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Growing evidence suggests that global climate change promotes the dominance of mixotrophic algae especially in oligotrophic aquatic ecosystems. While theory predicts that mixotrophy increases trophic transfer efficiency in aquatic food webs, deleterious effects of some mixotrophs on consumers have also been reported. Here, using a widespread mixotrophic algal genus Dinobryon, we aimed to quantify how colonial taxa contribute to secondary production in lakes. We, therefore, studied the dietary effects of Dinobryon divergens on Cladocera (Daphnia longispina) and Copepoda (Eudiaptomus gracilis), representing two main taxonomic and functional groups of zooplankton. In feeding experiments, we showed that Dinobryon was largely grazing resistant and even inhibited the uptake of the high-quality reference food in Daphnia. Eudiaptomus could to some extent compensate with selective feeding, but a negative long-term food quality effect was also evident. Besides, Eudiaptomus was more sensitive to the pure diet of Dinobryon than Daphnia. Low lipid content and high C:P elemental ratio further supported the low nutritional value of the mixotroph. In a stable isotope approach analysing a natural plankton community, we found further evidence that carbon of Dinobryon was not conveyed efficiently to zooplankton. Our results show that the increasing dominance of colonial mixotrophs can result in reduced dietary energy transfer to consumers at higher trophic levels. In a wider perspective, global climate change favours the dominance of some detrimental mixotrophic algae which may constrain pelagic trophic transfer efficiency in oligotrophic systems, similarly to cyanobacteria in eutrophic lakes.

Free-living (FLC) and particle-associated (PAC) bacterial communities contribute differentially to the cycling of matter in the environment. In this work we have for the first time studied the taxonomic composition and diversity of FLC and PAC in the oligotrophic freshwater Lake Baikal during the under-ice plankton peak. The communities on the bottom ice surface and in the water column under the ice were studied. Analysis by light microscopy showed that the bottom surface of the ice was dominated by green algae Chlorella spp. A complex of microalgae developed in the water column: green algae Monoraphidium griffithii, Monoraphidium contortum, Chlorella spp., chrysophyte Dinobryon cylindricum, haptophyte Chrysochromulina parva, and diatom Synedra acus. Algal abundance on the ice sub-surface was several orders of magnitude higher than that in the water column. According to pyrosequencing data of the bacterial 16S rRNA V3-V4 region, diversity of FLC (as measured by Shannon, Simpson, Chao1 and ACE indices) was higher than that of PAC. Proteobacteria (Burkholderiaceae) dominated the FLC associated with ice; FLC of the water column under ice were dominated by Actinobacteria (Sporichthyaceae and Ilumatobacteraceae) and Verrucomicrobia (Methylacidiphilaceae). PAC associated with ice were dominated by Bacteroidetes (Flavobacteriaceae), while water column-associated PAC were dominated by Verrucomicrobia (FukuN18_freshwater_group, Methylacidiphilaceae) and cyanobacteria (Cyanobiaceae). The difference between free-living and particle-associated, as well as between water column and ice sub-surface bacterial communities, were explored on operational taxonomic unit (OTU) and phylotype levels.

To assess the current state of phytoplankton in the littoral area of Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the 44 littoral and 3 pelagic stations covering all three basins of the lake. The study examined chemical parameters of water (NH4+, NO2−, NO3−, PO4−3, Si, COD), species composition, abundance, and biomass of phytoplankton in Lake Baikal during late spring 2017. Sharp spatial heterogeneity was observed in the distribution of phytoplankton biomass along the western (399 ± 72 mg/m3) and eastern (1319 ± 220 mg/m3) shores of the lake. The phytoplankton were diverse, with 79 species; dominant algae were different from site to site and from south to north throughout the lake. In Southern and Central Baikal, we recorded an intense bloom of the diatom Synedra acus subsp. radians (28–1400 cells/mL), similar to that observed for the past 10 years, while the chrysophyte Dinobryon cylindricum dominated in Northern Baikal. The diatoms Aulacoseira baicalensis, A. islandica, and Stephanodiscus meyeri that were dominant in the 1960s–1990s were not numerous in 2017 (0.5–10 cells/mL). This change in dominant species indicates structural changes in the phytoplankton of Lake Baikal, which have led to the disappearance of the main distinctive feature of the Baikalian phytoplankton – the alternation of extremely high (with the algal biomass over 1000 mg/m3) and extremely low (less than 100 mg/m3) productivity years. The ecological equilibrium appears to have shifted towards a new steady state.

Recent studies have revealed how the freshwater biota of Lake Baikal responds to climate change and anthropogenic impacts. We studied phyto- and zooplankton, as well as phyto- and zoobenthos, in the open coastal waters of the southern basin of the lake and of Listvennichny Bay. A total of 180 aquatic organism taxa were recorded. The response of the Baikal ecosystem to climate change can be traced by changes in the species composition of planktonic communities of the lake’s open coasts in summer. The key species were thermophilic the Anabaena lemmermannii P. Richt. (Fij = +0.7) blue-green algae, the Asplanchna priodonta Gosse (Fij = +0.6) rotifers in 2016, the Rhodomonas pusilla (Bachm.) Javorn. (Fij = +0.5) cold-loving algae, and the Cyclops kolensis Lilljeborg (Fij = +0.9) copepods in the past century. The proportion of Chlorophyta decreased from 63% to 17%, the Cyanophyta increased from 3% to 11% in the total biomass of phytoplankton, and the proportion of Cladocera and Rotifera increased to 26% and 11% in the biomass of zooplankton, respectively. Human activity makes an additional contribution to the eutrophication of coastal waters. The Dinobryon species, the cosmopolitan A. formosa and F. radians, dominated phytoplankton, and filamentous algae, Spirogyra, dominated at the bottom in the area with anthropogenic impact. The trophic level was higher than at the unaffected background site: the saprobity index varied from 1.45 to 2.17, the ratio of eutrophic species to oligotrophic species ranged from 1:2 to 3:1, and the ratio of mesosaprobiont biomass to endemics biomass ranged from 2:1 to 7:1. Currently, the boundaries of eutrophication zones of shallow waters in Lake Baikal are expanding, and its coastal zone has acquired features typical of freshwater bodies of the eutrophic type.

The diet of a symbiont, Brandtia parasitica parasitica (Dybowsky 1874), of Baikal sponges collected during an ecological crisis in the littoral zone of Lake Baikal is analyzed. In June 2015, the main components of the diet of the amphipod that lived on diseased sponges were fine detritus, sedimented chrysophycean algae of the genus Dinobryon, and planktonic diatoms of the genus Synedra. These algae dominate in phytoplankton in the southern part of Baikal during the study period. Abundant blue-green algae were present on the surface of diseased sponges, but B. p. parasitica did not feed on these algae. As toxins secreted by blue-green algae are known to render a negative effect on hydrobionts, mass overgrowth of sponges with blue-green algae should reduce the population of the symbiotic amphipod.

The chrysophyte genus Dinobryon Ehrenberg consists of 44 taxa, which occur in freshwaters, rarely marine waters, mostly in temperate regions of the world. The taxa of Dinobryon produce characteristic solitary or dendroid colonies and resting stages called stomatocysts. Only 20 Dinobryon taxa have information on produced stomatocysts and only four stomatocysts are reliably linked with vegetative stages using modern identification standards employing scanning electron microscopy (SEM) analyses. In this study, an encysted material of Dinobryon pediforme (Lemmermann) Steinecke was collected in two lakes in contrasting regions of Poland. Light microscopy (LM) and scanning electron microscopy (SEM) analyses revealed that Dinobryon pediforme produces stomatocyst #61, Piątek J. that is described here as new morphotype following the International Statospore Working Group (ISWG) guidelines. This raises to five the number of reliable links between vegetative stages of Dinobryon species and corresponding stomatocysts. Phenotypic similarities between Dinobryon species and their stomatocysts, analysed for five reliably established links, showed no relationships in size and shape between loricas and stomatocysts belonging to the same species. The morphological characters of loricas and stomatocysts mapped onto the phylogenetic tree of the five Dinobryon species revealed only little congruence between their morphology and phylogenetic relationships.

Seasonal variations in species composition and growth dynamics of phytoplankton in Uzuncayir Dam Lake (Tunceli, Turkey) were studied in relation to ecological factors by collecting horizontal water and phytoplankton samples for over a year. A total of 46 phytoplankton taxa were recorded, where Bacillariophyta was the most abundant in species number representing 24 taxa. Diatoms were the most conspicuous phytoplankton in terms of abundance as well as occurrence frequency. Charophyta, Chlorophyta, Cyanobacteria, Ochrophyta, Miozoa, and Euglenozoa were the least abundant. However, some Diatoms (Gyrosigma attenuatum, Hippodonta hungarica, Meridion circulare, Nitzschia clausii, Nitzschia frustulum, Pantocsekiella ocellata, Rhoicosphenia abbreviata), Charophytes (Cosmarium granatum, Mougeotiopsis calospora), Cyanobacteria (Leiblenia epiphytica, Planktothrix agardhii); Dinoflagellates (Ceratium hirundinella, Parvodinium africanum, Parvodinium inconspicuum, Peridinium cinctum), and Ochrophyta (Dinobryon pediforme) were also noticeable, with their occurrence in all seasons. Canonical correspondence analysis (CCA) and principal component analysis (PCA) were employed to analyze the relationship between occurrence and abundance of phytoplankton species as well as the ecological factors. The results showed that pH and the concentrations of NH4, NO3, and PO4 influenced seasonal occurrence and abundance of phytoplankton species in the lake. Uzuncayir Dam Lake may be classified as an oligotrophic lake with the mean value of nitrate 2.62 mg L-1 and phosphate 0.23 mg L-1 as supported by the occurrence of various phytoplankton groups. Findings related to pollution indices yielded that Uzuncayir Dam Lake is on the edge of the moderate state of organic pollution.

The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m(-2) · s(-1) , with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m(-2) · s(-1) ). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m(-2) · s(-1) ), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%-30% of the carbon budget could be attributed to bacterivory at low temperatures. Grazing experiments in nutrient-modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.

Harriman and Bear Mountain State Parks, New York, contain a rich and previously under-documented algal flora. We report 382 algal taxa (excluding diatoms), including 294 taxa not previously reported from the parks. Our inventory suggests that the algal flora has changed significantly since it was last studied in 1918 with a general increase in the number of desmid taxa (Zygnematophyceae) and changes in the species composition of other green algae. We hypothesize that these changes are primarily due to normal succession in constructed lakes. Some of the species encountered are infrequently reported from North America. Consequently Harriman and Bear Mountain State Parks represents an important locality for their study. Factors possibly contributing to the apparent rarity of species are discussed. A new species of Dinobryon (Chrysophyceae: Dinobryaceae) is described: Dinobryon sertularioides. Two new taxonomic combinations are also made: Stauridium tetras var. tetraodon (Chlorophyceae: Hydrodictyaceae) and Cosmarium verrucosum var. alatum (Zygnematophyceae: Desmidiaceae).

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m-2 · s-1 and at 4-5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C-15°C range at light levels ≤50 μmol photon · m-2 · s-1 . At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m-2 · s-1 and 200 μmol photon · m-2 · s-1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m-2 · s-1 ) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.

Polar marine ecosystems are characterized by low water temperatures, sea ice cover, and extreme annual variation in solar irradiance and primary productivity. A review of the available information from the Arctic suggests that mixotrophy (i.e. the combination of photosynthetic and phagotrophic modes of nutrition in one cell) is wide spread among plankton. In the central Arctic Ocean (AO) in summer, mixotrophic flagellates such as Micromonas and Dinobryon can account for most of bacterivory. Planktonic ciliates with acquired phototrophy form the bulk of microzooplankton biomass in both the ultra-oligotrophic deep basins of AO and its productive shelf seas. With the exception of the diatom bloom in the marginal ice zone, mixotrophic ciliates often dominate total chlorophyll in the mixed layer in summer taking advantage of the 24-h insolation. Their relatively high growth rates at low temperatures indicate that they are important component of primary and secondary production. The key Arctic copepod species preferentially feed on chloroplast-bearing ciliates, which form an important link in the planktonic food web. The limited year round data indicate that are available show that mixotrophic plankton persist in the water column during the long polar winter when irradiance is low or absent and ice cover reduces further light penetration. These observations suggest that at high latitudes an alternative food web based on mixotrophy may dominate the pelagic lower food web during much of the year.

International audience; Like many large freshwater ecosystems in Europe, Lake Bourget suffered from eutrophication during the second part of the 20th century and since the 1980s has been partially restored by reductions in nutrient loadings. Here, we analyse a data set comprised of field measurements of physicochemical and biological variables in Lake Bourget covering the period from 2004 to 2011 and complement this data set with laboratory experiments, to gain an understanding of the changes in phytoplankton community structure during recent years and drivers of these changes. Between 1995 and 2008, Lake Bourget was characterised by the proliferation of the red-coloured filamentous and toxic cyanobacterium Planktothrix rubescens, comprising 34.1-52.6% of the total phytoplanktonic biomass between 2004 and 2008. In 2009, although the contribution of P.rubescens to the total biomass was still considerable (25.3%), it was significantly lower (P

Morpho-functional classifications of phytoplankton are increasingly used in ecological studies of different aquatic ecosystems. The aim was to compare three different classifications: (a) functional groups (FG); (b) morpho-functional groups (MFG); and (c) morphologically based functional groups (MBFG), and to detect how well can the biomass of phytoplankton groups based on different classifications be explained by environmental conditions of two different karstic lakes in the National Park Plitvice Lakes. Phytoplankton biomass in Lake Kozjak was lower than in Lake Prosce (total avg. 1.13 and 2.59 mg l−1, respectively). Several diatoms (Cyclotella spp., Discostella stelligera, Synedra sp., Ulnaria ulna var. acus) with Dinobryon divergens were dominant in Kozjak, while Prosce was characterized by Dinobryon sociale, D. divergens, Cryptomonas sp., Stephanodiscus sp. and Fragilaria crotonensis. The best results in describing the phytoplankton succession were obtained using MBFG approach although it is less sensitive in describing variability of individual descriptive algal groups in this environment than FG and MFG. Nonetheless, because of distinct differences among dominant phytoplankton groups in these systems, MBFG classification was shown to be applicable, as supported by statistical analyses. FG and MFG classifications showed a high level of similarity, thus proving to be applicable to deep karstic lakes.

This study assessed the water quality of Mengkuang Reservoir, Penang, Malaysia, by its trophic status according to a Carlson Modified Trophic Index (CMTSI) and by its biological parameters using Shannon–Wiener diversity index (H′) and saprobic index. The study conducted from August 2005 to July 2006 showed that mean values of CMTSI (nutrients), CMTSI (chlorophyll a) and CMTSI (Secchi depth) were 27.18 ± 8.73, 40.63 ± 7.12 and 41.74 ± 6.38, respectively. The mean values of CMTSI indicated that the reservoir was oligotrophic. Mean value of H′ was 2.15 bits/individual, showing that the water quality based on H′ value was in class III (slightly polluted). Saprobic index value (2.24) also revealed that the reservoir was moderately polluted (class II). The occurrence of Anabaena, Microcystis, Oscillatoria, Nostoc, Dinobryon, Chroococcus, Staurastrum paradoxum and Mallomonas which are indicators of toxic and polluted waters was also recorded. This study therefore showed the importance of phytoplankton composition and community structure as a reliable and important tool to assess the degree of pollution in Mengkuang Reservoir. Long-term assessments of biological and chemical parameters in the reservoir are necessary, and phytoplankton community structure as bioindicator provides unique information about the ecosystem. This information is potentially useful as an early warning sign of deteriorating condition and thus gives insight into the overall ecology of lakes and will assist in the future conservation and management of this lentic ecosystem.

The aim of the study was to perform an ecological status assessment based on the phytoplankton in the vendace-type Lake Dejguny in accordance with the requirements of the Water Framework Directive. The phytoplankton analyses were conducted during three growth seasons in 2006, 2007, and 2008. The phytoplankton multimetric Phytoplankton Metric for Polish Lakes (PMPL) was used to assess the lake’s ecological status. The average total biomass of phytoplankton ranged from 1.6 to 3.9 mg dm-3, while the average biomass of Cyanoprokaryota ranged from 0.4 to 1.4 mg dm-3, with the minimum noted in 2008. The phytoplankton assemblages were dominated mainly by filamentous Cyanoprokaryota and pennate Bacillariophyceae in 2006 and 2008, or exclusively by pennate Bacillariophyceae in 2007. The relatively low total biomass and Cyanoprokaryota biomass, as well as seasonal phytoplankton dynamics with the dominant taxa of Tabellaria flocculosa, Dinobryon sociale, and D. divergens confirmed the lake’s mesotrophic state and some of the features of reference conditions in this lake, whereas the predominance of filamentous species Planktothrix agardhii and Planktolyngbya limnetica was characteristic of eutrophic conditions. However, a clear tendency towards progressive eutrophication stemming from the significant domination of filamentous Cyanoprokaryota was observed, and according to the PMPL the assessment indicated that Lake Dejguny had a good ecological status in 2006 and 2007 and even a high one in 2008.

This paper presents the preliminary results of a study of the phytoplankton structure and dynamics and physicochemical properties of Lake Swarzędzkie in 2011. The subject of the study is a shallow, elongated, post-glacial lake located in western Poland. The surface area is 93.7 ha with a maximum depth of 7.2 m. Its poor water quality led to the implementation of chemical and biological restoration procedures in an attempt to improve it. The highest concentration of total nitrogen was 13.07 mg l-1 N. Secchi depth (SD) was low in the summer with a minimum value of 0.5 m in September. The most abundant group of phytoplankton were cyanobacteria, and the maximum value of chlorophyll a concentration was 278.0 μg l-1. The dominant species were Pseudanabaena limnetica and Aphanizomenon gracile. Cyanobacteria were the most abundant phytoplankton until November. Maximum diatom, cryptophyte, and chrysophyte density was noted in the spring, and the most abundant were Nitzschia acicularis, Cryptomonas marssonii, Rhodomonas lacustris, Erkenia subaequiciliata, and Dinobryon sociale. One-hundred and thirty-six phytoplankton taxa belonging to nine taxonomic groups were identified in Lake Swarzędzkie. The highest number of taxa was noted among chlorophytes (57 taxa), cyanobacteria (19), diatoms (16), and chrysophytes (12), while other taxonomic groups were represented by smaller number of taxa.

A new freshwater species of Chrysophyceae, Dinobryon taiyuanensis, is described from Linde Lake in Shanxi province, China. This new species is similar to D. sertularia, the type species of the genus, in the shape of the lorica and organization of the colony. The cells have two heterokont flagella surrounded by a lorica and occurred both as free-living, solitary cells or in branched colonies. The lorica of our new species like a bent or S-shaped cone, and shorter than the lorica in D. sertularia. In addition to describing the morphological features of D. taiyuanensis, a phylogenetic analysis based on sequences of the nuclear small subunit ribosomal DNA (SSU rDNA) and internal transcribed spacer (including internal transcribed spacer 1, 5.8S rDNA and internal transcribed spacer 2) placed this alga in single clade with a considerable sequence distance from the other Dinobryon species. Thus, results of both morphological comparisons and phylogenetic analysis based on molecular data suggest this alga as a new species, increasing the total number of recognized freshwater Chrysophyta species in China.

Detailed studies of the Chrysophyceae class of algae have not been undertaken in Serbia thus far. The golden algae usually occur during the winter and spring months. Chrysophyceae of the Zasavica River in Serbia were studied at two localities from December 2012 to Jun 2013. In our research, 26 taxa were recorded and the genus with the highest diversity was Mallomonas (15 species). The most abundant species during the whole study period were Synura uvella, Dinobryon divergens and Dinobryon sociale. At the beginning of summer, Chrysophyceae disappeared from the phytoplankton community. [Projekat Ministarstva nauke Republike Srbije, br. 176020 i br. III 43004]

Dinobryon spp. are common components of the phytoplankton in temperate lakes. While these chrysophytes link bacterial carbon as well as primary production to the larger food web, few studies have examined their vertical distribution over a season. Data were collected over a 2.5 yr period in mesotrophic Lake Lacawac in eastern Pennsylvania (USA) to examine water col- umn attributes relating to seasonality of the mixotrophic alga D. cylindricum, and specifically to address a hypo thesis that abundance and vertical distribution in the genus are associated with temperature. This information was used to guide laboratory experiments examining temperature and light effects on growth, feeding, and vertical migration of cultured Dinobryon. Data from Lake Lacawac and the literature indicated that high abundances of Dinobryon were associated with a narrow range of temperature (9�18°C) relative to temperatures where they were present (3�26°C). High abundances of several species of Dynobryon were associated with this tempera- ture range, and occurred from late winter to late spring, depending on latitude and depth in the water column. Although high Dinobryon abundances were not tied directly to levels of photosyn- thetically active radiation in Lake Lacawac, a UV-exclusion experiment in a nearby oligotrophic lake indicated a temperature-dependent negative effect of UV radiation. UV may limit the occur- rence of Dinobryon populations in surface waters of clear oligotrophic lakes. Laboratory experi- ments showed that both light and temperature affected growth and feeding rates of Dinobryon, and that maximum feeding and growth rates occurred within the temperature range where high Dinobryon abundances were observed in field studies.

A significant outbreak of fishy odor occurred in a reservoir located in Inner Mongolia, China, in the winter of 2011, and the odor rating, algal density and concentrations of some potential odorous compounds were monitored over a period of two months. The peak odor rating of the fishy odor was 7 according to flavor profile analysis. Among the dominant algal species (two diatom and one chrysophyte species) observed during the survey, the chrysophyte Dinobryon sp. was the most abundant species, with the peak density recorded at 88,520 cells/mL. Seven potential algal metabolites including heptanal, 2,4-heptadienal, 2,4-decadienal, nonanal, 2-octenal, 2,6-nonadienal and hexanal were detected. The principal component analysis result showed that n-hexanal, n-heptanal and 2,4-decadienal, possibly the metabolites of diatoms, and 2,4-heptadienal, possibly the metabolite of Dinobryon sp., might have contributed to the fishy odor episode. This study demonstrated that the fishy odor episode in this reservoir might be caused by the abnormal growth of chrysophytes and diatoms under the ice-cover.

* Globally, freshwater ecosystems are warming at unprecedented rates and northern temperate lakes are simultaneously experiencing increased runoff of humic substances (brownification), with little known consequences for future conservation of biodiversity and ecosystem functioning. * We employed an outdoor mesocosm experiment during spring and summer to investigate the combined effects of gradually increasing warming and brownification perturbations on the phytoplankton community structure (biodiversity and composition) and functioning (biomass). * While we did not observe overall significant treatment effects on total phytoplankton biomasses, we show that predicted increases in warming and brownification can reduce biodiversity considerably, occasionally up to 90% of Shannon diversity estimates. Our results demonstrate that the loss of biodiversity is driven by the dominance of mixotrophic algae (Dinobryon and Cryptomonas), whereas several other phytoplankton taxa may be temporarily displaced from the community, including Cyclotella, Desmodesmus, Monoraphidium, Tetraedron, Nitzschia and Golenkinia. * The observed loss of biodiversity coincided with an increase in bacterial production providing resources for potential mixotrophs along the gradient of warming and brownification. This coupling between bacterial production and mixotrophs was likely a major cause behind the competitive displacement of obligate phototrophs and supports evidence for the importance of consumer–prey dynamics in shaping environmental impacts on phytoplankton communities. * We conclude that warming and brownification are likely to cause a profound loss of biodiversity by indirectly affecting competitive interactions among phytoplankton taxa. Importantly, our results did not show an abrupt loss of biodiversity; instead the reduction in taxa richness levelled off after exceeding a threshold of warming and brownification. These results exemplify the complex nonlinear responses of biodiversity to environmental perturbations and provide further insights for predicting biodiversity patterns to the future warming and brownification of freshwaters.

Global warming has been shown to affect ecosystems worldwide. Warming may, for instance, disrupt plant herbivore synchrony and bird phenology in terrestrial systems, reduce primary production in oceans, and promote toxic cyanobacterial blooms in freshwater lakes. Responses of communities will not only depend on direct species-specific temperature effects, but also on indirect effects related to bottom-up and top-down processes. Here, we investigated the impact of warming on freshwater phytoplankton community dynamics, and assessed the relative contribution of nutrient availability, fungal parasitism, and grazing therein. For this purpose, we performed an indoor mesocosm experiment following seasonal temperature dynamics of temperate lakes and a warmed (+4°C) scenario from early spring to late summer. We assessed phytoplankton biomass, C:N:P stoichiometry and community composition, dissolved nutrient availabilities, fungal parasite (i.e., chytrid) prevalence, and zooplankton abundance. Warming led to an overall reduction in phytoplankton biomass as well as lower C:P and N:P ratios, while phytoplankton community composition remained largely unaltered. Warming resulted in an earlier termination of the diatom spring bloom, and an epidemic of its fungal parasite ended earlier as well. Furthermore, warming advanced zooplankton phenology, leading to an earlier top-down control on phytoplankton in the period after the spring bloom. Linear model analysis showed that most of the observed variance in phytoplankton biomass was related to seasonal temperature dynamics in combination with zooplankton abundance. Our findings showed that warming advanced grazer phenology and reduced phytoplankton biomass, thereby demonstrating how bottom-up and top-down related processes may shape future phytoplankton dynamics.

Este artículo contiene 11 páginas, 2 tablas, 5 figuras, Many phototrophic flagellates ingest prokaryotes. This mixotrophic trait becomes a critical aspect of the microbial loop in planktonic food webs because of the typical high abundance of these flagellates. Our knowledge of their selective feeding upon different groups of prokaryotes, particularly under field conditions, is still quite limited. In this study, we investigated the feeding behavior of three species (Rhodomonas sp., Cryptomonas ovata, and Dinobryon cylindricum) via their food vacuole content in field populations of a high mountain lake. We used the catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) protocol with probes specific for the domain Archaea and three groups of Eubacteria: Betaproteobacteria, Actinobacteria, and Cytophaga-Flavobacteria of Bacteroidetes. Our results provide field evidence that contrasting selective feeding exists between coexisting mixotrophic flagellates under the same environmental conditions and that some prokaryotic groups may be preferentially impacted by phagotrophic pressure in aquatic microbial food webs. In our study, Archaea were the preferred prey, chiefly in the case of Rhodomonas sp., which rarely fed on any other prokaryotic group. In general, prey selection did not relate to prey size among the grazed groups. However, Actinobacteria, which were clearly avoided, mostly showed a size of 0.5 m, markedly smaller than cells from the other groups. I, This research was supported by the Spanish Ministry of Science project ECOFOS (CGL2007-64177/BOS) with a predoctoral scholarship to M.A.B., Spanish Ministry of the Environment project EGALA (OAPN-124/2010), and a Generalitat de Catalunya research grant (SGR 2014-1249).

Algae are simplest and chlorophyll bearing organism and not differentiated into true leaves, stems and roots. Algae habitat is fresh water. Algae have pivotal role on earth. They are primary producers and form strong food chains mostly in aquatic environment. It constitute important group, so it was desired to work out the freshwater algae of District Peshawar. In the research area total of 13 genera with 51 species of algae found in District Peshawar which belong to Chlorophyta (64%), Cyanophyta (18%), Xanthophyta (2%), Charophyta 6 % and Chrysophyta (10%) were identified and properly key referenced. The frequent genus in term of species was Spirogyra with 11 species (22%), Oscillatoria with 9 species (18%), Chara, Zygnema and Nitzschia have 3 species each 6 %, Cladophora with 7 species (14%), Closterium with 5 specie (10%), Ulotehrix with 4 species (8 %), Rhizoclonium with 2 species (4%), Vachoria, Mougeotia, Ophiocytium and Dinobryon have 1 spp. (2%). The present study will help to know the ecological distribution of fresh water algae in Peshawar.

Yellow River source water has long suffered from odor problems in winter. In this study, odor characteristics, potential odorants, and algae in the source water of six cities (Lanzhou, Yinchuan, Hohhot, Zhengzhou, Jinan and Dongying) along the Yellow River were determined in winter (February to March 2014). According to flavor profile analysis (FPA), moderate to strong fishy odors occurred in all cities, except for Lanzhou. At the same time, mild earthy/musty odors and septic/swampy odors were also detected. The strong fishy odor (FPA intensity, 8.5) in Yinchuan was attributed to the abnormal growth of Dinobryon (cell density, 5.7 × 10 4 cells/mL), while the fishy odors in Hohhot, Zhengzhou, Jinan, and Dongying might be caused by Melosira and Cyclotella, Cryptomonas, Dinobryon , and Synedra, respectively. Unsaturated aldehydes, which have been reported to cause fishy odors, were not detected in all samples. However, some saturated aldehydes, including hexanal, heptanal, nonanal, decanal, and benzaldehyde, were detected with a total concentration range of 690 ng/L to 2166 ng/L, and might have partly contributed to the fishy odors. In addition, 2-MIB (5.77–21.12 ng/L) and geosmin (2.26–9.73 ng/L) were responsible for the earthy/musty odors in the Yellow River source waters, and dimethyl disulfide (648.2 ng/L) was responsible for the rancid/swampy odor (FPA intensity, 8.0) episode in Yinchuan. This is a comprehensive study reporting on the occurrence and possible reasons for the odor issues in the Yellow River source water during winter.

Siliceous stomatocysts of chrysophyte algae, along with diatom frustules, are well preserved in bottom sediments of various water bodies. Analysis of microfossils from a core sample of the Upper Pleistocene and Holocene sediments from the southern part of Lake Hovsgol revealed 36 different morphotypes of chrysophycean stomatocysts. Some of them were attributed to species of the genera Mallomonas Perty, Chrysosphaerella Lauterborn., Paraphysomonas (Stokes) De Saedeleer, and Dinobryon Ehr.; 20 morphotypes were described as novel. The abundance and diversity of stomatocyst morphotypes in the core sample varied depending on the age of sediments. The results obtained in the study broaden views on the biological diversity of microalgae and confirm that chrysophycean stomatocysts can serve as good environmental indicators in paleolimnological and paleoclimatic reconstructions.

Liuxihe reservoir is a deep, monomictic, oligo-mesotrophic canyon-reservoir in the subtropical monsoon climate region of southern China. Phytoplankton functional groups in the reservoir were investigated and a comparison made between the succession observed in 2008, an exceptionally wet year, and 2009, an average year. The reservoir shows strong annual fluctuations in water level caused by monsoon rains and artificial drawdown. Altogether 28 functional groups of phytoplankton were identified, including 79 genera. Twelve of the groups were analyzed in detail using redundancy analysis. Because of the oligo-mesotrophic and P-limited condition of the reservoir, the dominant functional groups were those tolerant of nutrient (phosphorus) deficiency. The predominant functional groups in the succession process were Groups A (Cyclotella with greatest axial linear dimension10 μm), B (Cyclotella with greatest axial linear dimension10 μm), LO (Peridinium), LM (Ceratium and Microcystis), E (Dinobryon and Mallomonas), F (Botryococcus), X1 (Ankistrodesmus, Ankyra, Chlorella and Monoraphidium) and X2 (Chlamydomonas and Chroomonas). The development of groups A, B and LO was remarkably seasonal. Group A was dominant during stratification, when characteristic small size and high surface/volume ratio morphology conferred an advantage. Group LO was dominant during dry stratification, when motility was advantageous. Group B plankton exhibited a high relative biomass during periods of reduced euphotic depth and isothermy. Groups LM, E, F, X1 and X2 occasionally exhibited high relative biomasses attributable to specific environmental events (e.g. drawdown, changes in zooplankton community). A greater diversity of phytoplankton functional groups was apparent during isothermy. This study underscores the usefulness of functional algal groups in studying succession in subtropical impoundments, in which phytoplankton succession can be significantly affected by external factors such as monsoonal hydrology and artificial drawdown, which alter variables such as retention time, mixing regime and thermal structure and influence light and nutrient availability.

Freshwater organisms synthesize a wide variety of fatty acids (FAs); however, the ability to synthesize and/or subsequently modify a particular FA is not universal, making it possible to use certain FAs as biomarkers. Herein we document the occurrence of unusual FAs (polymethylene-interrupted fatty acids; PMI-FAs) in select freshwater organisms in the Laurentian Great Lakes. We did not detect PMI-FAs in: (a) natural seston from Lake Erie and Hamilton Harbor (Lake Ontario), (b) various species of laboratory-cultured algae including a green alga (Scenedesmus obliquus), two cyanobacteria (Aphanizomenon flos-aquae and Synechococystis sp.), two diatoms (Asterionella formosa, Diatoma elongatum) and a chrysophyte (Dinobryon cylindricum) or, (c) zooplankton (Daphnia spp., calanoid or cyclopoid copepods) from Lake Ontario, suggesting that PMI-FAs are not substantively incorporated into consumers at the phytoplankton-zooplankton interface. However, these unusual FAs comprised 4-6% of total fatty acids (on a dry tissue weight basis) of native fat mucket (Lampsilis siliquoidea) and plain pocketbook (L. cardium) mussels and in invasive zebra (Dreissena polymorpha) and quagga (D. bugensis) mussels. We were able to clearly partition Great Lakes' mussels into three separate groups (zebra, quagga, and native mussels) based solely on their PMI-FA profiles. We also provide evidence for the trophic transfer of PMI-FAs from mussels to various fishes in Lakes Ontario and Michigan, further underlining the potential usefulness of PMI-FAs for tracking the dietary contribution of mollusks in food web and contaminant-fate studies. © 2011.

With the discovery of a high molecular diversity of protists, a discrepancy between morphological and molecular species richness estimates became apparent. Solving the current concerns requires a comparative analysis of different sequences combined with morphological analyses of single cells originating from preserved field samples. We refined a single-cell PCR (SC-PCR) protocol for analyzing cells from field samples preserved with Lugol’s iodine solution. We linked microscopic screening with multiplex PCR targeting the SSU rDNA, internal transcribed spacer 1 (ITS1), 5.8S rDNA, internal transcribed spacer 2 (ITS2), and the mitochondrial cytochrome oxidase 1 (CO1) in a single PCR reaction. Using this method, we investigated the intraspecific molecular variation in Dinobryon populations originating from two lakes in the Salzkammergut area of Austria. All investigated genetic markers showed two separated clusters within the investigated populations of Dinobryon divergens O. E. Imhof, indicating a reproductive isolation of the two coexisting populations. Based on these findings, we describe a lineage, which is morphologically similar to D. divergens but, based on the molecular data, is reproductively isolated.

Plankton in mountain lakes are confronted with generally higher levels of incident ultraviolet radiation (UVR), lower temperatures, and shorter growing seasons than their lower elevation counterparts. The direct inhibitory effects of high UVR and low temperatures on montane phytoplankton are widely recognized. Yet little is known about the indirect effects of these two abiotic factors on phytoplankton, and more specifically whether they alter zooplankton grazing rates which may in turn influence phytoplankton. Here, we report the results of field microcosm experiments that examine the impact of temperature and UVR on phytoplankton growth rates and zooplankton grazing rates (by adult female calanoid copepods). We also examine consequent changes in the absolute and relative abundance of the four dominant phytoplankton species present in the source lake (Asterionella formosa, Dinobryon sp., Discostella stelligera, and Fragilaria crotonensis). All four species exhibited higher growth rates at higher temperatures and three of the four species (all except Dinobryon) exhibited lower growth rates in the presence of UVR versus when shielded from UVR. The in situ grazing rates of zooplankton had significant effects on all species except Asterionella. Lower temperatures significantly reduced grazing rates on Fragilaria and Discostella, but not Dinobryon. While UVR had no effect on zooplankton grazing on any of the four species, there was a significant interaction effect of temperature and UVR on zooplankton grazing on Dinobryon. Discostella and Dinobryon increased in abundance relative to the other species in the presence of UVR. Colder temperatures, the presence of zooplankton, and UVR all had consistently negative effects on rates of increase in overall phytoplankton biomass. These results demonstrate the importance of indirect as well as direct effects of climate forcing by UVR and temperature on phytoplankton community composition in mountain lakes, and suggest that warmer climates and higher UVR levels may favor certain species over others.