Centric diatoms (Centrophyceae,Bacillariophyta) in watercourses and bodies of water in southeast of West Siberian Plain and Polar Ural

The study of phytoplankton from rivers and lakes in the southeastern part of the West Siberian Plain and the eastern macrosclope of the Polar Ural by scanning electron microscopy has revealed 25 taxa of Bacillariophyta from the class Centrophyceae (seven Aulacoseira, one Cyclostephanos, four Cyclotella, two Discostella, one Melosira, one Puncticulata, seven Stephanodiscus, and two Thalassiosira), including new species for the flora of the investigated bodies of water. The revision of the species composition of Centrophyceae in bodies of water and watercourses in the southeast part of the West Siberian Plain has allowed more exact identifying the taxonomic spectrum of this class. At present, the list includes 55 species, varieties and forms. During first studies conducted in rivers and lakes of the Lyapin River basin (Polar Ural) 16 species of centric diatoms that belong to the genera Aulacoseira, Cyclostephanos, Cyclotella, Discostella, Puncticulata, and Stephanodiscus have been recorded.     

New data on the flora of diatom algae (Centrophyceae) in waterbodies of Sakhalin Island

The first studies of phytoplankton in inland waterbodies of Sakhalin Island by electron microscopy have revealed 19 representatives of the class Centrophyceae, including some that are new for the flora of the region (Aulacoseira subarctica, Coscinodiscopsis commutata, Stephanodiscus delicatus, S. makarovae, Thalassiosira baltica, and T. cf. hyalina). Species of centric diatoms that are new for these waterbodies have been documented in lakes Vavaiskiye and Tunaicha, and the species composition of Centrophyceae have been revised. The first complete data on the taxonomical spectrum of Centrophyceae in Lake Sladkoye, lakes of Mount Spamberg, and the Tym River have been obtained. A revision of the species composition of Centrophyceae in the waterbodies of Sakhalin Island has been made, and the list of the class has been broadened to 44 taxa from 17 genera.     

Centric diatoms (Bacillariophyta,Centrophyceae) in Karelian waterbodies

Materials on phytoplankton from 11 Karelian lakes located in the basins of the White and Baltic seas were studied by scanning electron microscopy; 22 representatives of diatom algae of the class Centrophyceae, including those that are new for the flora of the lakes (Aulacoseira lacustris, A. perglabra, A. tenella, A. valida, Discostella cf. pseudostelligera, S. invisitatus) and new for Karelia (Brevisira arentii, Stephanodiscus delicatus), have been recorded. A revision of the species composition of Centrophyceae in the waterbodies of Karelia has been made. Diagnoses and the systematic status of some species, varieties, and forms have been specified. A new list includes 51 taxa from 12 genera: Acanthoceras (1), Aulacoseira (23), Brevisira (1), Cyclostephanos (1), Cyclotella (7), Discostella (2), Ellerbeckia (2), Melosira (2), Puncticulata (1), Rhizosolenia (3), Stephanodiscus (7), and Thalassiosira (1).     

Subsurface Chlorophyll Maximum and Associated Cyclotella Pulse in Lake Superior

An investigation of the subsurface chlorophyll layer (SCL) in Lake Superior was conducted from 1 May through 15 October. During spring unstratified conditions (1 May–17 July), chlorophyll a and phytoplankton biomass were vertically and temporally uniform. Phytoflagellates such as Rhodomonas minuta, Cryptomonas spp., and Ochromonas spp. were dominant at this time. The photosynthetic maximum was associated with the depth receiving 10% of surface irradiance, ca. 15–25 m. Once thermal stratification occurred, a SCL developed around 20 m. Although epilimnetic chlorophyll concentrations remained similar to spring mixing levels, concentrations in the SCL increased 3-fold. In situ production was the principal process associated with the development of the SCL. The upper portion of the SCL was dominated by Cyclotella species; C. stelligera, C. comensis, and C. ocellata. The increased abundance of Cyclotella appeared to be related to stable irradiance fields produced during thermal stratification.     

Centric diatom algae of volcanic Verkhneavachinsk lakes (Kamchatka)

Eleven representatives of diatom algae of the class Centrophyceae from the genera Aulacoseira (1), Conticribra (1), Cyclotella (5), Discostella (1), Stephanodiscus (2), and Thallasiosira (1) have been found in the phytoplankton of 5 volcanic lakes (Bakening volcano, Kamchatka). Stephanodiscus popovskayae, a species new for science, has been discovered in all the lakes, and a species new for the flora of Russia, Cyclotella gordonensis, has been found only in three lakes. The closest similarity in the composition of centric diatoms has been revealed between the lakes of a single water system: Lake Medvezh’e and Lake Verkhneavachinskoe.     

Algal growth on organic compounds as nitrogen sources

Two experimental series were run to evaluate the potential of algal development on dissolved organic nitrogen (DON) compounds as the sole source of nitrogen (N) nutrition. Monocultures of several common Lake Kinneret algae (Pediastrum duplex, Synechococcus sp., Microcystis aeruginosa, Aphanizomenon ovalisporum and Cyclotella sp.) were incubated for 3 weeks in the laboratory with different inorganic (NH4⁺, NO3^-) or organic (hypoxanthine, urea, guanine, ornithine, glucosamine, lysine) nitrogen sources. Even though the cultures were not axenic, marked differences were observed in algal growth response. Pediastrum, Cyclotella and Aphanizomenon grew well on most N sources, and cyanobacterial growth and yield were consistently greatest when the urea was the only N source. We also followed algal growth and eventual species dominance in batch samples of GF/F-filtered lake water, supplemented with orthophosphate and different inorganic or organic N compounds and inoculated with concentrated lake phytoplankton. Although no clear impact on phytoplankton growth (as chlorophyll concentration) was observed, in seven out of 11 experiments we could discern changes in the algal species that became dominant in flasks with different organic and inorganic N sources. Our results are consistent with the proposition that components of the DON pool are not only an important potential, direct or indirect N source for phytoplankton, but also that different algal species can exploit these sources with varying capabilities so that different N substrates may selectively stimulate the development of dominant algal species.      

The effects of initial population density on the competition for limiting nutrients in two freshwater algae

Eighteen long-term competition experiments were performed on two freshwater algae, a blue-green alga, Anabaena flos-aquae, and a diatom, Cyclotella sp., under controlled light and temperature conditions and various nutrient limitations. As predicted, Anabaena displaced Cyclotella when nitrate was in short supply to both species, whereas Cyclotella became dominant when both species were phosphate-limited. The two species stably coexisted when phosphate and silicate were limited. Anabaena either displaced or coexisted with Cyclotella when nitrate and phosphate or nitrate, phosphate and silicate were limited, depending on their initial density ratios. This study revealed strong effects of initial population densities on the outcomes of algal competition for limiting nutrients.     

Field and Laboratory Studies on Nile Phytoplankton in Egypt IV. Phytoplankton of Aswan High Dam Lake (Lake Nasser)

Seasonal, local and monthly vertical variations in chlorophyll a concentration and in qualitative and quantitative counts in Aswan High Dam Lake (AHDL) phytoplankton were followed from March 1982 to February 1984. The chlorophyll a values correlated more or less with the total phytoplankton counts. Total algal counts exhibited considerable local variations in the different seasons and tended to decrease in the most southern part of AHDL, especially during the flood period. The temporal course of algal development showed an almost inverse trend to that of dissolved nitrate-nitrogen. The possibility of nitrogen limitation of algal growth was verified. Diatoms and blue-green algae alternated in the dominance of the phytoplankton community. The genera Cyclotella and Anabaenopsis respectively were the most predominant genera among the diatoms and blue-greens and consequently in the phytoplankton community.     

Seasonality in river phytoplankton: multivariate analyses of data from the Ohio River and six Kentucky tributaries

Two years of physical/chemical and algal abundance data obtained from national Stream-Quality Accounting Network records of 10 river sites in Kentucky USA (4 Ohio River sites and 6 Ohio River tributaries) were analyzed to determine how seasonal changes in river phytoplankton related to changes in physical and chemical parameters. Phytoplankton assemblages differed among rivers as a function of drainage basin characteristics, but exhibited common seasonal changes related to temporal variation in the physical/chemical environment. Distinct shifts in algal dominance were identified between spring (March, April), late summer (July, August, September), and transitional (May, June, November) periods in the 10 systems. Nine common algal genera were found to differ in their response to changes in physical or chemical parameters. Abundances of Anacystis, Oscillatoria, Scenedesmus, and Melosira were strongly positively correlated with temperature while Chlamydomonas and Navicula abundances were inversely related to temperature. Other physical/chemical factors that were significantly positively ( + ) or negatively ( - ) correlated with algal abundances included discharge and alkalinity (Oscillatoria, +), pH CChlamydomonas and Cyclotella, (both + ), turbidity (Anacystis, \s- ; Navicula + ), silica (Cyclotella, - ), and ammonium/organic N (Anacystis, -). Genera within the same algal division exhibited different seasonal patterns and responded to different physical/chemical parameters.     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.     

Materials on the flora of diatoms (Centrophyceae) from lakes of the Baikal Region and Transbaikalia

The species composition of Centrophyceae (Bacillariophyta) in the phytoplankton of nine lakes in the Baikal Region and Transbaikalia was studied using electron microscopy (SEM) methods. Nineteen species and varieties of Centrophyceae were recorded; Aulacoseira distans var. septentrionalis and Cyclotella arctica were registered in this region for the first time. Aulacoseira baicalensis, Cyclotella minuta, and Stephanodiscus inconspicuus were also found in the studied lakes and attributed to being endemic to Lake Baikal.     

Competitive growth characteristics between Microcystis aeruginosa and Cyclotella sp. accompanying changes in river water inflow and their simulation model

When the water quality in Lake Tega was the worst among Japanese lakes in the 1970s, cyanobacteria (mainly the genus Microcystis) were observed to be the dominant species in the summer. Since 2000, for water quality improvement, a large amount of the Tone River water was discharged into Lake Tega, resulting in an improvement in the water quality together with transition of algal dominant species from cyanobacteria to diatoms (mainly the genus Cyclotella). Although several factors including nutrient concentration and daily renewal rate (d) could have been related to the succession of algal dominant species, these effects have not been understood very well. This study investigated the effects of the daily renewal rate and nitrate‐nitrogen (hereafter nitrogen) concentration (N) on the competition between the cyanobacterium Microcystis aeruginosa and the diatom Cyclotella sp. through monoculture and monoxenic culture experiments. Based on the experimental results, a simulation model was constructed to predict the competitive growth pattern of each species. Monoxenic culture experiments showed that M . aeruginosa outcompeted Cyclotella sp. under conditions of N = 0.5 (1.0 mg‐N L^?1) and d = 5, 15, and 20%. The domination of M . aeruginosa could be attributed to smaller values for the half‐saturation constant and the minimum nitrogen cell quota for this species with respect to Cyclotella sp. However, Cyclotella sp., possessing higher values of nitrogen cell quota and nitrogen uptake rate, dominated by an increasing nitrogen concentration (N = 1.0 mg L^?1) and daily renewal rate (d = 30%). The competitive growth patterns of M . aeruginosa and Cyclotella sp. could roughly be predicted by the simulation model. These results suggested that the daily renewal rate as well as the nitrogen concentration, could affect the competition and be influential factors as to which species dominates between M . aeruginosa and Cyclotella sp.     

Responses of Two Coastal Algae (Skeletonema costatum and Chlorella vulgaris) to Changes in Light and Iron Levels1

Iron (Fe) is essential for phytoplankton growth and photosynthesis, and is proposed to be an important factor regulating algal blooms under replete major nutrients in coastal environments. Here, Skeletonema costatum, a typical red-tide diatom species, and Chlorella vulgaris, a widely distributed Chlorella, were chosen to examine carbon fixation and Fe uptake by coastal algae under dark and light conditions with different Fe levels. The cellular carbon fixation and intracellular Fe uptake were measured via ¹⁴C and ⁵⁵Fe tracer assay, respectively. Cell growth, cell size, and chlorophyll-α concentration were measured to investigate the algal physiological variation in different treatments. Our results showed that cellular Fe uptake proceeds under dark and the uptake rates were comparable to or even higher than those in the light for both algal species. Fe requirements per unit carbon fixation were also higher in the dark resulting in higher Fe: C ratios. During the experimental period, high Fe addition significantly enhanced cellular carbon fixation and Fe uptake. Compared to C. vulgaris, S. costatum was the common dominant bloom species because of its lower Fe demand but higher Fe uptake rate. This study provides some of the first measurements of Fe quotas in coastal phytoplankton cells, and implies that light and Fe concentrations may influence the phytoplankton community succession when blooms occur in coastal ecosystems.     

Roles of dilution rate and nitrogen concentration in competition between the cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and the diatom <Emphasis Type="Italic">Cyclotella</Emphasis> sp. in eutrophic lakes

In Lake Tega, Japan, the shift of dominant algal species was caused as a result of discharging water from the adjacent river into the lake. The transition from cyanobacteria (mainly the genus Microcystis) to diatoms (mainly the genus Cyclotella) resulted in a disappearance of algal blooms. Although some environmental conditions such as flow rate, nutrient concentration, and transparency were changed by the project, the decisive factor for the transition has not been clarified yet. For the effective control of algal blooms by water discharge, this study aimed to elucidate the effects of daily renewal rate and nitrogen concentration on the interspecific competition between Microcystis aeruginosa and Cyclotella sp. Monoculture experiments were conducted to obtain growth characteristics for each species and mixed culture experiments were performed to examine their competitive abilities under various daily renewal rates of the culture medium (15 and 30 %) and nitrate concentrations (71.4, 178, and 357 μM). In addition to prepared medium, Lake Tega water was also used for mixed culture experiments. The results showed that the increase in a daily renewal rate contributed to the dominance of Cyclotella sp., while a nitrate concentration had little influence on the competition. We conclude that algal blooms composed of the genus Microcystis would be controlled by maintaining a daily renewal rate up to 30 % or more, which corresponded to the dilution rate of 0.36 day^?1, under a nitrate concentration of ≤357 μM. The study would include essential information for the management of lakes suffering from frequent occurrences of algal blooms.     

Phytoplankton sterol contents vary with temperature,phosphorus and silicate supply: a study on three freshwater species

The understanding of environmentally induced changes in the biochemical composition of phytoplankton species is of great importance in both physiological studies and ecological food web research. In extensive laboratory experiments we tested the influence of two different temperatures (10°C and 25°C) and a phosphorus supply gradient on the sterol concentrations of the three freshwater phytoplankton species Scenedesmus quadricauda, Cryptomonas ovata and Cyclotella meneghiniana. The diatom C. meneghiniana was additionally exposed to a silicate gradient. In two separate experiments we analysed (1) possible interactive effects of temperature and phosphorus supply and (2) the effect of four phosphorus levels and three silicate levels on algal sterol concentrations. We observed that sterol concentrations were higher at 25°C than at 10°C in S. quadricauda and C. meneghiniana, but were not affected by temperature in C. ovata. Interactive effects of temperature and phosphorus supply on sterol concentrations were found in C. meneghiniana. This presumably was due to the bioconversion of one sterol (24-methylenecholesterol) into another (22-dihydrobrassicasterol). Increasing phosphorus supply resulted in species-specific effects on sterol concentrations, viz. an optimum curve response in S. quadricauda, a saturation curve response in C. meneghiniana and no change in sterol concentration in C. ovata. Effects of silicate supply on the sterols of C. meneghiniana equalled the effects of phosphorus supply. Albeit we did not observe a general trend in the three phytoplankton species tested, we conclude that sterol concentrations of phytoplankton are strongly affected by temperature and nutrient supply. Interactive effects point out the importance of taking into account more than just one environmental factor when assessing the effects of environmentally induced changes on phytoplankton sterol concentrations.     

Molecular genetic divergence of the centric diatom Cyclotella and Discostella (Bacillariophyceae) revealed by nuclear ribosomal DNA comparisons

The centric diatom Cyclotella, including the recently separated Discostella, is commonly present in freshwater and several species are important bio-indicators. Here, we describe molecular characteristics of the nuclear rDNA, spanning 18S to D1/D2 region of the 28S rDNA, of two genera Cyclotella and Discostella, particularly using Korean isolates of C. meneghiniana, Discostella sp. c.f. D. pseudostelligera. Molecular and morphological analyses showed that our isolates had nearly identical genotypes in rDNA and similar morphology as compared to presumably the same species from other geographical areas. Phylogenetic analyses of individual 18S and partial 28S rDNAs of Cyclotella sensu lato showed that all sequences were separated into two clades: one containing Cyclotella, the other Discostella including C. ocellata and C. bodanica. Statistical tests with pairwise genetic distance scores showed that the two genera were significantly different (one-factor ANOVA, p?<?0.01). In addition, divergence in the partial 28S rDNA was significantly high (p?<?0.01) as compared to 18S rDNA. This provides evidence that the two genera, Cyclotella and Discostella, belong to genetically well-separated groups. In addition, 28S rDNAs is a more suitable molecular marker for the discrimination of Cyclotella sensu lato.     

The unicellular freshwater cyanobacterium Synechococcus and mixotrophic flagellates: evidence for a functional association in an oligotrophic, subalpine lake

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 Z_MX (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.     

沉水植物化感作用对西湖湿地浮游植物群落的影响

通过微宇宙实验,在控制光照和营养盐浓度的条件下分别研究了苦草(Vallisneria spiralis)、金鱼藻(Ceratophyllum demersum)和穗花狐尾藻(Myriophyllum spicatum)的化感作用对采集于杭州西湖湖西湿地的藻类密度、叶绿素a浓度、群落结构、多样性指数等的影响。其结果表明,3种沉水植物对微宇宙系统中的藻类都具有明显影响,藻类密度与叶绿素a浓度受到显著抑制,3个草-藻研究系统中藻类群落结构都发生了变化。在实验末期苦草组、金鱼藻组和穗花狐尾藻组中藻类总生物量(以细胞密度计)分别较初始值降低了37.06%、78.37%和83.40%。栅藻对3种沉水植物的化感作用敏感性较弱。藻类生物多样性方面,穗花狐尾藻系统中最高,其次是金鱼藻组,最后是苦草组,其Shannon-Wiener指数(H)分别为2.76、2.06和0.72,穗花狐尾藻组中H的显著高于苦草组(P0.05)。     

Spatial and temporal variation in phytoplankton community structure in a southeastern U.S. reservoir determined by HPLC and light microscopy

Spatial and temporal variation in phytoplankton community structure within a large flood-control reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production. Handling editor: L. Naselli-Flores     

CHANGES IN THE PLANKTONIC DIATOM FLORA OF A LARGE MOUNTAIN LAKE IN RESPONSE TO FERTILIZATION1

Fertilization (phosphorus and nitrogen) of Kootenay Lake, British Columbia, was begun in 1992 in an attempt to increase food resources for declining stocks of kokanee salmon. In 1992 and 1993, significant changes in diatom abundance, species composition, diversity, and morphology of individual species were observed in the fertilized North Arm in comparison to the unfertilized South Arm. Effects of fertilization were most obvious during the spring. During summer stratification, fertilization did not result in significant changes in total abundance, but changes in species composition were observed. In 1993, with continued fertilization of the North Arm, diatom abundance in both spring and summer was significantly higher than at the same sites in 1992. No significant differences were observed in the unfertilized South Arm. Diatom abundance was significantly correlated with dissolved inorganic nitrogen (positive) and dissolved reactive silica (negative). Diatom assemblages in the fertilized North Arm in both the spring and summer of 1993 were dominated by Asterionella formosa and Fragilaria crotonensis, taxa considered mesotrophic. Abundance of the oligotrophic taxa Rhizosolenia eriensis and Cyclotella michiganiana was higher in the South Arm than in the North Arm. Differences in diatom assemblages between the two arms in both years were further summarized by multivariate statistical analyses. Morphological variations in two small Cyclotella species (C. comensis and C. cf. pseudostelligera) were observed between the fertilized and “control” stations. Populations of both species from fertilized stations exhibited stronger silicification with coarser striations and a smaller mean size.