Phytoplankton Community Dynamics Research Articles

The effects of Cefixime and Aspirin on phytoplankton community structure and dynamics: A Mesocosm approach

Pharmaceuticals are emerging contaminants of interest due to their ability to induce changes in the environment. These chemical compounds are discharged into aquatic ecosystems with a high likelihood of affecting non-target organisms such as phytoplankton. However, there is a gap in knowledge regarding the effects of pharmaceuticals on phytoplankton. This study used the mesocosm approach to investigate the effects of cefixime, a cephalosporin antibiotic and aspirin, a nonsteroidal anti-inflammatory drug on the community structure (species diversity, richness, and abundance) of phytoplankton. The mesocosm approach studied the effects of three treatments of pharmaceuticals: cefixime, aspirin and a combination of cefixime and aspirin, alongside a control experiment for 21 days. A total of 31 phytoplankton species belonging to five groups were identified; with diatoms and green algae having higher diversity compared to the other algae groups. Scenedesmus sp., Pediastrum sp. and Zygnema sp. were the top three recurring species in all the samples taken throughout the experimental period. Navicula sp. were the most recurring diatoms. The exposure of phytoplankton to cefixime, aspirin, and a combination of cefixime and aspirin significantly reduced the diversity, richness, and abundance of all species by the 21st day of the experiment. The control had the highest cell density (8,910 cells mL) of phytoplankton species on the 21st day, while the cefixime treatment had the lowest cell density (48 cells mL) f phytoplankton species on the seventh day of the study. This study demonstrated that cefixime and aspirin had major impacts on the phytoplankton community.

Allelopathic activity of cyanobacteria isolated from Lake Tuzkol.

Allelopathy plays a crucial role in shaping phytoplankton community dynamics and diversity. It influences competition between photoautotrophs for resources and affects species succession in aquatic ecosystems. This article evaluates the allelopathic activity of cyanobacteria isolated from Lake Tuzkol, Kazakhstan. The allelopathic effects, including growth inhibition or stimulation, were assessed by adding cell-free filtrates of the cyanobacteria Oscillatoria sp. SS-9, Nostoc sp. CZS 2205, Synechococcus sp. SS-5, or Anabaena sp. SS-8 to the tested microalgae. The most pronounced effect was observed with Nostoc sp. CZS 2205, which reduced the cell counts of Chlorella vulgaris SP BB-2 and Chlamydomonas reinhardtii CC-124 by 60% and 57%, respectively, and Scenedesmus quadricauda CC-1 and Ankistrodesmus falcatus CB-2 by 55% and 53%, respectively. Synechococcus sp. SS-5, in contrast, stimulated the growth of Chlorella vulgaris SP BB-2 and Scenedesmus quadricauda CC-1 by 11% and 8.8%, respectively. Filtrates from Oscillatoria sp. SS-9 and Anabaena sp. SS-8 had no significant impact on microalgal growth. Considering the significant allelopathic activity of Nostoc sp. CZS 2205, an agar diffusion test using biomass extracts confirmed a significant inhibitory effect, with the biomass extracts showing stronger activity than cell-free filtrates. A detailed analysis of the cell-free filtrates revealed eight compounds, including methyl heptadecanoate, methyl eicosanoate, tricosane, methyl octadeca-9,12-dienoate, methyl 13,16-octadecadienoate, and 2,2-dimethoxybutane. Additionally, nostocyclamide, a cyclic peptide, was identified in the biomass extract. The detection of nostocyclamide emphasizes its ecological importance and potential evolutionary role. These results enhance our understanding of the role of cyanobacteria in aquatic ecosystems and lay the groundwork for future research into their ecological applications.

Dynamics of phytoplankton community in relation to environmental variables in tropical mangrove estuary, Sundarbans, India

Aim: To explore the spatio-temporal variation of phytoplankton diversity and community structure, in response to associated environmental variables in Matla estuary, Sundarbans, India. Methodology: Monthly sampling was carried out from August 2022 to July 2023 at three locations within the estuary. Plankton was identified and its dynamics were studied in relation to the environment variables. Results: A total of 38 genera of phytoplankton, belonging to 8 classes, were identified. Spatial diversity was high in the upper reaches of the estuary, while temporal diversity peaked during the monsoon season. The majority of the abundance (96%) was contributed by four classes: Coscinodiscophyceae (35%), Mediophyceae (27%), Bacillariophyceae (25%) and Dinophyceae (9%). Bacillariophyceae exhibited higher species richness, while Coscinodiscophyceae dominated in terms of density. Cluster analysis and non-metric multidimensional scaling revealed four separate groups with varying spatio-temporal attributes. Analysis of variance (ANOVA) post-hoc tests highlighted significant variations in environmental parameters across seasons. Various phytoplankton groups were positively correlated with the physio-chemical parameters such as temperature, alkalinity, free CO2, NO3, NO2, silicate, temperature, orthophosphate and chlorophyll-a. Biota-environment stepwise analysis (BIO-ENV) underscored the importance of air temperature and free CO2 (ρ= 0.4929) as key factors shaping phytoplankton distribution and community structure. Canonical Correspondence Analysis (CCA) further showed the significant influence of parameters such as temperature, silicate, nitrite and orthophosphate on the phytoplankton community. Interpretation: Finding of this study enriches our comprehension of estuarine ecosystem dynamics, and this information may serve as a baseline study and thereby aid in framing management measures for long-term conservation and management of both biotic and abiotic components within estuaries. Key words: Environmental variables, Estuary, Mangrove, Phytoplankton, Sundarbans

Seasonal Dynamics of Trichodesmium and Phytoplankton Communities in the Eastern Arabian Sea: Winter Vs Spring-inter monsoon

The filamentous marine cyanobacterium Trichodesmium forms extensive blooms in tropical seas, where it plays an important role in nitrogen fixation. This study investigated Trichodesmium-associated phytoplankton in the Eastern Arabian Sea (EAS) during bloom and nonbloom conditions. Trichodesmium blooms over the continental shelf primarily comprised of T. erythraeum and T. thiebautii during the Spring Inter Monsoon (SIM) and T. erythraeum during the Winter Monsoon (WM). T. erythreaum blooms have rarely been reported from the north-east Arabian Sea during WM. Trichomes comprised of 143-1552 cells during the WM, with filaments ranging from 1339 to 13163 µm in length. Non-diazotrophic groups like diatoms and dinoflagellates were associated with Trichodesmium during both seasons within the bloom waters. The study found a novel symbiotic relationship between the heterocystous diazotroph Richelia intracellularis and Nitzschia sicula during WM blooms. This research expands knowledge of lesser-known phytoplankton species and their associations in the EAS.

Biotic homogenization in multisystem cascade reservoirs: insights from sedimentary photopigment analysis.

The existing literature provides limited insights into the dynamics of phytoplankton communities and the spatial heterogeneity of physicochemical parameters in multisystem cascade reservoirs (interconnected reservoirs derived from different rivers). The existing studies are concentrated on cascade reservoirs (interconnected reservoirs derived from the same river). To address this knowledge gap, the aims of the present study were as follows: (1) investigate the spatial heterogeneity, within and between reservoirs, of geochemical parameters associated with the eutrophication process, considering total phosphorus, chlorophyll-a, pheophytin, and metals (chromium, copper, nickel, lead, zinc, iron, and manganese); (2) evaluate sediment quality at the designated locations; (3) assess differences in the richness and concentration of sedimentary photopigments between the reservoirs. Application of principal component analysis revealed discernible gradients for the abiotic variables, although the differences were not statistically significant (one-way PERMANOVA test, p > 0.05). The observations suggested a tendency towards spatial homogeneity within and between the reservoirs. The metal concentrations were consistent with regional reference values, while phosphorus levels in the sediment approached the threshold for classification as pollution (~ 2000mg/kg). Analysis of pigments indicated low dissimilarity among the reservoirs, which could be mainly attributed to the eutrophication process and high connectivity of the sampled areas. To counteract ongoing biotic homogenization, it is essential to reduce nutrient inputs and invest in ecological protection and restoration programs. The analysis of sedimentary photopigments provides an efficient and cost-effective alternative way to assess phytoplankton communities.

Pollution load and dynamics of phytoplankton communities in relation to environment variables in Lake Babogay, Ethiopia

ABSTRACT The objective of this study was to investigate the water quality of Lake Babogaya in Ethiopia. Water samples were collected from six different sites, and analyzed for total coliform (TC), fecal coliforms (FC), and Escherichia coli (E.coli) content. Additionally, potential of hydrogen (pH), dissolved oxygen (DO), total dissolved solids (TDS), electrical conductivity (EC), and Secchi depth were measured. Nutrients and heavy metals were determined using standard methods. The abundance of phytoplankton was estimated by calculating the biovolume of the species. The results indicated that pH, TDS, DO, and turbidity ranged from 8.78 + 0.31 to 9.52 + 0.04, 129 + 4 to 419 + 3 ppm, 5.50 to 7.25 mg/l, and 0.96 to 17.29 NTU, respectively. TC bacteria exceeded the World Health Organization (WHO) standards at all sites, while FC levels exceeded in most samples. Cadmium and chromium were low in both seasons, whereas lead in the dry season exceeded the WHO limits. The levels of iron were high across all sites in the dry season and low in most sites in the wet season. Five major taxonomic phytoplankton groups were identified, comprising a total of 31 species with highest richness of green algae, blue-green algae, and diatoms species.

Dynamics of phytoplankton communities in the Baltic Sea: insights from a multi-dimensional analysis of pigment and spectral data—part I, pigment dataset

This study aims to investigate the seasonal and spatial distribution of surface phytoplankton communities in the Baltic Sea, using pigment analysis and hydrological parameters. Data were collected during six oceanographic campaigns between 2005 and 2008, including high-performance liquid chromatography (HPLC) pigment characterization and hydrological measurements. The first part of this comprehensive study was focused on the HPLC phytoplankton pigment dataset in relation to hydrological conditions. The research highlighted the importance of high-quality input data for accurate taxonomic analysis. Several unsupervised machine learning approaches, such as hierarchical cluster analysis (HCA), principal component analysis (PCA), and network-based community detection analysis (NCA), were used to analyze the data and identify phytoplankton communities based on biomarker pigments. Five main phytoplankton communities were identified: diatoms, dinoflagellates, cryptophytes, green algae, and cyanobacteria. The results evidenced distinct seasonal patterns, with diatom blooms dominating in spring, cyanobacterial blooms in mid-summer, and haptophyte and dinoflagellate peaks occurring in late summer and autumn. While PCA and NCA provided consistent insights into community structure, HCA offered less clarity in distinguishing between groups. The results of the statistical analysis were then compared with those of traditional approaches such as CHEMTAX and region-specific bio-optical algorithms, providing new perspectives on the taxonomic composition of phytoplankton groups. This study provides valuable insights into phytoplankton dynamics in the Baltic Sea and the effectiveness of different analytical approaches in understanding community structure, providing metrics that can enhance current and future advancements in remote sensing, including support for hyperspectral ocean color remote sensors.

A New Method for the Detection of Siliceous Microfossils on Sediment Microscope Slides Using Convolutional Neural Networks

AbstractDiatom communities preserved in sediment samples are valuable indicators for understanding the past and present dynamics of phytoplankton communities, and their response to environmental changes. These studies are traditionally achieved by counting methods using optical microscopy, a time‐consuming process that requires taxonomic expertise. With the advent of automated image acquisition workflows, large image data sets can now be acquired, but require efficient preprocessing methods. Detecting diatom frustules on microscope images is a challenge due to their low relief, diverse shapes, and tendency to aggregate, which prevent the use of traditional thresholding techniques. Deep learning algorithms have the potential to resolve these challenges, more particularly for the task of object detection. Here we explore the use of a Faster Region‐based Convolutional Neural Network model to detect siliceous biominerals, including diatoms, in microscope images of a sediment trap series from the Mediterranean Sea. Our workflow demonstrates promising results, achieving a precision score of 0.72 and a recall score of 0.74 when applied to a test set of Mediterranean diatom images. Our model performance decreases when used to detect fragments of these microfossils; it also decreases when particles are aggregated or when images are out of focus. Microfossil detection remains high when the model is used on a microscope image set of sediments from a different oceanic basin, demonstrating its potential for application in a wide range of contemporary and paleoenvironmental studies. This automated method provides a valuable tool for analyzing complex samples, particularly for rare species under‐represented in training data sets.

Microbial assessment of the ecological linkage between a red tide of Karenia brevis and bottom water anoxia off the coast of Fort Myers and Sanibel Island, Florida

Coastal ecosystem management necessitates a comprehensive understanding of the physical, chemical, and biological components and their interplay with socio-economic activities. Red tides of Karenia brevis reoccur almost annually on the West Florida Shelf and cause significant human and environmental health problems that often result in negative economic impacts. It is crucial that we understand the processes and dynamics of both phytoplankton and microbial communities as conditions necessary for the formation of hypoxia and anoxia in the coastal ecosystem. With the aim of identifying key microbial communities responsible for anoxia, we investigated the 2017–2018 Karenia bloom. Various water quality parameters, phytoplankton, and microbial community compositions were studied at eight sites on the West Florida Shelf. K. brevis densities were highest at the site of the plume of the Caloosahatchee River. At the site with the highest K. brevis abundance (6.3 ×106 cells/L), dissolved oxygen (DO) was supersaturated (303 %) at the surface, and the chlorophyll a concentration was 118 µg/L. The highest bacterial cell count (9.0 ×106 cells/mL) and the lowest bacterial diversity were also observed at this site. The bacterial community determined by high-throughput amplicon sequencing at this bloom site was unique and dominated by Bacteroidetes, which occupied 65 % of the relative abundance of the microbial community. The bottom water was generally hypoxic (mean ± SD: 0.98 ± 1.13 mg/L), with select stations having DO as low as 0.06 mg/L (anoxic). The anoxic bottom water harbored unique microbial taxa that were associated with the low oxygen conditions. Significant negative correlations were found between DO and the relative abundance of Deltaproteobacteria, Firmicutes, Spirochaetes, and unclassified Proteobacteria. Our investigation lays the groundwork for subsequent studies delving into the responses of phytoplankton and microbial communities to disturbances caused by Karenia blooms, as well as future strategies for mitigation and ecosystem restoration.

Investigation on phytoplankton dynamics and its environmental correlates in the Xiangjiaba channel-type reservoir

Mega reservoirs, such as the Three Gorges Reservoir on the Yangtze River, have garnered significant attention due to their environmental impacts. However, the ecological ramifications of upstream cascade reservoirs remain understudied, despite their potential influence on the Yangtze River ecosystem. The Xiangjiaba Reservoir (XJB), presents a unique case for understanding the ecological impacts of large channel-type reservoirs marked with considerable water depth and extensive runoff, which lies between the characteristics of rivers and lakes. This study delves into the phytoplankton community dynamics and associated environmental factors within the XJB. Through field surveys and laboratory analysis, we explore the drivers of phytoplankton distribution and their temporal shifts. Our findings revel significant changes in phytoplankton dominance among various phyla. Bacillariophyta and Chlorophyta dominated throughout the year, while Cryptophyta prevailed in spring and Xanthophyta peaked in autumn, indicating a unique ecological feature of XJB. The reservoir’s water quality was found to be moderate. The average chlorophyll-a exhibited significant spatial–temporal variations, peaking at 26 μg/L at the mainstream-tributary confluence. Our investigation reveals a tenfold increase in algal abundance since the reservoir’s inception, accompanied by a significant transition from a Bacillariophyta-dominated community to a diverse, multi-phylum system. This shift has been significantly influenced by hydrodynamic conditions, with water stratification favoring flagellated algae like Chlorophyta and Cryptophyta. Notably, differences in phytoplankton composition between XJB and the Three Gorges Reservoir were linked to the latter’s pronounced vertical mixing. The slower ecological responses of the phytoplankton community to hydrodynamic changes underscore the importance of long-term, continuous monitoring to maintain the reservoir’s ecological balance. Our research offers insights into the ecological impacts of reservoir construction, highlighting the role of hydrodynamics in reservoir ecosystems and aiding in understanding reservoir functioning, water quality management, and biodiversity conservation.

Effectiveness of artificial reefs in enhancing phytoplankton community dynamics: A meta-analysis

Artificial reefs (ARs) are widespread globally and play a positive role in enhancing fish communities and restoring habitat. However, the effect of ARs on phytoplankton, which are fundamental to the marine food chain, remains inconclusive. Conducting a literature review and meta-analysis, this study investigates how ARs influence phytoplankton community dynamics by comparing the biomass, density, and diversity of phytoplankton between ARs and natural water bodies across varying deployment durations, constituent materials, and climatic zones. The study findings suggest that, overall, ARs enhance the biomass, density, and diversity of phytoplankton communities, with no significant differences observed compared to natural water bodies. The enhancement effect of ARs on phytoplankton communities becomes progressively more pronounced with increasing deployment time, with the overall status of phytoplankton communities being optimal when artificial reefs are deployed for 5 years or longer. Concrete and stone ARs can significantly enhance the biomass and diversity of phytoplankton, respectively. The effect of ARs on phytoplankton diversity is unrelated to climatic zones. However, deploying ARs in temperate waters significantly enhances phytoplankton biomass, while in tropical waters, it significantly reduces phytoplankton density. The research findings provide practical implications for the formulation of artificial reef construction strategies tailored to the characteristics of different aquatic ecosystems, emphasizing the need for long-term deployment and appropriate material selection. This study offers a theoretical basis for optimizing AR design and deployment to achieve maximum ecological benefits.

Diel and seasonal mixing patterns and water quality dynamics in a multipurpose tropical semiarid reservoir.

Eutrophication has become a recurrent concern in reservoirs worldwide. This problem is intensified in tropical semiarid regions, where the reservoirs have high seasonal and annual variability of water level and volume. Therefore, an extensive understanding of the diel variation of water quality key-parameters can help improve management of such reservoirs. This study focuses on Castanhão reservoir with the largest multipurpose dam in the Brazilian semiarid. Its main water uses are irrigation, fish farming, and human supply. The reservoir faced a decline in water quality due to a prolonged drought period. While previous research has predominantly emphasized the seasonal dynamics of thermal and chemical stratification, our investigation provides diel assessments of multiple water quality parameters, including nutrient concentrations and phytoplankton abundance. Our primary objective is to compare seasonal and diel variations in stratification and nutrient distribution within the reservoir. Key findings reveal a diel cycle of thermal stratification, primarily during dry season, driven by higher wind speeds. This is corroborated by a significant negative correlation between wind speed and the relative water column stability index. In contrast, during the rainy season, the reservoir experiences continuous thermal stratification due to inflowing water being warmer than the reservoir's water temperature. Notably, a significant negative correlation between total phosphorus and chlorophyll-a, along with a two-fold increase of this nutrient throughout the day during the rainy season, underscores the influence of the phytoplankton community dynamics on the diel nutrient variation. Chemical stratification of dissolved oxygen occurred during dry and rainy seasons, indicating that even during the dry season, where there is no significant inflow, the internal nutrient loading can also significantly impact the water quality of a reservoir. This study advances the understanding of diel water quality dynamics in tropical semiarid reservoirs, shedding light on both climatic and anthropogenic influences on water resources.

Seasonal Phytoplankton Characteristics Related with Region-Specific Coastal Environments in the Korean Peninsula

The seasonal dynamics of phytoplankton communities in Korean coastal waters (KCWs) are influenced by complex interactions between ocean currents and nearshore human activities. Despite these influences, the understanding of seasonal phytoplankton changes and their environmental relationships in KCWs remains limited. We investigate the influence of the distinct characteristics of the three seas surrounding the KCWs (the Yellow Sea, the South Sea, and the East Sea) on seasonal phytoplankton communities based on field surveys conducted at 23 stations between 2020 and 2021. The East Sea exhibited higher winter temperatures due to the Jeju and Tsushima warm currents, while summer temperatures were lower compared to the other regions, highlighting the role of currents and deeper oceanic waters. The Yellow Sea showed significant freshwater influence with low salinity levels from major rivers, contrasting with the higher salinity in the East Sea. These differences led to a disparity in the productivity of the two regions: the highest value of Chl. a was observed to be 6.05 µg L–1 in the Yellow Sea in summer. Diatoms dominated in nutrient-rich conditions, particularly in the Yellow Sea, where they comprised up to 80–100% of the phytoplankton community in summer, winter, and spring. PCA analysis revealed positive correlations between diatoms and Chl. a, while cryptophytes, which thrive in the absence of diatom proliferation, showed no such correlation, indicating their opportunistic growth in nutrient-limited conditions. This study highlights the significant impact of region-specific hydrographic factors on phytoplankton communities in KCWs, with diatoms dominating in summer and cryptophytes and dinoflagellates showing seasonal and regional variations. Understanding these dynamics is crucial for predicting phytoplankton bloom dynamics and their ecological implications in coastal ecosystems.

Dynamics of Phytoplankton Communities and Environmental Drivers in Chinese Mitten Crab Aquaculture Ponds: Highlighting the Need for Cyanobacteria Control

Pond culture is the primary method for cultivating Chinese mitten crab (Eriocheir sinensis), with phytoplankton significantly influencing their growth. Green algae benefit crab growth by serving as supplementary food, while cyanobacteria, particularly during blooms, hinder it and pose health risks. Environmental changes in nutrient levels, temperature, and light significantly affect phytoplankton communities in ponds, impacting both ecosystem stability and crab growth. However, there is a limited understanding regarding the patterns of phytoplankton changes within adult Chinese mitten crab culture ponds. This study conducted monthly collection and analysis of phytoplankton throughout the culture cycle in typical adult Chinese mitten crab culture ponds, concurrently measuring physical and chemical water parameters to explore the correlation between phytoplankton changes and environmental factors. The results revealed distinct seasonal variations in phytoplankton composition. Chlorophyta and Bacillariophyta, such as Chlorella, Pediastrum, and Cocconeis, predominated in spring, while Chlorophyta and cyanobacteria, such as Volvox, Anabaena, and Microcystis, dominated in summer, and cyanobacteria and Bacillariophyta, such as Microcystis, Dolichospermum, and Cocconeis, prevailed in autumn. Total phytoplankton density consistently increased throughout the culture period. Microcystis constituted the majority of cyanobacteria biomass throughout most months. Although the total phytoplankton biomass fluctuated, cyanobacteria biomass consistently rose each month, reaching a peak of 61.7 mg/L in October. Water temperature and pH emerged as the primary environmental drivers influencing changes in phytoplankton community structure. Cyanobacteria density reached its peak between 18 and 26 °C and at a pH range of 7.5–8.5. These findings highlight the need for environmental regulation and cyanobacteria control in Chinese mitten crab culture ponds, thus promoting the health and sustainability of the Chinese mitten crab culture.

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.

Quantifying the dynamics of phytoplankton communities and its driving factors: An example from an agricultural pond within a lowland polder in Lake Taihu Basin

Quantifying the dynamics of phytoplankton communities and its driving factors: An example from an agricultural pond within a lowland polder in Lake Taihu Basin