Response Of Phytoplankton Community Research Articles

High CO2 concentration and iron availability determine the metabolic inventory in an Emiliania huxleyi‐dominated phytoplankton community

Ocean acidification (OA), a consequence of anthropogenic carbon dioxide (CO2 ) emissions, strongly impacts marine ecosystems. OA also influences iron (Fe) solubility, affecting biogeochemical and ecological processes. We investigated the interactive effects of CO2 and Fe availability on the metabolome response of a natural phytoplankton community. Using mesocosms we exposed phytoplankton to ambient (390 μatm) or future CO2 levels predicted for the year 2100 (900 μatm), combined with ambient (4.5 nM) or high (12 nM) dissolved iron (dFe). By integrating over the whole phytoplankton community, we assigned functional changes based on altered metabolite concentrations. Our study revealed the complexity of phytoplankton metabolism. Metabolic profiles showed three stages in response to treatments and phytoplankton dynamics. Metabolome changes were related to the plankton group contributing respective metabolites, explaining bloom decline and community succession. CO2 and Fe affected metabolic profiles. Most saccharides, fatty acids, amino acids and many sterols significantly correlated with the high dFe treatment at ambient pCO2 . High CO2 lowered the abundance of many metabolites irrespective of Fe. However, sugar alcohols accumulated, indicating potential stress. We demonstrate that not only altered species composition but also changes in the metabolic landscape affecting the plankton community may change as a consequence of future high-CO2 oceans.

Phytoplankton Community Response to Environmental Changes in Mahanadi Estuary and Its Adjoining Coastal Waters of Bay of Bengal: a Multivariate and Remote Sensing Approach

The present study investigates seasonal variability of physicochemical parameters and phytoplankton community structure, abundance, and chlorophyll a (Chl a) during 2007–2009 in the Mahanadi estuary, Bay of Bengal (BoB). Seasonal variations of phytoplankton community depended upon the change in hydrographic conditions and nutrient concentrations of the estuarine ecosystem. The changing scenario of phytoplankton community structure in relation to the various physicochemical properties of the ambient water was influenced by the monsoon and post-monsoon cycle. Discernible variation was observed in phytoplankton species composition, population density, and Chl a concentration between the pre-monsoon (April), monsoon (July), and post-monsoon (October). The mean population density of phytoplankton varied from monsoon (29,276 cells l−1) to pre-monsoon (43,290 cells l−1) period. Multivariate analyses showed that diatom was the most dominant (57.63%) followed by dinoflagellates (33.05%) compared with other communities in the study area. The green and blue-green algae were dominant during monsoon, while coccolithophores and silicoflagellates were the major during pre-monsoon. The Chl a concentration leads to the population density and varied between 0.87 and 1.18 mg m−3 from pre-monsoon to post-monsoon. Salinity and suspended solids (SS) played a major role in the spatial and seasonal distribution of phytoplankton composition and showed a positive correlation (p < 0.01) between nitrogenous nutrients (NO3 and NO2) with phytoplankton density and Chl a, suggesting that nitrogenous nutrients have profound influence on the phytoplankton growth. The in situ Chl a data used for validation of composite satellite MODIS data and result found that both data showed a similar trend of distribution in the region. The Chl a concentration was significantly higher in the pre-monsoon period.

Response of Phytoplankton Assemblages From Naturally Acidic Coastal Ecosystems to Elevated pCO2

The interplay of coastal oceanographic processes usually results in partial pressures of CO 2 (pCO 2) higher than expected from the equilibrium with the atmosphere and even higher than those expected by the end of the century. Although this is a well-known situation, the natural variability of seawater chemistry at the locations from which tested organisms or communities originate is seldom considered in ocean acidification experiments. In this work, we aimed to evaluate the role of the carbonate chemistry dynamics in shaping the response of coastal phytoplankton communities to increased pCO 2 levels. The study was conducted at two coastal ecosystems off Chile, the Valdivia River estuary and the coastal upwelling ecosystem in the Arauco Gulf. We characterized the seasonal variability (winter/summer) of the hydrographic conditions, the carbonate system parameters, and the phytoplankton community structure at both sites. The results showed that carbonate chemistry dynamics in the estuary were mainly related to seasonal changes in freshwater discharges, with acidic and corrosive conditions dominating in winter. In the Arauco Gulf, these conditions were observed in summer, mainly associated with the upwelling of cold and high pCO 2 (>1,000 µatm) waters. Diatoms dominated the phytoplankton communities at both sites, yet the one in Valdivia was more diverse. Only certain phytoplankton groups in this latter ecosystem showed a significant correlations with the carbonate system parameters. When the impact of elevated pCO 2 levels was investigated by pCO 2 manipulation experiments, we did not observe any significant effect on the biomass of either of the two communities. Changes in the phytoplankton species composition and abundance during the incubations were related to other factors, such as competition and growth phases. Our findings highlight the importance of the natural variability of coastal ecosystems and the potential for local adaptation in determining responses of coastal phytoplankton communities to increased pCO 2 levels.

The effects of absolute and relative nutrient concentrations (N/P) on phytoplankton in a subtropical reservoir

Abstract The elemental composition of phytoplankton is a critical factor for primary production and nutrient recycling. The increase anthropogenic nutrient input into freshwater ecosystems is affecting phytoplankton assemblage structure and its stoichiometry. Reservoirs of South China generally show low level of phosphate and it is not clear how phytoplankton can grow and occasionally bloom in such conditions. Therefore, an indoor experiment was conducted to investigate the response of natural phytoplankton communities to 25 levels of supplied nitrogen to phosphorus ratios (N/P), arising from the combination of 5 levels of N and P. Our aim was to check the effects of absolute and relative N and P on phytoplankton growth and structure. We assumed that Alkaline Phosphatase (APA) provides a way to use alternative P resource. Our hypotheses include: (1) phytoplankton stoichiometry would be in homeostasis (sensu Sterner & Elser, 2002) under different N and P treatments; (2) absolute nutrient values rather than its ratio matters for phytoplankton assemblage; and (3) phytoplankton cell size declines to lower P requirements facing P limitation. Results showed that phytoplankton in this subtropical reservoir use alternative P sources via APA to support its growth. The absolute values of N and P instead and not their ratios were important for phytoplankton. The N/P ratio cannot be a reliable indicator for nutrient limitation or phytoplankton shift. During the fast-growing phase, their elemental contents were not sensitive to supplied nutrients, and their stoichiometry was more constrained compared to that in slow-growing phase. The plasticity of cellular stoichiometry was mainly due to the variations of cellular P. Phytoplankton stoichiometry was weakly homeostatic, and this mechanism provides a strategy to keep growth relatively stable in a variable nutrient environment.

Phytoplankton diversity and community responses to physicochemical variables in mangrove zones of Guangzhou Province, China.

The phytoplankton diversity and community response to physicochemical variables in mangrove zones of Guangdong Province along the South China coast was investigated from October to December, 2017. This study was set to investigate the phytoplankton community structure in the mangrove zone and assess the relationship between the physicochemical variables and phytoplankton species diversity. Physicochemical variables such as water temperature, total dissolve solids (tds), pH, salinity, turbidity, electrical conductivity (EC) and nutrient salts were measured in situ across the 27 stations. A total of 451 species of phytoplankton were identified belonging to 10 groups (Bacillariophta > Cyanophyta > Chlorophyta > Euglenophyta > Dinoflagellate > Eubacteria > Ochrophyta > Crytophyta > Rhodophyta > Charophyta) and quantified to constitute a standing crop of 7.11 × 108 cells dm-3. The principal component analysis (PCA) reveals that reactive nitrate, phosphate, electrical conductive (EC) and turbidity were the best abiotic factors that controlled the phytoplankton community structure in the area. However, Cannon Corresponding Analysis and Pearson correlation have explicitly revealed the impact of reactive nitrate, phosphate, EC and turbidity on the phytoplankton community structure. For instance, the CCA ordination revealed that species richness and evenness were positively influenced by reactive nitrate but negatively affected by EC, turbidity and water temperature. Diatoms were mostly controlled by total dissolved solids (tds) and salinity, whereas Euglena, cyanobacteria and green algae were impacted EC and turbidity, apart from the general contribution of the nutrient salts as delineated by CCA ordination. The Shannon diversity index value exposed different levels of organic pollution across the mangrove zone of which GD37 was the most impacted station.

Phytoplankton transcriptomic and physiological responses to fixed nitrogen in the California current system.

Marine phytoplankton are responsible for approximately half of photosynthesis on Earth. However, their ability to drive ocean productivity depends on critical nutrients, especially bioavailable nitrogen (N) which is scarce over vast areas of the ocean. Phytoplankton differ in their preferences for N substrates as well as uptake efficiencies and minimal N requirements relative to other critical nutrients, including iron (Fe) and phosphorus. In this study, we used the MicroTOOLs high-resolution environmental microarray to examine transcriptomic responses of phytoplankton communities in the California Current System (CCS) transition zone to added urea, ammonium, nitrate, and also Fe in the late summer when N depletion is common. Transcript level changes of photosynthetic, carbon fixation, and nutrient stress genes indicated relief of N limitation in many strains of Prochlorococcus, Synechococcus, and eukaryotic phytoplankton. The transcriptomic responses helped explain shifts in physiological and growth responses observed later. All three phytoplankton groups had increased transcript levels of photosynthesis and/or carbon fixation genes in response to all N substrates. However, only Prochlorococcus had decreased transcript levels of N stress genes and grew substantially, specifically after urea and ammonium additions, suggesting that Prochlorococcus outcompeted other community members in these treatments. Diatom transcript levels of carbon fixation genes increased in response to Fe but not to Fe with N which might have favored phytoplankton that were co-limited by N and Fe. Moreover, transcription patterns of closely related strains indicated variability in N utilization, including nitrate utilization by some high-light adapted Prochlorococcus. Finally, up-regulation of urea transporter genes by both Prochlorococcus and Synechococcus in response to filtered deep water suggested a regulatory mechanism other than classic control via the global N regulator NtcA. This study indicated that co-existing phytoplankton strains experience distinct nutrient stresses in the transition zone of the CCS, an understudied region where oligotrophic and coastal communities naturally mix.

Storm impacts on phytoplankton community dynamics in lakes.

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions.

Intra‐annual variation of phytoplankton community responses to factorial N, P, and CO2 enrichment in a temperate mesotrophic lake

Abstract Across primary producer communities in different lakes, nitrogen (N) and phosphorus (P) can exhibit many different patterns of limitation. Here, we look at the intra‐annual variability of these patterns in a single lake. Furthermore, we investigate whether a third resource, carbon dioxide (CO2) can have significant effects on phytoplankton biomass and community composition. We performed five in situ lacustrine mesocosm experiments at different times of the year. In each experiment, we had a factorial design with two levels of N, P and CO2 enrichment (no enrichment or double lake concentrations for N and P and atmospheric (400 ppm) and c. 1,000 ppm for CO2) resulting in a total of eight treatments. Mesocosms of c. 1,600 L were suspended in a temperate, mesotrophic lake (Lac Hertel, Canada). Each experiment lasted 2 weeks and chlorophyll a biomass, coarse chemotaxonomic community composition (measured using fluorometry), and several environmental variables were recorded at a minimum of four time points. We found that the limiting, synergistic, and community composition effects of N and P varied between experiments. TN:TP ratios explained, in part, some of this variability, along with insolation and water temperature. Despite relatively high levels of CO2 in the control mesocosms, we found a constant synergistic effect of CO2 with N. In combination with the synergistic effect of P with N found in some experiments, this provides support for CO2 as one of the multiple limiting resources in nutrient‐enriched systems. This finding could have implications for eutrophic lakes exposed to increasing concentrations of CO2. We also found that the effects of CO2 on community composition varied intra‐annually. Thus, we conclude that generalised predictions about the effect of CO2 on community composition at a coarse chemotaxonomic scale are unlikely to hold, but predictions specific to season and system are likely to be reliable.

Specific oceanographic characteristics and phytoplankton responses influencing the primary production around the Ulleung Basin area in spring

The East Sea (Sea of Japan) is a marginal, semi-closed sea in the northwestern Pacific. The Ulleung Basin area, which is located near the subpolar front of the East Sea, is known to have high primary production and good fisheries in spring season. After episodic wind-driven events during the spring of 2017, horizontal and vertical profiles of physical chemical biological factors were investigated at 29 stations located in the Ulleung Basin area. In addition, growth responses of phytoplankton communities to nutrient additions were evaluated by bioassay experiments to understand the fluctuation of phytoplankton biomass. Because of strong northwestern wind, phytoplankton biomass was scattered and upwelling phenomenon might be suppressed in this season. The phytoplankton abundances in the coastal stations were significantly higher than offshore and island stations. In contrast, the nutrient and chlorophyll a (Chl a) concentrations and the phytoplankton biomass were quite low in all locations. Bacillariophyceae was dominated group (75.1% for coastal, 40.0% for offshore and 43.6% for island stations). In the algal bioassays, the phytoplankton production was stimulated by N availability. The in vivo Chl a values in the +N and +NP treatments were significantly higher than the values in the control and the +P treatments. Based on the field survey, the higher nutrients in coastal waters affected the growth of diatom assemblages, however, little prosperity of phytoplankton was observed in the offshore waters despite the injection of sufficient nutrients in bioassay experiments. The growth of phytoplankton depended on the initial cell density. All of results indicated that a dominant northwestern wind led to a limited nutrients condition at euphotic layers, and the low level of biomass supply from the coasts resulted in low primary production. Both supplying nutrients and introducing phytoplankton through the currents are critical to maintain the high productivity in the Ulleung Basin area of the East Sea.

Responses of lake phytoplankton communities to changing inorganic nitrogen supply forms

A shift has been predicted in future nitrogen emission scenarios from nitrous oxide to higher proportions of ammonium compounds. To investigate the interaction between increasing nitrogen load and varying nitrate:ammonium ratios (NO3−:NH4+), we performed a mesocosm experiment in an oligotrophic lake in southern Germany. We fertilized mesocosms with both roughly natural and four times the natural nitrogen wet deposition amounts in molar NO3−:NH4+ ratios of 4:1 and 1:4. We observed greater phytoplankton biomass in treatments with a relatively higher ammonium supply, but not in those with nitrate and total nitrogen load. Ammonium significantly increased the total chlorophyll a concentrations, and especially the growth of small nanophytoplankton species. The effects observed indicate that NH4+ was taken up preferentially and that spring phytoplankton in oligotrophic lakes appear to be able to respond to variations in nitrogen forms (available NO3−:NH4+ ratios) by adjusting their community composition. Such communal changes at the base of the food web may affect higher trophic levels. Therefore, the effects of varying available forms of nitrogen should also be considered in primarily phosphorus-limited aquatic systems.

Kelp cultivation effectively improves water quality and regulates phytoplankton community in a turbid, highly eutrophic bay

Coastal eutrophication and its associated harmful algal blooms have emerged as one of the most severe environmental problems worldwide. Seaweed cultivation has been widely encouraged to control eutrophication and algal blooms. Among them, cultivated kelp (Saccharina japonica) dominates primarily by production and area. However, the responses of water quality and phytoplankton community to kelp farming remain unclear. Here, thirteen cruises were conducted in the kelp farms and control areas in the turbid, highly eutrophic Xiangshan Bay of the East China Sea from 2008 to 2015. Results indicated that kelp cultivation slightly increased dissolved oxygen and pH, but reduced dissolved inorganic nitrogen and phosphorus. We estimated that kelp harvesting would remove 297 t of nitrogen and 42 t of phosphorus from this bay annually. Because of decreased flow velocity, turbulence, and sediment resuspension, kelp farming greatly reduced suspended solids and increased transparency, resulting in increases in phytoplankton chlorophyll a and abundance. Additionally, kelp farming appreciably increased phytoplankton species number, Marglef richness, and Shannon–Wiener diversity indices by 51.6%, 40.1%, and 13.1%, respectively. Analysis of similarity and similarity percentages demonstrated that phytoplankton community composition differed significantly between the farm and control area, which was mostly attributed to long-chained diatoms and single-celled dinoflagellates. However, after the kelp harvesting, all measurements of water quality and phytoplankton biomass, diversity, and community composition exhibited no significant difference. Our study highlights that kelp cultivation alleviates eutrophication and acidification and enhances phytoplankton diversity, thus providing guidance for macroalgal aquaculture and remediation in eutrophic waters.

Downstream transport processes modulate the effects of environmental heterogeneity on riverine phytoplankton

Environmental heterogeneity (EH) in space and time promotes niche-partition, which leads to high variation in biological communities, such as in algae. In streams, EH is highly related to the intensity of the water flow and may lead to community variation mainly during the low flow conditions. Despite the wide knowledge on the responses of phytoplankton communities to EH in lentic and semi-lentic systems, studies of riverine phytoplankton community variation are still scarce. Here, we first investigated the relationship between phytoplankton community variation and EH in different courses of the river and between seasons. We expected that under low or intermediate flow conditions, there is a positive correlation between community variation and EH. Alternatively, we did not expect any relationship between EH and community variation under high flow condition because stronger downstream transport would mask environmental filtering. We sampled nine sites monthly (May 2012 to April 2013) in a tropical river of Brazilian Southeast. We calculated EH from abiotic data whereas for community variation, here community distinctiveness (CD), we used Sorensen (CDSor) and Bray-Curtis (CDBray) dissimilarities. Differences in EH, CDSor and CDBray were tested at between-season and among-course levels. We found lower distinctiveness during the dry season when EH was the highest. Contrastingly, phytoplankton CD was the highest even when EH was low during the wet season. We found that this pattern raised from the increasing in individuals dispersal during the wet season, promoting mass effects. Finally, our results thus reject the first hypothesis and show a negative relationship between EH and distinctiveness. However, results support our alternative hypothesis and show that during the wet season, distinctiveness is not driven by EH. These results provide new insights into how EH drives community variation, being useful for both basic research about riverine algal communities and biomonitoring programs using phytoplankton communities as bioindicators.

Response of a coastal Baltic Sea diatom-dominated phytoplankton community to experimental heat shock and changing salinity.

Climate change has been altering the ocean environment, affecting as a consequence the biological communities including microorganisms. We performed a mesocosm experiment to test whether biodiversity loss caused by one stressor would influence plankton community sensitivity to a subsequent stressor, as envisioned in Vinebrooke's multiple stressor concept. A natural Baltic Sea diatom-dominated phytoplankton assemblage was used as a model system where we examined whether a preceding heat shock would affect the community's response to changing salinity. Initially, the community was treated by a short-term temperature increase of 6°C, which resulted in a loss of species compared to the control. Thereafter, the control and the heat-shocked communities were subject to a salinity change (- 5psu, control, + 5psu). The species Skeletonema dohrnii, Thalassiosira anguste-lineata, Thalassiosira nordenskioeldii, Chaetoceros socialis and Ditylum brightwellii were major components of the control and heat-shocked assemblages (> 80% of the total biomass). We examined the effect on species composition and biodiversity (morphospecies and operational taxonomic units (OTUs) related to phytoplankton) and on phytoplankton biomass. In addition, we explored the single species response of five dominant diatoms on these environmental perturbations. Our results showed that increased salinity significantly reduced the OTUs richness both in the control and the less diverse heated community as well as the phytoplankton biomass in the heated community. On the other hand, decreased salinity significantly increased species richness and phytoplankton biomass in both communities and OTUs richness in the control community. The five dominant diatoms reached their highest biomass under decreased salinity and responded negatively to increased salinity (lower biomass than ambient salinity). Contrary to Vinebrooke's multiple stressor concept, there was no indication that the heat treatment had altered the community's sensitivity to the salinity stress in our study system.

Responses of marine phytoplankton communities to environmental changes: New insights from a niche classification scheme

Predicting changes of phytoplankton communities in response to global warming is one of the challenges of ecological forecasting. One of the constraints is the paucity of general principles applicable to community ecology. Based on a synecological analysis of a decadal-scale database, we created a niche habitat classification scheme relating nine phytoplankton groups to fifteen statistically refined realized niches comprised of three niche dimensions: temperature, irradiance, and nitrate concentrations. The niche scheme assigned the nine phytoplankton groups to three types of niches: a cold type, a warm type, and a type associated with high irradiance and high nitrate concentrations. The fact that phytoplankton groups in cold niches were governed by irradiance and those in warm niches by nitrate is consistent with general ecological theories, but the fact that diatoms were the only dominant group in high-irradiance, high-nitrate niches challenges the idea based on autecological studies that diatoms are generally better adapted to low-irradiance, high-nutrient conditions. When combined with an irradiance model, the niche scheme revealed that photoinhibition of Prochlorococcus, which is predicted from autecological studies, is a function of temperature. We used the niche scheme to predict the responses of phytoplankton communities to environmental changes due to seawater warming and eutrophication. The results of the study suggest that a synecological analysis of large databases from field studies facilitates identification of general principles of community ecology that can be used to forecast responses of biological communities to environmental changes.

Temperature-Dependent Bifurcated Seasonal Shift of Phytoplankton Community Composition in the Coastal Water off Southwestern Korea

Coastal water around the archipelago off southwestern Korea has been bathed in an unprecedented pool of warm water in summer in recent years. Here, we examined phytoplankton community responses to amplified seasonal temperature fluctuation around the archipelago based on chemotaxonomic analysis in association with physicochemical properties in the shallow coastal water from June 2016 to March 2018. Concentrations of dissolved inorganic nutrients were significantly higher during the warm season than during the cold season. Canonical correspondence analysis revealed that water temperature was a main driver controlling the phytoplankton community. Generalized additive models denoted that small phytoplankton groups (cryptophytes, cyanobacteria, and prasinophytes) were more resistant to high temperatures (> 25°C) compared with diatoms. Indeed, dominance of diatoms was significant (80%) during the cold season and sharply declined (to 49%) during the warm season. Small phytoplankton were dominant (62%) as the water temperature exceeded 22°C. Our results highlight the effects of temperature-dependent bifurcated seasonality on phytoplankton communities in coastal waters. Furthermore, unprecedentedly high summer temperatures in August 2016 coincided with a remarkable increase in the importance (∼70%) of small phytoplankton. Accumulating evidence provides indications regarding future scenarios: while small phytoplankton will probably account for summer blooms, diatom blooms will shift to winter.

Phytoplankton community responses to temperature fluctuations under different nutrient concentrations and stoichiometry

Nutrient availability and temperature are important drivers of phytoplankton growth and stoichiometry. However, the interactive effects of nutrients and temperature on phytoplankton have been analyzed mostly by addressing changes in average temperature, whereas recent evidence suggests an important role of temperature fluctuations. In a laboratory experiment, we grew a natural phytoplankton community under fluctuating and constant temperature regimes across 25 combinations of nitrogen (N) and phosphorus (P) supply. Temperature fluctuations decreased phytoplankton growth rate (rmax ), as predicted by nonlinear averaging along the temperature-growth relationship. rmax increased with increasing P supply, and a significant temperature×P×N interaction reflected that the shape of the thermal reaction norm depended on nutrients. By contrast, phytoplankton carrying capacity increased with N supply and in fluctuating rather than constant temperature. Higher phytoplankton N:P ratios under constant temperature showed that temperature regimes affected cellular nutrient incorporation. Minor differences in species diversity and composition existed. Our results suggest that temperature variability interacts with nutrient supply to affect phytoplankton physiology and stoichiometry at the community level.

Characteristics of phytoplankton community and water net primary productivity response to the nutrient status of the Poyang Lake and Gan River, China

AbstractPhytoplankton community characteristics and associative primary productivity, which reflect the ecological and nutritional status of water, are sensitive to environmental change. Particularly, nutrient inputs have a significant effect on phytoplankton growth and development as well as the biogeochemical cycle of watersheds. We investigated the phytoplankton community and nutrient status downstream from the Gan River into Poyang Lake. On a catchment scale, the phytoplankton communities and associative primary productivity from these two water bodies differed. The Poyang Lake phytoplankton community is composed of seven phyla of algae, whereas the Gan River is composed of six, the dominant phyla of phytoplankton being Bacillariophyta and Cryptophyta in Poyang Lake and Gan River, respectively. Phytoplankton abundance and primary productivity were significantly higher in Poyang Lake. Lower nitrogen (N) and phosphorous (P) concentrations and higher carbon (C) and silicon (Si) concentrations significantly affected the phytoplankton communities and primary productivity distribution in the entire Poyang Lake Basin. In this regard, we found a significant correlation between the phytoplankton community of the Gan River and P and N, whereas N and Si primarily regulated the phytoplankton community structure of Poyang Lake. Moreover, we found a significant correlation between DTN, Si/P, DIC/P, and primary productivity in the Gan River, whereas NH4+ jointly controlled primary productivity in Poyang Lake. Furthermore, the Margalef Richness Index (0.84–2.41) can be indicative of the environmental water quality status; and we determined that the most area of Poyang Lake and Gan River both were P restriction and moderately polluted, whereas the entrance of the Gan River into Poyang Lake was seriously polluted, which confirms that the Gan River is a main and crucial source of Poyang Lake pollution. Nanjishan Nature Reserve was already slightly eutrophic due to the high nutrient content and a large number of algae in the south‐east of Poyang Lake, but the Gan River had good river fluidity, so some areas of the Gan River were oligotrophic.

Responses of Phytoplankton Communities in Selected Eutrophic Lakes to Variable Weather Conditions

It is well-known that recent climatic changes have strongly affected aquatic ecosystems. In this study, we examined the complex factors determining the development of phytoplankton communities during the vegetative growth season in eutrophic lakes located in a temperate zone in eastern Poland. Our analysis enabled us to divide the data into two different periods: years with a cold winter and low total precipitation, and those with a mild winter and high total precipitation. The analysis showed that the soluble and total nitrogen content, concentration of chlorophyll a, total phytoplankton biomass, and biomasses of Cyanobacteria and Cryptophyceae were significantly higher in the vegetative growth season in the year after a mild winter, whereas the soluble and total phosphorus content and phytoplankton biodiversity were significantly lower in these years. Hence, climate warming indirectly led to the loss of biodiversity in the phytoplankton communities in the studied lakes of temperate zone. During this study, we also tested the effects of increases in air temperature and total precipitation on phytoplankton communities over short time periods (14 and 28 days). The results showed that the total phytoplankton biomass and the chlorophyll a concentration were only positively correlated with the air temperature. All of the features described in this study showed how sensitive lake ecosystems are to climatic fluctuations.

Seasonal variation of phytoplankton community and its relationship with environment in subtropical reservoirs: A comparison between two methods of functional groups classification

Phytoplankton is the most important biological component in the reservoir ecosystem, which could indicate the status of aquatic ecosystem due to its sensitive to environmental variation. To understand the application and difference between two methods of phytoplankton functional group classification, functional groups (FG) and morphology-based functional groups (MBFG), in indicating the changes of reservoir environment, we investigated water quality and phytoplankton in Qingshitan Reservoir monthly from March 2016 to February 2017. Two phytoplankton functional groups classifications (FG and MBFG) were used to analyze phytoplankton community composition, seasonal succession, and its driving factors. We compared the application and differences of two methods of functional group classifications in indicating environmental changes. The results showed that there were 109 species belonged to seven phylum, which could be classified into 17 FG or 5 MBFG functional groups. Results from both methods indicated that the reservoir was meso-eutrophic. The phytoplankton seasonal succession under 8 or 9 steps with FG or 8 steps with MBFG. Results from the redundancy analysis showed that the response of phytoplankton community reflected with FG to environmental variation was more sensitive than that with MBFG, especially in the response to the changes of pH and nitrate concentration. In conclusion, FG was more appropriate in describing community succession and exploring the relationship between phytoplankton and environment.

Diversity and toxic potential of algal bloom-forming species from Takaroa lagoon (Tuamotu, French Polynesia): a field and mesocosm study

Pearl farming lagoons are economically important, yet poorly studied ecosystems in French Polynesia. This paper describes a study conducted in 2016 in Takaroa (Tuamotu Archipelago), an atoll recurrently affected by harmful algal bloom (HAB) events. The objectives were to gain insight into phytoplankton community composition, identify the main bloom-forming species and investigate their potential for toxicity. A mesocosm approach was used to assess the response of phytoplankton communities to 3 nutrient treatments: Conway with Si, Si-depleted f/2 and a commercial N-P fertilizer. In total, 87 morpho-species were described from Takaroa lagoon, with dinoflagellates as the most diverse group. Diatoms (Extubocellulus sp., Cylindrotheca closterium, Nitzschia spp.), dinoflagellates (Gymnodinium spp., Heterocapsa spp.) and flagellates (Cryptomonas sp., Pyraminonas spp.) were among the major bloom-forming species identified. Most markedly, Extubocellulus sp., a diatom never reported from French Polynesia before, was able to bloom even in Si-poor environments. Additionally, in vitro cultures of 12 bloom-forming strains were successfully established and tested for their toxicity. Preliminary results suggest that 9 strains, including dinoflagellates (Prorocentrum lima, Amphidinium spp., Heterocapsa sp.), Pyraminonadales (Pyramimonas sp.) and cryptophytes (Cryptomonas sp.), are the likely producers of cyclic imine neurotoxins and toxins acting on voltage-gated sodium channels. The contribution of these toxins to the mortality events previously reported in Takaroa lagoon is further discussed. Overall, this study highlights the relevance of a mesocosm approach which can be applied to other understudied atolls of French Polynesia recurrently threatened by HABs.