05). There was no significant difference in the abundance of phytoplankton at the 10-year scale, however, the fluctuation range of the abundance has increased. Under the conditions of a decreasing species number and no significant difference in abundance, the species diversity of phytoplankton showed a downward trend. In addition, the dominant phytoplankton species in the nearshore waters were relatively homogenous, and the abundance of phytoplankton in the nearshore waters was higher than that in the open waters, which suggested that human activities have a great influence. This review can form the basis for facilitating health management in the PRE ecosystem. Further, relevant guidelines can be developed and implemented for promoting the ecological health of the Guangdong-Hong Kong-Macao Greater Bay Area and ensuring its sustainable development.

Insights into the deglacial variability of phytoplankton community structure in the eastern equatorial Pacific Ocean using [231Pa/230Th]xs and opal-carbonate fluxes

Fully and accurately reconstructing changes in oceanic productivity and carbon export and their controls is critical to determining the efficiency of the biological pump and its role in the global carbon cycle through time, particularly in modern CO2 source regions like the eastern equatorial Pacific (EEP). Here we present new high-resolution records of sedimentary 230Th-normalized opal and nannofossil carbonate fluxes and [231Pa/230Th]xs ratios from site MV1014-02-17JC in the Panama Basin. We find that, across the last deglaciation, phytoplankton community structure is driven by changing patterns of nutrient (nitrate, iron, and silica) availability which, in turn, are caused by variability in the position of the Intertropical Convergence Zone (ITCZ) and associated changes in biogeochemical cycling and circulation in the Southern Ocean. Our multi-proxy work suggests greater scrutiny is required in the interpretation of common geochemical proxies of productivity and carbon export in the EEP.

Phytoplankton assemblage shifts with dissolved organic matter properties: A functional perspective for sentinel lakes

Abstract Climate change is altering both dissolved organic matter (DOM) properties and phytoplankton dynamics in lakes. High‐altitude lakes are good sentinels of global change. However, their value as sentinels depends on how well we understand their functioning. This study analysed physical, chemical and biological data during three pre‐defined periods running from complete ice‐cover right to the end of the ice‐free season, in a high‐altitude oligotrophic lake. A functional approach was used to assess how relationships between DOM and the planktonic community vary over time. Phytoplankton functional change was found to occur with shifts in DOM. During the ice‐influenced period, from February to the end of the thaw, the phytoplankton community was dominated by small autotrophs and mixotrophic flagellates and DOM from sediment and terrestrial origin dominated the DOM pool of the lake. Phytoplankton diversity and richness increased during the post‐snowmelt overturn period, when terrestrial DOM dominated the DOM pool. Finally, large siliceous autotrophs, competitive under low nitrogen concentrations and high temperature, dominated almost exclusively during the late summer period (LSP). Increased phytoplankton biomass meant that phytoplankton‐derived DOM was dominant during the LSP. These phenological changes in the phytoplankton community resulted in functional shifts at the base of the food web. Based on the relationships between the variables in the study, it can be deduced that the nature of the relationship between phytoplankton and bacteria progressively shifted from strong top‐down control exerted by phytoplankton over bacteria towards predominantly bottom‐up control at the end of the ice‐free season. Synthesis. Using a field survey starting from complete ice‐cover and lasting right to the end of the ice‐free season in a sentinel lake, we show seasonal shifts in the link between DOM properties and plankton community traits. Differences in environmental conditions and DOM origin explained variation in phytoplankton community structure and function, pointing to seasonal shifts in microbial food web interactions. Our research suggests that, under climate change, the balance between mixotrophy and autotrophy and the control exerted by phytoplankton over bacterioplankton will change in oligotrophic high‐altitude lakes with large, vegetated catchments.

Responses of phytoplankton communities driven by differences of source water intrusions in the El Niño and La Niña events in the Taiwan Strait during the early spring

The El Niño Southern Oscillation (ENSO) is one of the most important drivers of interannual variations of marine ecosystems, especially monsoonal ecosystems. The channel effect in a strait amplifies the impact of monsoons and may be an ideal area to study ecosystem responses to ENSO events. Previous studies have shown that physical processes in the Taiwan Strait (TWS) vary during the different ENSO phases, but the biological responses are still unclear. In this study, we found clear differences in the physical, chemical, and biological characteristics of the TWS between different ENSO phases based on data from satellites and field cruises during the 2015–2016 El Niño and 2017–2018 La Niña events. Although the monsoonal patterns were similar during early spring cruises during two ENSO events, the influence of the China Coastal Current (CCC), which is characterized by low sea surface temperature, low salinity, and high nutrient concentrations, was 1.5 times greater during the 2015–2016 El Niño than the 2017–2018 La Niña. The average chlorophyll a concentration was therefore higher in 2016 than that in 2018. The phytoplankton consisted mainly of diatoms, dinoflagellates, and cryptophytes during the 2015–2016 El Niño, but concentrations of those phytoplankton groups decreased, and concentrations of prasinophytes, Synechococcus, and Prochlorococcus increased during the 2017–2018 La Niña. Their influence of the CCC and warm currents were associated with the variations in phytoplankton community structure in the TWS. The results of this study enhance understanding of the responses of marine ecosystems to climate variabilities, and of the changes that climate change may bring to strait ecosystems.

Vertical Distribution Characteristics and Influencing Factors of Phytoplankton Community Structure in Qiandao Lake

Clear vertical variations in phytoplankton community structure are usually observed in deep-water lakes and reservoirs, which is one of the key components of water quality and ecosystem functioning. However, the vertical patterns and ecological drivers of phytoplankton communities in deep-water lakes and reservoirs are still understudied. In this study, we took Qiandao Lake, a deep-water reservoir, as an example to reveal the vertical distribution characteristics of phytoplankton communities and its influencing factors by investigating phytoplankton community structure and the associated water quality index at 12 sites across the whole lake in two seasons (spring and autumn). The results showed that the phytoplankton abundance and chlorophyll a were highest in the surface layer in autumn and then decreased toward deep water, whereas in spring, the maximum value occurred in the subsurface layer (2-5 m), and the dominant phytoplankton species showed obvious vertical stratification characteristics. Specifically, in spring, Cryptomonas and Pseudanabaena dominated the surface and subsurface layers, Cryptomonas dominated in the middle layer, and the abundance of Cyclotella at the bottom layer was significantly higher than that of the other algae genera. The dominant genera in autumn were Pseudanabaena and Aphanizomenon. In the subsurface and middle layers, Leptolyngbya and Pseudanabaena occupied the dominant position, and Leptolyngbya became the only dominant genus. In the bottom layer, Leptolyngbya was the only dominant genus. The key environmental indicators of the water also had obvious vertical changes. The contents of N and P nutrients had a negative correlation with the water depth in spring, whereas the reverse trend was observed in autumn. The correlation analysis showed that the vertical variation in phytoplankton abundance in spring was significantly positively correlated with phosphate concentration, whereas the vertical distribution of phytoplankton abundance in autumn was significantly positively correlated with intensity of light, and the water temperature, NH4+-N, and total nitrogen were the main factors driving the vertical changes in the dominant genera of phytoplankton community in the two seasons. To summarize, environmental conditions such as water temperature, light, and nutrients had strong effects on the vertical distribution of phytoplankton. In the ecological investigation and quality assessment of deep-water lakes and reservoirs, the vertical distribution characteristics of the phytoplankton community structure and the influence of environmental conditions should be fully considered.

Phytoplankton community structure of Tang-Pu Reservoir: status and ecological assessment in relation to physicochemical variability.

Seasonal variation in phytoplankton community structure within Tang-Pu Reservoir (Shaoxing city, Zhejiang province, China) was investigated in relation to variation in physicochemical and hydrological characteristics. Over the three-study seasons (autumn, winter, and spring), phytoplankton abundance and biomass showed a gradual increase with the peak in spring season. During this study period, phytoplankton community comprised of 7 phyla, 80 genera, and 210 species. The dominating phyla were Chlorophyta 80 species, Bacillariophyta 46, and Cyanophyta 44 as well as other phyla of freshwater ecosystems except Xanthophyta. The phytoplankton density and biomass varied in the six sampling sites between a minimum of 257.42 × 104 cells/L to 1054.15 × 104 cells/L and 1.60mg/L to 4.56mg/L respectively. Spring season had higher biomass and density values than autumn and winter. Furthermore, the results indicated that the Shannon-Wiener (H') and Pielou evenness (J') indices of phytoplankton community were stable although with slightly higher values in spring. Based on the calculated indices, Tang-Pu reservoir could be considered mesosaprobic in all the three seasons. Redundancy analysis (RDA) revealed that pH, total nitrogen (TN), total phosphorus (TP), transparency, chlorophyll a (Chl a), dissolve oxygen (DO), and water temperature (WT) were responsible for most phytoplankton community shift from Bacillariophyta and Cryptophyta to Cyanophyta and Chlorophyta in spring. These environmental parameters play an essential role in the community structure variation of phytoplankton in the downstream and upstream of Tang-Pu Reservoir. A decreasing phytoplankton abundance trend from the river area (inlet) to the lake (outlet) was also observed.

Phytoplankton dynamics and implications for eutrophication management in an urban river with a series of rubber dams

Rubber dams are widely used in urban rivers for landscape construction and flood control. However, the increased water residence time by dams usually causes phytoplankton accumulation. Developing a greater understanding of the phytoplankton dynamics and the effecting factors is essential for the eutrophication control of dammed rivers. Here, we investigated the variations in biomass and structure of phytoplankton communities along an urban landscape river with 30 rubber dams, and the main controlling factors during a 2-yr field monitoring. The biomass of phytoplankton significantly increased from 12.7 μg/L-Chl a and 1.14 × 107 ind./L-cells at the natural river part above dams to 65.2 μg/L-Chl a and 1.16 × 108 ind./L-cells at the 30th dam on average. There were different dominant taxa of phytoplankton between river sections with and without dams in different seasons. As Bacillariophyta dominated at the natural river part above dams throughout the year, accounting for 64.6% on average, and dominated at the 13th and 30th dams during the cold seasons (69.6% on average). But during the warm seasons, Cyanophyta and Chlorophyta increased obviously in the dammed river sections and became dominant taxa at the 30th dam, accounting for 55.9% and 34.7% respectively. The α-diversity of phytoplankton decreased along the series of dams. While the β-diversity between river sections with and without dams increased because of species replacement. Redundancy analysis revealed that nutrients, flow velocity and temperature were the main factors influencing the spatial-temporal variation in phytoplankton community structure in this river. High-frequency monitoring data further indicated that phosphorus and discharge explained most of the variations in phytoplankton biomass within the 13th dam impoundment. It suggested that management strategies should focus on reducing the phosphorus input concentration under 0.164 mg/L and increase the discharge higher than 0.64 m3/s during warm seasons, to prevent phytoplankton bloom and further eutrophication problems in this dammed river.

Seasonal variation of phytoplankton community structure in the Tianhe Reservoir of the Daluoshan Mountain in southern Zhejiang Province, China and its indication to water quality

To explore the association between phytoplankton community structure and water quality of the Tianhe Reservoir in Wenzhou, Zhejiang, we examined the phytoplankton and physico-chemical factors in the Tianhe Reservoir from February 2019 to January 2020. A total of 89 phytoplankton species belonging to 60 genera and 7 phyla were identified. The annual average abundance and biomass of phytoplankton were 2.02×105 cells·L-1 and 0.26 mg·L-1 respectively. Bacillariophyta was dominant in the whole year. Chlorophyta was dominant in spring and autumn. Cyanophyta was dominant in summer. Both Euglenophyta and Pyrrophyta appeared in the whole year. Cryptophyta appeared in autumn and winter. However, none of them was dominant due to their low abundance. The dominant species throughout the year were Melosira granulata, Synedra acus, Navicula cryptocephala, Asterionella formosa, Pseudoanabaena, Closterlum venus, Pediastrum duplex, Peridinium bipes, Dinobryon cylindricum and Cryptomonas ovata. Results of redundancy analysis (RDA) showed that water temperature, total nitrogen, CODMn and pH value were the main factors driving phytoplankton community structure in the whole year. According to the evaluation based on diversity indices, including Shannon index, Pielou evenness index, Margalef richness index and comprehensive trophic status index (TLI), water quality of Tianhe Reservoir is between oligotrophication and mesotrophication.

Seasonal variations and driving factors of phytoplankton community shift in Datun Lake with long-term stress of arsenic contamination.

Heavy metal is an important environmental stress that threatens water quality and ecological health of surface waters. Therefore, it is vital to identify the responses of lake community to long-term pollution for sustainable ecological restoration of polluted lakes. From June 2017 to March 2018, we conducted a seasonal survey of phytoplankton and environmental factors in Datun Lake, which had a decadal history of tailing-related arsenic contamination. Consistent with results from previous studies, phytoplankton were dominated by As-tolerant taxa such as Cyanophyta. Results of the analysis of similarities and analysis of variance showed that there were significant temporal variations in phytoplankton community structure and biomass, but without spatial variation. Results of the Pearson correlation analysis demonstrated that the total phytoplankton biomass was positively related to lake-water soluble orthophosphate and arsenic, which was consistent with the differential effect of arsenic on algae growth (e.g. promotion at low concentration and suppression at high concentration). The increases of phosphate might alleviate the toxic impacts of arsenic on phytoplankton. Redundancy analysis showed that the soluble nutrients and arsenic were significant factors driving phytoplankton community variations. The results of variation partitioning demonstrated that nutrients and water temperature explained 17.6% and 3.8% of community variations, respectively, with strong interaction with arsenic (15.1%). Arsenic did not affect phytoplankton community assembly, indicating that the dominant algae were tolerant to arsenic and thus highly insensitive to the arsenic stress. Therefore, the seasonal variations of phytoplankton dominated by As-tolerant algae in Datun demonstrated that the low-As promotion effect on phytoplankton should be considered in ecological restoration of polluted lakes.

Variation of phytoplankton community structure in Quang Ngai coastal waters during 2015–2019

Phytoplankton in coastal waters are important for the evaluation of either biodiversity or environmental impacts because of this highly vulnerable ecosystem. Seasonal and annual changes in the phytoplankton community structure in Quang Ngai waters during the period 2015 to 2019 were analyzed to assess the phytoplankton diversity and reveal possible causes of these changes. A total of 366 phytoplankton taxa belonging to 10 classes were identified throughout this present study. The highest species number was found in 2019 with 295 taxa, followed by those in 2015 (247), 2017 (185), and 2018 (99). The waters of Ly Son transect showed the highest diversity and most stable phytoplankton communities in both dry and rainy seasons, whereas the stations of Quang Ngai coast revealed high variability of the communities. All diversity indices including Margalef, Pielou, Shannon, Simpson did not reflect well differences in average values but a certain degree of variances, indicating possible environmental impacts. During the study time, there were blooms of certain diatom species including Skeletonema spp. in 2015 and Pseudo-nitzschia spp. in 2019. Analysis of a diatoms index, Centric/Pennate ratio, indicated that the waters were in eutrophic status with a decreasing trend from the coast area to Ly Son island in 2015 and 2019. This research built up fundamental data on phytoplankton communities for Quang Ngai province. The Centric/Pennate diatom index and diversity would be used as indicators for environmental changes and their values provided warning of eutrophication in this coastal waters including the water surrounding Ly Son island.

Interannual stability of phytoplankton community composition in the North-East Atlantic

As primary producers, phytoplankton play a pivotal role in the marine environment and are central to many biogeochemical processes. Changes to phytoplankton community composition could have major consequences for wider ecosystem functioning and may occur in response to climate change. Here we describe multi-decadal variability in phytoplankton community structure using taxonomic data from the Continuous Plankton Recorder collected in the North-East Atlantic from 1969-2013, using a total of 42 diatom and dinoflagellate taxa. We considered a range of characteristics of community structure, including taxonomic diversity and community stability and disorder, and how these characteristics change in response to sea surface temperature, mixed layer depth and the North Atlantic Oscillation. We found that phytoplankton community composition was largely stable on interannual timescales. A change in community composition occurred between 1985 and 1995 due to an increased dominance of 2 diatom taxa (Rhizosolenia styliformis and Thalassiosira spp.); however, after this period, the community returned to its previous composition. Further, a community disorder analysis found that phytoplankton compositional structure became more rigid in recent years, which may lead to an eventual community shift in the future. In contrast to previous studies that revealed relationships between total phytoplankton abundance or biomass and environmental forcing, we found that community structure had, at most, a very weak relationship with the environmental parameters tested. Changes to the physical environment may therefore have less influence at interannual timescales on phytoplankton community structure than previously thought.

Spatial and Temporal Variation of Phytoplankton Community Structure and Its Influencing Factors in Shanghai River Channels

In order to explore the spatial and temporal characteristics of the phytoplankton community structure and its influencing factors in Shanghai rivers, the water quality and phytoplankton community structure at 44 river channel sites in a central urban area, new town area, and rural area in Shanghai were investigated from September to October 2018 (autumn) and July to August 2019 (summer). The results showed that:① Chlorophyta was the dominant phyla during the autumn and summer, and was followed by Cyanobacteria and Bacillariophyta. Cyanobacteria dominated the phytoplankton community in terms of density. The number of species and density of phytoplankton were 24% and 2.77 times higher, respectively, than those during the summer and autumn. The dominance of Microcystis sp. was obvious during the autumn (Y=0.16), but there was no absolute dominant species during the summer. ② The difference in the number of phytoplankton species among the three regions was not significant, and the density of the total phytoplankton and cyanobacteria species showed a similar spatial pattern:rural area > new town area > central urban area. Additionally, no significant difference was observed in the total phytoplankton and Cyanobacteria density among the three regions during the autumn (P>0.05), whereas it was 1.82 and 1.93 times higher, respectively, in the rural area in comparison to the central urban area during the summer (P<0.05). Montecarlo test results revealed that the main factors affecting the phytoplankton community structure during the autumn were secchi disk transparency (SD), total phosphorus (TP), total nitrogen (TN), and turbidimetry (Turb), whereas these were TN, Turb, SD, and pH during the summer. ③ The results of a redundancy analysis (RDA) indicated that during the autumn, the phytoplankton in the rivers of the new town area were mainly affected by Turb, TN, and TP, while the rural rivers were mainly affected by SD. During the summer, the phytoplankton in the rivers of the new town and rural areas were mainly affected by TN and Turb. The influencing factors in the central urban area were complex.

Variability in phytoplankton community structure and influence on stabilization pond functioning

Density of phytoplankton in stabilization ponds influences treatment performance. The study hypothesized that the phytoplankton community structure varies according to local and temporal changes and consequently influences the treatment of the effluent. Phytoplankton community structure in facultative and maturation ponds in central Brazil was analyzed to provide guidance on system operation and maintenance. Further, species density, abundance, diversity, richness, dominance and beta diversity were measured. The efficiency of the treatment was evaluated based on Biochemical Oxygen Demand (BOD). Additionally, a Canonical Correspondence Analysis (CCA) was used to investigate how physical and chemical variables influenced the composition of the most abundant species in the dry and rainy seasons and the microalgae that were most related to the removal of BOD. One hundred and sixty-eight taxa were recorded, and the most abundant classes in both ponds were Chlorophyceae and Cyanophyceae (40% potentially toxic). The maturation pond had greater adaptability in the rainy season, while the facultative pond was more flexible in the dry season. The best period of growth varied among species. In both ponds, Chlorella minutissima was the one which most contributed to the optimization of the treatment. Thus, identifying phytoplankton species and relating them to water quality parameters and weather can help to understand the ecological dynamics of wastewater treatment and provide useful information for the operation and maintenance of stabilization ponds.

Regional disparities of phytoplankton in relation to different water masses in the Northwest Pacific Ocean during the spring and summer of 2017

The West Pacific Ocean is considered as the provenance center of global marine life and has the highest species diversity of numerous marine taxa. The phytoplankton, as the primary producer at the base of the food chain, effects on climate change, fish resources as well as the entire ecosystem. However, there are few large-scale surveys covering several currents with different hydrographic characteristics. This study aimed to explore the relationships between the spatio-temporal variation in phytoplankton community structure and different water masses. A total of 630 water samples and 90 net samples of phytoplankton were collected at 45 stations in the Northwest Pacific Ocean (21.0°–42.0°N, 118.0°–156.0°E) during spring and summer 2017. A total of 281 phytoplankton taxa (>5 µm) belonging to 61 genera were identified in the study area. The distribution pattern of the phytoplankton community differed significantly both spatially and temporally. The average abundances of phytoplankton in spring and summer were 797.07×102 cells/L and 84.94×102 cells/L, respectively. Whether in spring or summer, the maximum abundance always appeared in the northern transition region affected by the Oyashio Current, where nutrients were abundant and diatoms dominated the phytoplankton community; whereas the phytoplankton abundance was very low in the oligotrophic Kuroshio region, and the proportion of dinoflagellates in total abundance increased significantly. The horizontal distribution of phytoplankton abundance increased from low to high latitudes, which was consistent with the trend of nutrient distributions, but contrary to that of water temperature and salinity. In the northern area affected by the Oyashio Current, the phytoplankton abundance was mainly concentrated in the upper 30 m of water column, while the maximum abundance often occurred at depths of 50–75 m in the south-central area affected by the Kuroshio Current. Pearson correlation and redundancy analysis (RDA) showed that phytoplankton abundance was significant negatively correlated with temperature and salinity, but positively correlated with nutrient concentration. The phytoplankton community structure was mainly determined by nutrient availability, especially the N:P ratio.