The effect of mercury on the growth rate of Fragilaria crotonensis kitton and Asterionella formosa Hass.

The effects of two mercury salts Hg(NO₃)₂ and HgCl₂ on the growth rate ofFragilaria crotonensis Kitton andAsterionella formosa Hass. were investigated.Fragilaria crotonensis showed total inhibition at 0.1 ppm and a 4 day increase in lag phase along with a 2–4 fold reduction in growth rate at 0.05 ppm.Asterionella formosa showed a gradual increase in lag phase and reduction in growth rate with increasing concentrations of mercury up to 0.25 ppm with total inhibition at 0.5 ppm. Mercury salts in cultures of both species with soil extract additives were significantly less toxic than in totally defined systems. Cultures ofA. formosa deviated from the typical 8–16 celled stellate colony at sublethal concentrations to form large cylindrical stacks composed of 25 to 30 colonies.This study was supported in part by funds provided by the Navajo and Kaiparowits project participants.This study was supported in part by funds provided by the Navajo and Kaiparowits project participants.     

Responses of the planktonic diatom Asterionella formosa Hassall to abiotic environmental factors in a reservoir complex (south-eastern France)

The River Durance and its main tributary, the Verdon, are both highly regulated rivers flowing in south-eastern France. The course of both rivers is interrupted by a series of reservoirs with quite different geographical, morphometric, climatic, hydrodynamic and chemical characteristics. The planktonic diatom Asterionella formosa Hassall, which has undesirable cyclic effects from the water management point of view, was studied in this complex of reservoirs located in the Mediterranean region. The results indicate that only the monomictic calcareous reservoirs show a bimodal pattern of Asterionella formosa abundance. The population dynamics of this algal species was found to depend on both the morphometric features and the hydraulic mode of management (retention time) used at each reservoir, as well as on the physical (temperature, suspended matter) and chemical (nitrogen, silica, calcium) characteristics of the water.     

Resource requirements of four freshwater diatom taxa determined by in situ growth bioassays using natural populations from alpine lakes

We performed a series of in situ batch culture experiments to assess the resource requirements of common diatom taxa in alpine lakes of the central Rocky Mountains of North America. While physiological data are available on the resource requirements of some of these taxa, it is unclear whether intraspecific generalizations can be made across aquatic systems due to the potential development of ecotypes. In these experiments, we used amended lake water for a culture medium and natural diatom populations. Growth kinetics were determined for Asterionella formosa Hassall, Fragilaria crotonensis Kitton, Staurosirella pinnata (Ehr.) Williams and Round and Tetracyclus glans (Ehr.) Mills. Staurosirella pinnata, a historically abundant alpine diatom, had very low N and P requirements. Asterionella formosa and F. crotonensis, generally considered meso- or eutrophic species, exhibited low P requirements if N and Si were in moderate supply. Tetracyclus glans had the highest Si requirement. These experiments reveal that the recent changes in diatom community structure in these alpine lakes may be driven by changes in nutrient supply. We suggest that local diatom taxa and a natural culturing medium should be used to obtain more representative algal physiological data from a particular area.     

GENETIC VARIATION IN ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE): IS IT LINKED TO FREQUENT EPIDEMICS OF HOST‐SPECIFIC PARASITIC FUNGI?1

Understanding of the genetic basis for susceptibility and resistance is still lacking for most aquatic host–parasite systems, for instance, for phytoplankton and their fungal parasites. Fungal parasites can have significant effects on phytoplankton populations, mainly through their ability to decimate algal host populations during epidemics. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) analysis to study levels of genetic variation within a population of the freshwater diatom Asterionella formosa Hassall in relation to parasitism by the obligate, host‐specific, fungal parasite Zygorhizidium planktonicum Canter. The level of genetic variation within the A. formosa population in Lake Maarsseveen, The Netherlands was found to be high despite the presumed absence or very low frequency of sexual reproduction in this species, the limited gene flow, and the severity of parasite attack that would purge the population from susceptible genotypes. RAPD analysis revealed four distinct banding patterns, with 3 of 21 markers (14%) being polymorphic. In AFLP analysis, every single isolate of A. formosa showed a unique banding pattern, and 120 of the 210 AFLP markers (57%) were found to be polymorphic. Furthermore, character compatibility analysis revealed that sexual reproduction may be one of the mechanisms that generates and maintains genetic variation in the A. formosa population in Lake Maarsseveen. The presence of genetic variation in A. formosa was reflected in infection experiments, which showed that genetically different A. formosa strains differed in their susceptibility to various Z. planktonicum strains and that parasite strains differed in their ability to infect particular host strains.     

Studies on the grazing rate of notholca squamula Müller on asterionella formosa hass. at different temperatures

The grazing rate of Notholca squamula on Asterionella formosa has been estimated to be 3.2 cells per female per hour at 6°C and 11.5 cells per female per hour at 10°C.Part of a dissertation for the Degree of Doctor of Philosophy to the Council for National Academic Awards at Paisley College, Scotland, in conjunction with the Institute of Terrestrial Ecology, Edinburgh, Scotland. Supported by Research Training Grant from the Natural Environment Research Council.     

Phytoplankton succession in a Eutrophic lake with special reference to blue-green algal blooms

Summary An investigation of phytoplankton in Astotin Lake was made between mid-May of 1966 and September of 1967 with particular attention to the ice-free seasons. Astotin Lake is a typical, small eutrophic, kettle lake with shallow, landlocked, hard water in the Canadian prairies. High concentrations of nutrients supported heavy blooms of blue-green algae throughout the summer. The spring communities were dominated by Asterionella formosa in 1966 and by Cyclotella meneghiniana in 1967. Oxygen depletion under ice-cover probably explains the failure of an Asterionella formosa population to appear in 1967. Deficiency of silica and a rise in water temperature apparently caused the decline of the spring pulses of diatoms. Relatively high summer water temperature favoured the blue-green algal blooms and resulted in a high concentration of organic matter. The decomposition of dead Anabaena cells played an important part in the development of subsequent waterblooms, i.e., Microcystis aeruginosa and Aphanizomenon flos-aquae. The sequence of waterblooms of those species was closely related to the change in water temperature. A flos-aquae became incompatible with M. aeruginosa when the temperature fluctuated in a wide range. Most of the non-blue green algae apparently were inhibited by these cyanophyte blooms. Great species diversity appeared intermittently between blooms and a few species of the Scenedesmaceae and the Oocystaceae were relatively compatible to these blooms.Part of a thesis submitted to the Department of Botany, University of Alberta, Edmondton, Alberta, in partial fulfillment of the requirements for the M. Sc. degree.     

On the ecology of notholca squamula muller in Loch Leven,Kinross, Scotland

Notholca squamula was rarely found in Loch Leven when the water temperature rose above 10°C. Under favourable temperature conditions its abundance appeared to be closely related to that of Asterionella formosa. In the laboratory the animal was seen to feed on this diatom by breaking open the frustule and ingesting the cell contents.Part of a dissertation for the Degree of Doctor of Philosophy to the Council for National Academic Awards at Paisley College, Scotland, in conjunction with the Institute of Terrestrial Ecology, Edinburgh, Scotland     

Divergent responses of diverse microalgae commonly found in drinking water source water to UV-C treatment

Microalgae pose major problems for drinking water treatment processes either through membrane fouling or through blooming events in source water during the summer months. Disinfection treatments such as chlorination and UV-C treatment of drinking water are designed to remove microorganisms including microalgae and bacteria. In order to treat water efficiently it is critical to understand the effect of UV-C treatment on the viability and vitality of phytoplankton. Moreover, this information can be used to assess the utility of UV-C treatment as a potential pre-treatment option for water clean-up. In this study we tested the population growth of 6 phytoplankton species representing three major taxonomic groups (green algae, diatoms and cyanobacteria), commonly found in freshwater lakes in North America and relevant for water treatment facilities. We exposed these species to UV-C treatment and monitored their post-exposure population growth over a 52–55-day period using a plate-based MPN (most probable number) method. We found the green alga Scenedesmus quadricauda and the cyanobacterium Anabaena flos-aquae to be most tolerant to the treatment, while the cyanobacterium Microcystis aeruginosa and the diatom Asterionella formosa were found to be most sensitive with viability being reduced at comparatively lower doses. No significant delays in growth post treatment (i.e. time lags) were reported within species. Asterionella formosa and Aulacoseira granulata showed the longest time lags of all species, which might be in part correlated with DNA repair mechanisms and other physiological adaptations. This work provides the basis for the assessment of UV-C treatment efficacy on freshwater phytoplankton.

     

Hidden diversity in the freshwater planktonic diatom Asterionella formosa

Many freshwater and marine algal species are described as having cosmopolitan distributions. Whether these widely distributed morphologically similar algae also share a similar gene pool remains often unclear. In the context of island biogeography theory, stronger spatial isolation deemed typical of freshwater lakes should restrict gene flow and lead to higher genetic differentiation among lakes. Using nine microsatellite loci, we investigate the genetic diversity of a widely distributed freshwater planktonic diatom, Asterionella formosa, across different lakes in Switzerland and the Netherlands. We applied a hierarchical spatial sampling design to determine the geographical scale at which populations are structured. A subset of the isolates was additionally analysed using amplified fragment length polymorphism (AFLP) markers. Our results revealed complex and unexpected population structure in A. formosa with evidence for both restricted and moderate to high gene flow at the same time. Different genetic markers (microsatellites and AFLPs) analysed with a variety of multivariate methods consistently revealed that genetic differentiation within lakes was much stronger than among lakes, indicating the presence of cryptic species within A. formosa. We conclude that the hidden diversity found in this study is expected to have implications for the further use of A. formosa in biogeographical, conservation and ecological studies. Further research using species‐level phylogenetic markers is necessary to place the observed differentiation in an evolutionary context of speciation.     

PHOSPHATE AND SILICATE GROWTH AND UPTAKE KINETICS OF THE DIATOMS ASTERIONELLA FORMOSA AND CYCLOTELLA MENEGHINIANA IN BATCH AND SEMICONTINUOUS CULTURE1

Information on the nutrient kinetics of Asterionella formosa Hass. and Cyclotella meneghiniana Kutz. under either phosphate or silicate limitation was obtained for use in a Monod model and in a variable internal stores model of growth. Short-term batch culture growth experiments were fit to the Monod model and long-term semicontinuous culture experiments and short-term uptake experiments were fit to the variable internal stores model. Mathematical analysis indicates that the parameters of the 2 models may be expressed in terms of each other at steady state. The qualitative results of both batch and steady state culture methods agree. For limiting phosphate experiments. A. formosa is better able to grow at low PO₄-P concentrations than C. meneghiniana, as shown by its lower K for PO₄-P limited growth. The k_Q of A. formosa compared to C. meneghiniana found in long-term semicontinuous culture indicates that A. formosa is almost an order of magnitude more efficient at using internal phosphate for growth. The qualitative results under silicate-limited growth of C. meneghiniana is less than that of A. formosa. The k_Q from semicontinuous culture experiments indicates that C. meneghiniana is the more efficient at using internal silicate for growth. Nutrient uptake experiments showed more variability from a Michaelis-Menten relationship than short-term growth experiments. There were no significant differences between the 2 species in half saturation constants for either phosphate or silicate uptake. We observed a marked dependence of the coefficient of luxury consumption (R) of phosphate on the steady state growth rate. A. formosa has a higher R than C. meneghiniana.     

Automated Pattern Recognition of Phytoplankton – Procedure and Results

Pictures of phytoplankton samples were analyzed as raster images by means of a television camera and a Robotron 4200 computer. A feature vector described the objects irrespective of their angle. Each of the five genera involved were identifiable by a characteristic point cluster in a p-dimensional feature space. A learning method was used during development of the classification structure, and the quality of identification was increased incrementally to the greatest possible degree. Asterionella formosa was identified in all cases without error despite the relatively coarse scanning grid. Errors in the identification of Fragilaria crotonensis can be reduced by improving the resolution (over 100 picture elements per colony).     

THE RELATIVE PHOTOSYNTHETIC EFFICIENCY OF ASTERIONELLA FORMOSA HASS. (BACILLARIOPHYTA) IN NATURAL PLANKTON ASSEMBLAGES1

The relative photosynthetic efficiencies of net vs. nanoplankton and diatom vs. non-diatom plankton were estimated weekly in Woodcock Creek Reservoir, Pennsylvania, from April to November 1979, using carbon-14 in conjunction with size fractionation and germanium as a diatom inhibitor. The nanoplankton contributed a proportionally greater share of the community carbon assimilation than their share of the community biomass would indicate. Diatoms, specifically Asterionella formosa Hass. were photosynthetically inefficient and contributed significantly less than expected. The mechanism of periodic diatom dominance in lakes remains unexplained.     

Variability in sinking rate of the freshwater diatom Asterionella formosa Hass.: The influence of the excess density of colonies

Changes in the densities of live and killed colonies of Asterionella formosa Hass. from both exponentially increasing and stationary phase cultures, were investigated in relation to variation in cell size and mean sinking rates. The small variations in apparent excess colony density (range: 152–254 kg m^-3) between exponential and senescent cells could not alone account for the two- to six-fold observed differences in sinking rate. Neither the sinking rate nor the density were greatly affected by the diminution in cell size brought about by frequent subculturing.     

Studies on Gull Lake, Michigan

The seasonal and depth distribution of phytoplankton in Gull Lake, a moderately large, temperate, dimictic, recreational lake in southern Michigan, U.S.A., is described and discussed. Diatoms (Fragilaria crotonensis, Cyclotella michiganiana, Asterionella formosa, and Synechococcus) grow mainly in summer. Diatoms grew under the winter ice, and objections are lodged to the classic explanation of seasonal growth in temperate lakes, and to a recent hypothesis concerning the `paradox of the plankton'. Two raphe-bearing large diatom species were considered to be truly planktonic. A Synechococcus species was similar to that described previously only from Loch Leven.     

Evidence of interference of Asterionella formosa with the feeding of Bosmina longirostris: a field study in a south Andes lake

Intensive sampling of a small temperate lake of the Araucanian region (Argentina), revealed changes in the demography of Bosmina longirostris when the diatom Asterionella formosa density increased (to 54 000 cells ml^–1). Bosmina population behaviour in the field was consistent with the idea that large numbers of Asterionella caused its starvation. Individuals were actually colourless and fecundity dropped to zero, as was evident when Asterionella reached 99.4% of total phytoplankton biovolume. Since cyanophytes, as a whole, are scarce in these lakes, we propose that the flagellate/diatom ratio has a direct effect on cladoceran demography.     

Regulation of phosphoribulokinase and glyceraldehyde 3‐phosphate dehydrogenase in a freshwater diatom,Asterionella formosa1

The regulation of phosphoribulokinase (PRK) and glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) was investigated in a freshwater pennate diatom, Asterionella formosa Hassall, and compared to the well‐studied chlorophyte Chlamydomonas reinhardtii P. A. Dang. As has been reported for a marine centric diatom, in A. formosa, PRK was not regulated by reduction with dithiothreitol (DTT) apart from a weak induction in the presence of NADPH and DTT. However, NADPH‐GAPDH was strongly activated when reduced, in contrast to a previous report on a diatom. Surprisingly, it was inhibited by NADPH, unlike in C. reinhardtii, while NADH‐GAPDH was not affected. NADH‐GAPDH was also strongly activated by DTT in contrast to most other photosynthetic cells. In A. formosa, unlike C. reinhardtii, 1,3‐bisphosphoglycerate, the substrate of GAPDH, activated this enzyme, even in the absence of DTT, when using both NADH and NADPH as cofactors. Some of these kinetic behaviors are consistent with regulation by protein–protein interactions involving CP12, a small protein that links PRK and GAPDH in cyanobacteria, green algae, and higher plants. This conclusion was supported by immunodetection of CP12 in crude extracts of A. formosa, using antibodies raised against CP12 from C. reinhardtii. This is the first report of the existence of CP12 in a diatom, but CP12 may be a common feature of diatoms since a bioinformatic search suggested that it was also present in the Thalassiosira pseudonana Hasle et Heimdal genome v3.0. Despite the presence of CP12, this work provides further support for the differential regulation of Calvin cycle enzymes in diatoms compared to green algae.     

Parasitic chytrids could promote copepod survival by mediating material transfer from inedible diatoms

Diatoms form large spring blooms in lakes and oceans, providing fuel for higher trophic levels at the start of the growing season. Some of the diatom blooms, however, are not grazed by filter-feeding zooplankton like Daphnia due to their large size. Several of these large diatoms are susceptible to chytrid infections. Zoospores of chytrids appeared to be excellent food for Daphnia, both in terms of size, shape, and quality (PUFAs and cholesterol). Thus, zoospores of chytrids can bridge the gap between inedible diatoms and Daphnia. In order to examine the effects of diatoms and chytrids on the survival of copepods, we performed one grazing and one survival experiment. The grazing experiment revealed that the diatom, Asterionella formosa, was not grazed by the copepod, Eudiaptomus gracilis, even after being infected by the chytrid Zygorhizidium planktonicum. However, carbon and nitrogen concentrations were significantly reduced by E. gracilis only when A. formosa was infected by Z. planktonicum, indicating that the chytrids might facilitate material transfer from inedible diatoms to the copepods. The survival experiment revealed that E. gracilis lived shorter with A. formosa than with the cryptophyta Cryptomonas pyrenoidifera. However, the survival of E. gracilis increased significantly in the treatment where A. formosa cells were infected by Z. planktonicum. Since E. gracilis could not graze A. formosa cells due to their large colonial forms, E. gracilis may acquire nutrients by grazing on the zoospores, and were so able to survive in the presence of the A. formosa. This provides new insights into the role of parasitic fungi in aquatic food webs, where chytrids may improve copepod survival during diatom blooms.     

Algal bioassay of the water from two linked but contrasting Welsh lakes

SUMMARY. A comparison of the potential water fertility of two linked lakes, Llyn Peris and Llyn Padarn, was carried out over a year using Asterionella formosa as the test organism in batch cultures. In unenriched lake water, growth was more rapid in Padarn water during autumn-winter-spring, but there was no significant difference between growth in water from the two lakes during the period of thermal stratification. Mean growth rates in treatments with additions of nitrogen and chelated iron were not significantly different from unenriched water samples, both between treatments and lakes during thermal stratification. Growth in water from both lakes was increased greatly by addition of phosphate. Maximum growth rates occurred on addition of nitrogen, phosphate and chelated iron, and there was no significant difference between growth rates in this treatment for the two lakes throughout the year. Comparisons of mean growth rates in bioassays by Tukey's interval estimate showed significant differences between other treatments and the two lakes. The potential fertility of water samples from the two lakes differs more during mixed water conditions than in the period of thermal stratification. Inhibition of A. formosa growth was recorded four times in unenriched filtered water from Peris, once on addition of nitrogen and once on addition of iron. Inhibition was alleviated by the addition of nutrients. The addition of diluted sewage effluent which enters the drainage system between the two lakes, resulted in similar rates of growth of A. formosa in water from both lakes. Results of the bioassays are discussed in relation to differences in phytoplankton between the two lakes. Although A. formosa will grow in samples of unenriched lake water from Peris, other features, including a shorter retention time of water, lower level of incident radiation and, occasionally, inhibitory substances in the lake water, contribute to the rare occurrence of this diatom in Peris. Padarn is enriched by sewage effluent which aids the growth of A. formosa.     

TEMPERATURE EFFECTS ON SILICON- AND PHOSPHORUS-LIMITED GROWTH AND COMPETITIVE INTERACTIONS AMONG THREE DIATOMS1

Three diatom species, Stephanodiscus hantzschii (Ehr.) Grun., Asterionella formosa Hass. and Fragilaria crotonensis Kitt. Hass. were isolated from Lake Maarsseveen where they are dominant and show a successional sequence. The physiological responses of each species to temperature and limitation by silicon and phosphorus were determined over the temperature range of 5° to 20° C using short-term batch culture methods. Stephanodiscus hantzschii had higher maximum growth rates than the other two species at all temperatures, and the maximum growth rates of all species increased with increasing temperature. Temperature affected not only maximum growth rates but also half-saturation constants (K_s) and the minimum cell quotas. S. hantzschii had low silicon requirements for growth under Si-limiting conditions, and A. formosa and F. crotonensis had higher and nearly identical silicon requirements. The K_s values for silicon for S. hantzschii were essentially constant from 5° to 20° C but varied greatly for the other two species. A. formosa had the lowest requirements for growth under phosphorus limitation, F. crotonensis was intermediate and S. hantzschii had the highest growth requirements for phosphorus. The K₁ values for phosphorus were constant over the temperature range for both A. formosa and F. crotonensis and were much higher and variable for S. hantzschii. Nutrient competition experiments were performed in continuous cultures at four temperatures and various Si:P ratios. The results generally, but not always, confirmed the predictions based on the Monod relationships for each species. Results not in agreement with predictions were usually because of similar physiological properties of A. formosa and F. crotonensis or because of decreased loss rates for F. crotonensis due to wall growth. In cultures with all three species phosphorus-limited (Si:P > 75), A. formosa often dominated as predicted, although F. crotonensis was sometimes the most abundant species. As predicted, S. hantzschii never dominated at high Si:P ratios. At intermediate Si:P ratios when A. formosa and F. crotonensis were both Si-limited and S. hantzschii P-limited, all three species coexisted because A. formosa and F. crotonensis have almost identical silicon requirements, although sometimes F. crotonensis was more abundant than predicted. At 10°C the results agreed best with the predictions; A. formosa dominated at high Si:P ratios and S. hantzschii dominated as predicted at low Si:P ratios when all three species were Si-limited.     

Phylogenetic Position of Parasitic Chytrids on Diatoms: Characterization of a Novel Clade in Chytridiomycota

Chytrids are true fungi that reproduce with posteriorly uniflagellate zoospores. In the last decade, environmental DNA surveys revealed a large number of uncultured chytrids as well as undescribed order‐level novel clades in Chytridiomycota. Although many species have been morphologically described, only some DNA sequence data of parasitic chytrids are available from the database. We herein discuss five cultures of parasitic chytrids on diatoms Aulacoseira spp. and Asterionella formosa. In order to identify the chytrids examined, thallus morphologies were observed using light microscopy. We also conducted a phylogenetic analysis using 18S, 5.8S, and 28S rDNA sequences to obtain their phylogenetic positions. Based on their morphological characteristics, two cultures parasitic on As. formosa were identified as Rhizophydium planktonicum and Zygorhizidium planktonicum. The other three cultures infecting Aulacoseira spp. (two on Aulacoseira ambigua and the other on Aulacoseira granulata) were regarded as Zygorhizidium aff. melosirae. The results of the molecular phylogenetic analysis revealed that R. planktonicum belonged to the known order Chytridiales, while the two species of Zygorhizidium were placed in a novel clade that was previously reported as an undescribed clade composed of only the environmental sequences of uncultured chytrids.