Phytoplankton Community Structure Research Articles

Grazing strategies determine the size composition of phytoplankton in eutrophic lakes

AbstractAlthough the general impacts of zooplankton grazing on phytoplankton communities are clear, we know comparatively less about how specific grazing strategies interact with environmental conditions to shape the size structure of phytoplankton communities. Here, we present a new data‐driven, size‐based model that describes changes in the size composition of lake phytoplankton under various environmental constraints. The model includes an ecological trade‐off emerging from observed allometric relationships between (1) phytoplankton cell size and phytoplankton growth and (2) phytoplankton cell size and zooplankton grazing. In our model, phytoplankton growth is nutrient‐dependent and zooplankton grazing varies according to specific grazing strategies, namely, specialists (targeting a narrow range of the size‐feeding spectrum) vs. generalists (targeting a wide range of the size‐feeding spectrum). Our results indicate that grazing strategies shape the size composition of the phytoplankton community in nutrient‐rich conditions, whereas inorganic nutrient concentrations govern phytoplankton biomass. Under oligotrophic regimes, the phytoplankton community is dominated by small cell sizes and the grazers have little to no impact. Under eutrophic regimes, dominating specialist grazers push phytoplankton towards small cells, whereas dominating generalist grazers push phytoplankton towards large cells. Our work highlights that trait‐based modeling, based on realistic eco‐physiological trade‐offs, represents a valuable tool for disentangling the interactive roles played by nutrient regimes and grazing strategies in determining the size compositions of lake phytoplankton. Ultimately, our study offers a quantitative basis for understanding how communities of lake phytoplankton may reorganize in the future in response to changes in nutrient levels and zooplankton grazing strategies.

Analysis of the structure of phytoplankton communities in the ecological monitoring of Lake Zaozernoe (Russia)

In this work, the taxonomic composition, biodiversity, abundance, biomass, ecological features of planktonic algae and water quality in Lake Zaozernoye of the Pskov Region were studied a year after the territory was recognized as a natural monument. A twofold increase in the species richness of plankton was revealed, a two-fold decrease in representatives of the Euglenozoa phylum and a 40% decrease in representatives of Cyanobacteria. 145 phytoplankton taxa ranked below the genus from 8 phylums have been identified: Bacillariophyta (50 species taxa), Chlorophyta (36), Ochrophyta (18), Cyanobacteria (12), Euglenozoa (12), Miozoa (8), Cryptophyta (5) and Charophyta (4). The biomass was dominated by diatoms and cryptophytic algae. Toxic cyanobacteria species Aphanocapsa delicatissima and Aphanothece sp. have been identified among the dominant species in terms of numbers. 2 rare species of algae have been identified for reservoirs in the Northwestern region – Anabaena sphaerica Bornet Flahault (Cyanobacteria) and Phacus monilatus (A. Stokes) Lemmerman (Euglenozoa). The analysis of species diversity using the Sierensen–Chekanovsky, Shannon, Simpson, and Margalef diversity indices revealed changes in the structure of the plankton community in different areas of the lake. The species composition of Zaozernoye is compared with the lakes closest to it.

Marine Heat Waves in the Indian Ocean: A Major Climate Impact on Marine Microalgae

A clearly defined, lengthy (five days or longer) period of extraordinarily high ocean temperatures is known as Marine Heat Waves (MHWs) (above the e0th percentile). These events significantly impact the structure, abundance, cell size, metabolic functions, physico-chemical interactions between microalgae cells and their surroundings in the Indian Ocean. In the tropical Indian Ocean, the average sea surface temperature (SST) increased by 1.0°C (0.15°C/decade) on average between 1951 and 2015, while the global average SST warmed by roughly 0.7°C (0.11 °C/decade). This resulted from the incidence of Marine microalgal bloom MMBs (including Harmful Algal Bloom) and the number of causal taxa may grow as SST increases. Trichodesmium and Noctiluca contributed 34.4% and 31.8%, respectively, to the overall blooms. Such a heating phenomenon also triggers the dominance of small-sized algal cells, harmful diatoms and pico-plankton. The present paper reviews the Indian as well as global episodes of MHWs such as Western South Atlantic, North-East Pacific, Western Australia, Alaskan Sea etc. and their impact on phytoplankton. The combination of warming and heatwaves triggers blooms of buoyant cyanobacteria and its combined impacts of MHWs and ocean warming/acidification on phytoplankton community structure have not been fully studied in the Indian Ocean.

HPLC validation as a management tool in artificial water storage ponds

Pigment analysis through high-performance liquid chromatography (HPLC) offers a faster and more replicable study of the phytoplankton community structure than traditional taxonomy, but its application to small-sized freshwater ecosystems is infrequent. We carried out a taxonomy-based validation for the application of HPLC to the management of two artificial water storage ponds. We also investigated the error and variability sources that affected the relationships between calculated biovolumes of phytoplankton groups and associated pigment concentrations. For both qualitative and quantitative approaches, agreement was obtained between techniques that consistently identified biomass peaks and structural trophic differences between the ponds. Considering the most relevant pigment to biovolume ratios for total biomass, and partial biomass proxies of green algae and fucoxanthin containing algae, a decreasing tendency was obtained as total and partial biomass increased in all the studied models. Bidirectional variability affecting these relationships scaled under high biomass conditions and suggested a better suitability of HPLC application under oligotrophic conditions, which is in line with previous studies. Additionally, pigment data was able to identify mean stored volume as the main environmental factor that drove trophic differences between the ponds. We conclude that HPLC is accurate not just for monitoring purposes, but to carry out ecosystem-level assessments in artificial ponds. Therefore, we endorse the use of HPLC as part of the monitoring networks in small-sized freshwater ecosystems.

Unveiling the evolution of phytoplankton communities: Decades-long insights into the southern Yellow Sea, China (1959–2023)

We obtained historical and observational data on phytoplankton communities from 1959 to 2023 to explore the responses of the phytoplankton community structure to long-term environmental changes in the southern Yellow Sea (SYS), China. The results revealed a decrease in the proportions of diatom cell abundance within the phytoplankton community by 8 %, accompanied by a corresponding increase in that of dinoflagellates. Dominant phytoplankton species were mainly chain-forming diatoms before 2000, and large dinoflagellate species from the genera Tripos and Noctiluca increased their dominance after 2000. Warm-water phytoplankton species have increased in dominance over the study period. Correlation analysis revealed that the ocean warming and alterations in nutrient structure (N/P and Si/N ratios) were mostly responsible for the long-term evolution trend, and these changes may result in an increase in dinoflagellate harmful algal blooms, reduced efficiency of the biological carbon pump, and heightened hypoxia in the future, which should draw our attention.

Linking satellites to genes with machine learning to estimate phytoplankton community structure from space

Abstract. Ocean color remote sensing has been used for more than 2 decades to estimate primary productivity. Approaches have also been developed to disentangle phytoplankton community structure based on spectral data from space, in particular when combined with in situ measurements of photosynthetic pigments. Here, we propose a new ocean color algorithm to derive the relative cell abundance of seven phytoplankton groups, as well as their contribution to total chlorophyll a (Chl a) at the global scale. Our algorithm is based on machine learning and has been trained using remotely sensed parameters (reflectance, backscattering, and attenuation coefficients at different wavelengths, plus temperature and Chl a) combined with an omics-based biomarker developed using Tara Oceans data representing a single-copy gene encoding a component of the photosynthetic machinery that is present across all phytoplankton, including both prokaryotes and eukaryotes. It differs from previous methods which rely on diagnostic pigments to derive phytoplankton groups. Our methodology provides robust estimates of the phytoplankton community structure in terms of relative cell abundance and contribution to total Chl a concentration. The newly generated datasets yield complementary information about different aspects of phytoplankton that are valuable for assessing the contributions of different phytoplankton groups to primary productivity and inferring community assembly processes. This makes remote sensing observations excellent tools to collect essential biodiversity variables (EBVs) and provide a foundation for developing marine biodiversity forecasts.

Sources of uncertainty in satellite-derived chlorophyll-a concentration—An Adriatic Sea case study

This paper analyses a time series of chlorophyll-a profiles in the Adriatic from 1997 to 2019, and compares the data with satellite products with the view of analysing and reducing uncertainties in the corresponding satellite products. Three sources of uncertainties in satellite chlorophyll-a concentration are examined: (a) the algorithm itself; (b) the vertical structure of the water column; and (c) the phytoplankton community structure. Global and regional algorithms were examined, along with a local algorithm tuned using the time series data. The global algorithm produced the largest uncertainties when compared with the in situ data, followed by the regional and local algorithms. Correlation coefficient for the local algorithm was 0.690 - a significant increase from regional’s 0.420 and global’s 0.042. Both the global and the regional algorithms exhibited systemic errors that inversely were related to chlorophyll-a concentration, while the local algorithm displayed some reduction in the systematic errors, highlighting the value of local in situ observations, for improving sub-regional and local algorithms for retrieval of chlorophyll-a concentration from satellite ocean colour data. While the mixed layer has not shown any direct correlation with the uncertainties, it may facilitate exceptionally strong vertical gradients in chlorophyll-a profiles after summer blooms that take role as the main source of high differences between satellite observations and surface chlorophyll-a concentration. As such, it is important to supplement satellite measurements with vertical profiles to ensure valid readings and exercise caution when dealing with data post-blooms. These instances occurred in less than 3% of all cases. Differences in the phytoplankton community structures have shown direct correlation to estimation error - Miozoa is associated with low error, Bacillariophyta with high error, while Phytoflagellates abundance tips the error between underestimation and overestimation.

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.

Function rather than structure of phytoplankton community reveals changes of water quality in an ecological restored lake.

Although phytoplankton is well known as robust bioindicators to aquatic environments, their indicating functions based on different community parameters remain to be understood. In order to filter effective bioindicators in aquatic ecosystems, four phytoplankton community parameters including species richness (SR), total biomass (SBP), functional groups (FGBP), and size-fractionated chlorophyll-a (SC) were demonstrated in a subtropical artificial lake with ecological restoration in South China. Our results indicated that all the above four parameters exhibited high sensitivity to environmental variations and illustrated distinct aspects of indicating functions to aquatic environments due to their individual biological characteristics. Based on FGBP, both spatial and temporal differences in phytoplankton community could be identified. SR and SBP only classified the spatial and temporal distributions, respectively, while SC could distinguish the sewage outfalls from other sites. In terms of ecological management, two parameters (SR and FGBP) could distinguish the restored waters from untreated environments as non-point source pollution, and another parameter SC could indicate the sewage outfalls as point source pollution. Therefore, the combination of the above two categories of phytoplankton community parameters could make the strongest indicating functions. Our study provided greater insight into indicating functions of phytoplankton community parameters in an ecological restored lake and enabled better managements in such artificial lakes.

Spatio-temporal dynamics of phytoplankton diversity and community structure in relation to environmental variables in the Northwest Coasts of India

Spatio-temporal dynamics of phytoplankton diversity and community structure in relation to environmental variables in the Northwest Coasts of India

The effects of salinity on phytoplankton community structure in the 6 lagoons of the Marmara Basin (Türkiye)

The effects of salinity on phytoplankton community structure in the 6 lagoons of the Marmara Basin (Türkiye)

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.

Planktonic habitats in the Amazon Plume region of the Western Tropical North Atlantic

The Western Tropical North Atlantic is a highly dynamic marine system where the Amazon River Plume (ARP) generates a patchwork of environmental conditions that favor different phytoplankton groups. To study phytoplanktonic community structure in such heterogeneous conditions, we used a set of five standard ship-based measurements taken from oceanographic surveys between 2010 and 2021 to characterize different habitat types. We then utilized a variety of multiparametric approaches to examine phytoplankton biodiversity in the different habitats to assess the biological relevance of our delineated habitats. Our approach generated a consistent set of habitat types across cruises carried out in multiple different years and the Amazon’s two predominant (wet and dry) seasons. Our phytoplankton community analyses revealed strong distinctions among all habitats along the plume gradient using in-vivo fluorescence and diagnostic pigments, and clear contrasts of diazotroph community along the mesohaline waters using direct cell-count, a pattern consistent with niche partitioning among similar species. The few apparent mismatches we found between phytoplankton community composition and habitat may reflect recent hydrographic changes driven by mixing and/or upwelling and thus may be a useful index to biologically-relevant temporal variation. Our habitat classification approach is straightforward and broadly applicable in identifying biologically distinct areas within heterogeneous and dynamic regions of the ocean.

Effects and mechanisms of glyphosate as phosphorus nutrient on element stoichiometry and metabolism in the diatom Phaeodactylum tricornutum.

The ability to utilize dissolved organic phosphorus (DOP) gives phytoplankton competitive advantages in P-limited environments. Our previous research indicates that the diatom Phaeodactylum tricornutum could grow on glyphosate, a DOP with carbon-phosphorus (C-P) bond and an herbicide, as sole P source. However, direct evidence and mechanism of glyphosate utilization are still lacking. In this study, using physiological and isotopic analysis, combined with transcriptomic profiling, we demonstrated the uptake of glyphosate by P. tricornutum and revealed the candidate responsible genes. Our data showed a low efficiency of glyphosate utilization by P. tricornutum, suggesting that glyphosate utilization costs energy and that the alga possessed an herbicide-resistant type of 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase. Compared to the P-limited cultures, the glyphosate-grown P. tricornutum cells up-regulated genes involved in DNA replication, cell growth, transcription, translation, carbon metabolism, and many genes encoding antioxidants. Additionally, cellular C and silicon (Si) increased remarkably while cellular nitrogen (N) declined in the glyphosate-grown P. tricornutum, leading to higher Si:C and Si:N ratios, which corresponded to the up-regulation of genes involved in the C metabolism and Si uptake and the down-regulation of those encoding N uptake. This has the potential to enhance C and Si export to the deep sea when P is limited but phosphonate is available. In sum, our study documented how P. tricornutum could utilize the herbicide glyphosate as P nutrient and how glyphosate utilization may affect the element content and stoichiometry in this diatom, which have important ecological implications in the future ocean.IMPORTANCEGlyphosate is the most widely used herbicide in the world and could be utilized as phosphorus (P) source by some bacteria. Our study first revealed that glyphosate could be transported into Phaeodactylum tricornutum cells for utilization and identified putative genes responsible for glyphosate uptake. This uncovers an alternative strategy of phytoplankton to cope with P deficiency considering phosphonate accounts for about 25% of the total dissolved organic phosphorus (DOP) in the ocean. Additionally, accumulation of carbon (C) and silicon (Si), as well as elevation of Si:C ratio in P. tricornutum cells when grown on glyphosate indicates glyphosate as the source of P nutrient has the potential to result in more C and Si export into the deep ocean. This, along with the differential ability to utilize glyphosate among different species, glyphosate supply in dissolved inorganic phosphorus (DIP)-depleted ecosystems may cause changes in phytoplankton community structure. These insights have implications in evaluating the effects of human activities (use of Roundup) and climate change (potentially reducing DIP supply in sunlit layer) on phytoplankton in the future ocean.

Temporal phytoplankton dynamics and environmental variables in four Ethiopian soda lakes

We investigated the spatio-temporal dynamics of phytoplankton composition, chlorophyll-a as a proxy for algal biomass, and abundance in relation to environmental parameters in four Ethiopian soda lakes: Arenguade, Beseka, Chittu, and Shala. Triplicate water samples were collected from each lake from January to December 2020, four times in different seasons. Lake Chittu had the highest chlorophyll-a concentration, followed by Lake Arenguade, Beseka and Shala. Chlorophyll-a concentrations generally increased during the post rainy and dry season. The results of LR models are high for lakes Arengude, Beseka and Chittu. Lakes Shala and Beseka had the highest number of phytoplankton taxa, with both taxa composition and abundance dominated by Bacillariophyceae. Cyanoprokaryota, particularly Limnospira fusiformis, predominated in the abundance of Lakes Arenguade and Chittu. Water temperature, Secchi depth, turbidity, electrical conductivity, soluble reactive phosphorus, nitrate and silica significantly influenced the phytoplankton community structure. Long-term trend analysis revealed changes in phytoplankton biomass and lake taxonomic composition. The alteration in phytoplankton biomass and species composition of the lakes could be attributed to three factors: (1) frequent high-velocity explosions conducted for seismological studies in the past. This impact caused a dramatic increase in lake level in the case of Lake Beseka leading to a drop in nutrient concentration; (2) climate change and (3) salt content. Overall, our findings suggest that phytoplankton composition, biomass, and abundance varied according to seasonal fluctuations, emphasizing the possible effects of anthropogenic and natural causes on their community structure.

Responses of phytoplankton and periphyton community structure to an anthropic eutrophication gradient in tropical high-altitude Lake Titicaca

Eutrophication is a global environmental problem in aquatic ecosystems, mainly caused by increased nutrient loads (nitrogen and phosphorus). Phytoplankton and periphyton responses to the nutrients increase and temporal variation may be related to mutual seeding and/or variable environmental constraints. Each of these communities may be useful for characterizing and monitoring eutrophication processes. However, little information exists about the simultaneous responses or interactions between such communities during eutrophication, even less in high-altitude tropical lakes such as Lake Titicaca. Here, we first established a eutrophication gradient with stable isotopes (δ15N and δ13C) and physicochemical variables in a shallow bay of Lake Titicaca. Later, we analyzed the shifts in taxonomic and morphological forms of phytoplankton and periphyton colonizing the underwater stems of totora (Schoenoplectus californicus ssp. tatora), an emergent aquatic macrophyte, along the eutrophication gradient. There is a clear turnover (groups, genera, and morphological forms) in phytoplankton and periphyton and decreased biodiversity along the eutrophication gradient. Gomphonema genus relative abundance increase with eutrophication in both communities, while Achnanthidium abundance decreases. However, other genera behave differently in each community, allowing for the identification of specific bioindicators of eutrophication for phytoplankton (Oscillatoria, Spirogyra, and Euglena) and periphyton (Oedogonium, Stigeoclonium, and Characium). They share genus composition with some taxa showing similar behaviors, thus interactions between phytoplankton and periphyton may exist. We also believe that each compartment can act as a seeding reservoir for the other, though remaining independent to some extent.

Phytoplankton community structure and water quality assessment in Xuanwu Lake, China

Phytoplankton community structure influences the water quality of freshwater lakes and attracts the attention worldwide. The physicochemical parameters including dissolved oxygen (DO), total nitrogen, total phosphorus, NH4+-N and CODMn and biological index such as Chl.a concentrations were measured in water of different sites of Xuanwu Lake, China in varied seasons. The Trophic level index (TLI) was calculated to evaluate the trophic status of the lake based on critical water quality parameters. The phytoplankton community structure and biomass in the water was also identified and detected. Obvious change of physicochemical parameters and biological index was detected in varied sampling time. The results showed that TN, TP, NH4+-N, CODMn and Chl.a had higher concentrations in June and August with higher temperature. Obtained Trophic level index values from key water quality indicators revealed that Xuanwu Lake exhibited a state of mesotrophic level in December 2021, mild eutrophic level in October and February, and remained in a state of moderate eutrophication during other periods having higher temperature. Chlorophyta exhibited the highest species diversity and accounted for 48.1% of the entire community. Cyanobacteria had higher density compared to other phytoplankton, which suggesting the potential ecological risk in the lake. These findings aligned with the outcomes of the analysis of the phytoplankton community structure, underscoring a certain degree of correlation between the primary water quality indicators and phytoplankton abundance in Xuanwu Lake. That is, higher discharge of contaminant including nutrients potentially dominated the phytoplankton community structure. The continuous monitoring of phytoplankton community and water quality enabled the assessment of its trophic status of urban lake. Appropriate measures such as adjustment of phytoplankton community structure were proposed to mitigate the eutrophication status of lake. The investigation indicated that phytoplankton variation was the important indicator of water quality and supplied direct evidence for the water quality management and ecosystem restoration of urban lakes.

Factors Influencing the Variation in Phytoplankton Functional Groups in Fuchunjiang Reservoir

To explore the distribution characteristics, blooming risk mechanism and driving factors of phytoplankton community structure in Fuchunjiang Reservoir. The variation characteristics of phytoplankton, zooplankton and physicochemical indicators in Fuchunjiang Reservoir and its upper and lower reaches were investigated in 2020 and 2021. Based on the phytoplankton functional groups, non-metric multidimensional scale analysis, redundancy analysis and other statistical methods, the seasonal succession characteristics and driving factors of phytoplankton functional groups were analyzed. A total of 18 phytoplankton functional groups were identified, in of which 10 were predominant. The composition of phytoplankton functional groups in the Fuchunjiang Reservoir was significant different. Spatially, the upstream were dominated by group C and P while the represent species were Cyclotella and Aulacoseira,reflecting the mixed meso-eutrophic environments. However, group P was the main group in Fuchunjiang reservoir, and the dominance decreased gradually along the stream direction. Meanwhile, in the downstream, MP has an absolute advantage at Qiantang River estuary. It reflected the environmental characteristics of frequent disturbance and high turbidity of tide-sensing rivers. In addition, the predominant functional groups demonstrated strong seasonal variations. The dominant functional groups were diverse in summer and consisted of P+L0+J+M+S1+H1+MP. In addition to group P (Aulacoseira), which was dominant throughout the year, it also included several groups represented by cyanobacteria and chlorophyta, reflecting the environmental characteristics of changeable habitats and vigorous productivity. In autumn, the succession was dominated by H1 group represented by Dolichospermum and the representative function groups were P and H1, reflecting the hydrological background of reduced flow and static flow. In winter, the increase of Cyclotella led to the predominance of group C, which was dominated by P+C, reflecting the changing conditions of weakened water exchange and intensified eutrophication problems. In spring, the dominant functional groups were gradually enriched and were composed of C, D, P, and MP, which also reflected the changing environmental habitat characteristics which caused by increasing rainfall and air temperature. According to the results of the C-R-S growth strategy, the Fuchunjiang Reservoir has been in the R strategy for a long time, which was consistent with the habitat characteristics of Fuchunjiang Reservoir and its upper and lower reaches with high disturbance and low stress. In addition, C strategy and S strategy appeared in some reaches, reflecting the variability of water quality and hydrology. RDA analysis showed that water temperature, discharge, zooplankton biomass, permanganate index, total nitrogen and total phosphorus were significantly correlated with the seasonal succession of phytoplankton functional groups (P &lt; 0.05), and temperature and flow pattern were probably the most critical factors for the succession. Studies have shown that the impact of hydrometeorological processes on phytoplankton in the Fuchunjiang Reservoir is crucial:high temperature and changing discharge during the summer may lead to cyanobacterial blooms in the Fuchunjiang reservoir; To reduce the risk of algal blooms, it is still necessary to increase the control of nitrogen and phosphorus load in rivers, and fully consider the coordination of water conservancy dispatch methods.

Coupling of nitrogen biogeochemical cycling and phytoplankton community structure before and after the Late Ordovician mass extinction in South China

The Ordovician–Silurian transition (OST) is a crucial geological interval in Earth history, coinciding with the first of the ‘Big Five’ Phanerozoic mass extinction events (ca. 445 Ma). In addition to the dramatic loss of biodiversity, significant environmental change course such as redox conditions and nutrient availability have been the focus of debate. Previous studies have used isotopes of nitrogen (N) to reconstruct the redox evolution of the paleo-ocean and have identified biological nitrogen fixation as the main mode of nitrogen cycling during the OST. However, low δ15N values, ranging from −2‰ to +1‰, possibly correspond to four different redox conditions. The precise roles of these redox conditions and the spatial distributions of phytoplankton communities under different nitrogen cycles remain elusive. Here we present high-resolution nitrogen isotope, carbon isotope and lipid biomarker datasets from two drilled sections located on a submerged high of the Yangtze Basin to unravel the coupling between nitrogen biogeochemical cycling and phytoplankton community structure across the OST. The results suggest that there was a dominantly biological nitrogen fixation with local aerobic nitrogen cycling in the Yangtze Sea, and the nitrate inventory during the OST was smaller than that in the modern ocean. Particularly, before the Late Ordovician mass extinction (LOME), N-fixing cyanobacteria were likely extensively developed in the photic zone, while eukaryotic algae were limited. After the LOME, sea levels rose and the chemocline was higher than before the LOME. There was probably some NO3− that did not undergo denitrification in the surface ocean, favoring the development of eukaryotic algae. The ecological diversification from prokaryotic cyanobacteria to eukaryotic phytoplankton to eukaryotic zooplankton is likely to be a response to the enhanced biological pump, which generates positive feedbacks among the evolution of eukaryotic phytoplankton, organic matter enrichment, ocean oxygenation and atmospheric oxygen levels.

Phytoplankton community structure during the melting phase of the land-fast ice in Prydz Bay, east Antarctica

Phytoplankton, the primary producers of all aquatic systems, form the base of the marine food web. Any change in the environmental settings of the given ecosystem will affect the phytoplankton community structure of the region. In the present work, water sampling was carried out from the poorly explored polar region, beneath the sea ice during the melting phase of land-fast ice near Indian Antarctic Research Station Bharati in Prydz Bay, East Antarctica. The water samples were analyzed for phytoplankton species diversity, nutrients, temperature, salinity, and Chlorophyll a (Chl a). Our observations indicate marked variations in phytoplankton biomass and community. A shift from diatom (Thalassiosira sp., Fragilariopsis sp.) to dinoflagellate (Protoperidinium sp.) community, along with the emergence of grazers was seen by the end of the observation period. The background environmental conditions also showed marked variations, as the concentration of nitrate at 0m depth reduced from 31.8 μM at Obs-1 to a non-detectable limit at Obs-3. Furthermore, at 0m depth, temperature increased from −1.32 °C at Obs-1 to −0.38 °C at Obs-3 while salinity decreased from 34.11 at Obs-1 to 33.68 at Obs-3, thus indicating the melting phase of sea ice from Obs-1 to Obs-3. These observations showed vertical stratification resulting from the basal melting of land-fast sea ice resulted in better availability of light, phytoplankton community change due to nutrient availability/utilization/limitation, followed by the presence of grazer community. This preliminary understanding will serve as a baseline dataset to design the targeted sampling/experiments in the future from the land-fast ice ecosystem.