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Urbanization is one of the most serious threats to stream ecosystems worldwide. It is crucial to understand its effects on stream organisms as a prerequisite for the mitigation of urban degradation. Our aim was to investigate the general effects of urbanization in a moderately urbanized landscape and to assess the relationship between local environmental variables and biotic attributes of macroinvertebrate assemblages. Multiple sites at low-order streams flowing from natural forested areas to moderately urbanized landscapes were surveyed. We found that local habitat properties presented degraded conditions at urban sites. Urbanization had a negative effect on the richness and Shannon diversity of macroinvertebrate assemblages, and altered assemblage composition. Biotic assemblage parameters showed negative, neutral or positive relationships with local physical parameters. Concrete cover was one of the most important variables, which explained a decreasing richness and diversity of macroinvertebrates. In natural conditions, microhabitat-level environmental variables significantly impacted community variation, while in degraded conditions microhabitat and site-level environmental variables had a substantial impact together. Individual streams showed considerable variability under natural conditions, as well as in their response to urban effects. Subsequently, the mitigation of the effects of urbanization might also need considerable variability in the type of actions required.

Understanding the dynamics of phytoplankton assemblages in various and variable aquatic ecosystems is of paramount importance, given the strategic supporting services offered by these organisms. Such knowledge is implicitly based on the analysis of the realized niche of the different populations, i.e. of the sets of conditions within which populations show a positive growth. The range of phytoplankton morphological traits variability is evolutionarily selected to maximize the ecological performance of species while they are entrained in the spectrum of turbulent flows. In addition, most phytoplankton species exhibit high morphological plasticity that can further optimize their performance under reduced environmental variability. Although this plasticity is well known, it is seldom considered in phytoplankton studies. Morphological analysis could therefore be used as a tool to estimate the environmental variability within which a species can persist and, ultimately, the niche width of phytoplankton populations. This opinion paper tries to answer the questions: to what extent can the morphological variability of phytoplankton offer a synthesis of the environmental variability of aquatic ecosystems?. Do the morphological traits contain sufficient information to describe the width of the realized niche of phytoplankton species? What can we do to fill eventual gaps in our knowledge?

Silica-scaled chrysophytes are a unique group of protists representing a major component of numerous aquatic habitats where they can significantly contribute to human well-being in many ways. In the present review, altogether 14 ecosystem services provided by silica-scaled chrysophytes were identified highlighting their importance and roles in aquatic ecosystems. The most important supporting services are related to primary production, nutrient- and biogeochemical cycling, as well as sediment formation. Additionally, they are involved in the regulation of climate, maintenance of air quality, biological control and water purification processes (as regulating services). The most relevant provisioning services include their usefulness in environmental monitoring (paleolimnology, ecological status assessment and climate modelling), production of biochemicals and provision of genetic resources. Cultural services are associated with aesthetic values, inspiration source and knowledge system as well. Although silica-scaled chrysophytes are one of the least studied groups of algae, here they are shown to provide important benefits and to have many further powerful opportunities for humans, thus their detailed research in the future is emphasised as an important key for human well-being.

Diatoms, a unique group of algae colonising a wide range of aquatic habitats and contributing to human well-being in many ways. We list and summarise these services using the classification of the Millennium Ecosystem Assessment (MEA), i.e. supporting, regulating, provisioning and cultural services. The most relevant supporting services are photosynthesis and primary production, as well as sediment formation. They also play a key role in nutrient cycling and habitat provisioning and serve as food for many organisms. Regulating services as oxygen production, climate control or sediment stabilisation are difficult to discuss without diatoms. Many provisioning services, directly used by humans, can be obtained from diatoms. These are tangible products such as medicines and immunostimulants but direct technologies such as wastewater treatment, micro- and nanotechnologies were also developed using diatoms. Studying of the past, present, and future linked to diatoms as a tool for palaeolimnology, ecological status assessment of waters and climate modelling is essential. Finally, the impressive morphology and ornaments of diatom frustules make them one of the most spectacular microorganisms, inspiring artists or providing a number of educational opportunities. Therefore, protecting aquatic habitats they inhabit is not simply a nature conservation issue but the key for human well-being in the future.

The desiccation of the Mediterranean Basin at the end of the Miocene was a milestone in the evolution of the Mediterranean sandfly fauna. This severe environmental change should have notably influenced their paleobiogeography as well as paleoecology and might have triggered the rapid speciation of the ancestors of the extant European sandfly species. The aim of this study was to explore how the Messinian Salinity Crisis could influence the distribution and migration routes of the ancient Mediterranean sandfly species. The unknown ecological requirements of this ancient species were replaced by the distribution-limiting climatic values of three species of extant European phlebotomine sandflies which represent the three ecological types of European sandfly fauna. The former potential occurrence patterns were determined by Climate Envelope Modelling Method. As a climate model for the Messinian Period in the Mediterranean Basin, the modified mid-Pliocene warm period model was used. The thermal surplus of the desiccated seafloor was reconstructed based on the atmospheric lapse rate. It was found that the extraordinary hot climate of the Mediterranean abyssal plain did not allow the direct cross-migration of the ancient sandfly species anywhere between Europe and North Africa neither through Gibraltar nor the Strait of Sicily. While Phlebotomus neglectus and Phlebotomus papatasi could colonize the Adriatic Plain, Phlebotomus ariasi could not. The results indicate that the Messinian played an important role in the speciation rather than migration of the ancestors of present-day Mediterranean sandflies.

The presence of oral contraceptives (basically applying estrogens and/or progestogens) poses a challenge to animals living in aquatic ecosystems and reflects a rapidly growing concern worldwide. However, there is still a lack in knowledge about the behavioural effects induced by progestogens on the non-target species including molluscs. In the present study, environmental progestogen concentrations were summarised. Knowing this data, we exposed a well-established invertebrate model species, the great pond snail (Lymnaea stagnalis) to relevant equi-concentrations (1, 10, 100, and 500 ng L−1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) for 21 days. Significant alterations were observed in the embryonic development time, heart rate, feeding, and gliding activities of the embryos as well as in the feeding and locomotion activity of the adult specimens. All of the mixtures accelerated the embryonic development time and the gliding activity. Furthermore, the 10, 100, and 500 ng L−1 mixtures increased the heart rate and feeding activity of the embryos. The 10, 100, and 500 ng L−1 mixtures affected the feeding activity as well as the 1, 10, and 100 ng L−1 mixtures influenced the locomotion of the adult specimens. The differences of these adult behaviours showed a biphasic response to the progestogen exposure; however, they changed approximately in the opposite way. In case of feeding activity, this dose-response phenomenon can be identified as a hormesis response. Based on the authors’ best knowledge, this is the first study to investigate the non-reproductive effects of progestogens occurring also in the environment on molluscan species. Our findings contribute to the global understanding of the effects of human progestogens, as these potential disruptors can influence the behavioural activities of non-target aquatic species. Future research should aim to understand the potential mechanisms (e.g., receptors, signal pathways) of progestogens induced behavioural alterations.

This paper offers a brief overview of the contributions provided by widely recognised phytoplankton ecologists to honour the memory of an undisputed leader in the field of aquatic sciences: Colin S. Reynolds. Colin passed away quite unexpectedly in December 2018 causing a wave of sorrow that rapidly circulated among friends and colleagues all over the world. The 14 review papers collected in this Special Issue form a tribute to Colin’s scientific thinking, which survives the man and represents a legacy to all the scientists in the field, especially to young generations. Although authors and editors carefully selected 14 different topics, a certain degree of overlap exists among the collected contributions. This, far from being a limit, further underlines the holistic nature of Colin’s vision about phytoplankton and shows the need to develop a comprehensive cultural framework when analysing this complex ecological group of organisms.

A new marine strain of picoplanktonic algae, PMPFPPE4, was isolated from a mixed net-phytoplankton sample taken from the upper euphotic layer of the southeastern Adriatic Sea. Evaluation of the new strain included morphological investigation (by light and electron microscopy), phylogenetic analysis (utilizing plastid 16S rRNA and nuclear 18S rRNA genes), and physiological characterization (screening of pigment/lipid composition and capturing photosynthesis measurements). The new strain was proven to belong to the genusPicochlorumand the lipid composition revealed an unexpected accumulation of triacylglycerols, indicating an evolutionary adaptation for growth under unfavourable conditions. In addition, lipid remodelling in the exponential to stationary growth phase was characterized by an increased share of membrane-forming digalactosyldiacylglycerols and phosphatidylcholines. Maximum photosynthetic activity measured was at 30 degrees C, but the most rapid increase of photosynthetic activity was at lower temperatures (15-20 degrees C). Moreover, the thermotolerant strain did not exhibit photoinhibition below 40 degrees C and survived a one-month cultivation period in complete darkness. The strain's survival in low light and dark conditions suggests a potential shift from autotrophy to mixotrophy under unfavourable growth conditions. Thus, the unique physiological attributes represented by a high growth rate, thermotolerance, phototolerance and high triacylglycerol synthesis may render the strain highly attractive for biofuel production and growth in large outdoor systems.

Assigning species to functional response groups in phytoplankton ecology reduces the number of functional units, which helps understand the processes that shape diversity and functioning of planktonic assemblages. Although the concept has become widespread in recent years, numerical characterization of the groups’ positions in the niche space remained a challenging task. Using a large river phytoplankton dataset, we characterized the functional groups (FGs) of phytoplankton by their niche position and niche breadth in the niche space defined by the relevant environmental variables using the Outlying Main Index approach. The niche space has been defined primarily by trophic-related (nutrients) and river size-related variables (water residence time, discharge). Although we hypothesized that FGs with central niche position would have wide, while those with marginal niche position have narrow niche breadth, these have not been corroborated by the results. Rather, FGs occurred both with central niche position and intermediate breadth, as well as with marginal niche position and wide breadth. Niche position of several FGs was different from that suggested by their known habitat templates in lakes. Furthermore, we found no significant relationship between niche position and niche breadth, suggesting that the occurrence of FGs in rivers is simultaneously influenced by both niche characteristics.

Picocystis salinarum is a globally widespread picoplanktonic green alga of saline lakes. This tiny alga has been recorded in four continents, and in some cases, it has become the dominant phytoplankton species. We examined the ecophysiology of a Kenyan strain of P. salinarum, collected from Lake Nakuru. The photosynthetic activity of the species was measured in seventy-two combinations of light intensity and temperature. The photosynthetic activity was low along the temperature gradient with an optimum at 31.9 °C; it varied between 0.097 and 1.233 μg C μg−1 Chl a h−1. The ability of P. salinarum to utilize low light intensity (α varied between 0.0061 and 0.1 (μg C μg−1 Chl a h−1) (μmol photons m−2 s−1)−1) and its susceptibility to photoinhibition at different temperatures confirm the species’ preference for low light intensity, which is already shown by its Ik values (1.0–89.3 μmol photons m−2 s−1). The salinity tolerance of P. salinarum, more specifically the effect of changes in the concentration of chloride (NaCl) and carbonate forms (Na2CO3 and NaHCO3), was investigated in continuous cultures. The dominant ion of the medium greatly affected the growth of P. salinarum: significantly higher growth rates were recorded in carbonate form-dominated media as compared to chloride-dominated ones; the highest growth rate was observed at the highest concentration. The observed physiological properties (slow growth, low photosynthetic activity) are not typical of a dominant species; however, the high conductivity tolerance could be a key factor explaining the success of P. salinarum.

Saline lakes, among the most seriously endangered ecosystems, are threatened due to climate change and human activities. One valuable feature of these environments is that they constitute areas of high biodiversity. Ecologists are, therefore, under great pressure to improve their understanding of the effects of natural and anthropogenic disturbances on the biodiversity of saline lakes. In this study, a total of 257 samples from 32 soda pans in Central Europe between 2006 and 2015 were examined. The effects of environmental variables and of geographical and limnoecological factors on functional diversity were analyzed. Furthermore, the explanatory power of the trait‐based approach was assessed, and the applicability of the indices for biomonitoring purposes was determined. It was found that low habitat heterogeneity and harsh environments lead to the selection of a small number of suitable traits, and consequently, to a naturally low level of functional diversity. Anthropogenic activities enhance diversity at functional level due to the shift toward freshwater characteristics. On the regional scale, the effects of the region and status (natural, degraded, reconstructed) on diatom functional diversity were significant and more pronounced than that of the environmental and other limnoecological factors. The degree of variance found in functional diversity ascribed to environmental variables is five times greater in the case of the application of a trait‐based approach, than when a taxonomic one is employed in the literature. Each of the tested functional diversity indices was sensitive to the most important environmental variables. Furthermore, these were type‐specific and proved to be more complex indicators than taxonomic metrics. It is possible to suggest four functional diversity indices (FGR, FRic, FDis, and FDiv) which emphasize their independence from substrate and seasonal variations for ecological status assessment and conservation planning., In pristine soda pans, low habitat heterogeneity and harsh environment led to the selection of small number of suitable traits. Variance of the functional diversity indices explained by the environmental variables was five times higher applying trait‐based approach than taxonomic one. Functional diversity indices were type specific and more complex indicators than taxonomic metrics.

Phytoplankton, the ecological group of microalgae adapted to live in apparent suspension in water masses, is much more than an ecosystem’s engineer. In this opinion paper, we use our experience as phytoplankton ecologists to list and highlight the services provided by phytoplankton, trying to demonstrate how their activity is fundamental to regulate and sustain Life on our Planet. Although the number of services produced by phytoplankton can be considered less numerous than that produced by other photosynthetic organisms, the ubiquity of this group of organisms, and their thriving across oceanic ecosystems make it one of the biological engines moving our biosphere. Supporting services provided by phytoplankton include almost half of the global primary and oxygen production. In addition, phytoplankton greatly pushes biogeochemical cycles and nutrient (re)cycling, not only in aquatic ecosystems but also in terrestrial ones. In addition, it significantly contributes to climate regulation (regulating services), supplies food, fuels, active ingredients and drugs, and genetic resources (provisioning services), has inspired artistic and craft works, mythology, and, of course, science (cultural services), and much more. Therefore, phytoplankton should be considered in all respects a true biosphere’s engineer.

Bacteria play key roles in the function and diversity of aquatic systems, but aside from study of specific bloom systems, little is known about the diversity or biogeography of bacteria associated with harmful cyanobacterial blooms (cyanoHABs). CyanoHAB species are known to shape bacterial community composition and to rely on functions provided by the associated bacteria, leading to the hypothesized cyanoHAB interactome, a coevolved community of synergistic and interacting bacteria species, each necessary for the success of the others. Here, we surveyed the microbiome associated with Microcystis aeruginosa during blooms in 12 lakes spanning four continents as an initial test of the hypothesized Microcystis interactome. We predicted that microbiome composition and functional potential would be similar across blooms globally. Our results, as revealed by 16S rRNA sequence similarity, indicate that M. aeruginosa is cosmopolitan in lakes across a 280 degrees longitudinal and 90 degrees latitudinal gradient. The microbiome communities were represented by a wide range of operational taxonomic units and relative abundances. Highly abundant taxa were more related and shared across most sites and did not vary with geographic distance, thus, like Microcystis, revealing no evidence for dispersal limitation. High phylogenetic relatedness, both within and across lakes, indicates that microbiome bacteria with similar functional potential were associated with all blooms. While Microcystis and the microbiome bacteria shared many genes, whole-community metagenomic analysis revealed a suite of biochemical pathways that could be considered complementary. Our results demonstrate a high degree of similarity across global Microcystis blooms, thereby providing initial support for the hypothesized Microcystis interactome.

In the tropics, seasons are delimitated by the extent of rainfall resulting in seasonal differences in water parameters shaping phytoplankton community dynamics. Dry periods can intensify eutrophication and often result in seasonal or even perennial cyanobacterial dominance. This study was developed to evaluate phytoplankton response to trophic state and seasonal differences of environmental filters (dry and rainy periods) using the morphology-based functional groups (MBFG) approach. We also aimed at identifying environmental thresholds of each MBFG dominance in six man-made lakes located in the tropical semiarid region of Brazil. Our results showed clear MBFG association with lakes’ trophic states. The dominant groups in mesotrophic conditions were members of MBFGs V (unicellular flagellates) and VI (non-flagellated with a siliceous exoskeleton), and in meso-eutrophic MBFG IV (medium size without specialized traits) dominated. Conversely, MBFG VII (with mucilage and aerotopes) and VIII (nitrogen-fixing cyanobacteria) dominated mostly under eutrophic conditions, though linked to shallower euphotic zones. Light and phosphorous were the most important environmental thresholds associated with MBFG’s dominance. Overall, most of the lakes displayed seasonal differences in environmental filters. In contrast to what was expected, the rainy season was associated with higher nutrients, suspended solids, and reduced euphotic depth compared to the dry season. Our results, overall, show that the effects of seasonality varied across lakes and highlight eutrophication as the main environmental factor for MBFG selection suggesting reduced seasonality effects during dry years in the tropics.

In order to examine temporal patterns and the hydrological cycle of shallow soda pans, six pans in Hungarian Great Plain were sampled at monthly intervals over a period of 2.5 years. Water chemistry and physical parameters (temperature, pH, dissolved oxygen, conductivity, light, water color - Pt color -, turbidity, phosphorous and nitrogen forms, silica, alkalinity, chloride, sulfate content, chemical oxygen demand) were measured both in the field and laboratory and analyzed using multivariate statistical methods. It was possible to distinguish the pans on the basis of water color, separating them into two groups: G1, consisting of colored pans characterized by low turbidity and high Pt color, and G2, consisting of turbid pans characterized by high turbidity and low Pt color. Both groups displayed temporal (seasonal, as well as annual) trends, and their hydrological cycles followed regular cyclical patterns. Three hydrological phases (filling, drying, and desiccated) were described in the case of the colored pans, and five for the turbid (filling, diluted, drying, concentrated, desiccated). Regarding the recommendation that there be a reduced time interval in the sampling to determine the typical chemical characterization of the pans.

Shallow, saline inland lakes occur over large areas in Central-Europe and they bear exceptionally high biological conservation values. Climate change and anthropogenic activities threaten their natural conditions, or even their existence. These aquatic ecosystems are exposed to multiple stress like naturally high conductivity, pH and nutrient load with very low transparency for light. As they are subjects of criteria set by the EC Water Framework Directive and biological conservation managment, there is an urgent need for developing a suitable quality index for their ecological status assessment. As one major Biological Quality Element, benthic diatoms may provide a reliable basis for their ecological status indication. Here, in a large data set covering the soda lakes of the Carpathian basin, we developed a species- and a trait-based diatom ecological status index. First, based on the weighted average method, we developed a type specific, species-based diatom index (DISP = Diatom Index for Soda Pans) using conductivity as master variable of environmental constrains; and therefore the ecological status in soda lakes. Furthermore, by adapting and improving further the widely-used diatom ecological guild concept, we also developed an alternative trait-based index, which helps avoiding some limitations arising from the obvious complexity of the taxonomy-based approach. Our DISP index covered a significantly larger species pool for index calculation, and responded to conductivity in a more reliable way compared to other available indices. In the trait-based index (TBI) motility, small cell size, and less roundish, more elongated shape as functional and morphological traits indicated pristine ecological conditions (i.e high conductivity) of the soda pans. Planktic life form, high and low ecological guild profiles, as well as the large cell size indicated worse ecological conditions (e.g. lower conductivity). Our study highlights that benthic diatoms provide a reliable basis for ecological status assessment in soda lakes. While both the taxonomic and the functional trait approaches performed well in our analysis, the success of the trait-based approach may enable the use of our TBI index in biomonitoring and conservation management of soda lakes outside of the Carpathian basin, independently of the geographic location.

As prokaryotes, cyanobacteria lack a cell nucleus and other cell organelles, allowing their microscopic distinction from most other microalgae. The morphology of cyanobacterial cells shows a number of characteristics that can be used for microscopic examination and identification: primarily, the shape and size of cells, subcellular structures and specialised cells. Most cyanobacterial taxa form multicellular aggregates, and the size and shape of which can be used for the identification of cyanobacteria in freshly collected field samples. Cyanobacteria can produce a large diversity of secondary metabolites. For cyanobacteria, taxonomy is further complicated by the fact that two basically different systems of nomenclature have become established, the International Code of Nomenclature for algae, fungi, and plants and the International Code of Nomenclature of Bacteria. Cyanobacteria occur as unicellular, colonial or multicellular filamentous forms. The position, number and distribution of the heterocytes and akinetes are important morphological characteristics of species and genera.

The aim of this pilot study was to investigate the potential of eDNA techniques to detect the presence of the two dragonfly species Cordulegaster heros and Cordulegaster bidentata. Both species are classified as “near threatened” according to the IUCN Red List and are strictly protected in several countries. Monitoring these species with traditional sampling methods is often difficult, time-consuming and invasive. In this pilot study, we first collected tissue samples from C. heros and C. bidentata to sequence the traditional DNA-barcode gene fragment COI. We then collected further dragonfly COI sequences from BOLD to design species-specific primers. This, however, was impossible given the enormous variability of COI. Therefore, we refrained from species-specific eDNA assays and followed eDNA metabarcoding protocol using universal (BF2/BF2) and a newly designed dragonfly specific primer. For the evaluation of the method, we took water samples from places where Cordulegaster specimens are known to occur. After the extraction, we used two sequential PCR steps for obtaining the desired amplicon (two-step PCR) using universal primers in the first step, and group (dragonfly) specific primers or universal primers. Amplicons were sequenced on an Illumina MiSeq platform and then analysed the data with the JAMP pipeline. With the newly designed primers and we could effectively detect the targeted dragonfly species from tissue samples, and also from filtered environmental samples. The detection of the species with the traditional method is time consuming and involves the destruction of the specimens. In comparison, with the eDNA method we could easily detect these near threatherned odonates and other dragonfly species in a non-invasive way.

The presence of sex steroid hormones in aquatic ecosystems is of rapidly growing concern worldwide since they can affect the different non-target species including cladocerans. Although data are available on the effects of estrogens on the well-established ecotoxicological model organism Daphnia magna, the molecular or behavioural alterations induced by environmentally relevant concentrations (from a few ng L-1 to a few hundred ng L-1 in average) of progestogens have not been investigated on this species. In the present study, we exposed neonates of D. magna to relevant equi-concentrations (1, 10, 100, 500 ng L-1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) in short-term (6 days) and long-term (21 days) experiments. Significant alterations were observed at the molecular, cellular, and individual levels. During the short-term exposure, all of the mixtures increased the gene expression of glutathione S-transferase (GST) detoxification enzyme, moreover, the activity of GST was also significantly increased at the concentrations of 10, 100, and 500 ng L-1. In long-term exposure, the number of days until production of the first eggs was reduced at the 10 ng L-1 concentration compared to control, furthermore, the maximum egg number per individual increased at the concentrations of 1 and 10 ng L-1. Based on the authors' best knowledge, this is the first study to investigate the effects of progestogens in mixtures and at environmentally relevant concentrations on D. magna. Our findings contribute to the understanding of the possible physiological effects of human progestogens. Future research should be aimed at understanding the potential mechanisms (e.g., perception) underlying the changes induced by progestogens.

Global warming and eutrophication contribute to the worldwide increase in cyanobacterial blooms, and the level of cyanobacterial biomass is strongly associated with rises in methane emissions from surface lake waters. Hence, methane-metabolizing microorganisms may be important for modulating carbon flow in cyanobacterial blooms. Here, we surveyed methanogenic and methanotrophic communities associated with floating Microcystis aggregates in 10 lakes spanning four continents, through sequencing of 16S rRNA and functional marker genes. Methanogenic archaea (mainly Methanoregula and Methanosaeta) were detectable in 5 of the 10 lakes and constituted the majority (~50%-90%) of the archaeal community in these lakes. Three of the 10 lakes contained relatively more abundant methanotrophs than the other seven lakes, with the methanotrophic genera Methyloparacoccus, Crenothrix, and an uncultured species related to Methylobacter dominating and nearly exclusively found in each of those three lakes. These three are among the five lakes in which methanogens were observed. Operational taxonomic unit (OTU) richness and abundance of methanotrophs were strongly positively correlated with those of methanogens, suggesting that their activities may be coupled. These Microcystis-aggregate-associated methanotrophs may be responsible for a hitherto overlooked sink for methane in surface freshwaters, and their co-occurrence with methanogens sheds light on the methane cycle in cyanobacterial aggregates.

There is hardly any sunshine exposed surface on this Earth, be it water or terrain, which would not support some biota. Still, many habitats offer harsh conditions requiring specialized physiological adaptations to survive. These environments are referred to as extremes; often inhabited by extremophilic organisms. In this review, characteristic species and assemblage properties of phytoplankton inhabiting extreme environments (especially lakes and pools where planktic life is potentially possible and independently of their origin) in terms of alkalinity, acidity, DOC, salinity, temperature, light and mixing regime will be outlined. Lakes characterized by more than a single extreme are common (e.g. saline + alkaline; acidic + high DOC + high metal content + low light). At the edge of extremes (e.g. pH of 1; salinity over ~ 100–150 g l−1) single species with appropriate physiological adaptation are selected and the phytoplankton is often dominated by a single species (monodominant) setting compositional diversity to zero. Under less extreme conditions permanent equilibria may persist; in many cases over several years in contrast to „average” lakes where equilibria are rare and ephemeral. Food webs depending on „extreme phytoplankton” are often atypical for example because the microbial loop is of prior importance or because birds are top predators.

In this study, driving forces and diversity patterns of a benthic diatom metacommunity across small freshwater lakes exhibiting environmental heterogeneity were investigated. Furthermore, local (LCBD) and species (SCBD) contributions to β-diversity and their driving parameters were assessed with abundance- and incidence-based analyses. Our results revealed that both spatial distance and environmental heterogeneity affected the community assembly, which corresponds most to the mass-effect (ME) concept. This theory was confirmed by high α-diversity of sampling sites; however, high overall β-diversity enhanced mainly by turnover contradicted the ME paradigm. LCBD indices were affected by environmental variables; furthermore, LCBD and LCBD in terms of species replacement showed a strong positive correlation. The ecologically most unique sites hosted relatively low species richness, and common species with intermediate-sized or broad niches contributed mostly to the regional β-diversity. However, abundance- and incidence-based calculations revealed different relationships of SCBD with the species’ total abundance and the number of occupied sites. Consequently, we favor the previous suggestions that comprehensive research focusing on conservation should incorporate the investigation of LCBD, SCBD, species-rich sites and also ecologically restricted species. Moreover, in assessing ecological uniqueness, both abundance and binary data sets should be considered since they might shed light on distinct patterns.

Analysis of a long-term (1994–2014) data set of phytoplankton and zooplankton in the deep, dimictic, oligo-mesotrophic Lake Stechlin (Germany) revealed trend-like changes: phytoplankton biomass and resource use efficiency increased with proliferation of heterocytic cyanobacteria (Dolichospermum spp. and Aphanizomenon flos-aquae), and those of especially large-sized zooplankton (Eudiaptomus, Eurytemora) decreased. These reverse trends are clear eutrophication symptoms and suggest a long-term trophic decoupling with potential decrease in energy transport towards higher tropic levels. Total phosphorus increased significantly over time; however, there is no known external P load for Lake Stechlin. Causality analysis enabled us to identify the primary reason of the observed changes. According to the results, stronger and longer-lasting stratification (measured as relative water column stability) drove the observed changes and the gradual regime shift was initiated by an extreme weather event—both indicating that climate change has been the crucial driver of the planktic community in this lake. Our study also documents that there might be decadal delays between cause and consequences in aquatic food webs, supporting the essential importance of long-term monitoring efforts.

Photosynthetic performances of two freshwater red algal populations from freshwaters of the Carpathian basin were measured in this study. Populations were collected from different habitats: Bangia atropurpurea from Lake Balaton and Batrachospermum gelatinosum from the Tapolca stream. Their photosynthesis was studied in a wide range of temperature (5–35 °C) and light intensity (0–1150 μmol m−2 s−1) in a photosynthetron. We found both species’ photosynthesis maxima at 25 °C but B. atropurpurea had significantly higher photosynthetic production. Low and medium values were calculated for the species’ photoadaptation parameters. Compensation light intensities determined in this study were similar to those obtained in previous studies. Both species utilized light efficiently; photoinhibition was detected only at two measuring temperatures for Bangia and at four measuring temperatures for Batrachospermum. P-T characteristics of the species revealed that both have temperature optima at 25 °C under high and medium light intensities but there are no such remarkable optima at low irradiance. The biomass specific respiration of both species increased with increasing temperature. We confirmed the good light utilization of these red algal species but found temperature optima higher than reported previously.

The diversification of Mediterranean Phlebotomus species occurred during the Neogene and Quaternary periods. The climatic and geographical history of the Mediterranean area plausibly influenced the climatic requirements of recent sand fly species. Our aim was to investigate the European zoogeography and the climate-based ecological groups of eight Phlebotomus species considering the phylogeography of the studied taxa. Jaccard index calculation, hierarchical cluster and principal component analyses were performed. The results of Jaccard-coefficient calculations may indirectly refer to the former existence of three possible glacial refuges of sand fly populations in Europe: an Iberian, an Apennine and a Balkan Peninsula–Asia Minor refuge. Three main climatic groups of the studied sand fly species were distinguished, namely the so-called ‘Trans-Mediterranean’, ‘East Mediterranean’ and ‘West Mediterranean’ groups. Our results suggest that the ancestor of Phlebotomus similis and Phlebotomus sergenti wa...

Small soda lakes represent one of the most vulnerable ecosystem types due to their high hydrological sensitivity to climate change and anthropogenic interventions. Since diatoms are excellent bioin...

Phytoplankton communities respond rapidly to environmental selection at a given locality, and they are also shaped by spatial processes at certain scales. The extracted effect of environmental selection and spatial processes may vary if different classification approaches are applied to phytoplankton and the spatial scales. In this study, summer phytoplankton of 43 lakes from three major lake regions in China were investigated and phytoplankton were classified with three approaches: taxonomy of species, habitat template-based functional groups, and morphology-based functional groups. Within a single lake region, the pattern of phytoplankton meta-community was significantly explained by environmental but not by spatial variables. In a larger scale covering all the three lake regions, both environmental and spatial variables explained the variance of the phytoplankton community, but the spatial variables were detected only by classification with species, and only the environmental variables were detected with phytoplankton functional groups. This study revealed that although vegetative populations of different species sorted into the same functional group have common response to environmental changes, their dispersal abilities, mechanisms, and strategies might differ markedly and therefore the species-specific approach cannot be disregarded when studying phytoplankton patterns at spatial scales.

Although species–area relationship (SAR) is among the most extensively studied patterns in ecology, studies on aquatic and/or microbial systems are seriously underrepresented in the literature. We tested the algal SAR in lakes, pools and ponds of various sizes (10−2–108 m2) and similar hydromorphological and trophic characteristics using species‐specific data and functional groups. Besides the expectation that species richness increases monotonously with area, we found a right‐skewed hump‐shaped relationship between the area and phytoplankton species richness. Functional richness however did not show such distortion. Differences between the area dependence of species and functional richness indicate that functional redundancy is responsible for the unusual hump‐backed SAR. We demonstrated that the Small Island Effect, which is a characteristic for macroscopic SARs can also be observed for the phytoplankton. Our results imply a so‐called large lake effect, which means that in case of large lakes, wind‐induced mixing acts strongly against the habitat diversity and development of phytoplankton patchiness and finally results in lower phytoplankton species richness in the pelagial. High functional redundancy of the groups that prefer small‐scale heterogeneity of the habitats is responsible for the unusual humpback relationship. The results lead us to conclude that although the mechanisms that regulate the richness of both microbial communities and communities of macroscopic organisms are similar, their importance can be different in micro‐ and macroscales.

Global warming affects the thermal stratification of freshwater lakes, and thus can lead to thermocline deepening. To follow the direct and indirect effects of thermocline shifts on processes at the sediment–water interface, the thermoclines in six of twelve lake enclosures were deepened by pumping warm surface water below the thermocline. Hypolimnetic temperatures increased and oxygen concentrations decreased due to the treatment. Path modeling suggests a correlation of the treatment to epilimnetic chlorophytes and hypolimnetic diatoms, while the dominant cryptophytes and cyanobacteria remained unaffected by the treatment. Sedimentation rates, ranging between 0.1 and 1.9 g m−2 day−1 per enclosure, correlated strongly with the selected phytoplankton groups, but were not affected by the treatment. Concentrations of elements (Ba, Mn, S, Sr), nutrients (NH4 +, PO4 3−, Si), and greenhouse gases (CO2, CH4, N2O) in the upper centimeter of the sediment were not affected by the hypolimnetic changes. Methane and carbon dioxide emission from the enclosures to the atmosphere were negligible. Bacterial and viral abundance in sediments were not affected by the treatment. Results suggest that the benthic ecosystem remains unaffected by slight changes in the pelagial. Further, we conclude that short-term warming does not increase greenhouse gas emissions from temperate, deep, oligo-mesotrophic lakes.

Climate forecasts project a global increase in extreme weather events, but information on the consequences for ecosystems is scarce. Of particular significance for lakes are severe storms that can influence biogeochemical processes and biological communities by disrupting the vertical thermal structure during periods of stratification. An exceptional storm passing over northern Germany in July 2011 provided an opportunity to assess the consequences and underlying mechanisms of such extreme events on the interplay between the physics and ecological characteristics of a deep, nutrient-poor lake. Wind speeds were among the most extreme on record. A suite of variables measured throughout the event consistently indicates that a cascade of processes pushed the clear-water lake into an exceptionally turbid state. Specifically, thermocline deepening by the storm-entrained cyanobacteria of a deep chlorophyll maximum located at about 8 m depth into the surface mixed layer. Released from light limitation, intense photosynthesis of the cyanobacteria boosted primary production, increased algal biomass, raised the pH and thus induced massive calcite precipitation to a level never observed within three decades of lake monitoring. As a consequence, water transparency dropped from 6.5 to 2.1 m, the minimum on record for 40 years, and the euphotic zone shrank by about 8 m for several weeks. These results show that cyanobacterial blooms not only are promoted by climate warming, but can also be triggered by extreme storms. Clear-water lakes developing a deep chlorophyll maximum appear to be particularly at risk in the future, if such events become more intense or frequent.

International audience; Extensive studies on the taxonomic resolution required for bioassessment purposes have determined that resolution above species level (genus, family) is sufficient for their use as indicators of relevant environmental pressures. The high‐throughput se - quencing (HTS) and meta‐barcoding methods now used for bioassessment tradition - ally employ an arbitrary sequence similarity threshold (SST) around 95% or 97% to cluster sequences into operational taxonomic units, which is considered descriptive of species‐level resolution. In this study, we analyzed the effect of the SST on the resulting diatom‐based ecological quality index, which is based on OTU abundance distribution along a defined environmental gradient, ideally avoiding taxonomic as - signments that could result in high rates of unclassified OTUs and biased final values. A total of 90 biofilm samples were collected in 2014 and 2015 from 51 stream sites on Mayotte Island in parallel with measures of relevant physical and chemical param - eters. HTS sequencing was performed on the biofilms using the rbcL region as the genetic marker and diatom‐specific primers. Hierarchical clustering was used to group sequences into OTUs using 20 experimental SST levels (80%–99%). An OTU‐ based quality index (Idx OTU ) was developed based on a weighted average equation using the abundance profiles of the OTUs. The developed Idx OTU revealed significant correlations between the Idx OTU values and the reference pressure gradient, which reached maximal performance using an SST of 90% (well above species level delimi - tation). We observed an interesting and important trade‐off with the power to dis - criminate between sampling sites and index stability that will greatly inform future applications of the index. Taken together, the results from this study detail a thor - oughly optimized and validated approach to generating robust, reproducible, and complete indexes that will greatly facilitate effective and efficient environmental monitoring

International audience; Land-use imposes an important potential threat on the aquatic ecosystems of riverine habitats. In this study, DNA metabarcoding was used to assess the effect of land-use on diatom assemblages, with a special focus on cropland area as an integrative proxy for several direct-acting pressures. The so-called taxonomy-free approach was tested using exact sequence variants (ESVs) without pre-clustering and without assigning them to traditional taxonomy. Our hypothesis is that the taxonomy-free approach gives better interpretation of the effect of agricultural land use and it provides a more efficient index to indicate agricultural stress than the classical method with taxonomical clustering. Classical ordination techniques (PCA, NMDS) were performed to study the effects of cropland area proportion on diatom assemblages and a modified version of the Zelinka-Marvan equation for the index development. Results showed that (i) although ESVs provided better results when studying land-use effects on diatoms, taxonomic assignment after analysis was necessary to give ecological interpretations and that (ii) a better performing index could be developed by using the taxonomy-free approach. By using ESVs without taxonomic assignment, information on the ecology of sequences belonging to the same species and of unassigned sequences could be kept. New types of clustering methods are welcome in the future of biomonitoring where the delimitation of taxonomic units should be refined based on a higher emphasis on their ecology rather than on morphological or genetical criteria.

Leaf litter represents a significant energy source for headwater ecosystems. Its breakdown includes dissolution, microbial activity, fragmentation by shredders, and physical abrasion. As a consequence of red sludge spill that took place in October 2010 in Hungary, the fauna of Torna-stream was killed, offering a “natural laboratory” to measure mass loss without shredder activity. Decomposition of nine leaf litter types was investigated with litter-bag method in 2011 (no macroinvertebrates; post-disaster experiment, POST), 2012 (after macroinvertebrate recolonization, at two sites: POSTRE: impacted site and POSTREF: reference site) in the Torna-stream. In the POST it was possible to measure leaf mass loss without shredder activity and to separate the leaf decomposition rates for each contributor of decomposition with a newly developed model. The model simulates the mass loss through three processes: physical abrasion and drifting, leaching and microbial mineralization, and macroinvertebrate consumption. In 2011, physical abrasion, microbial decomposition, and leaching accounted for 10–50% of initial mass loss, while in the POSTRE and in POSTREF for only 5–47%. The rate of litter decomposition driven by shredders in POST was between 5 and 44%, and in the POSTRE and POSTREF it accounted for 24–90%. The most apparent result of the experiments described in this paper is that the presence or absence of macroinvertebrates determines the decay characteristics and underlines the key role of macroinvertebrates in leaf litter decomposition.

In this paper the concept of resilience is discussed on the base of 13 case studies from the German branch of the International Long-Term Ecological Research Program. In the introduction the resilience approach is presented as one possibility to describe ecosystem dynamics. The relations with the concepts of adaptability and ecological integrity are discussed and the research questions are formulated. The focal research objectives are related to the conditions of resilient behaviour of ecosystems, the role of spatio-temporal scales, the differences between short- or long-term dynamics, the basic methodological requirements to exactly define resilience, the role of the reference state and indicators and the suitability of resilience as a management concept. The main part of the paper consists of 13 small case study descriptions, which demonstrate phase transitions and resilient dynamics of several terrestrial and aquatic ecosystems at different time scales. In the discussion, some problems arising from the interpretation of the time series are highlighted and discussed. The topics of discussion are the conceptual challenges of the resilience approach, methodological problems, the role of indicator selection, the complex interactions between different disturbances, the significance of time scales and a comparison of the case studies. The article ends with a conclusion which focuses on the demand to link resilience with adaptability, in order to support the long-term dynamics of ecosystem development. published

Saline lakes are threatened all over the world and their conservation has been a key issue. Various diversity indices are available for ecological status assessments, however, with poorly explored relevance and applicability in saline, alkaline pans. Therefore, traditional diversity measures (species richness and Shannon diversity) and taxonomic distinctness indices (Average [AvTD] and Variance of Taxonomic Distinctness [VarTD]) were tested in more than 100 sampling sites of 39 soda pans in Central-Europe to find sufficient indicators of the ecological condition and simultaneously to facilitate their preservation according to the modern conservation practices. Results of the analyses showed that healthy soda pan ecosystems with high level of natural stress and reduced habitat heterogeneity are characterized by low diversity diatom assemblages. In soda pans where the stress can be extremely high from natural reasons, oligopoly of closely related species can develop: the average taxonomic distinctness appeared between genus and family level. The non-DNA-sequence based phylogenetic diversity measures (AvTD and VarTD), were generally sensitive to the trophic state of the lakes, in contrast to traditional diversity metrics, which were unequivocally indicative for the special physical and chemical parameters (e.g. conductivity, pH) of the soda pans. In some cases, when the response of the diversity measures for a given environmental variable (pH, temperature) overlapped, the AvTD was found to be a more precise indicator of the environmental changes (pH) than traditional ones. The decreasing tendency of the AvTD along the intensified natural impact may be explained by the long available time for the species to adapt to these special environments.

Growth patterns of different plant species are primarily determined by edaphic factors, climate conditions and their species-specific adaptation properties. Changing sub-regional aridity trends due to the projected climate change like soil erosion and the invasion of alien plant species threaten the ligneous vegetation of karst areas. We aimed to study and model the potential effect of aridity on the growth rate of young individuals of the native Fraxinus ornus and its two important two competitors, the exotic Pinus nigra and the aggressive invader Ailanthus altissima in a karstic forest-steppe of the Veszprem plateau, Hungary on different soil depths. Mean soil depth and the Thornthwaite agrometeorological index were used as covariates. Climate data were gained from the E-OBS gridded dataset for the period of 1950 to 2013 and from the MPI Echam5 climate model for the period of 2081 to 2100. We found significant correlation between the soil depth values and the measured heights and the average of monthly Thornthwaite agrometeorological indices. In conclusion, aridity and soil-depth have significant, but different effect on the growth patterns of the studied species. While the annual growth season of Pinus nigra and Fraxinus ornus are determined by the aridity of the months of January to May, and from February to June, respectively, the growth of Ailanthus altissima is mainly determined by the period of March to August. The climate prediction-based growth model predicts the decline of the growth patterns of each species for the 2081-2100 period in Hungary due to climate change.