Total Phytoplankton Research Articles

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

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

A CHEMTAX‐derived phytoplankton community structure during 12‐year observations in the Gulf of Naples (LTER‐MC)

AbstractThe rapid response of phytoplankton communities to environmental changes makes this compartment one of the most important biological variable to consider in dealing with ecology and trophodynamic of coastal areas, especially in relation with ongoing climate changes and increased human pressures. In the last 30 years, the use of chemotaxonomy has improved the capability to detect phytoplankton community composition in terms of chemofunctional groups, especially for small size species requiring specific expertise and techniques, as well as time‐consuming observation with light microscope. In this study, the temporal variability of chemotaxonomic functional groups has been investigated in surface waters of a LTER station in the Gulf of Naples over 12‐year weekly sampling activities (2003–2015). Data reveal increasing trends in the percentage contribution of diatoms, prasinophytes, cryptophytes to the total phytoplankton biomass, while other groups show a decreasing trend. Nevertheless, strong differences in the intervals of periodicity for each chemofunctional group have emerged, both in terms of timescale and strength of periodicity over time, implying that temporal dynamics of groups were not stationary over the time and that they have different relationships with environmental variability. Our results contribute to enrich scientific knowledge on the ecology of this LTER site and underline the importance of chemotaxonomy as a monitoring tool in coastal marine systems.

Potential risks of climate change and tropical storms on ecosystem and clams culture activities in Giao Thuy, Nam Dinh, Vietnam

Ecosystem and aquaculture in estuary areas are sensitive to climate change and severe climatic events. In this study, three environmental monitoring events were carried out on a 1800-ha clam culture area in Giao Thuy district, Nam Dinh province, Vietnam. The first monitoring was carried out in fair weather. The second and 3rd monitorings were conducted two days after the Ma On and Noru storms, respectively. The variation of water and sediment physicochemical variables, zoobenthos and plankton composition and density, and clam pathogen were investigated at five locations. In addition, long-term variations of temperature, rainfall, and sunshine duration in the area were investigated. The results illustrated the increased temperature, rainfall, and sunshine duration tendency. The clam-cultured species and activities had substantially changed. Ma On and Noru negatively impacted water quality by decreasing the water quality index by 39% and 30%, respectively. Storms decreased water salinity, alkalinity, and sediment’s phosphorus, iron, lead. However, they increased water’s nitrite, phosphorus, total suspended solid, phytoplankton, zooplankton density, and sediment’s total nitrogen, cadimium. The total Vibrio spp. density in clam highly fluctuated between the two storm events. The effect of storm varied according to site location. Shallow and domestic wastewater adjacent sites suffered high risks of extreme temperature, salinity variation, and organic pollution.

Dissolved Oxygen and Water Temperature Drive Vertical Spatiotemporal Variation of Phytoplankton Community: Evidence from the Largest Diversion Water Source Area.

In order to study the vertical distribution characteristics of phytoplankton in the Danjiangkou Reservoir, the water source of the Middle Route Project of the South-North Water Diversion, seven sampling sites were set up in the Reservoir for quarterly sampling from 2017 to 2019, and water environment surveys were conducted simultaneously. The results showed that 157 species (including varieties) were identified, belonging to 9 phyla and 88 genera. In terms of species richness, Chlorophyta had the largest number of species, accounting for 39.49% of the total species. The Bacillariophyta and Cyanobacteria accounted for 28.03% and 13.38% of the total species, respectively. From the whole Danjiangkou Reservoir, the total phytoplankton abundance varied from 0.09 × 102 to 20.01 × 106 cells/L. In the vertical distribution, phytoplankton were mainly observed in the surface-thermospheric layer (I-II layer) and the bottom layer, while the Shannon-Wiener index showed a trend of gradually decreasing from the I-V layer. The Surfer model analysis showed that there was no significant stratification in the Q site's water temperature (WT) and dissolved oxygen (DO) levels in the water diversion area during the dynamic water diversion process. A canonical correspondence analysis (CCA) showed that DO, WT, pH, electrical conductivity (Cond), chemical oxygen demand (CODMn), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN) had significant effects on the vertical distribution of phytoplankton (p < 0.05). A partial Mantel analysis showed that the vertical distribution of the phytoplankton community was related to WT, and the phytoplankton community structure at the other sites, except for Heijizui (H) and Langhekou (L), was affected by DO. This study has positive significance for exploring the vertical distribution characteristics of a phytoplankton community in a deep-water dynamic water diversion reservoir.

Optimal Assimilation Number of Phytoplankton in the Siberian Seas: Spatiotemporal Variability, Environmental Control and Estimation Using a Region-Specific Model

The maximal value of the chlorophyll-specific carbon fixation rate in the water column or the optimal assimilation number (Pbopt) is an important parameter used to estimate water column integrated primary production (IPP) using models and satellite-derived data. The spatiotemporal variability in the Pbopt of the total and size-fractionated phytoplankton in the Siberian Seas (SSs) and its links with environmental factors were studied based on long-term (1993–2020) field and satellite-derived (MODIS-Aqua) observations. The average value of Pbopt in the SSs was equal to 1.38 ± 0.76 mgC (mg Chl a)–1 h–1. The monthly average values of Pbopt decreased during the growing season from 1.95 mgC (mg Chl a)–1 h–1 in July to 0.64 mgC (mg Chl a)–1 h–1 in October. The average value of Pbopt for small (&lt;3 μm) phytoplankton 1.6-fold exceeded that for large (&gt;3 μm) phytoplankton. The values of Pbopt depend mainly on incident photosynthetically available radiation (PAR). Based on the relationship between Pbopt and PAR, the empirical region-specific algorithm (E0reg) was developed. The E0reg algorithm performed better than commonly used temperature-based models. The application of E0reg for the calculation of Pbopt will make it possible to more precisely estimate IPP in the SSs.

Effects of fungicide chlorothalonil on freshwater plankton communities: a microcosm study.

Direct and indirect effects of the fungicide chlorothalonil on aquatic plankton community structure were investigated by exposing plankton to chlorothalonil concentrations of 0.010, 0.025, 0.100, 0.250 and 1.000mg/L over 20days in 18 microcosms (glass tanks having 8 L of pond water). Each treatment was executed in three replicates. Total phytoplankton and zooplankton abundance and chlorophyll-a concentrations in microcosms were measured 5, 10 and 20days after pesticide exposure. Plankton community and taxa response to pesticide concentrations were analyzed using the similarity of percentages procedure (SIMPER) and one-way ANOVA test. The results of the study indicated that highest concentration levels of chlorothalonil exposure had a significant impact on phytoplankton and zooplankton taxa. Phytoplankton taxa Amphora sp. and Staurastrum sp. and zooplankton taxa Moina sp. and copepod Nauplius were highly sensitive to chlorothalonil exposure. Phytoplankton taxa Mougeotia sp. increased with increased chlorothalonil (0.1-1.0mg/L) concentrations, and zooplankton taxa of Aeolosoma sp. showed no significant reduction of individuals in response to pesticide exposure. Results showed that pesticide residues have a direct and rapid impact on phytoplankton and zooplankton community structure. Changes in diversity and species composition induced by pesticides indicate the importance of considering indirect effects of pesticides on the ecological food chain in the aquatic environment.

Spatio-temporal connectivity of the aquatic microbiome associated with cyanobacterial blooms along a Great Lake riverine-lacustrine continuum.

Lake Erie is subject to recurring events of cyanobacterial harmful algal blooms (cHABs), but measures of nutrients and total phytoplankton biomass seem to be poor predictors of cHABs when taken individually. A more integrated approach at the watershed scale may improve our understanding of the conditions that lead to bloom formation, such as assessing the physico-chemical and biological factors that influence the lake microbial community, as well as identifying the linkages between Lake Erie and the surrounding watershed. Within the scope of the Government of Canada's Genomics Research and Development Initiative (GRDI) Ecobiomics project, we used high-throughput sequencing of the 16S rRNA gene to characterize the spatio-temporal variability of the aquatic microbiome in the Thames River-Lake St. Clair-Detroit River-Lake Erie aquatic corridor. We found that the aquatic microbiome was structured along the flow path and influenced mainly by higher nutrient concentrations in the Thames River, and higher temperature and pH downstream in Lake St. Clair and Lake Erie. The same dominant bacterial phyla were detected along the water continuum, changing only in relative abundance. At finer taxonomical level, however, there was a clear shift in the cyanobacterial community, with Planktothrix dominating in the Thames River and Microcystis and Synechococcus in Lake St. Clair and Lake Erie. Mantel correlations highlighted the importance of geographic distance in shaping the microbial community structure. The fact that a high proportion of microbial sequences found in the Western Basin of Lake Erie were also identified in the Thames River, indicated a high degree of connectivity and dispersal within the system, where mass effect induced by passive transport play an important role in microbial community assembly. Nevertheless, some cyanobacterial amplicon sequence variants (ASVs) related to Microcystis, representing less than 0.1% of relative abundance in the upstream Thames River, became dominant in Lake St. Clair and Erie, suggesting selection of those ASVs based on the lake conditions. Their extremely low relative abundances in the Thames suggest additional sources are likely to contribute to the rapid development of summer and fall blooms in the Western Basin of Lake Erie. Collectively, these results, which can be applied to other watersheds, improve our understanding of the factors influencing aquatic microbial community assembly and provide new perspectives on how to better understand the occurrence of cHABs in Lake Erie and elsewhere.

Case where a mesoscale cyclonic eddy suppresses primary production: A Stratification-Lock hypothesis

Cyclonic eddies in the ocean often increase primary production and phytoplankton biomass. The main mechanism is the rise of the nutricline in the cyclone's core, which determines the intensification of the ascending flow of deep nutrients into the photic layer. However, some cyclones suppress primary productivity, and the natural processes underlying them are little studied and are of great fundamental interest. In August 2021, a vast cyclonic zone with two mesoscale cyclones occupied the Black Sea deep-water basin. A powerful quasi-tropical atmospheric vortex amplified one of the cyclones, which increased the Ekman pumping and led to strong sea surface cooling by 4 °C. However, the inflow of thermocline water into the euphotic layer and higher nutricline gradients did not lead to elevated depth-integratedconcentration of chlorophyll a (Chl)and phytoplankton biomass. Moreover, the surface Chl and the average primary production was less than in the outside waters. The proposed Stratification-Lock hypothesis explains this phenomenon. A combination of several factors led to its appearance. The drastic water cooling, followed by calm weather and vigorous summer heating, led to strong thermal stratification, dampening turbulent mixing in the near-surface layer. At the same time, the velocity and shear of current in and below the thermocline were low in the entire cyclonic zone, which prevented substantial diapycnal mixing generated at depth. As a result, a 'stratification lock' appeared in the entire water column, suppressing nutrients' upward flux. The proposed hypothesis is consistent with the effect of thermal stratification on primary productivity revealed in the entire cyclonic zone. The higher was the thermal stratification the lower was the depth-integrated total phytoplankton biomass and primary production. Also, diatoms developed in the upper layer in waters with weaker thermal stratification. The described stage lasted two weeks and was interrupted by strong wind mixing, which destroyed the 'stratification lock' and caused an increase in Chl at the sea surface. This stage of the cyclone life cycle occurs under a strictly defined combination of hydro-meteorological conditions, suggesting a relatively rare occurrence. Nevertheless, some evidence of the similar effect of a cyclone on primary productivity can be found in other studies, indicating that this natural mechanism, consisting of a complex weather-current-eddy combination, can operate in various marine areas.

On the Role of the Amazon River for N2 Fixation in the Western Tropical Atlantic

AbstractThe high rates of N2 fixation observed in the Western Tropical Atlantic Ocean are powered, at least in parts, by large influx of nutrients from the Amazon River. To disentangle the impact of the Amazon on different factors controlling N2 fixation in the region, we use a high‐resolution regional model (Regional Oceanic Modeling System‐Biogeochemical Elemental Cycling model) that includes two diazotrophic phytoplankton classes (Trichodesmium and Diatom‐Diazotroph‐Assemblages, DDAs). In our simulations, the Amazon enhances marine N2 fixation by 74% (3.8 Tg N yr−1), with most of the enhancement driven by DDAs that represent 90% of the diazotrophic community in plume waters. To determine how the Amazon creates the conditions in which DDAs thrive, we analyze bottom‐up and top‐down controls on phytoplankton along the plume pathway and how the phytoplankton competition is disrupted by the delivery of nutrients by the river. Along the entire plume pathway, DDAs out‐compete Trichodesmium as their higher maximum growth makes them more efficient in building biomass. Nevertheless, DDAs never account for more than 25% of the total phytoplankton biomass as they face the competition of other non‐diazotrophic phytoplankton types in the use of the riverine nutrients. Overall, DDAs thrive in the offshore plume region where their nutrient uptake advantages (N‐fixation, DOP uptake) is concomitant with a relaxed grazing pressure.

The effect of single versus dual nutrient decreases on phytoplankton growth rates, community composition, and Microcystin concentration in the western basin of Lake Erie

The primary management strategy for minimizing harmful algal blooms (HABs) in Lake Erie has been to reduce springtime loading of phosphorus (P) to the lake. However, some studies have shown that the growth rate and toxin content for the HABs-causing cyanobacterium Microcystis also respond to the availability of dissolved inorganic nitrogen (N). This evidence is based on both observational studies that correlate bloom development with changes in N forms and concentrations in the lake, and experiments in which P and/or N are added at concentrations in excess of those present in the lake. The goal of this study was to determine whether a combined decrease in N and P concentrations from ambient levels in Lake Erie could limit the development of HABs more than a reduction in P concentration only. To directly test the impact of P-only versus dual N and P concentration decreases on phytoplankton in the western basin of Lake Erie, we evaluated changes in growth rate, community composition, and microcystin (MC) concentration through eight bioassay experiments performed from June through October 2018, which encompassed the normal Lake Erie Microcystis-dominated HAB season. Our results showed that during the first five experiments covering June 25 to August 13, the P-only and the dual N and P decrease treatments had similar effects. However, when ambient N became scarce later in the season, the N and P decrease treatments resulted in negative growth rates for cyanobacteria, whereas –P only decreases did not. During low ambient N conditions, dual nutrient decreases lowered the prevalence of cyanobacteria among the total phytoplankton community and decreased microcystin concentrations. The results presented here complement previous experimental work on Lake Erie and suggest that dual nutrient control could be an effective management strategy to decrease microcystin production during the bloom and even possibly diminish or shorten the duration of the bloom based on creating nutrient limiting conditions sooner in the HAB growing season.

Water quality assessment using phytoplankton functional groups in the middle-lower Changjiang River, China

The Changjiang River (CR) is the third longest and fifth largest river in the world. However, assessments of its water quality, especially those based on relatively large-scale investigations, are still limited. Our study illustrated the phytoplankton community structure in the CR and assessed its ecological status using the phytoplankton assemblage index for rivers (Qr index). Samples were collected at 85 sites covering the middle-lower CR in May 2017. The total phytoplankton biomass was higher in the lower section of the river and was characterized by diatoms and cryptophytes. In terms of Reynolds functional groups, the phytoplankton biomass was dominated by TB, Y, D, and MP, which accounted for 31%, 23%, 13%, and 11% of the mean total biomass, respectively. The ecological status was generally “good” in the CR, with a mean Qr of 3.70, which was higher in the middle section. Generalized linear models showed significant positive correlations between Qr and RFGs with the highest F value, i.e. TB and P (both p values<0.001). Qr showed an absence of correlation with the phytoplankton biomass, which was low in our study. The results of our study suggested that Qr can be used in ecological assessments in the CR, which will benefit local water quality assessments.

State of marine biota in the water area of the Muchke Bay’s Coal Terminal of the Tatar Strait

An analysis of the species composition of phytoplankton and ichthyoplankton was carried out for the first time in the port water area of the Muchke Bay (Tatar Strait) in autumn. The species composition, distribution features and structure of macrozoobenthos were considered. Phytoplankton density is evenly distributed in the study area. The density of diatoms reached 97 % of the total phytoplankton density, and the biomass was 99 %. The microalgae Sceletonema costatum (Greville) Cleve, 1873 and Cylindrotheca closterium (Ehrenberg) Reimann &amp; J.C.Lewin, 1964, species that live in polluted waters, were discovered. The development of phytoplankton in the autumn period was active, but the peak of flowering was not observed. Ichthyoplankton in October 2017 is represented by live eggs of Limanda sakhalinensis (Schmidt, 1904) (8 ind./m3), in September 2018 - by the larvae of Hexagrammos stelleri Tilesius, 1810 (0.003-0.056 ind./m3) and H. octogrammus (Pallas, 1814) (0.01-0.077 ind./m3). Up to 85 representatives of macrozoobenthos were registered from the research area, including 40 species of Polychaeta, 19 ones of Crustacea, 16 species of Mollusca, 5 ones of Echinodermata and 5 species of other fauna groups. After dredging, a decrease in the species diversity of phytoplankton, ichthyoplankton and macrozoobenthos was found in the samples.

Species diversity and community structure of phytoplankton in the Velikaya Salma Strait (Kandalaksha Bay, White Sea) in 2021

The species diversity and community structure of phytoplankton in the Velikaya Salma Strait (Kandalaksha Bay, the White Sea) were investigated from May to September 2021. A total of 128 algal taxa were identified, comprised of diatoms (80% of the total phytoplankton species number), dinophytes (15%), cyanobacteria (3%), ochrophytes (1%) and cercozoans (1%). The phytoplankton abundance varied from 1.84х106 cells/m3 (in August) to 23.27х106 cells/m3 (in July); phytoplankton biomass varied from 31.4 mg/m3 (in May) to 246.7 mg /m3 (in July). Diatoms was the dominant group in terms of quantity and biomass, one dinophyte species, Sсrippsiella acuminata, was dominant in terms of quantity too.

Dynamics of phytoplankton in the coastal waters at Vladivostok in 2019–2021

Structure and abundance of phytoplankton community in the Sportivnaya Harbour and Paris Bay in Vladivostok (western coast of the Japan Sea) was monitored from October 2019 to December 2021. In total, 130 and 144 phytoplankton taxa were identified in these two areas, respectively. The overall cell abundance ranged from 1.3 · 103 to 19 · 106 cells/L (on average 21 · 104 and 84.5 · 104 cells/L); the total phytoplankton biomass — from 3.0 mg/m 3 to 38.5 g/m 3 (on average 0.8 and 2.6 g/m 3 , respectively, by areas). The long-term observations were made for the first time in the Sportivnaya Harbour. The community composition was typical of eutrophic waters, with usual seasonal succession in the Paris Bay but frequent blooms in the Sportivnaya Harbour, when diatoms were replaced by flagellates and filamentous cyanobacteria. Such dynamics is presumably caused by anthropogenic eutrophication due to uncontrolled wastewater discharge.

Climate features or the composition of submerged vegetation? Which factor has a greater impact on the phytoplankton structure in temperate lakes?

This study compares the composition and biomass of phytoplankton assemblages of lakes with abundant vegetation dominated by (1) charophytes (Chara-lakes) and (2) angiosperms (Potamogeton-lakes). These two groups of submerged macrophytes effectively control the phytoplankton development in lakes, but differ in the feedback mechanisms involved. Despite increasing interest, the phytoplankton development in charophyte- and angiosperm-dominated lakes under different climatic circumstances remains poorly recognized. Each type of lakes was studied in two distant (>500 km apart) regions of Poland, characterized by distinctly different climate features (western – warmer, and north-eastern – cooler), with temperature differences corresponding to the predicted magnitude of the global warming-related temperature rise in the near future. Twelve lakes were selected for this study, three Chara- and three Potamogeton-lakes in each region. In addition to phytoplankton analysis, macrophytes and climatic conditions, water chemistry, and the use of land in the catchment area were studied. Although we expected that climatic differences would have greater impact on the structure of phytoplankton assemblage than that expected due to higher macrophyte biomass and lower nutrient availability in Chara- than in Potamogeton-lakes, multidimensional statistical analyses clearly distinguished between the two macrophyte types of lakes. Significantly lower values of the total phytoplankton biomass, and the biomass of diatoms and cyanobacteria occurred in Chara- vs Potamogeton-lakes. We therefore postulate that not only abundantly developed submerged macrophytes, but also the type of vegetation are important factors structuring phytoplankton development and by interacting with the physical and chemical characteristics of water show potential in mitigating the effects of climate change.

Seasonal measurements of the nitrogenous osmolyte glycine betaine in marine temperate coastal waters

Glycine betaine (GBT) is a nitrogenous osmolyte ubiquitous throughout the marine environment. Despite its widespread occurrence and significance in microbial cycling, knowledge of the seasonality of this compound is lacking. Here, we present a seasonal dataset of GBT concentrations in marine suspended particulate material. Analysing coastal waters in the Western English Channel, GBT peaked in summer and autumn but did not follow the observed maxima in total phytoplankton biomass or chlorophyll a. Instead, we found evidence that GBT concentrations were associated with specific phytoplankton groups or species, particularly in the summer when GBT correlated with dinoflagellate biomass. In contrast, autumn maxima corresponded with a period of rapidly changing salinity and nutrient availability, with potential contributions from some phytoplankton species and Harpacticoid copepods. This suggests distinct environmental drivers for different periods of the GBT seasonality. Building on evidence that GBT and dinoflagellate biomass peak in summer, concomitantly with low nutrients, we propose that GBT positively affects dinoflagellate fitness, allowing them to outcompete other plankton when inorganic nutrients are depleted. By using this assumption, we improved the performance of a marine ecosystem model to reproduce the observed increase in dinoflagellates biomass in the transition from spring to summer. This work sheds light on the interplay between phytoplankton succession, competitive advantage and changing environmental factors relevant to climate change. It paves the way for future multidisciplinary research aiming to understand the importance of dinoflagellates in key coastal ecosystems and their potential significance for methylamine production, compounds relevant for particle growth in atmospheric chemistry.

Interfacial photochemistry of marine diatom lipids: Abiotic production of volatile organic compounds and new particle formation

The global importance of abiotic oceanic production of volatile organic compounds (VOCs) still presents a source of high uncertainties related to secondary organic aerosol (SOA) formation. A better understanding of the photochemistry occurring at the ocean-atmosphere interface is particularly important in that regard, as it covers >70% of the Earth's surface. In this work, we focused on the photochemical VOCs production at the air-water interface containing organic material from authentic culture of marine diatom Chaetoceros pseudocurvisetus. Abiotic VOCs production upon irradiation of material originating from total phytoplankton culture as well as the fraction containing only dissolved material was monitored by means of PTR-ToF-MS. Furthermore, isolated dissolved lipid fraction was investigated after its deposition at the air-water interface. All samples acted as a source of VOCs, producing saturated oxygenated compounds such as aldehydes and ketones, as well as unsaturated and functionalized compounds. Additionally, a significant increase in surfactant activity following irradiation experiments observed for all samples implied biogenic material photo-transformation at the air-water interface. The highest VOCs flux normalized per gram of carbon originated from lipid material, and the produced VOCs were introduced into an atmospheric simulation chamber, where particle formation was observed after its gas-phase ozonolysis. This work clearly demonstrates abiotic production of VOCs from phytoplankton derived organic material upon irradiation, facilitated by its presence at the air/water interface, with significant potential for affecting the global climate as a precursor of particle formation.

Phytoplankton productivity and community structure changes in the middle Okinawa Trough since the last deglaciation

Marine phytoplankton plays an important role in the ocean biological pump, whereas our understandings of phytoplankton growth in response to global climate and enviromment changes are still debated. Due to the forcing from the strong land-ocean interaction between the East Asia and the Indo-Pacific Warm Pool, the Okinawa Trough is characterized by high phytoplankton productivity and fast sediment accumulation, therefore it provides ideal archives to study marine productivity changes on millennial-to-orbital timescales. In this study, lipid biomarkers of C37 alkenones, dinosterol and brassicasterol, were analyzed in a sediment core M063–05 retrieved from the middle Okinawa Trough to reconstruct phytoplankton productivity and community structure changes over the last 15.8 kyr. We find that temporal variations of these lipid biomarker contents are parallel with precipitation changes in the Changjiang drainage basin during the last deglaciation, with high values during increased precipitation interval (14.5–12.7 ka) and low values during decreased precipitation intervals (15.8–15.0 ka and 12.7–11.5 ka). We propose that precipitation-induced terrestrial nutrient supply controlled phytoplankton growth in the middle Okinawa Trough during the last deglaciation. Lipid biomarker ratios reveal high (low) contributions of diatoms and dinoflagellates to total phytoplankton productivity during increased (decreased) precipitation intervals. The phytoplankton community structure record is also consistent with precipitation-induced terrestrial nutrient forcing during the deglacial stage, with higher nutrient condition favored diatom and dinoflagellate growth. Precipitation in the Changjiang drainage basin was mainly controlled by the East Asian summer monsoon change and the Intertropical Convergence Zone migration, however the deglacial sea level rise also modulated the forcing of precipitation on phytoplankton growth by affecting the delivery distance of terrestrial nutrients to our site. From the last deglaciation to the Holocene, the biomarker content decreased and the contribution of coccolithophorids to total phytoplankton productivity increased at the expense of dinoflagellates and diatoms. The most likely explanation is the regime shift of major nutrient sources supporting phytoplankton growth, from terrestrial riverine nutrients during the deglaciation to the Kuroshio subsurface water nutrients during the Holocene. Our results provide new insight of past phytoplankton responses to climate and environment changes.

Assessing spatio-temporal dynamics of phytoplankton assemblage and ecohydrological interaction in a community managed reservoir using GIS for sustainable fisheries management

The present study assessed the spatio-temporal dynamics of phytoplankton community structure and diversity using GIS platform, and their ecohydrological interactionsof a tropical reservoir located in Eastern India. Altogether, 74 species of phytoplankton belonging to 54 genera under seven taxonomic algal groups were recorded whose average annual abundance was 74.11 × 104 ± 17.73 × 104 cells l−1. Among seven algal groups, Chlorophyta, Cyanophyta, Bacillariophyta and Euglenophyta were remarkably influencing the total phytoplankton population contributing 97% of the total phytoplankton population in the reservoir. Cyanophyta absolutely dominated in the total phytoplankton compositions, and contributed a major share of 54% at the annual average level, however the species richness was maximum under the group Chlorophyta (35 genera). In total, thirteen phytoplankton taxa emerged as dominant (γ = < 0.02) across seasons. Among them, Phormidium sp. solely contributed (16.16%) to the total phytoplankton population, marked as dominant one in the reservoir. The diversity indices indicated the greater phytoplankton diversity in the lotic zone as compared to the transitional and lacustrine zone, showing significant variations (p<0.05) across seasons. PERMANOVA analysis exhibited a significant temporal variations of phytoplankton abundance (F=1.15, p=0.02) as well asenvironmental variables (F=1.82, p<0.05), but no significant spatial variations were recorded. The Principal Component analysis (PCA) revealed water temperature, transparency, total hardness, pH, specific conductivity, total alkalinity and nutrients parameters viz., phosphate, nitrate and silicate were the most important abiotic factors having the significant influence on the phytoplankton community compositions. Canonical Correspondence Analysis (CCA) depicted the environmental factors such as temperature, total alkalinity, total hardness, transparency, pH, and nutrients (NO3-N, PO4-P and SIO4-Si) were the determinants for the distribution of overall phytoplankton population especially the dominant phytoplankton species of the reservoir. The findings provide a better understanding of the influence of ecohydrology on phytoplankton community of a community managed reservoir and also discuss management and researchable issues considering the feeding guild of reservoir fishes and phytoplankton assemblage for ecosystem based conservation and management.

Composition and genetic diversity of picoeukaryotes in the northeastern South China Sea during the Luzon winter bloom

We analyzed picoeukaryotes during the Luzon winter bloom, in combination with remote sensing, flow cytometry and high throughput sequencing. Satellite images showed a seasonal increase in phytoplankton in the study area during winter, and the in situ campaign observed an extremely high abundance of photosynthetic picoeukaryotes, which were the main contributors to the total phytoplankton biomass. Auto- and mixotrophic picoalgae (Chlorophyta, Ochrophyta, and Dinophyta), heterotrophic flagellates (Radiolaria) and parasites (Syndiniale) were found to be potentially numerous components of picoeukaryote communities. Overall, auto- and mixotrophic photosynthetic picoeukaryotes were mainly distributed in the upper layers (0–100 m) while heterotrophic flagellates and parasites dominated the deep layers (200–300 m). The Kuroshio-induced upwelling stimulated the growth of photosynthetic picoeukaryotes, which mainly belonged to Chlorophyta, especially the class Mamiellophyceae.