Freshwater Plankton Communities Research Articles

High resolution chlorophyll-a in-situ fluorescence sensors versus in-vitro chlorophyll-a measurements in mesocosms with contrasting nutrient and temperature treatments

Harmful algal blooms (HABs) are a significant threat to freshwater ecosystems, and monitoring for changes in biomass is therefore important. Fluorescence in-situ sensors enable rapid and high frequency real-time data collection and have been widely used to determine chlorophyll-a (Chla) concentrations that are used as an indicator of the total algal biomass. However, conversion of fluorescence to equivalent Chla concentrations is often complicated due to biofouling, phytoplankton composition and the type of equipment used. Here, we validated measurements from 24 Chla and 12 phycocyanin (cyanobacteria indicator) fluorescence in-situ sensors (Cyclops-7F, Turner Designs) against spectrophotometrically (in-vitro) determined Chla and tested a data-cleaning procedure for eliminating data errors and impacts of non-photochemical quenching. The test was done across a range of freshwater plankton communities in 24 mesocosms (i.e. experimental tanks) with a 2x3 (high and low nutrient x ambient, IPCC-A2 and IPCC-A2+50% temperature scenarios) factorial design. For most mesocosms (tanks), we found accurate (r2 ≥ 0.7) calibration of in-situ Chla fluorescence data using simple linear regression. An exception was tanks with high in-situ phycocyanin fluorescence, for which multiple regressions were employed, which increased the explained variance by >16%. Another exception was the low Chla concentration tanks (r2 < 0.3). Our results also show that the high frequency in-situ fluorescence data recorded the timing of sudden Chla variations, while less frequent in-vitro sampling sometimes missed these or, when recorded, the duration of changes was inaccurately determined. Fluorescence in-situ sensors are particularly useful to detect and quantify sudden phytoplankton biomass variations through high frequency measurements, especially when using appropriate data-cleaning methods and accounting for factors that can impact the fluorescence readings.

Fate and effects of a new generation fluorosurfactant (cC6O4) in freshwater mesocosms

Per- and polyfluorinated alkyl substances (PFAS) have raised international concerns due to their widespread use, environmental persistence and potential bioaccumulative and ecotoxicological effects. Therefore, the chemical industry has been dedicated to develop new generation fluorosurfactants which are aimed to replace the most concerning PFAS. Here we investigated the fate and effects of cyclic C6O4 (cC6O4), a compound used as alternative to long-chain perfluorocarboxylic acids, in freshwater mesocosms located in the Mediterranean region (Spain) over a period of 90 days. cC6O4 was applied as ammonium salt once at the following nominal concentrations: 0 µg/L (control), 1 µg/L, 20 µg/L, 400 µg/L, and 8,000 µg/L. The study shows that cC6O4 is relatively persistent in water (dissipation: 34–37 % after 90 days), has very low sorption capacity to sediments (sediment-water partition coefficient: 0.18–0.32 L/kg) and very limited bioconcentration (BCF: 0.09–0.94), bioaccumulation (BAF: 0.09–4.06) and biomagnification (BMF: 0.05–0.28) potential. cC6O4 did not result in significant adverse effects on aquatic populations and communities of phytoplankton and zooplankton at the tested concentrations. As for the macroinvertebrate community, the ephemeropteran Cloeon sp. showed a population decline at the highest test concentration on day 60 onwards, and a significant effect on the macroinvertebrate community was identified on the last sampling day at the same exposure level. Therefore, the calculated NOEC for cC6O4 in freshwater mesocosms exposed over a period of 90 days was 400 µg/L, which corresponded to a time weighted average concentration of 611 µg/L, given the water evaporation in the test systems. This concentration is about an order of magnitude higher than the highest exposure concentration monitored in freshwater ecosystems. Therefore, it can be concluded that cC6O4 poses insignificant ecological risks for freshwater plankton and macroinvertebrate communities given the current environmental exposure levels.

Impacts of salinity stress caused by ballast water discharge on freshwater ecosystems

Global commodity trade and the transportation of goods rely heavily on shipping. But the discharge of large quantities of hypersaline ballast water carried by maritime vessels into freshwater ports, lakes, rivers and other water bodies cause salinity stress, which can be detrimental to native freshwater organisms. In this study, the effects of marine hypersaline ballast water discharge and the rate of discharge (abrupt vs. gradual) on inland freshwater lakes were assessed by observing changes in freshwater plankton communities under salinity stress. The findings indicate that increasing salinity has a negative impact on plankton community composition, density and biodiversity. Zooplankton were more sensitive to changes in salinity than phytoplankton through 10 consecutive days of experiments. Moreover, the plankton community showed some ability to recover itself at low salinities (S≤6.5 PSU). In terms of the rate of ballast water discharge, plankton were more likely to survive in aquatic environments with gradual changes in salinity than with abrupt changes. This research is of great significance for the scientific management of ballast water discharge in freshwater ports and the conservation of freshwater ecosystems.

Interspecific insights into direct and indirect effects of acetochlor on interactions between daphnids and microalgae: Toxic, trophic, and grazer-infochemical responses

As the herbicide acetochlor (ACT) affects the plankton food web, this study investigated the effects of ACT and exocrine infochemicals from daphnids (after ACT exposure and/or starvation) on Scenedesmus obliquus growth, as well as the effects of ACT and starvation on life-history traits of Daphnia magna. Filtered secretions from daphnids increased algal ACT tolerance, dependent on different ACT exposure histories and food intake. Endogenous and secretory metabolite profiles of daphnids following ACT and/or starvation appear to be regulated by the fatty acid synthesis pathway and sulfotransferases and were related to energy allocation trade-offs. Oleic acid (OA) and octyl sulfate (OS), screened by secreted and somatic metabolomics, affected algal growth and ACT behavior in the algal culture in opposite ways. Trophic and non-trophic interspecific effects caused by ACT were observed in microalgae-daphnid microcosms, including algal growth inhibition, daphnid starvation, OA down-regulation, and OS up-regulation. Based on these findings, risk assessment of ACT on the freshwater plankton communities should take species interactions into account.

Experimental assessment the effects of saline discharge on plankton community of the recipient freshwater ecosystem – Inputs to scientific ballast water management of inland ports

Expanding international trade has accelerated the transfer of ballast water worldwide, the change in salinity is expected to be detrimental to recipient areas’ species, especially to freshwater ports’. This study simulated the changes in freshwater plankton community with respect to salinity stress resulting from ballast water discharged. The prepared saline water (simulates ballast water that meets D-2 standards) was discharged into the collected freshwater samples (from natural lake) at different volume ratios, which represented the salinity changes in localized areas of the receiving waters. The samples were counted and identified for ≥ 10–50 µm and ≥ 50 µm organisms with FDA (Florescein Diacetate) & CMFDA (Chloromethylflurescein Diacetate) method and Microscope counting method. From the first day after saline water discharged, it was found that when water salinity reached 12.2 PSU (Practical salinity units), the density of ≥ 50 µm organism was about 0 ind./m3, while only when water salinity reached 24.8 PSU, the density of ≥ 10–50 µm organisms was 0 cells/mL from the sixth day after saline water discharged. When the salinity was less than or equal to 2.1 PSU, the composition of species of ≥ 50 µm organisms in samples were similar to the control group, but for ≥ 10–50 µm organisms, when the salinity was less than or equal to 6.5 PSU, the community structure in samples were similar to the control group. The ≥ 10–50 µm and ≥ 50 µm organisms, these two groups were differently responsive to the changes in salinity. Besides, when the change of water salinity doesn’t exceed 6.5 PSU, the density of plankton first decreased and then increased, but when salinity changes exceed 6.5 PSU, the density of plankton exhibited a great decline during ten days. The results indicated that high-salt ballast water discharge could negatively affect freshwater harbor organisms, the salinity indicators could provide the basis for future studies of actual water samples, pay attention to the impact of ballast water discharge on inland ports is urgent.

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.

The response of freshwater plankton communities to temporal concurrence of agrochemical mixtures

Freshwater ecosystems regularly experience pulsed inputs of nutrients and other pollutants as a result of temporally variable applications of agrochemicals combined with runoff events. In this study, we evaluate how planktonic communities respond to repeated and pulsed insecticide disturbances and if the response depends on temporal concurrence with nutrient pulses. We conducted an experiment using mesocosms to assess the ecotoxicological effects of a commonly used insecticide (chlorpyrifos) and nutrients (nitrogen and phosphorus) on plankton communities. The mesocosms (300 L) were established outdoors for 10 weeks. The experiment consisted of 3 treatments: nutrient pulse of nitrogen and phosphorus every two weeks (N; considered as control), nutrients and insecticide pulsed simultaneously every two weeks (NI), and nutrients and insecticide pulsed in alternating weeks (N_I). Insecticide and nutrient pulses consisted of 2 μg/L of chlorpyrifos, 560 μg/L of nitrogen, and 39.9 μg/L of phosphorus. Zooplankton abundance, community structure, and diversity were used as structural indicators. Chlorophyll a and net production were used as functional indicators. We found no effect of the treatments on zooplankton abundance, while richness and Shannon diversity was lower in treatments with pulsed insecticide (NI and N_I) compared to control treatment (N). Phytoplankton biomass was higher in the treatments with insecticide than in the controls (N). Higher phytoplankton biomass could be explained by an indirect effect shift from a cladocera-dominated to a copepod-dominated community in response to the insecticide treatment. Overall, the insecticide disturbance had direct and indirect effects on the community and did not depend on whether insecticides were pulsed synchronously or asynchronously with nutrients.

The Species Structure of Plankton Communities as a Response to Changes in the Trophic Gradient of the Mouth Areas of Large Tributaries to a Lowland Reservoir

The mouth areas of large rivers can serve as a good model of heterogeneity sites with a pronounced trophic gradient to assess the impact of the degree of eutrophication on different plankton communities. The aim of this research was to identify the possible response of the diversity indicators of phyto- and zooplankton communities to trophic gradients in the mouth area of two large tributaries of the reservoir, formed in the Middle Volga River (Russia). Both linear regression models and canonical correlation analysis (CCA) were used to assess the role of abiotic and biotic predictors in the structural organization of plankton communities and to assess the changes in the parameters of the species plankton community structure in the trophic gradient. It was found that the species diversity (Adjusted R2 = 0.116) and evenness (Adjusted R2 = 0.114) of phytoplankton significantly decreased with an increase in the degree of eutrophication, while the species diversity (Adjusted R2 = 0.059) and evenness (Adjusted R2 = 0.073) of zooplankton increased. According to the CCA models, electrical conductivity (EC) explained the largest proportion of the observed dispersion. The Trophic State Index (TSI) explained 3.0% of the total variance in the phytoplankton community species structure and 7.8% in the zooplankton one. The variation in phyto- and zooplankton dominant complexes generally corresponded to the well-known patterns of plankton species succession in the gradient of trophic conditions and can be considered as a classic manifestation of the cascade effect in the food chains of freshwater plankton communities. Our results highlight the necessity of studying the mouth river areas, as well as applying an integrated approach to investigating the response of plankton communities to eutrophication processes of continental water bodies.

Interactive effects of increasing chloride concentration and warming on freshwater plankton communities

AbstractAcross the Northern hemisphere, chloride concentrations in lakes are increasing from decades of road salt use, threatening aquatic ecosystems. Zooplankton are sensitive to increasing chloride but few studies have considered how additional stressors, such as soft water or increasing lake temperatures interact with the negative effects of chloride. To determine the effects of increasing chloride and temperature on freshwater zooplankton and phytoplankton communities, we conducted a mesocosm experiment using 30 concentrations of chloride from ambient levels to 1500 mg L−1, ambient or warmed (+2.7°C) temperatures, and plankton from a softwater lake. We compared the results with current Canadian Water Quality Guidelines (CWQG) for chronic exposure to chloride. Although warming elicited little response, increasing chloride concentrations led to reduced zooplankton biomass and richness, even at concentrations below the CWQG, and an increase in cyanobacteria abundance, suggesting that policies regulating road salt application should be reevaluated to better protect aquatic ecosystems.

Molecular Data Reveal a Cryptic Diversity in the Genus Urotricha (Alveolata, Ciliophora, Prostomatida), a Key Player in Freshwater Lakes, With Remarks on Morphology, Food Preferences, and Distribution.

Species of the ciliate genus Urotricha are key players in freshwater plankton communities. In the pelagial of lakes, about 20 urotrich species occur throughout an annual cycle, some of which play a pivotal role in aquatic food webs. For example, during the phytoplankton spring bloom, they consume a remarkable proportion of the algal production. In ecological studies, urotrich ciliates are usually merely identified to genus rank and grouped into size classes. This is unsatisfying considering the distinct autecological properties of individual species and their specific spatial and temporal distribution patterns. As a basis for future research, we characterized in detail four common urotrich morphotypes, i.e., specimens identified as U. furcata and tentatively as U. agilis, U. pseudofurcata, and U. castalia, using state-of-the-art methods. We used an integrative polyphasic approach, in which morphological studies (in vivo observation, silver staining methods, scanning electron microscopy) were linked with a molecular approach exploiting four different gene fragments as taxonomic DNA barcodes with different resolution potential (SSU rDNA, ITS-1, ITS-2, hypervariable V4 and V9 regions of the SSU rDNA). We shed light on the diversity of urotrich ciliates as well as on their global distribution patterns, and annual cycles. Additionally, we coupled individual species occurrences and environmental parameters, and subsequently modeled the distribution and occurrence, using logistic regressions. Furthermore, for one strain putatively identified as U. castalia, we ascertained the optimal cultivation media and food preferences. Thereby, our comprehensive view on these important freshwater ciliates that frequently occur in environmental high throughput sequencing datasets worldwide will allow future studies to better exploit protistan plankton data from lakes.

Eutrophication decrease compositional dissimilarity in freshwater plankton communities

Human activities, such as land use change and eutrophication, threaten freshwater biodiversity and ecosystem function. In this study, we examined both the α- and β-diversity of plankton communities, that is, bacteria/prokaryotic algae, eukaryotic algae, and zooplankton/metazoans, using both classical microscopy and high-throughput sequencing methods across 40 lakes of the Yangtze River Basin. The spatial variations in plankton communities were explained by environmental variables such as trophic status index (TSI) and environmental heterogeneity according to non-metric multidimensional scaling analyses, mantel tests, and structural equation model. Our results showed that the compositional dissimilarities of bacteria, cyanobacteria, eukaryotic algae, and metazoans all decreased with the increasing TSI values, and were significantly positively related to environmental dissimilarity. Both the species richness and compositional dissimilarity of zooplankton had positive effects on zooplankton/phytoplankton biomass ratio. Zooplankton diversity was not directly affected by TSI and environmental dissimilarity; however, it was indirectly affected by the biotic interactions with cyanobacteria or eukaryotic algae. In addition, there were significant positive relationships between bacteria/cyanobacteria and eukaryotic algae dissimilarities. Our results indicated that increased trophic status and decreased environmental dissimilarity as consequences of eutrophication may weaken the trophic cascading effects of planktonic food chain via reducing the top-down effects of zooplankton on phytoplankton.

Temporal dynamics of freshwater planktonic parasites inferred using a DNA metabarcoding time-series.

Parasites are important components of biodiversity and contributors to ecosystem functioning, but are often neglected in ecological studies. Most studies examine model parasite systems or single taxa, thus our understanding of community composition is lacking. Here, the seasonal and annual dynamics of parasites was quantified using a 5-year metabarcoding time-series of freshwater plankton, collected weekly. We first identified parasites in the dataset using literature searches of the taxonomic match and using sequence metadata from the National Center for Biotechnology Information (NCBI) nucleotide database. In total, 441 amplicon sequence variants (belonging to 18 phyla/clades) were classified as parasites. The four phyla/clades with the highest relative read abundance and richness were Chytridiomycota, Dinoflagellata, Oomycota and Perkinsozoa. Relative read abundance of total parasite taxa, Dinoflagellata and Perkinsozoa significantly varied with season and was highest in summer. Parasite richness varied significantly with season and year, and was generally lowest in spring. Each season had distinct parasite communities, and the difference between summer and winter communities was most pronounced. Combining DNA metabarcoding with searches of the literature and NCBI metadata allowed us to characterize parasite diversity and community dynamics and revealed the extent to which parasites contribute to the diversity of freshwater plankton communities.

Effects of chloride and nutrients on freshwater plankton communities

AbstractIncreasing chloride concentrations threaten freshwater zooplankton. We questioned the protectiveness of the Canadian Water Quality Guideline for chloride because it is based on individual species studied under laboratory conditions and does not account for potential interactive factors, such as nutrient concentration. We exposed plankton communities to 30 chloride concentration increments for 6 weeks, crossed with either ambient or high nutrient treatments. Total zooplankton abundance, biomass, and richness declined with increasing chloride, with losses observed below the Canadian Water Quality Guideline. Nutrients did not affect the impact of chloride on zooplankton. Phytoplankton and protist responses varied by nutrient level. Under low nutrients, phytoplankton and protist abundance, biomass, and richness increased with chloride. Under high nutrients, phytoplankton and protist abundance and biomass were unaffected while richness decreased with chloride. These results indicate that current water quality guidelines do not sufficiently protect plankton and that nutrient context may alter phytoplankton and protist response.

First circumpolar assessment of Arctic freshwater phytoplankton and zooplankton diversity: Spatial patterns and environmental factors

Abstract Arctic freshwaters are facing multiple environmental pressures, including rapid climate change and increasing land___use activities. Freshwater plankton assemblages are expected to reflect the effects of these stressors through shifts in species distributions and changes to biodiversity. These changes may occur rapidly due to the short generation times and high dispersal capabilities of both phyto___ and zooplankton. Spatial patterns and contemporary trends in plankton diversity throughout the circumpolar region were assessed using data from more than 300 lakes in the U.S.A. (Alaska), Canada, Greenland, Iceland, the Faroe Islands, Norway, Sweden, Finland, and Russia. The main objectives of this study were: (1) to assess spatial patterns of plankton diversity focusing on pelagic communities; (2) to assess dominant component of __ diversity (turnover or nestedness); (3) to identify which environmental factors best explain diversity; and (4) to provide recommendations for future monitoring and assessment of freshwater plankton communities across the Arctic region. Phytoplankton and crustacean zooplankton diversity varied substantially across the Arctic and was positively related to summer air temperature. However, for zooplankton, the positive correlation between summer temperature and species numbers decreased with increasing latitude. Taxonomic richness was lower in the high Arctic compared to the sub___ and low Arctic for zooplankton but this pattern was less clear for phytoplankton. Fennoscandia and inland regions of Russia represented hotspots for, respectively, phytoplankton and zooplankton diversity, whereas isolated regions had lower taxonomic richness. Ecoregions with high __ diversity generally also had high __ diversity, and turnover was the most important component of __ diversity in all ecoregions. For both phytoplankton and zooplankton, climatic variables were the most important environmental factors influencing diversity patterns, consistent with previous studies that examined shorter temperature gradients. However, barriers to dispersal may have also played a role in limiting diversity on islands. A better understanding of how diversity patterns are determined by colonisation history, environmental variables, and biotic interactions requires more monitoring data with locations dispersed evenly across the circumpolar Arctic. Furthermore, the importance of turnover in regional diversity patterns indicates that more extensive sampling is required to fully characterise the species pool of Arctic lakes.

The ecological network approach to algal-bacterial relationships: Review and prospects

<p indent=0mm>Algae and bacteria numerically dominate oceanic and freshwater planktonic communities. They play a central biogeochemical role in the marine ecosystem, including producing biomass to support aquatic food webs, cycling nutrients and trace elements, and decomposing organic matter. Algae and bacteria synergistically affect each other’s physiology and metabolism and have coexisted ever since the early stages of evolution that revolutionized many aspects of life on Earth. The relationship between algae and bacteria influences ecosystems and represents all conceivable modes of interaction from mutualism to parasitism. The interactions between these two groups of plankton, and the influence of their interaction on each other and on a global scale have, therefore, become the focus of recent research interest. Previous studies have summarized a variety of algal-bacterial interactions and aimed to reveal the essence of those interactions. However, it is clear that their interactions are diverse and not static, and can be initiated and broken in response to environmental and developmental cues. Traditional research methods have been unable to reveal the complexity behind algal-bacterial symbiosis. As microbial omics technology has developed and the influence of global change on marine ecosystems has become apparent, the research perspective on algal-bacterial relationships has gradually risen to the level of systemic ecology. The rapid-blooming of high-throughput sequencing technology and the ability to analyze big data offer new opportunities for a thorough study of algal-bacterial interaction. Ecological networks are prominent among these new methods: They can integrate multiple types of information and might represent systems-level behavior. Network theory methods are powerful approaches for quantifying relationships between biological components and their relevance to phenotypes, environmental conditions or other external variables within a system. In this paper, we review the research advances in the algal-bacterial ecological network based on big data. We begin by introducing the network parameters and attributes commonly used in ecological network analysis and review the existing network modeling methods in microbial studies and algorithm features and application scenarios. By comparing some common algorithms or software, researchers can choose appropriate network construction methods when confronted with different data characteristics. Next, the ecological network analysis used in the study of algal-bacterial relationships is presented at multiple layers from taxonomy to function (e.g., molecular and metabolic networks). The problems and experiences encountered during research into algal-bacterial relationships are then discussed. For example, when focusing on the interaction between host and microorganism, the time/space shift correlations among the variables will lead to wrong conclusions, including false-positive or false-negative results. We also attempt to introduce metabolic and dynamic biological networks into the study of the algal-bacterial relationship to reveal further the mechanism of their interaction from the perspectives of function and causality. Finally, our novel proposal to establish a knowledge network database of algal-bacterial interactions and a graphic database of photosphere biological profiles is discussed. We highlight the need for microbial ecological network inference and suggest strategies to infer networks more reliably. Our study aimed to explore the holistic information behind algal-bacterial relationships and provide new cues for further revealing the molecular mechanisms of algal-bacterial interactions.

A unified framework for herbivore-to-producer biomass ratio reveals the relative influence of four ecological factors

The biomass ratio of herbivores to primary producers reflects the structure of a community. Four primary factors have been proposed to affect this ratio, including production rate, defense traits and nutrient contents of producers, and predation by carnivores. However, identifying the joint effects of these factors across natural communities has been elusive, in part because of the lack of a framework for examining their effects simultaneously. Here, we develop a framework based on Lotka–Volterra equations for examining the effects of these factors on the biomass ratio. We then utilize it to test if these factors simultaneously affect the biomass ratio of freshwater plankton communities. We found that all four factors contributed significantly to the biomass ratio, with carnivore abundance having the greatest effect, followed by producer stoichiometric nutrient content. Thus, the present framework should be useful for examining the multiple factors shaping various types of communities, both aquatic and terrestrial.

Artificial Eutrophication Decrease Compositional Dissimilarity in Freshwater Plankton Communities

Artificial Eutrophication Decrease Compositional Dissimilarity in Freshwater Plankton Communities

Ecological impacts of freshwater algal blooms on water quality, plankton biodiversity, structure, and ecosystem functioning

Harmful algal blooms are among the emerging threats to freshwater biodiversity that need to be studied further in the Anthropocene. Here, we studied freshwater plankton communities in ten tropical reservoirs to record the impact of algal blooms, comprising different phytoplankton taxa, on water quality, plankton biodiversity, and ecosystem functioning. We compared water quality parameters (water transparency, mixing depth, pH, electrical conductivity, dissolved inorganic nitrogen, total dissolved phosphorus, total phosphorus, chlorophyll-a, and trophic state), plankton structure (composition and biomass), biodiversity (species richness, diversity, and evenness), and ecosystem functioning (phytoplankton:phosphorus and zooplankton:phytoplankton ratios as a metric of resource use efficiency) through univariate and multivariate analysis of variance, and generalized additive mixed models in five different bloom categories. Most of the bloom events were composed of Cyanobacteria, followed by Dinophyta and Chlorophyta. Mixed blooms were composed of Cyanobacteria plus Bacillariophyta, Chlorophyta, and/or Dinophyta, while non-bloom communities presented phytoplankton biomass below the threshold for bloom development (10 mg L−1, WHO alert level 2). Higher phytoplankton biomasses were recorded during Cyanobacteria blooms (15.87–273.82 mg L−1) followed by Dinophyta blooms (18.86–196.41 mg L−1). An intense deterioration of water quality, including higher pH, eutrophication, stratification, and lower water transparency, was verified during Cyanobacteria and mixed blooms, while Chlorophyta and Dinophyta blooms presented lower pH, eutrophication, stratification, and higher water transparency. All bloom categories significantly impacted phytoplankton and zooplankton structure, changing the composition and dominance patterns. Bloom intensity positively influenced phytoplankton resource use efficiency (R2 = 0.25; p < 0.001), while decreased zooplankton resource acquisition (R2 = 0.51; p < 0.001). Moreover, Cyanobacteria and Chlorophyta blooms negatively impacted zooplankton species richness, while Dinophyta blooms decreased phytoplankton richness. In general, Cyanobacteria blooms presented low water quality and major threats to plankton biodiversity, and ecosystem functioning. Moreover, we demonstrated that biodiversity losses decrease ecosystem functioning, with cascading effects on plankton dynamics.

Biogeographic patterns of planktonic and meiobenthic fauna diversity in inland waters of the Russian Arctic

Abstract Broad‐scale assessment of biodiversity is needed for detection of future changes across substantial regions of the Arctic. Presently, there are large data and information gaps in species composition and richness of the freshwater planktonic and meiobenthos communities of the Russian Arctic. Analysis of these data is very important for identifying the spatial distribution and temporal changes in species richness and diversity of rotifers, cladocerans, and copepods in the continental Russian Arctic. We investigated biogeographic patterns of freshwater plankton and meiobenthos from c. 67° to 73°N by analysing data over the period 1960–2017. These data include information on the composition of rotifers, cladocerans, and copepods obtained from planktonic and meiobenthic samples, as well as from subfossil remains in bottom sediments of seven regions from the Kola Peninsula in the west, to the Indigirka River Basin (east Siberia) in the east. Total richness included 175 species comprised of 49 rotifer genera, 81 species from 40 cladoceran genera, and 101 species from 42 genera of calanoid, cyclopoid, and harpacticoid copepods. Longitudinal trends in rotifer and micro‐crustacean diversity were revealed by change in species composition from Europe to eastern Siberia. The most common and widespread species were 19 ubiquitous taxa that included Kellicottia longispina (Rotifera), Chydorus sphaericus s. lat. (Cladocera), Heterocope borealis, Acanthocyclops vernalis, and Moraria duthiei (Copepoda). The highest number of rare species was recorded in the well‐studied region of the Bolshezemelskaya tundra and in the Putorana Plateau. The total number of copepod and rotifer species in both Arctic lakes and ponds tended to increase with latitude. Relative species richness of copepods was positively associated with waterbody area, elevation, and precipitation, while relative species richness of cladocerans was positively related to temperature. This result is consistent with known thermophilic characteristics of cladocerans and the cold tolerance properties of copepods, with the former being dominant in shallow, warmer waterbodies of some western regions, and the latter being dominant in large cold lakes and waterbodies of eastern regions. Rotifers showed a negative association with these factors. Alpha‐ and β‐diversity of zooplankton in the Russian Arctic were strongly related to waterbody type. Lake zooplankton communities were more diverse than those in pond and pool systems. Moreover, the highest β‐diversity values were observed in regions that showed a greater breadth in latitude and highly heterogeneous environmental conditions and waterbody types (Bolshezemelskaya tundra and Putorana Plateau). Redistribution of freshwater micro‐fauna caused by human activities occurred in the 1990s and 2000s. As a result of climate warming, a few cladoceran species appear to have extended their range northward. Nevertheless, the rotifer and micro‐crustacean fauna composition and diversity of the majority of Arctic regions generally remain temporally conservative, and spatial differences in composition and species richness are chiefly associated with the differences between the warmer European and colder east Siberian climates.

Warming advances virus population dynamics in a temperate freshwater plankton community

Viruses are important drivers in the cycling of carbon and nutrients in aquatic ecosystems. Since viruses are obligate parasites, their production completely depends on growth and metabolism of hosts and therefore can be affected by climate change. Here, we investigated if warming (+4°C) can change the outcome of viral infections in a natural freshwater virus community over a 5‐month period in a mesocosm experiment. We monitored dynamics of viruses and potential hosts. Results show that warming significantly advanced the early summer peak of the virus community by 24 d, but neither affected viral peak abundances nor time‐integrated number of viruses present. Our results demonstrate that warming advances the timing of viruses in a natural community. Although warming may not necessarily result in a stronger viral control of bacterial and phytoplankton communities, our results suggest it can alter host population dynamics through advanced timing of infections, and thus timing of carbon and nutrient recycling.