Phytoplankton Community Dynamics Research Articles

Water stratification alters phytoplankton assemblages in scallop farming waters of the North Yellow Sea in China

As evaluation indicators of the primary productivity, the phytoplankton biomass and community structure are of great significance to the fishery industry, which can be driven by ocean currents, nutrients and water stratification. In the present study, the characteristics of phytoplankton assemblages in different water layers of a typical Yesso scallop farming area in Zhangzi Island, the North Yellow Sea were investigated from March 2021 to January 2022. According to the vertical distribution of temperature, water stratification was observed from June to August (stratification period), and disappeared in March, October and the following January with vertical homogeneity (mixing period). 18S rRNA gene sequencing results revealed that Pyrrophyta was the most dominant phylum during the sampling period, with high gene proportions in the stratification (63.36%) and mixing periods (77.35%). The gene proportion of Bacillariophyta in the stratification period was 5.44%, which was significantly lower than that in the mixing period of 8.93% (p < 0.05). Moreover, Pseudo-nitzschia, a toxin-producing taxon affiliated with Bacillariophyta, exhibited a significantly higher proportion in the stratification period than in the mixing period. During the stratification period, a number of toxin-producing taxa such as Pseudo-nitzschia and Karlodinium were enriched in the bottom layer, which was 1.29-fold and 1.37-fold of that in the surface layer, respectively. Redundancy analysis showed that phosphate and water temperature were major environmental factors driving the vertical distribution of phytoplankton assemblages. The phosphate (0.11 μM) and silicate (2.09 μM) concentrations in the surface layer approached the minimum threshold for phytoplankton growth, and the stoichiometric limitation of phosphate was detected in the surface and middle layers. Collectively, these results indicated that the decreased proportion ratio of Bacillariophyta to Pyrrophyta and unfavorable community composition of Bacillariophyta for scallops were observed during summer, which might result from the phosphate limitation driven by water stratification. The results will further our understanding of the dynamics of phytoplankton communities under the background of intensifying ocean stratification and provide ecological guidance for mollusc mariculture.

Effect of increased pCO2 and temperature on the phytoplankton community in the coastal of Yellow Sea

In order to study the dynamics of marine phytoplankton communities in response to anticipated in temperature and CO2, a shipboard continuous culture experiment (Ecostat) was conducted. The experiment involved simulations under current atmospheric CO2 concentrations (400 ppm) and projected year-2100 CO2 levels (1000 ppm), as well as varying temperature under present (22 °C) versus increased temperature (26 °C) in the Yellow Sea during the summer of 2020. The results showed that both the increased pCO2 and temperature had significant effects on microphytoplankton and picophytoplankton, with the warming effect proving to be more significant. The different responses of various species to acidification and warming and their coupling effect led to the changes in microphytoplankton and picophytoplankton community structure. Elevated temperature and greenhouse treatments promoted the growth of dominant diatoms and Synechococcus, such as Guinardia flaccida and Pseudo-nitzschia delicatissima. This phenomenons widened the ecological niche, and the changes in the growth patterns of dominant species consequently influenced the content of cellular elements. Mantel's analysis further demonstrated that both warming and greenhouse promoted the growth of diatoms and Synechococcus. Projections of marine phytoplankton community trends by the end of the century based on Growth Rate Ratio (GRR), indicated that not only would species with GRR < 1 decrease, but also numerous species with growth rates >1 at elevated pCO2 levels would be ousted from competition. This experiment demonstrates the need to investigate whether extended exposure to increased pCO2 and temperature over more extended time scales would similarly induce shifts in the biological and biogeochemical dynamics of the Yellow Sea.

Phytoplankton Community Dynamics in Ponds with Diverse Biomanipulation Approaches

The rising challenge of eutrophication in aquatic systems globally necessitates an understanding of phytoplankton community dynamics under diverse biomanipulation approaches. This study, conducted from June 2022 to July 2023 in the Yuqiao Reservoir’s ponds in China, explored phytoplankton dynamics across ponds under different biomanipulation strategies. The study included a pond (BL) without fish stocking, a pond (CH) stocked with carnivorous and herbivorous fish, and another pond (CFD) incorporating a mix of carnivorous, filter-feeding, and detritus-feeding fish. Substantial seasonal variations in phytoplankton density and biomass were observed. In the BL pond, phytoplankton density ranged from 0.23 × 107 to 3.21 × 107 ind/L and biomass from 0.71 to 7.10 mg/L, with cyanobacteria predominantly in warmer seasons and a shift to cryptophytes and chrysophytes in winter. The CH pond exhibited a density range from 0.61 × 107 to 8.04 × 107 ind/L and biomass of 1.11 to 7.58 mg/L. Remarkably, the CFD pond demonstrated a significant reduction in both density (0.11 × 107 to 2.36 × 107 ind/L) and biomass (0.27 to 5.95 mg/L), indicating the effective implementation of its biomanipulation strategy. Key environmental factors including total nitrogen, water temperature, pH, chlorophyll-a, and total phosphorus played a significant role in shaping phytoplankton communities. The study highlights the importance of tailored biomanipulation strategies in aquatic ecosystem management, emphasizing long-term monitoring for sustainable management of eutrophication.

Coastal environmental changes after the Saemangeum seawall construction

The coastal environment in the Saemangeum area has experienced persistent physical stresses owing to the irregular operation of the sluice gates and related artificial disturbances since seawall construction, which has led to restricted freshwater-seawater circulation. To understand the impacts of stress, we performed long-term (1999-2022, 24 years) in situ measurements of relevant biotic and abiotic parameters and employed the random forest (RF) technique to determine the phytoplankton community response to environmental disturbance. Specifically, we estimated chlorophyll-a (Chl-a) concentrations using an RF model based on various environmental factors such as sea surface temperature (SST), sea surface salinity (SSS), dissolved oxygen saturation (DO), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP) as input variables. From the RF analysis, each environmental factor contributed to variation in Chl-a concentration as follows: SSS (42.91%), SST (17.88%), DIP (14.38%), DIN (13.36%), and DO (11.48%). In addition, we performed sensitivity experiments by altering the salinity, which was revealed to be the most influential environmental parameter. As a result, Chl-a concentration increased by approximately 1.79 times in lower salinity conditions (from 7 to 27 psu) compared to the normal salinity conditions prior to the seawall construction (from 12 to 32 psu) in both areas, including the inside and outside the seawall. More importantly, lower salinity conditions stimulated dinoflagellate blooms, that is, red tides, implying that restricted freshwater-seawater circulation could worsen coastal ecosystems. Thus, this study contributes to understanding the impacts of environmental changes caused by sluice gate manipulation on marine ecosystems, such as phytoplankton community dynamics. Moreover, this study recommends an ecologically suitable operation scheme for Saemangeum sluice gates to ensure a healthy coastal ecosystem.

A Circum‐Antarctic Plankton Isoscape: Carbon Export Potential Across the Summertime Southern Ocean

AbstractThe Southern Ocean accounts for ∼30% of the ocean's CO2 sink, partly due to its biological pump that transfers surface‐produced organic carbon to deeper waters. To estimate large‐scale Southern Ocean carbon export potential and characterize its drivers, we measured the carbon and nitrogen isotope ratios of surface suspended particulate matter (δ13CSPM, δ15NSPM) for samples collected in summer 2016/2017 during the Antarctic Circumnavigation Expedition (364 stations). Concurrent measurements of phytoplankton community composition revealed the dominance of large diatoms in the Antarctic and nano‐phytoplankton (mainly haptophytes) in open Subantarctic waters. As expected, δ13CSPM was strongly dependent on pCO2, with local deviations in this relationship explained by phytoplankton community dynamics. δ15NSPM reflected the nitrogen sources consumed by phytoplankton, with higher inferred nitrate (versus recycled ammonium) dependence generally coinciding with higher micro‐phytoplankton abundances. Using δ15NSPM and a two‐endmember isotope mixing model, we quantified the extent of nitrate‐ versus ammonium‐supported growth, which yields a measure of carbon export potential. We estimate that across the Southern Ocean, 41 ± 29% of the surface‐produced organic carbon was potentially exported below the seasonal mixed layer during the growth season, with maximum export potential (50%–99%) occurring in the Antarctic Circumpolar Current's southern Boundary Zone and near the (Sub)Antarctic islands, reaching a minimum in the Subtropical Zone (&lt;33%). Alongside iron, phytoplankton community composition emerged as an important driver of the Southern Ocean's biological pump, with large diatoms dominating regions characterized by high nitrate dependence and elevated carbon export potential and smaller, mainly non‐diatom taxa proliferating in waters where recycled ammonium supported most productivity.

PHYTOPLANKTON COMMUNITY DYNAMICS RELATED TO CERTAIN PHYSICAL AND CHEMICAL VARIABLES IN ARDIÇTEPE RESERVOIR (BALIKESIR, TURKEY)

Ardıçtepe Reservoir (Balıkesir, Turkey) was sampled seasonally at three stations between October 2018 and August 2019 to determine the phytoplankton community dynamics in relation to water temperature, speciffic conductance (SC), total dissolved solids (TDS), pH, oxidation-reduction potential (ORP) and Secchi disk depth. A total of 43 phytoplankton species were identified, 27 from Bacillariophyta, 4 from Charophyta, 6 from Chlorophyta, 5 from Cyanobacteria and 1 from Euglenozoa. Bacillariophyta made 76% total number of species, Cyanobacteria 11%, Chlorophyta 6%, Charophyta 4% and Euglenozoa 3%. Aulacoseria granulata, Aulacoseira granulata var. angustissima, Cyclotella meneghiniana and Ulnaria ulna from Bacillariophyta and Anabaena circinalis from Cyanobacteria dominanted phytoplankton during the study. The CCA explained 90.8% of the cumulative variance in the relationships of dominant species-environment. The CCA also showed that water temperature, TDS, ORP and pH had significant effects on the phytoplankton community of Ardıçtepe Reservoir (Monte Carlo test, p 0.05)

Impact of anthropogenic accumulation on phytoplankton community and harmful algal bloom in temporarily open/closed estuary

Spatio-temporal variation in phytoplankton community dynamics in a temporarily open/closed Swarnamukhi river estuary (SRE), located on the South East coast of India was investigated and correlated to that of the adjacent coastal waters. Understanding the seasonal variability of the phytoplankton community and influencing factors are essential to predicting their impact on fisheries as the river and coastal region serve as the main source of income for the local fishing communities. Downstream before the river meets the sea, an arm of the Buckingham Canal (BC), carrying anthropogenic inputs empties into the Swarnamukhi River (SR1). The impact of anthropogenic effects on the phytoplankton community at BC was compared to other estuarine stations SR2 (upstream), SR1 (downstream), SRM (river mouth) and coastal station (CS). In BC station, harmful algal blooms (HABs) of Chaetoceros decipiens (2940 × 103 cells L−1) and Oscillatoria sp. (1619 × 103 cells L−1) were found during the southwest monsoon and winter monsoon, respectively. These HABs can be linked to the anthropogenic input of increased nutrients and trace metals. The HABs of Oscillatoria sp. were shown to be induced by elevated concentrations of nitrate (10.18 µM) and Ni (3.0 ppm) compared to ambient, while the HABs of C. decipiens were caused by elevated concentrations of silicate (50.35 µM), nitrite (2.1 µM), and phosphate (4.37 µM). Elevated nutrients and metal concentration from the aquaculture farms, and other anthropogenic inputs could be one of the prime reasons for the recorded bloom events at BC station. During this period, observed bloom species density was found low at other estuarine stations and absent at CS. The formation of bloom events during the closure of the river mouth could be a major threat to the coastal ecosystem when it opens. During the Osillatoria sp. bloom, both the Cu and Ni levels were higher at BC. The elevated concentration of nutrients and metals could potentially affect the coastal ecosystem and in turn fisheries sector in the tropical coastal ecosystem.

Phytoplankton Diversity and Blooms in Ephemeral Saline Lakes of Cyprus

The ephemeral saline lakes of Cyprus in the Mediterranean, situated in close proximity to each other, demonstrate pronounced seasonal and interannual fluctuations in their environmental conditions. Despite their extreme saline conditions, these lakes support phytoplankton diversity and bloom-forming species. Anthropogenic activities, particularly urban and artificial land uses within their catchments, contribute to eutrophication, warranting conservation attention within the context of European legislation. Over two years (2018–2019), we examined phytoplankton abundance and diversity alongside salinity in six lakes, with samples collected every three weeks. Chlorophytes were the dominant and most diverse group, followed by cyanobacteria and diatoms. Increasing salinity correlated with reduced compositional diversity and species richness. The proximity of lakes to each other suggested airborne microbe colonization from one lake to another as a significant factor in shaping these communities, while similar land use within each lake’s catchment impacted bloom formation. The highly halotolerant chlorophyte Dunaliella frequently dominated phytoplankton blooms, occasionally coexisting with other taxa in less saline lakes. Our findings provide insight into the phytoplankton community dynamics in temporal saline lakes, essential for developing effective conservation strategies and sustainable management practices.

Trait-based classification and environmental drivers of phytoplankton functional structure from anthropogenically altered tropical creek, Thane Creek India

The present study on variability in phytoplankton functional structure through a trait-based approach described the species-trait-environmental relationship and its possible impact on ecosystem functioning. Based on trait similarities 102 phytoplankton species were clubbed into 14 distinct functional groups. Among others, FGs-XI and XII (small size, chain-forming species with medium to high SA:V ratio and space between cells in chain) were the most dominant due to their competitive advantage in resource utilization and avoidance of loss processes. The morphological traits space between cells and cellular protrusion along with temperature and ammonia played a decisive role in their seasonal succession. Eutrophication in Thane Creek favors the dominance of anti-grazing traits which increases the phytoplankton biomass through efficient resource acquisition but can encumber the energy transfer efficiency. The dominance of HAB species impedes ecosystem functioning which raises public health concerns. The strong correlation of environmental variables with phytoplankton functional structure reinforces the practical implementation of a trait-based approach for understanding phytoplankton community dynamics under varying environmental conditions.

Spatial and Temporal Characteristics of Phytoplankton Communities in Drinking Water Source Reservoirs in Shenzhen, China

Phytoplankton diversity and community characteristics are closely associated with aquatic environmental factors. Understanding these dynamics can provide insights into the ecological health of water bodies. We investigate the spatial and temporal characteristics of phytoplankton communities in 27 drinking water source reservoirs in Shenzhen, China. As a method, we collected samples during the dry season in 2021 and the wet season in 2022, analyzed the alpha and beta diversities of phytoplankton communities, and correlated these with the environmental factors. The results reveal that Cyanobacteria dominate the phytoplankton communities in the Shenzhen reservoirs. Phytoplankton diversity is greater during the dry season. The algal composition varies spatially, and the phytoplankton diversity tends to decrease with increasing eutrophication. A co-occurrence network analysis indicates denser and stronger correlations among phytoplankton nodes during the wet season than dry season. Reservoirs with moderate eutrophication levels exhibit denser nodes and stronger correlations compared to those with low or high eutrophication levels. The chemical oxygen demand, water temperature, pH, and total nitrogen are identified as key influencers of the phytoplankton community structure. Our results contribute to the enhanced understanding of the spatial and temporal dynamics of phytoplankton communities in reservoirs in South China and provides insights into the management and conservation of these drinking water reservoirs.

Hydrological conditions can change the effects of major nutrients and dissolved organic matter on phytoplankton community dynamics in a eutrophic river

In river ecosystems with diverse hydrological conditions, major nutrients and dissolved organic matter (DOM) play significant roles in governing the abundance and composition of phytoplankton communities. Understanding the significance of these factors is crucial for mitigating phytoplankton blooms. An extensive study was conducted to explore this relationship including an examination of 108 phytoplankton communities in the mainstream and eight tributaries of the Dongjiang River during both rainy and dry seasons. The results demonstrated the profound impact of both major nutrients and DOM on phytoplankton communities (p < 0.05). Under high-flow velocity conditions, major nutrients dominated, explaining 20 % and 2.5 % of variance during the rainy and dry seasons, respectively. DOM had a smaller influence, contributing −2.4 % and 1.1 % during these seasons. Conversely, under low-flow velocity conditions, major nutrients explained less than 8.0 % of the variation, while DOM became prominent, explaining over 11.8 % of the phytoplankton community dynamics. The dominant genera exhibited pronounced blooms in response to increased major nutrient levels across all hydrological conditions. Specific DOM components (C2, C3, and C4) were positively correlated with phytoplankton in the low flow streams (p < 0.05). These findings indicate the dual influence of major nutrients and DOM on phytoplankton communities, with their relative significance contingent upon spatial variations in hydrological conditions. As the flow velocity decreased and the potential nutrient retention time increased, the importance of DOM surpassed that of the major nutrients. These insights have substantial implications for managing stream ecosystems and preventing phytoplankton blooms in eutrophic river systems.

Phytoplankton Community Dynamics in Sei Gesek Reservoir, Bintan Island

Bintan is a small island that has limited fresh water resources. Sei Gesek Reservoir is one of the drinking water sources in there. The aim of this research is to determine the dynamics of diversity and abundance phytoplankton in Sei Gesek Reservoir, Bintan Island, Riau Islands. Sampling was carried out at three area representing inlet, center, and outlet of Sei Gesek reservoir in periods 2016-2018. Phytoplankton samples were collected using plankton net by static method. Phytoplankton group were composed of 3 division: Chlorophyta, Cyanophyta, and Bacillariophyta. Each class of phytoplankton has dynamics of abundance and species each year. The highest average abundance was found in 2016 and then fluctuated to 2018. The highest species and abundance of the division were Chlorophyta, Cyanophyta, and Bacillariophyta, respectively. Phytoplankton community dynamics in Sei Gesek Reservoir is influenced by decreased water volume and acidic pH.

HABs and HAB nots: Dynamics of phytoplankton blooms across similar oligotrophic reservoirs

Increasing frequency and intensity of cyanobacterial Harmful Algal Blooms (HABs) threaten human and aquatic ecosystem health. Improving our understanding of HABs across a range of systems will be critical to understanding and potentially minimizing risk, especially where HABs are occurring in less productive and less studied waterbodies. Here, the characteristics and annual dynamics of phytoplankton communities were examined, focusing on the timing, magnitude, and predictability of cyanobacterial blooms in five multi-purpose flood-control reservoirs from the Willamette Basin, Oregon, USA. A high similarity in phytoplankton composition and consistency in the timing of cyanobacterial dominance was hypothesized to occur across these oligotrophic reservoirs. However, periods of dominance by potentially HABs producing genera were inconsistent both in their timing and abundances among reservoirs and across years within each reservoir. The lack of regional predictability indicates the importance of local drivers in the formation, intensity, and composition of phytoplankton blooms. These findings have important implications for reservoir management and safeguarding freshwater drinking sources, as not all reservoirs appear to experience cyanobacterial blooms at the same time, demonstrating non-concurrent risks of HABs.

Spatial and temporal variability of phytoplankton dynamics in-relation to essential oceanographic variables in the south east coast of Bangladesh

Phytoplankton form the base of food chain and play a key role in maintaining the global climate system. However, very limited knowledge is available about the phytoplankton ecology of Bangladesh coast which is a representation of sub-tropical coastal ecosystem. Thus, this study aimed to understand the spatial and temporal variability of phytoplankton community in-relation to environmental variables in the South East coast of Bangladesh. Monthly data on essential oceanographic variables (i.e. temperature, salinity, dissolved oxygen, turbidity, silicate, nitrate and phosphate) and phytoplankton species abundance were collected from January 2022 to December 2022. We found a strong spatial and temporal variability in essential oceanographic variables and phytoplankton community compositions in Naf – Saint Martin Peninsula of Bangladesh. Estuarine ecosystem is characterized by high nutrients and low salinity while offshore ecosystem was found with comparatively low nutrients and high salinity. About 154 phytoplankton species were identified from the study area through year round sampling events. In the estuarine ecosystem Skeletonema marino, Coscinodiscus centralis, Coscinodiscus argus and Coscinodiscus traducens were found as the major contributing species at the estuarine ecosystem while Chaetoceros radican, Tripos trichoceros, Cylindrotheca Closterium, Chaetoceros convulutus, Tripos muelleri, and Cyclotella striata were found as the major contributing species at the offshore ecosystem. Our study found that 6 explanatory variables (i.e. temperature, salinity, turbidity, silicate, nitrate and phosphate) jointly explained about 78% variability in phytoplankton community dynamics. Nitrate concentration explained maximum variability (19%) followed by phosphate (17%), salinity (15%), silicate (12%), turbidity (10%) and surface temperature (5%). This study will play a key role in understanding the spatial and temporal variability of phytoplankton dynamics in the sub-tropical coastal ecosystem.

Metal and metallothionein concentrations in mesozooplankton from an oligotrophic offshore area in the eastern Mediterranean Sea (Cretan Passage/Levantine Sea)

Spatial variability of Cd, Cu, Cr, Ni, Zn, Fe, Mn, Pb and metallothionein (MT) concentrations were determined in mesozooplankton samples along the west-east axis of the Cretan Passage in the western Levantine Sea (Eastern Mediterranean). Metal and MT values from the present study are proposed as background levels, due to the lack of substantial anthropogenic activities in the area, where only maritime traffic and atmospheric deposition could be potential sources. Higher concentrations, of both metals and MTs, were recorded mainly at the western stations indicating higher metal bioavailability than in the eastern part. An inverse relationship of the metal zooplankton levels with zooplankton biomass, abundance and vital rates (production, respiration and ingestion rates), as well as salinity, was evident. We discuss the hypothesis that physical and biological characteristics of the marine environment, affecting growth dynamics of phytoplankton and zooplankton communities, may also act on metal uptake in oligotrophic marine systems.

Responses of phytoplankton community dynamics to reduced underwater light in spring

Responses of phytoplankton community dynamics to reduced underwater light in spring

Environmental Controls of phytoplankton in the river dominated sub-tropical coastal ecosystem of Bangladesh

Sub-tropical coastal ecosystems are considered as the hotspot of species diversity. However, due to challenges regarding data collection, these regions are inherently data-limited and thus hindering informed species conservation strategies. Considering this, the present study aimed to assess the ecological characteristics of a river dominated sub-tropical coastal ecosystem of Bangladesh. More specifically, in this study we examined the spatial variability in environmental conditions and phytoplankton in the coastal ecosystems of Bangladesh. We also examined the causal relationship between environmental variables and phytoplankton species abundance. Data on environmental variables, including temperature, salinity, dissolved oxygen, turbidity, and macronutrients, was gathered in the north-east monsoon season between 2020 and 2022. We performed multivariate statistics to identify the variability in phytoplankton community dynamics. Results showed strong spatial variability in environmental conditions. Salinity, turbidity, nutrients concentrations and chlorophyll were found as the major drivers of this spatial heterogeneity. Central coast was characterized by low salinity, and high turbidity and silicate concentration while south-east coast was characterized by high salinity and low nutrient concentrations. In contrast, the south-west coast was characterized by high nitrate and phosphate, and moderate level of turbidity and salinity. Furthermore, our study identified 121 phytoplankton species. Maximum species diversity was observed in the south-west coast followed by central and south-east coast. Whereas 66 species occurred simultaneously in the three coastal zones, Coscinodiscus, Odontella and Nitzchia were the dominant phytoplankton genus in the central coastal zone. Skeletonema, Ditylum and Proboscia were found as dominant species in the south-east coastal zone. Coscinodiscus, Odontella, Nitzchia, Proboscia, Ditylum and Thalassionema were found as the key species in the south-west coastal zone. Seven explanatory variables (i.e. temperature, salinity, turbidity, silicate, nitrite, phosphate and zooplankton abundance) jointly explained about 44% to 73% variability in phytoplankton species abundance. We identified salinity and macronutrients as the major drivers of phytoplankton variability. This study is the first systematic report on phytoplankton community dynamics in-relation to environmental variables considering data from the entire coastal ecosystem of Bangladesh.

Global estimation of phytoplankton pigment concentrations from satellite data using a deep-learning-based model

Based on a global matchup between satellite observations and high performance liquid chromatography (HPLC) measurements, we developed a deep-learning-based model (DL-PPCE model) for globally estimating concentrations of 17 different phytoplankton pigments. The model adopted a fusion architecture of residual and pyramid networks to achieve robust estimation performance. The model inputs include three different data types: essential ocean color parameters, satellite-derived environmental parameters, and the slope of above-surface remote-sensing reflectance (Rrs). We compared the model performances with various input parameters to determine the most effective inputs. The results showed that Rrs in the essential ocean color parameters and sea surface temperature (SST) in the environmental parameters were the most critical input parameters. The estimation of phytoplankton pigment concentrations was validated against HPLC data using the leave-one-out cross-validation method. Except for three pigments, 19′-butanoyloxy-fucoxanthin, prasinoxanthin, and lutein, the estimated pigment concentrations and in-situ observations were strongly correlated for all other pigments (an average relative root-mean-square error of 0.59, R2≥0.60, and regression slopes close to 1). In addition, a time series analysis was performed on the MODIS retrieved global pigment concentrations during 2003–2021 using the established DL-PPCE model to explore the relationship between the distribution of phytoplankton groups and El Niño in the western equatorial Pacific. Our findings revealed that the prokaryotes-dominated area extended eastward from180°E to 150°W during the 2015/2016 El Niño event. From 2003 to 2021, prokaryotic abundance was positively correlated with El Niño intensity (R=0.65,P≪0.01) but negatively correlated with the abundance of the entire phytoplankton community (R=−0.53,P≪0.01). These results demonstrate that the DL-PPCE model presents a novel approach for estimating the concentration of 17 pigments worldwide, and the estimated pigment concentrations are advantageous for analyzing the phytoplankton community dynamics on a large spatiotemporal scale.

Determination of phytoplankton community structure and biomass with HPLC-CHEMTAX and microscopic methods during winter and summer in the Qinzhou Bay of the Beibu Gulf

The Qinzhou Bay, a typical semi-enclosed bay, is facing environmental pressure from local fast-growing industrial and aquacultural development. Dominant species of phytoplankton community (based on microscopic examination) show a trend of miniaturization, while pico-phytoplankton (based on CHEMTAX analysis) is widely distributed in Qinzhou Bay. However, most previous investigations of phytoplankton community based on microscopic method that undetected small-sized cell (&amp;lt; 3 μm), and limited by scarce studies on CHEMTAX analysis, the long-term dynamic data of small-size phytoplankton are lacking in Qinzhou Bay. It is recognized that combining microscopic examination with CHEMTAX analysis could provide a good taxonomic reliability for large cells and valuable information about small-size groups. In this study, microscopic examination and High Performance Liquid Chromatography (HPLC)-CHEMTAX analysis were employed to characterize the spatiotemporal variability of the phytoplankton community structure in Qinzhou Bay in winter and summer of 2021. The results of microscopic observations showed that the phytoplankton community was characterized by diatoms and dinoflagellates mainly. Diatoms dominated in both seasons, of which Skeletonema costatum bloom occurred in the summer. CHEMTAX analysis not only agreed well with microscopy data for diatoms and dinoflagellates, but also helped identification of other small-sized flagellates and cyanobacteria that hard to observe by microscope. The results of CHEMTAX analysis found that diatoms, prasinophytes and cryptophytes co-dominated the total chlorophyll a in winter while diatoms became the dominant group in summer. In addition, our results indicate that the proportion of small-sized flagellates has increased in the past decade in Qinzhou Bay, especially for cryptophytes. Temperature, nutrient availability, and selective grazing of oyster affected the succession of phytoplankton community from co-dominance of diatoms and flagellates in winter to absolute diatoms dominance in summer. The distribution of prasinophytes and cryptophytes on a spatial scale were related to the location of shellfish culture area and estuary, respectively, rather than by nutrients. Eutrophication, selective grazing of oyster and warming were the driving factors of long-term changes in phytoplankton composition in Qinzhou Bay. This study enhanced our understanding of entire phytoplankton community dynamics and its relationship with environmental factors in Qinzhou Bay.

Interaction among spring phytoplankton succession, water discharge patterns, and hydrogen peroxide dynamics in the Caloosahatchee River in southwest Florida

Phytoplankton communities are major primary producers in the aquatic realm and are responsible for shaping aquatic ecosystems. The dynamics of algal blooms could be determined by a succession of variable taxonomic groups, which are altered based on complex environmental factors such as nutrient availability and hydraulic factors. In-river structures potentially increase the occurrence of harmful algal blooms (HABs) by increasing water residence time and deteriorating water quality. How flowing water stimulates cell growth and affects the population dynamics of phytoplankton communities is a prioritized question that needs to be addressed for water management tactics. The goal of this study was to determine if an interaction between water flow and water chemistry is present, furthermore, to determine the relationship among phytoplankton community successions in the Caloosahatchee River, a subtropical river strongly influenced by human-controlled water discharge patterns from Lake Okeechobee. Particularly we focused on how phytoplankton community shifts influence the natural abundance of hydrogen peroxide, the most stable reactive oxygen species and a byproduct of oxidative photosynthesis. High-throughput amplicon sequencing using universal primers amplify 23S rRNA gene in cyanobacteria and eukaryotic algal plastids revealed that Synechococcus and Cyanobium were the dominant cyanobacterial genera and their relative abundance ranged between 19.5 and 95.3% of the whole community throughout the monitoring period. Their relative abundance declined when the water discharge increased. On the contrary, the relative abundance of eukaryotic algae sharply increased after water discharge increased. As water temperature increased in May, initially dominant Dolichospermum decreased as Microcystis increased. When Microcystis declined other filamentous cyanobacteria such as Geitlerinema, Pseudanabaena, and Prochlorothreix increased in their relative abundances. Interestingly, a peak of extracellular hydrogen peroxide was observed when Dolichospermum dominance was ended, and M. aeruginosa numbers increased. Overall, phytoplankton communities were strongly impacted by human-induced water discharge patterns.