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Here we introduce a method for quantitative analysis of planktonic protists and microalgae from preserved field samples combining morphological and small-subunit (SSU) rRNA gene sequence analysis. We linked a microscopic screening with PCR of single cells using field samples preserved with Lugol's iodine solution. Cells possessing a rigid cell wall were incubated with Viscozyme and subsequently with proteinase K for cell disruption; this was unnecessary for fragile cells. The addition of sodium thiosulfate to the PCR tube considerably decreased the inhibiting effect of the fixative (iodine) on the PCR and thus allowed for successful single-cell PCR even of long DNA fragments (up to as many as 3,000 base pairs). We further applied the protocol to investigate the dominant SSU rRNA genotypes in distinct flagellate morphospecies originating from different samples. We hypothesized that despite the morphological similarity, protist morphospecies in different habitats or sampled during different seasons are represented by different genotypes. Our results indicate species-specific differences: the two species Ochromonas sp. and Dinobryon divergens were represented by several different genotypes each, and for the latter species, the dominating genotype differed with habitat. In contrast, Dinobryon pediforme , Dinobryon bavaricum , and Synura sphagnicola were exclusively represented by a single genotype each, and the respective genotype was the same in different samples. In summary, our results highlight the significance of molecular variation within protist morphospecies.

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.

The Todebin dam reservoir has been constructed in central part of Abhar in the Zanjan province which has been studied with aquaculture purpose. This study was conducted on biotic and abiotic factors. The plankton, benthos and fishes were identified and the parasitology and bacteriology studies were performed on the lake fishes. Then the fisheries potential of the lake was calculated in respect of final fish farming amount and the fish releasing. The results showed the Bacillariophyta was dominated ِduring the study. the highest abundance of phytoplankton was between 2.1 and 12.5 million cells.l^-1 in the upper layer of lake as compared with the lower layer. The genus Cyclotella and Dinobryon belong to phytoplankton and Keratella and Polyathera belong to zooplankton were dominanted abundance. The mean biomass of benthos was varied from 5.5 to 29.5 g.m -2 and the Chironomidae had the most abundance. The ichtiology survey showed the presence of four cultured species and the Goldfish. The hydro-chemical results indicated no restriction for aquaculture activity. The oxygen average was more than 8 mg/l. The average of phosphate, nitrogen and hardness were measured 0.09±0.04, 2±0.8 and 237±94.5 mg/l., respectively. For the most hydrochemical factores, the values were significantly different between upper and bottom layers of the lake. The oxygen production and Chl-a amount were measured about 0.73 mg/l. and 7/03 µg/l., respectively. According to climatic restrictions, the cold fish culture is preferred than to culture of warm fishes. While the natural capacity of the lake was about 5 tones to warm fish culture, the fish production of trout was estimated about 40 tones. This volume will be available during four months periods and twice a year.

Drinking water supplies are often impacted by taste and odour (T/O) episodes caused by algal volatile organic compounds (AVOCs) from algal blooms. Treatment and control of these events is important to utility operators, as customer confidence in the safety of public drinking water supplies is based primarily on their palatability and odour. To manage T/O outbreaks successfully, knowledge about treatment responses of AVOCs and anticipation of their outbreaks are thus of major importance to the water industry. The Glenmore Reservoir and water treatment plant (GWTP) supplies drinking water to over 50% of the ca. 1 million consumers in Calgary (Alberta). Despite low nutrients and high raw water quality, the reservoir experiences periodic outbreaks of fishy/floral T/O, caused by chrysophytes and diatoms (Uroglena americana, Dinobryon spp., Synura petersenii, Asterionella formosa). These odours are produced by the unsaturated C7–C10 alkenes 2,4-heptadienal, 2,4,7-octatriene, 2,4-decadienal and 2,4,7-decatrienal, generated during from the enzymatic breakdown of algal polyunsaturated fatty acids (PUFAs). The formation, persistence and stability of these compounds in both the raw water and treatment plant is not well understood.

Vertical distribution of phytoplankton is highly influenced by physical and chemical factors, but the knowledge about these aspects remain unknown in Colombian Amazon lakes. In this work, the relations between the physico-chemical variables and the vertical distribution of phytoplankton community of a clear water lake (Lake Boa) are analyzed. Samples were taken at every 30 cm from surface to bottom in the center of the lake at different times of the hydrological cycle. Phytoplankton transformed from a diluted community dominated by cyanobacteria in high waters to one with elevated abundance of coccal chlorophytes in low waters. In the low water phase, the vertical distribution of Cryptomonas spp., Peridinium cf. umbonatum and Chlamydomonas spp. had significant statistical associations with the redox potential (RP), reactive phosphorus (PO4), and hydrogen sulfide (H2S) (p ≤ 0.05). During the flood stage the conditions were more varied and significant associations were detected between the vertical arrangement of Botryococcus braunii, Oscillatoria splendida, Dinobryon serturlaria, Euglena acus, and Trachelomonas volvocina with conductivity, dissolved oxygen (DO), pH, temperature, dissolved organic carbon (DOC), PO4, RP, and ammonia (NH4). The vertical structure of the Lake Boa’s phytoplankton responds to annual changes produced by the flood pulse, and to the vertical environmental variations, which are stronger during the high water phase.

Summary 1. We applied Reynolds's approach to the study of phytoplankton ecology through functional associations of species to identify possible algal species, which associate with the freshwater cyanobacterium Synechococcus. Previously an association among Synechococcus spp. and small-celled chlorophytes (association Z) has been recognised by evaluating phytoplankton associations according to functional criteria. 2. Biomass data for phytoplankton and picocyanobacteria from Lago Maggiore spanning more years were organised in a matrix and a cluster analysis was performed. The results showed four groups separated at a linkage distance of 0.20. Mixotrophic species which clustered with Synechococcus spp. were Ceratium hirundinella, Chrysochromulina parva, Cryptomonas erosa, Cryptomonas ovata, Dinobryon bavaricum, Dinobryon sociale, Rhodomonas minuta and Uroglena americana. The redundancy analysis (RDA) consolidated the association of Synechococcus with C. hirundinella and R. minuta showing greater probability of occurrence than random aggregates of species. 3. The association Synechococcus spp. –C. hirundinella also appeared from temporal variation of their biomass. In early summer both these species increased at the same time; later, the peak of C. hirundinella (potential predator) coincided with a minimum of Synechococcus spp. suggesting a possible predator-prey interaction. This implied that phytoplankton assemblages which form a functional group cannot only have similar adaptations and requirements but can also exhibit trophic interactions. 4. We propose to enlarge the association Z and create an association ZMX (where MX stands for mixotrophs) which would include Synechococcus spp. and C. hirundinella as the most representative of the mixotrophic species found in the oligotrophic Lago Maggiore.

【In order to grasp the structure and dynamics of phytoplankton communities, chlorophyll-a (Chl-a) and cell abundance were measured at 20 stations during the period from August 9 to August 21, 2003 in the southeastern Barents Sea on surface and subsurface chlorophyll maximum depth (SCM). Surface temperatures were varied from minimum $-0.7^{\circ}C(st. 18)$ to maximum $10.4^{\circ}C(st.1)$ . Salinities were varied from minimum 29.9 psu(st. 18) to maximum 35.8 psu(st.2). The maximum nutrient(phosphate, nitrate, silicate) concentrations were $0.12{\mu}M,\;0.11{\mu}M,\;7.53{\mu}M$ and minimum concentrations were $0.01{\mu}M,\;0.03{\mu}M,\;1.43{\mu}M$ , respectively. On SCM physical environmental factor were almost similar. Chl-a concentrations ranged from 0.23 to $2.13{\mu}g\;chi-a\;l^{-1}$ at SCM. Nano- and pico phytoplankton were the important contributors for increase of the Chl-a. It was about seven times difference between highest concentration to lowest. Phytoplankton communities were composed of diatoms, dinoflagellates, cryptophyceae, silicoflagellate, and prymnesiophyceae showing 37 taxa at surface and 38 taxa at SCM. Picophytoplankton was the most dominant in all stations and all layers, but the second groups were 2 and/or 3 taxa. Phytoplankton abundance ranged from minimum $4.3{\times}10^5\;cells\;l^{-1}$ (st. 20) to maximum $2.4{\times}10^6\;cells\;l^{\-1}$ . (st. 17) at surface water. As a result, phytoplankton might be controlled by physical factors such as North Atlantic ocean currents and northern melt water among environmental factors in Barents Set h addition the dominant species were nano- and pico phytoplankton such as Phaeocystis, Cryptomonas and Dinobryon in the study area.】

We studied the phytoplankton seasonality in the subarctic Lake Saanajarvi, Finnish Lapland, in two successive years with slightly different weather conditions. The total number of taxa studied during the period was 148. Characteristic phytoplankton species were chrysophytes Uroglena sp., Chrysococcus spp., Dinobryon spp and diatoms Cyclotella spp. The results were analysed in relation to weather patterns and physico-chemical variables measured from the lake during the 2 years. The seasonal dynamics of phytoplankton were characterized by (1) maxima in total densities during autumn and minima in winter; (2) different species reaching maximum and minimum densities during different seasons; (3) close to equilibrium state during strong thermal stratification in 1997 with dominance of only a few taxa; and (4) two annual maxima in species diversity at the beginning of the thermal stratification and during the autumn overturn. According to canonical ordinations, calcium buffer capacity, nutrients and temperature all play a role in regulating algal biomass and species compositions. With regard to physical factors, the length of the mixing cycle, thermal stability of the water column and water temperature seem to have a major control over the plankton dynamics. The length of the ice-free season seems to be more decisive for biomass production than the thermal stability during this period, which, in turn, appears to affect the algal biodiversity.

Species diversity and richness, and seasonal population dynamics of phytoplankton, planktonic protozoa, and bacterioplankton sampled from the epilimnion of Crystal Bog in 2000, were examined in order to test the hypothesis that these groups' diversity and abundance patterns might be linked. Crystal Bog, a humic lake in Vilas County, Wisconsin, is part of the North Temperate Lakes Long-Term Ecological Research Site. Phytoplankton and planktonic protozoa were identified and enumerated in a settling chamber with an inverted microscope. Bacterial cells were enumerated with the use of fluorescence 4', 6'-diamidino-2-phenylindole (DAPI)-staining procedures, and automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterioplankton diversity. Bacterial cell counts showed little seasonal variation and averaged 2.6 x 10(6) cells/mL over the ice-free season. Phytoplankton and planktonic protozoan numbers varied by up to two orders of magnitude and were most numerous in late spring and summer. Dinoflagellates largely dominated Crystal Bog throughout the ice-free period, specifically Peridiniopsis quadridens in the spring, Peridinium limbatum in summer, and Gymnodinium fuscum and P. quadridens in fall. Brief blooms of Cryptomonas, Dinobryon, and Synura occurred between periods of dinoflagellate domination. The dominant dinoflagellate, Peridinium limbatum, was calculated to have a growth rate of 0.065 day(-1) and a doubling time of 10.7 days. Heterotrophic nanoflagellates (HNFs) were a consistent component of the planktonic protozoa; seasonal patterns were determined for three genera of HNFs (Monosiga, Bicosoeca, and Desmarella moniliformis). Three genera of ciliates (Coleps, Strobilidium, and Strombidium) comprised the greater part of the planktonic protozoa in Crystal Bog. The number of species of planktonic protozoa was too low to calculate a diversity index. Shannon-Weaver diversity indices for phytoplankton and bacterioplankton in the epilimnion followed very similar seasonal patterns in this lake, supporting the hypothesis that in freshwaters, diversity patterns of these groups are linked.

Dynamics of phytoplankton communities were investigated at five stations in Youngsan River from December 1995 to November 1996. Phytoplankton were identified to the total of 466 taxa, which were composed of 136 genera, 438 species, 27 varieties and 1 forma. The standing crops ranged 1,163-50,765 cells during the investigation periods. The variation of classes was in order to Chrysophyceae - Bascillariophyceae - Chlorophyceae at St. 1 and was only Bacillariophyceae at the other stations. The dominant species were 12 taxa including Aulacoseira ambigua, A. garnulata, Cyclotella meneghiniana, C. pseudostelligera, Chlorella vulgaris, Dinobryon sertularia, Flagilaria elliptica, Monoraphidium contortum, Micractinium pusillum, Nitzschia palea, Scenedesmus grahneisii and Stephanodiscus hantzschii f. tenuis. The standing crops of dominant species ranged from 10.6% to 94.7%. The genus Dinobryon in Chrysophyceae was dominant species at St. 1 in December 1995, but not recorded in the other months. The dominant species were composed with the planktonic diatoms from winter to spring and were the tychoplanktonic and the benthic species at St. 2-5 from summer to fall. The relationships between total standing crops and water temperature, pH, , , and showed low positive or negative coefficients. Stephanodiscus hantzschii f. tenuis had low positive or negative coefficients with water temperature, , , and . The fluctuations of standing crops in the Youngsan river phytoplankton community were not caused by a single factor but controlled by the complex factors with interaction between phytoplankton community and envirowmental factors.

Photosynthesis and microbial plankton dynamics of two lakes in the Kongsfjorden catchment of Spitzbergen (Svalbard Archipelago, 78°N) were investigated during the summer of 2000. One of the lakes (Tvillingvatnet) served as the water supply for the village of Ny Alesund. The other was a deeper, larger unnamed lake in the Ossian Sarsfjella reserve—named Lake OS in this study. Both lakes can be classified as oligotrophic on the basis of chlorophyll a and inorganic nutrient concentrations. Chlorophyll a concentrations ranged between 0.33 and 1.65 µg l-1 in Tvillingvatnet and 0.2 and 0.3 µg l-1 in Lake OS. The phytoplankton was dominated by chrysophytes and cryptophytes, with the diatom Rhizosolenia and a number of dinoflagellate species. Rates of photosynthesis were typically low, between 24.5 µg and 1.0 mg l-1 day-1 in Tvillingvatnet (photosynthetic efficiency 0.004–0.26), and between 3.1 and 29.5 µg l-1 day –1 in Lake OS (photosynthetic efficiency 0.0019–0.0085). Among the phytoflagellates (PNAN) there were a number of mixotrophs which reached their peaks of abundance before other PNAN. Mixotrophy appeared to provide a competitive advantage. Grazing rates for the mixotroph Dinobryon ranged between 0.063 and 1.12 pg C cell-1 day-1 in Lake OS and between 0.22 and 1.11 pg cell-1 day-1 in Tvillingvatnet, with rates increasing between July and August. However, Dinobryon removed less than 1% of bacterial biomass day-1, while the heterotrophic nanoflagellates (HNAN) removed up to 28% of bacterial biomass day-1. Bacterial concentrations were low, with a maximum of 28.8×108 l-1 in Tvillingvatnet and 23.6×108 l-1 in Lake OS. Ciliated protozoan and rotifer diversity in the plankton was low.

The biomass and bacterial ingestion rates of mixotrophic phytoflagellates were examined on diurnal and seasonal scales in oligotrophic Lake Skarlen (S. Sweden). Ingestion rates were measured using fluorescent microspheres in situ on three depths every 6(th) hour during 24 hours in summer in order to quantify diurnal variations and once at midday during autumn, winter and spring. Mixotrophic phytoflagellates composed a large part of the phytoplankton biomass (18-31 %) throughout the year. Nonetheless, calculations suggest that the mixotrophs only consumed between 0.5 and 4.4 % of the bacterial carbon production, with the highest consumption percentage in winter under ice. Two groups of algae, Cryptomonas spp. and Dinobryon spp., were commonly found with ingested prey and both exhibited significant diurnal differences in bacterial ingestion rates with the highest mean rates measured in late afternoon (0.50 and 0.27 bacteria cell(-1) hour(-1), respectively) and very low rates during night (0.09 and 0.06 bacteria cell(-1) hour). In Cryptomonas spp., ingestion rates also varied.somewhat over the year and bacterial ingestion was highest during winter (0.57 bacteria cell(-1) hour), possibly as a result of the lengthy impaired light climate. (Less)

A year-long survey of Lough Bunny, a karst lake in County Clare, Ireland, was undertaken in 1992-3. Water transparency (as determined by Secchi disc depth), plant nutrients, chlorophyll a concentrations and phytoplankton were examined. High water transparency indicated that the euphotic zone extended over the majority of the lake and may, at times, have reached the deepest parts of the lake. Silicate-silicon and nitrate + nitrite-nitrogen showed marked seasonal changes with lowest values recorded in May 1992 and August 1992 respectively. Molybdate reactive phosphate-phosphorus showed no seasonality in concentration and was often below the limit of detection of the technique used. The maximum value obtained was 3.9tg P04-P dm3. Chlorophyll a concentrations were also low throughout the year, ranging from 0.5pg dm -3 to 2.6gg dm -3, and these also showed no seasonal pattern of change. Cryptophyta were present in all samples and were often the most numerous group in the phytoplankton. Small dinoflagellates occurred throughout the year, with Ceratium species appearing in the summer months. Cyanobacteria were common and most abundant in late autumn. Dinobryon species were found throughout the year but mostly as single thecate cells and only occasionally as large arbuscular colonies. Diatoms were not well represented in the plankton. The Chlorophyta showed greatest diversity of species but were never abundant. Quantitative counts showed cell numbers in all groups to be low, which is reflected in the low chlorophyll a concentrations. On this evidence it is suggested that the lake is oligotrophic. A comparison with two published lists of the lake's plankton was made. There are extensive beds of Charophyta in the lake. A list of species is given. We suggest that utihisation of plant nutrients by the charophytes and benthic diatoms may be responsible for the water clarity and small phytoplankton populations. C. Pybus (corresponding author; email: colin.pybus@gmit.ie)

In four deep karstic lakes (Lake Vransko, Lake Visovacko, Kozjak and Prosce) several functionally well-adapted phytoplankton groups interchange in dominance during the seasonal cycle from April to September and likely tolerate the constraining conditions of nutrients deficiency more successfully as an aggregated group than as taxonomic units. This paper considers the functional approach by Reynolds et al. (2002), a method capturing much of the species ecology and which is successfully used for describing phytoplankton successions. Deep karstic lakes are attributed with the early spring (April) formation of stratification, low phytoplankton biomass, and with maximum biomass accumulating in July. The co-occurrence of functional groups in those lakes is evident but typically distinct according to different biomass proportions. The functional groups A, B, C, D, P, E and LO, represented by different Cyclotella, Ulnaria/Fragilaria, Dinobryon, Ceratium/Peridinium species, co-occurred in 50% and up to 90% of phytoplankton biomass in all investigated lakes. By observing the co- occurrence across the Croatian karstic region we: (i) demonstrate the regional distribution of phytoplankton assemblages in relation to low nutrient environment, and (ii) build a simple uniform pattern which successfully describes a variety of phytoplankton in deep karstic lakes and provides information of reliable indicators for those systems.

Protists in the central Arctic Ocean are adapted to the harsh environmental conditions of its various habitats. During the Polarstern cruise ARK-XXVI/3 in 2011, at one sea-ice station, large aggregates accumulated at the bottom of the melt ponds. In this study, the protist assemblages of the bottom layer of the sea-ice and melt-pond aggregate were investigated using flow cytometry and 454-pyrosequencing. The objective is to provide a first molecular overview of protist biodiversity in these habitats and to consider the overlaps and/or differences in the community compositions. Results of flow cytometry pointed to a cell size distribution that was dominated by 3–10 µm nanoflagellates. The phylogenetic classification of all sequences was conducted at a high taxonomic level, while a selection of abundant (≥1% of total reads) sequences was further classified at a lower level. At a high taxonomic level, both habitats showed very similar community structures, dominated by chrysophytes and chlorophytes. At a lower taxonomic level, dissimilarities in the diversity of both groups were encountered in the abundant biosphere. While sea-ice chlorophytes and chrysophytes were dominated by Chlamydomonas/Chloromonas spp. and Ochromonas spp., the melt-pond aggregate was dominated by Carteria sp., Ochromonas spp. and Dinobryon faciluiferum. We suppose that the similarities in richness and community structure are a consequence of melt-pond freshwater seeping through porous sea ice in late summer. Differences in the abundant biosphere nevertheless indicate that environmental conditions in both habitats vary enough to select for different dominant species. Keywords: 18S rDNA; Arctic Ocean; biodiversity; next-generation sequencing; flow cytometry To access the supplementary material for this article, please see supplementary files in the column to the right (under Article Tools) (Published: 5 November 2014) Citation: Polar Research 2014, 33 , 23466, http://dx.doi.org/10.3402/polar.v33.23466

We studied the occurrence and dynamics of transparent exopolymer particles (TEP) and 4'-6'-diamidino-2-phenylindole (DAPI)-stained microaggregates (MA) and the bacterial colonization of the latter by fluorescence in situ hybridization with rRNA-targeted oligonucleotides in Lake Constance, Germany, from June to December 1996. MA were categorized into the size classes 8 to 20, 20 to 60 and >60 µm. Total abundance of TEP varied between 71 and 2554 ml -1 and that of MA between 310 and 1526 ml -1 with the largest proportion in the size class 8 to 20 µm (140 to 959 ml -1 ). Numbers of TEP and of MA >60 µm, never exceeding 100 ml -1 , decreased with depth and were cor- related to the biomass of total phytoplankton, diatoms, chrysophytes and dinoflagellates. Numbers of the smaller-sized MA did not systematically decrease with depth. Four types of DAPI-stained MA were identified: aggregates composed of bacterial and of cyanobacterial colonies, aggregates fluo- rescing yellow (DAPI yellow particles), and phytoplankton and zooplankton fragments fluorescing faintly blue after DAPI staining. The latter and DAPI yellow particles were most abundant. The majority of MA was densely colonized by bacteria. At least 20% of the DAPI-stainable cells were detected by the Bacteria-specific probe EUB338 and a mean between 44 and 56% of the various types of MA. β-Proteobacteria dominated aggregates composed of remains of diatoms and often also on fragments. On DAPI yellow particles bacteria of this phylogenetic lineage and the Cytophaga/Flavobacteria cluster were equally abundant. γ-Proteobacteria usually constituted only minor proportions except on fragments of Dinobryon spp. and of zooplankton origin on which they constituted up to 62% of the DAPI-stainable cells. α -Proteobacteria were not detected at all. Together, all group-specific probes constituted >95% of the bacteria detected by the EUB338 probe on MA except for bacterial aggregates on which only 59% were detected. The different spatio-tem- poral dynamics of TEP and MA and the bacterial colonization of the latter suggested that TEP and MA > 60 µm were early decomposition products mainly of diatoms and other algae whereas smaller MA were more degraded stages of detrital particulate organic matter.

Deep chlorophyll maxima (DCM) were found in all five Laurentian Great Lakes during August, 1998. Chlorophyll profiles were consistent over large areas in Lakes Superior and Michigan, while distinct inter-site differences were apparent in the other three lakes. Shade adaptation appeared to be primarily responsible for increases in chlorophyll at depth in Lakes Huron and Ontario, while in Lake Superior increases in phytoplankton biovolume were also noted. Deep living phytoplankton populations in the latter lake exhibited improved nutrient status at depth, where concentrations of both soluble phosphorus and silica were higher. Phytoplankton community composition in the DCM differed from that previously reported for the lakes, most notably in the reduced populations of Cyclotella, relative to the epilimnion, seen at most sites. Filamentous chlorophytes were often more abundant at depth, as were certain species of Dinobryon.

Temporal changes in the plankton community and trophic relations between the metazooplankton and its potential prey (bacteria, flagellates, ciliates and algae) were studied following the flooding of a new reservoir (Sep, France). The high dissolved organic matter (DOM) concentrations favoured the development of heterotrophic and mixotrophic organisms, which dominated the unicellular plankton after flooding. The proportion of strictly autotrophic organisms increased with time, reaching 67 % of the biomass of protistan plankton at the end of the study. A small-sized chrysomonade (2-5 μm) accounted for 53 % of the abundance of the heterotrophic nanoflagellates (HNF) throughout the study. The Chrysophyceae, Chrysidalis sp. accounted for 76 % of the mean relative abundance of all pigmented flagellates combined. Some mixotrophic species such as Dinobryon cylindricum and Cryptomonas ovata mainly occurred at the start of the study. The prostomatid ciliate Urotricha furcata, which dominated in terms of numbers immediately after flooding, was later replaced by mixotrophic species, an oligotrichid Pelagohalteria viridis then a peritrichid, Vorticella sp. The rotifers Polyarthra sp., Synchaeta sp. and Hexarthra mira were the first metazooplankton organisms to colonise the pelagic environment. They were replaced in the 3 rd year by Cladocera (Daphnia longispina and Ceriodaphnia quadrangula) and Copepoda, firstly calanoids (Eudiaptomus gracilis) and then cyclopoids (Cyclops vicinus and Acanthocyclops robustus). This study emphasizes the importance of the organisms of the microbial food web in the nutrition of the metazooplankton in the period following the flooding of a newly impounded reservoir.

Three previously undescribed species of the loricate chrysophyte genus Dinobryon (D. brucei K.H. Nicholls sp. nov., D. dillonii K.H. Nicholls sp. nov. and D. praecambrianum K.H. Nicholls sp. nov.) have been found in several lakes and ponds in Ontario, Canada. All possess a lorica morphology distinct from other members of the genus, thus allowing their designation as separate species. Stomatocysts for two of the new species, D. dillonii and D. praecambrianum are described, but the stomatocyst for D. brucei is still unknown, despite the presence of abundant vegetative material in two lakes.

Morphological observations of the siliceous cell coverings of five taxa of Synurophyceae are made based on specimens collected from acidic, seepage lakes situated in either the Ocala National Forest, Florida, U.S.A. or the Cape Cod National Seashore, Massachusetts, U.S.A. All but one of the lakes, Lake Dorr, were clearwater in nature. A new taxon, Mallomonas corymbosa var. poseidonii var. nov., is described based on differences in bristle structure. New morphological features of four additional taxa, Synura echinulata, Mallomonas mangofera f. foveata, M. acaroides var. muskokana, and M. duerrschmidtiae are presented and discussed in relation to their existing taxonomic descriptions. Other taxa of Synurophyceae, Dinobryon spp., Aulacoseira spp., Asterionella ralfsii, and dinofiagellates were common constituents of the phytoplankton from the seven study lakes at the times of collection.

Examination of 17 samples collected by a 20 ?m meshed meshed net in Kongsfjorden, Svalbard, 8–19 July 1988, showed a dominance of dinoflagellates and the chrysophyte Dinobryon Balticum in the surface layers, whereas the diatom and the haptophyte Phaecystis pouchetii abundance increased with depth. The diatom Pseudo-nitzschia granii appeared together with P. pouchetii through the whole water column, and Actinocyclus curvatulus was one of the few diatoms present also in the surface samples. Two samples, from 15 and 50 m, respectively, were cleaned of organic material and mounted in Naphrax for a more critical identification of the diatoms. We were able to group the species according to habitats, especially types of ice. The planktonic Thalassiosira antarctica var. borealis, T. hyalina, T. nordenskioeldii, Bacterosira bathyomphaia, Chaetoceros furcellatus, C. socialis and Fragilariopsis oceanica were present mainly as resting stages representing a post-bloom situation. These species and T. gravida appear early in the season and may have started to grow already under the ice. Fragilariopsis cylindrus and F. oceanica seem to have a closer affinity to ice than Thalassiosira and Chaetoceros spp. although they are common in the plankton. Some Nitzschia species which are usually regarded as typical sea-ice diatoms and have thicker and older ice as the main habitat were present only in small cell numbers in the plankton samples. The last component, evidently introduced from Atlantic water in the Norwegian Sea, consisted of diatoms with a more oceanic distribution, e. g. Fragilariopsis pseudonana and a small form of Thalassiosira bioculata.

The importance of protists as bacterivores in a coastal community and an offshore community of Lake Erie was compared during the summer of 1994. Bacterial density, cell size, and empirical conversion factors for bacterial productivity were highly variable at both sites and greater at the coastal site (P < 0.01). Bacterial productivity at the coastal site was 25-50 times higher than at the offshore site. Bacterivory was estimated in situ by fluorescently labeled native bacteria. Per-cell grazing rate and filtering rate for each taxon were routinely determined. Heterotrophic nanoflagellates (HNAN) were the most important protistan bacterivores at the offshore site, while HNAN and ciliates were similarly dominant bacterivores at the coastal site. Mixotrophic bacterivory was important only at the offshore site where Dinobryon was the dominant bacterivore. Bacterial carbon flux through protists was higher at the coastal site by an order of magnitude. Offshore protists grazed virtually the entire bacterial production, while coastal protists usually grazed less than half of the bacterial production. These results suggest that coastal and offshore sites differed fundamentally in the significance of protists to carbon flux through the microbial loop to higher trophic levels.

The temporal and spatial developments of 15 phytoplankton species widely distributed in European and North American lakes, have been studied by informations in the literature and especially by their behaviour during a 5 years development in the Danish lake Grane Langso. The species were characterized by temporal differences in maximum abundance, the density at the maximum, the number of maxima per year, the length of the vegetative period and the constancy of the annual maximum based on long-term studies. In several cases the phytoplankton species can be characterized by one individual behaviour in one group of lakes, while the same species behaves differently in another group of lakes. The results suggest that several species include two or more types with different tolerances and environmental requirements. Most of the species included are Chrysophytes, mainly species of Uroglena and Dinobryon. A remarkable feature of Grane Langso's Chrysophytes is their predilection to accumulate in the bottom water during the summer. A similar behaviour was not demonstrated by Chrysophytes in other lakes.

SUMMARY 1 Studies carried out in Lake Baikal in late spring (late May-early June) 1991 showed marked differences in the species composition and abundance of phytoplankton in different regions of the lake. The south and north basins were characterized by small forms of algae. The middle basin, Maloe More and the shallow waters of the Selenga had species with large cells including Aulacoseira islandica subsp. helvetica, Dinobryon cylindricum and D. divergens. 2 Areas of high biomass were correlated with shallow waters and river inputs. This was especially apparent in the region of the Selenga delta. The vertical distribution of phytoplankton indicated the non-synchronous start of the spring homothermy throughout the lake. Phytoplankton were concentrated in the upper 100 m layer with subsurface maxima resulting from the sinking of large algae. 3 The concentration of phytoplankton biomass in general at this time characterized the lake as moderately productive.

During the spring clear-water phase of 1993, an enclosure experiment was performed in the mesotrophic Schohsee (Plon, FRG) in order to assess the impact of crustacean zooplankton on the rotifer and phytoplankton community. Among the crustacean plankton, calanoid and cyclopoid cope- pods were abundant, but Daphnia 'longispina' reached the highest densities in this experiment. The colonial rotifer Conochilus unicomis was not affected by crustacean plankton. The two most abundant species, Synchaeta peclinata and Keratella cochlearis, increased exponentially when macrozooplankton had been excluded from the enclosures, but did not increase when crustaceans were present. Birth and death rates of K.cochlearis could be reliably determined in this field experiment, suggesting that this rotifer species was mainly controlled by exploitative competition rather than by mechanical interfer- ence or predation. Daphnia 'longispina' generally grazed selectively on the smaller ciliates and algae, thus depriving the rotifers of their phytoplankton resources. The dominant alga, the chrysophycean Dinobryon, increased, whether crustaceans were present or not, but appeared to be grazed upon to a certain extent despite its considerable cell size and colonial organization.

The vertical distribution of chlorophyll was examined in relation to physical and chemical parameters in oligomesotrophic Lake Samish, Washington state, during the latter half of a growing season. A majority of chlorophyll resided in the metalimnion in late July, with metalimnetic populations dominated by diatoms (Cydotella bodanica) and chrysophytes (Mallomonas caudata, Dinobryon scrtularia). A silica gradient appeared to be most important in determining the vertical position of these populations. Later in the season, segregation of nutrients and light, in the face of a deepening epilimnion, led to transient accumulations of phytoplankton at the top of the metalimnion. It appeared that losses due to heterotrophic activities accentuated the lower boundary of this chlorophyll peak.

The marine chrysophyte Dinobryon balticum (Schzutt) Lemm. was one of the dominant members of the phytoplankton community (1.8×103 cells-L−1) in June and July in Conception Bay, Newfoundland. Dinobryon balticum colonies were common only in samples from June and July. The cells were concentrated at 5 m (X±SD=1.11±4 × 105 cells.L−1) and at 40 m (3.32±2×104.L−1) depths. Colonies were composed of up to 560 cells with a mean (±SD) colony size of 10 ± 1 cells at 5 m and 40 ± 8 cells at 40 m. Fluorescent latex bead-uptake experiments conducted with field samples indicated that this marine species was capable of phagotrophy and that twice as many Dinobryon cells were ingesting beads at 40 m than at 5 m, although the ingestion rates for those cells actively ingesting beads were similar at both depths. This chrysophyte was found in association with bacteria-and nutrient-rich microhabitats of microaggregates and fecal pellets. The cells and colonies observed in this study appeared to be healthy, as demonstrated by their appearance and their ability to ingest beads.

The dynamics of chrysophyte populations and the onset of encystment in relation to several physical, chemical, and biological variables were studied in two Canadian lakes, Lake Opinicon (LO) and Upper Rock Lake (URL). LO is shallow and polymictic during the ice-free season, whereas URL is deep and dimictic. Seasonal patterns of many limnological variables, as well as species composition and seasonal dynamics of chrysophyte assemblages, were broadly similar in both lakes. Three groups of chrysophytes were recognized: 1) taxa that were more abundant during ice cover and/or early spring and occasionally in late fall (Dinobryon spp. Ehrenberg and Synura spinosa Korsh), 2) taxa that seemed to prefer moderately warm water proglena americana Calkins and Ochromonas sp. Wyssotzki) and had maximum densities in late summer and occasionally in the fall, and 3) taxa that occurred in low numbers and did not exhibit any discernible seasonality in the two lakes (Mallomonas spp. Perty). Encystment rarely occurred during ice cover in both lakes. Stomatocyst concentrations were highest shortly after ice breakup (late April or early May), declined to trace levels by June, and remained at those levels until the end of the sampling season (late November). Encystment rates (cyst concentrations) were higher in dimictic URL. Encystment in both lakes coincided with concurrent changes in physical and chemical variables and chrysophyte vegetative cell densities, but it was not possible to pinpoint the exact conditions responsible for triggering encystment. Only a small proportion of chrysophytes encysted. Cyst production within a lake may vary from year to year.

Particle uptake by two strains of the freshwater phytoflagellate Dinobryon was studied using cells grown in clonal batch cultures and presented with fluorescent microspheres. Clearance rates were found to be strongly dependent on temperature, with maximum clearance rate observed at around 20°C. Clearance rate over the diurnal light dark cycle was observed to be slightly higher during the dark phase. Cultures quickly died when placed in total darkness. cells of one strain grown for two weeks under dim irradiance (18 μEm -2 s -1 ) showed reduced clearance rates. For the other strain no relation was observed between clearance rate and irradiance

Developmental and seasonal changes in the preferred prey and the diet composition of the invertebrate predator Chaoborus punctipennis were determined in Plastic Lake, an acidified (pH 5.6) lake in south-central Ontario, Canada. All instars consumed rotifers (mainly Keratella cochlearis, Ploesoma sp., and Asplanchna priodonta), and instars III and IV fed preferentially on crustaceans (mainly bosminids and copepods). Phytoflagellates (Peridinium sp. and Dinobryon sp.), however, numerically dominated the diet of all instars examined (II–IV), and were consumed by instar II larvae in excess of their relative availability. On 40 and 20% of the sampling dates, instars III and IV, respectively, consumed phytoflagellates in accordance with their relative abundance in the lake. Although the contribution of phytoflagellates to the biomass-based diet of C. punctipennis was low, on one occasion phytoflagellates formed almost half of the diet biomass of instar II larvae. A review of the literature shows that in lakes where phytoflagellate densities are high (≥ 100–200/mL), phytoflagellates contribute ≥ 50% of the diet biomass of all instars of Chaoborus spp. These findings indicate that Chaoborus spp. are omnivores that frequently feed on phytoflagellates even when alternative animal prey are abundant. Consumption of phagotrophic phytoflagellates by Chaoborus spp. and other large invertebrate omnivores, such as Mysis spp., Epischura spp., and cyclopoid copepods, may increase the transfer efficiency of organic carbon from the microbial food web to the upper trophic levels in fresh waters. In acidified lakes, consumption of large dinoflagellates by Chaoborus spp. and other invertebrate omnivores may ameliorate the hypothesized bottleneck impeding the flow of carbon between phytoplankton and zooplankton.

Following the U.S. Environmental Protection Agency's specifications for pesticide registration tests, 12 experimental ponds were constructed. Colonization and succession of the pond phytoplankton communities were investigated during the first year after filling. Taxon richness and densities and biomass as chlorophyll-a were measured. In addition, water-quality data were collected and analyzed. The dominant taxonomic groups were the Cyanophyceae, Chlorophyceae (with Desmidiaceae dominating), Dinobryon (in the Chrysophyceae), Dinophyceae, and Bacillariophyceae. Similar successional patterns in all 12 ponds occurred; however, the community structure between ponds was not similar at any time. Although the ponds had statistically similar environmental characteristics, they varied in their community structure, indicating that after one year they were not mature enough for use as replicate test systems. The heterogeneity of the pond phytoplankton communities indicates that meso-cosms need to be managed to produce replicate experimental units.

Microfossils are described from Upper Cretaceous amber from Tishomingo County, Mississippi, the first fossils from this amber. They include the oldest fossil record of the chrysomonad Dinobryon and two new actinomycetes, Streptosporangiopsis russelli and Paleomonospora tishomingoensis, the earliest certain fossil representatives of the Streptosporangiaceae and Micromonosporaceae, respectively. Fungal spores and hyphae of uncertain affinities are also reported. The paleoenvironment of these fossils seems to have been aquatic or semi-aquatic. The description of these microfossils is used as a base to establish of these fossils seems to have been aquatic or semi-aquatic. The description of these microfossils is used as a base to establish principles for distinguishing true microfossils from pseudofossils in amber: true microfossils should be completely enclosed inside the amber matrix and should be comparable to living analogues, as far as can be observed, in size and cellular structure.

In enclosure and whole-lake experiments, I tested whether life-form shift (recruitment) is a passive process induced by turbulence, a seasonal phenomenon, or a behavior that can be induced by alterations in environmental variables. The number of algal cells recruited from the sediment varied considerably during the experimental period. The most important migrating genera in this study were: Cryptomonas, Dinobryon, Gonyostomum, Gymnodinium, Peridinium, and Synura. An obvious conclusion is that it is not the same factor in each case that causes life-form shift, but that different triggering factors operate in different algal species. Turbulence and temperature were similar in all treatments and therefore did not cause the considerable fluctuations and trends in algal recruitment in the enclosures. This suggests that life0form shift is not a passive process driven by wind and temperature-induced currents. In the enclosure experiment, alterations in the light régime explained a major part (up to 53%) of the variation in recruitment for most genera. For Gymnodinium this was corroborated in the whole-lake experiment, where the depth of the euphotic zone explained 41% of the variation in recruitment. For Cryptomonas, however, 64% of the variation in recruitment was explained by the depth of the "oxycline", whereas 52% of the variation in recruitment of Synura were explained by the depths of the euphotic zone and the oxyline. Peridinium pusillum and P. wisconsinense showed low recruitment at high zooplankton abundance and high recruitment at low zoo-plankton abundance in the lake experiment, as well as in the enclosure experiment. Thus, the hypothesis that the presence of grazers can induce shifts in behaviour of some algal groups cannot be rejected.

This study compares the composition and dynamics of phytoplankton communities and of periphyton communities growing on Plexiglas slides in a temperate oligotrophic lake. Ordination methods were used in the comparisons, which covered a three-month period during the summer. Plankton and periphyton communities differed considerably, and shared only six common taxa. An ephemeral Dinobryon pulse occurred simultaneously in both communities, and represented the largest source of variability in community composition. Recovery from the pulse was faster in the phytoplankton than in the periphyton. Attachment to substrata, through its effect on cell turnover times and nutrient cycling, is hypothesized to provide a temporal refuge for plankton species during periods of unfavorable environmental conditions.

6 pages, 3 figures, 2 tables, We report the presence and abundance of Dinobryon faculiferum (Chrysophyta) in NW Mediterranean coastal waters, as well as the first estimations of the grazing impact of this mixotrophic species on bacteria. In June 2006, D. faculiferum was detected at an abundance of 37 cell mL–1 (1.2% of total protistan abundance). By grazing with cell-specific rates of 7.8 bacteria cell h–1, this single species explained 4.5% of the total bacterial grazing losses, This study was supported by the ESTRAMAR (CTM2004-12631/MAR) and PROBA (CSIC-CONICET Programa "Luis Santaló") projects of R.M. Work of J.M.G. was supported by projects SUMMER (CTM2008-03309/MAR) and STORM (CTM2009-09 352/MAR) from Spanish MCy

Planktivorous fish can affect phytoplankton indirectly by control of herbivore communities, and directly by excretion of soluble nutrients. A field mesocosm study showed that nutrient regeneration by sockeye salmon (Oncorhynchus nerka) fry substantially increased biomass of zooplankton and phytoplankton relative to fishless controls. Plankton communities in enclosures treated with only fish-regenerated nutrients but not fish predation responded differently to two densities of fish. Enclosures with low fish densities exhibited significant increases in zooplankton biomass and small increases in phytoplankton biomass. Nutrients resulting from high fish densities stimulated blooms of ungrazable Dinobryon, and extremely low zooplankton biomass when compared with fishless controls. Phosphorus excretion rates by zooplankton and fish explained 55% of the variance in total plankton biomass in predation-free enclosures and 95% of the variance in chlorophyll a concentrations for enclosures with predators and fish-regenerated nutrients. The results of this experiment suggest that algal production is greatly enhanced by excretion of nutrients by fish, while grazer control is less important.

Samples of surface plankton in Lake Nojiri were collected monthly from July 1988 to October 1991.In zooplankton 26 species were found and 25 species in phytoplankton. The seasonal succession of main species was as follows.Bosmina longirostrisobserved through the year, but dicreased in winter.Diaphanosoma brachyrum, Bosminopsis deitersi, Daphnia galeata, Eodiaptomus japonicusandPolyphemus pediculus appearedfrom summer to autamn, andThermocyclops hyalinusfrom spring to summer. On the other hand, Kellicottia longispina, Polyarthra vulgarisand Keratella quadratawere found from winter to spring.Ceratium hirundinella, Melosira italics, Cyclotella comtaandFragilaria crotonensiswere obsreved through the year.Asterionella formosaappeared three season except in autumnThe prevalent species wereKeratella quadratain autumn, Ceratium hirundinellafrom spring to autumn, Dinobryon cylindricumin spring, Fragilaria crotonensisfrom autumn to early winter, Melosira italicaandAsterionella formosain winter.In this Lake, Uroglenainduced a fresh water red tide from June to July in 1989. but never appeared again.Uroglena americanaobserved twice in a year from the middle of spring to the middle of summer and from the middle of autumn to winter.

The seasonal dynamics of the small eukaryotic fraction (cell diameter, 0.2 to 5 μm) was investigated in a mesotrophic lake by tyramide signal amplification-fluorescence in situ hybridization targeting seven different phylogenetic groups: Chlorophyceae, Chrysophyceae, Cryptophyceae, Cercozoa, LKM11, Perkinsozoa (two clades), and Fungi. The abundance of small eukaryotes ranged from 1,692 to 10,782 cells ml −1 . The dominant groups were the Chrysophyceae and the Chlorophyceae, which represented 19.6% and 17.9% of small eukaryotes, respectively. The results also confirmed the quantitative importance of putative parasites, Fungi and Perkinsozoa, in the small heterotrophic eukaryotic assemblage. The relative abundances recorded for the Perkinsozoa group reached as much as 31.6% of total targeted eukaryotes during the summer. The dynamics of Perkinsozoa clade 1 coincided with abundance variations in Peridinium and Ceratium spp. (Dinoflagellates), while the dynamics of Perkinsozoa clade 2 was linked to the presence of Dinobryon spp. (Chrysophyceae). Fungi, represented by chytrids, reached maximal abundance in December (569 cells ml −1 ) and were mainly correlated with the dynamics of diatoms, especially Melosira varians . A further new finding of this study is the recurrent presence of Cercozoa (6.2%) and LKM11 (4.5%) cells. This quantitative approach based on newly designed probes offers a promising means of in-depth analysis of microbial food webs in lakes, especially by revealing the phylogenetic composition of the small heterotrophic flagellate assemblage, for which an important fraction of cells are generally unidentified by classical microscopy (on average, 96.8% of the small heterotrophic flagellates were identified by the specific probes we used in this study).

We documented permanent presence of heterotrophic filaments in three acidified lakes (pH5) in the Bohemian Forest. Due to acidification, crustacean zooplankton were absent in all but one lake. In terms of carbon flow, microorganisms were thus almost exclusive players in the pelagic food webs. Variety of extremely long (100 microm) heterotrophic filaments occurred in the lakes. The filaments usually accounted for50% of total heterotrophic microbial biomass in the pelagic zone (medians of the total biomass: 82-108 microg C l(-1)), except for anoxic bottom layers and for episodic appearance of Daphnia longispina in one lake. Seasonal filament formation was mainly induced and maintained by grazing of mixotrophic flagellates (Dinobryon spp.) on small unicellular bacteria in the absence of cladoceran filtration. The filaments were less active than unicellular suspended bacteria. Fluorescence in situ hybridisation revealed that usually50% of total bacteria were targeted with oligonucleotide probes for Eubacteria.

Mixotrophic organisms utilize both photosynthetic and phagotrophic nutritional modes and are increasingly recognized as important contributors to aquatic food webs. Dinobryon, a widespread freshwater genus of mixotrophs had dramatic seasonal and annual variation in Lake Lacawac, a mesotrophic kettle lake in northeastern Pennsylvania. Although light is required for population growth in Dinobryon, it does not appear to control vertical distribution patterns observed during a 3-year survey. One year, the maximum annual abundance was observed close to the surface, while the following year the maximum annual abundance occurred at 4 m depth where light levels were

The colonial algae Phaeocystis pouchetii and Dinobryon pellucidum dominated the phytoplankton crop at three stations in the Polar Front area of the Barents Sea. Lipid extracted from the seawater containing the phytoplankton was dominated by neutral lipid classes, particularly triacylglycerols, and phospholipids were more abundant than galactolipids at all stations. Polyunsaturated fatty acids comprised between 15 and 26% of fatty acids of total lipid. Of the carbon assimilated into lipid over 24 hours, 40% was located in the neutral lipid fraction. Phospholipids contained a smaller proportion of fixed carbon than galactolipids. No defiinte relationships were observed between the distribution of fixed carbon in photosynthetic end products and the temperature or irradiance at which the phytoplankton was incubated. At a constant irradiance of 8.5 ?mol m?2s?1, the highest proportion of fixed carbon was recovered in protein at 4.5°C, but at ?1.5°C most radioactivity was present in low molecular weight compounds. Regardless of incubation conditions, lipid always contained less than 30% of total assimilated carbon.

An enclosure experiment was conducted to assess the effects of a zooplankton elimination on the structure of a phytoplankton community. Phytoplankton biomass and production were higher in grazer-free enclosures, while the productivity per unit biovolume was lower. Exclusion of zooplankton favoured the majority of algal species, especially chrysophyceans (Dinobryon spp.) and the diatom Rhizosolenia, while mucilagineous green-algae were disfavoured. Middle sized algae (ESD 15–50 µm) and those with the largest Surface Area/Volume ratio were proportionally most favoured by the elimination of grazers.

Accumulation of heavy metals (Cd, Pb, Hg, Cr) in water and plankton of Sarýyar Dam Lake (SDR) was seasonally studied from April, 2000 to December, 2004. In addition, seasonal changes in phytoplankton and zooplankton populations and species abundance were also determinate. Some physio-chemical parameters of water and their correlation with heavy metals were also determinated. The dominant phytoplanktonic algae determined were Choroococcus, Gomphospheria, Oscillatoria, Phormidium, Anabaena, Nostoc, Cystodinium, Dinobryon, Ankistrodesmus, Chlorella, Coelastrum, Oocystis, Pediastrum, Scenedesmus, Cosmarium, Oedogonium, Cyclotella, Achnanthes, Amphora, Anomoneis, Cocconeis, Cymbella, Diatoma, Diploneis, Fragilaria, Gomphonema, Navicula, Nitzschia, Nitzschia, Rhoicosphenia, Surirella and Synedra. The dominant zooplanktonic organisms determined were Asplachna priodonta, Brachionus angularis, Keratella quadrata, Keratella cochlearis, Keratella tropica, Polyarthra vulgaris, Proales decipiens, Bosmina longirostris, Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia longispina, Diaphanosoma brachyurum, Macrothrix laticornis, Acanthocyclops robustus and Acanthodiaptomus denticornis. High concentrations of all heavy metals were recorded in the plankton. Hg was lowest and Pb highest; but the concentration of each metal varied seasonally.

In situ microcosms of a winter plankton community were exposed for 21 d to 0 0, 0 1, 0 5 and 1 0 mg/L of the herbicide simazine, approximating persistent levels found after application in other systems Physical-chemical parameters, phytoplankton, bacteria and zooplankton were quantified Simazine induced decreases in dissolved oxygen and pH, but induced increases in nitrate and am monia levels compared to control microcosms Phytoplankton were differentially affected by simazine Sensitive taxa included Trachelomonas, Glenodinium and diatoms Others, such as Dinobryon and small coccoids, were not significantly affected Bacteria data were variable and did not exhibit changes related to phytoplankton densities or simazine Rotifers dominated the zooplankton and were also differentially affected by simazine The dominant species, Kellicottia bostomensis, exhibited a positive response to simazine, as did Keratella cochlearis, due to lesser mortality in higher concentrations of simazine Polyarthra vulgaris was unaffected, but Synchaeta pectinata was impaired by simazine at day 21 Zooplankton (primarily rotifers) may have fed on heterotrophic cells more than on autotrophic cells, and may have been more closely associated with the detrital food chain than the autotrophic food chain

Seasonal fluctuation of phytoplankton with special reference to chrysophytes was studied in four ponds and lakes, Doro - ike, Hoshino - ike, Sengari Reservoir and Yasuba- ike, which are situated in the southern part of Hyogo Prefecture, Japan, and are in different stages of eutrophication. The chrysophytes increased in cell number from autumn to spring. The maximum density of the chrysophytes was recorded in March in all the ponds and lakes ; 5, 900 cells·ml-1 in Doro-ike Pond, 13, 000 cells·ml-1in Hoshino - ike Pond, 190 cells·ml-1 in Sengari Reservoir and 6, 900 cells·ml-1 in Yasuba- ike Pond. The chrysophytes were an abundant algal group in the low temperature period and Mallomonas akrokomos, Synura mammillosa, Chrysococcus rufescens and Dinobryon sociale were dominant in the freezing time. Many chrysophyte species occurred not only in oligotrophic waters but also in eutrophic ones, and the number of species increased with eutrophication. The chrysophytes appeared all the year round in oligotrophic waters, whereas, in eutrophic waters, they appeared in the low temperature period with higher density than in oligotrophic waters. But in heavily polluted waters where water blooms of the cyanophytes occurred, the number of species and the density were very low. Based on these, the chrysophytes are regarded as representatives of eutrophic waters as well as of oligotrophic ones.

We isolated 28 strains of 'Spumella-like' flagellates from different freshwater and soil habitats in Austria, People's Republic of China, Nepal, New Zealand, Uganda, Kenya, Tanzania and Hawaii by use of a modified filtration-acclimatization method. 'Spumella-like' flagellates were found in all of the samples and were often among the dominant bacterivorous flagellates in the respective environments. The small subunit ribosomal RNA (SSU rRNA) gene sequence of the isolates was determined and aligned with previously published sequences of members belonging to the Chrysophyceae sensu stricto. Phylogenetic analysis of the 28 new sequences confirmed their position within the Chrysophyceae sensu stricto and positioned them within different clades. Most of the sequences grouped within clade C and formed several subclusters separated from each other by green taxa including flagellates belonging to Ochromonas, Dinobryon, Poterioochromonas and others. All soil isolates clustered together (subcluster C1) with the soil strain Spumella elongata and the undescribed soil strain 'Spumella danica'. Aquatic isolates were affiliated with at least two branches (C2 and C3). Sequence similarity to the closest related member of the Chrysophyceae ranged between 92% and 99.6%, sequence divergence among the 'Spumella-like' flagellates was as high as 10%. We conclude that (i) the 'Spumella-like' flagellates are a diverse group both in terms of sequence dissimilarity between isolates and in terms of the number of genotypes, (ii) Spumella and Ochromonas are polyphyletic, and (iii) based on the SSU rRNA gene no biogeographical restriction of certain branches could be observed even though different ecotypes may be represented by the same genotype.

Quantitative samples were collected from Lake Atnsjoen five times per year in the growth seasons 1990-2000. The samples were analysed for variation in the phytoplankton composition, and the total volume and volume of the main groups of algae were calculated. Lake Atnsjoen is a large, deep and unregulated lake with a surface area of 4.8 km2 and a maximum depth of 80.2 m. It is a nutrient-poor, oligotrophic lake with a maximum phytoplankton volume varying between 125-393 mm3/m3 in the years 1990-2000. The phytoplankton community is dominated by species of the groups Chrysophyceae and Cryptophyceae. The chrysophytes dominate the phytoplankton in the early part of the growth season (May—June) while the cryptophytes increase throughout the season and dominate in the autumn. Among the chrysophytes different species of chrysomonads were most frequent together with common species of the genus Dinobryon like D. borgei, D. cylindricum var. alpinum and D. crenulatum. A total of 22 species or taxa of chrysophytes were recorded in the samples. Common among the cryptomonads were several species of the genus Cryptomonas. Most important quantitatively, however, were Rhodomonas lacustris and Katablepharis ovalis. The succesion of the phytoplankton throughout the growth season was similar from year to year in quantitative as well as qualitative terms, but some changes were recorded after the great flood in 1995. Canonical Correspondence Analysis (CCA) shows a slight, but significant, phytoplankton community change over the succeeding years.

Seasonal variations in plankton community response to pentachlorophenol (PCP) were studied in four mesocosm experiments using enclosures in a small lake. The mesocosms (860 l) were dosed with single applications of technical grade PCP (0, 4, 10, 24, 36, 54, 81 and 121 microg/l PCP) and monitored for 20 days. Multivariate statistical analyses showed that plankton community taxonomic composition varied with season. In winter and spring, communities were most stable in time; species diversity and abundance were lowest in winter. Seasonally, the communities varied little with respect to the dominant species, which were the copepod Calamoecia lucasi, the alga Peridinium sp. and the rotifer Ascomorpha ovalis. The direct effects of the PCP additions varied little between seasons, but indirect effects were evident at lower treatment levels in autumn. Indirect effects were not evident in winter. Minor variations in plankton community responses to PCP with season were apparent in the following order of decreasing sensitivity; autumnor = winter/springor = summer. At the species level, C. lucasi showed the largest response. The responses observed were greatest in autumn, with decreased abundance at PCP concentrationsor = 24 microg/l. In the other seasons, effects were observed at levels of 54 or 81 microg/l and higher. Ascomorpha ovalis was the most responding rotifer in winter and spring, whereas Anuraeopsis fissa responded more strongly in autumn and summer. The dinoflagellate alga Peridinium sp. had the largest negative response in all but winter, when Dinobryon cylindricum did. Cryptomonas sp. responded positively to PCP in all seasons, increasing in abundance in the highest treatments, possibly due to reduced grazing pressure, reduced competition, or increased decomposition. The plankton community no-observed effect-concentration (NOEC) was 24-36 microg/l PCP. Results reported here suggest that the Australian and New Zealand water quality guideline values for PCP are sufficient to protect plankton communities against adverse effects.