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  • 1
    Electronic Resource
    Electronic Resource
    The complex life-cycle of a polymorphic prokaryote epibiont of the photosynthetic bacterium Chromatium weissei (1993)
    Springer
    Archives of microbiology 159 (1993), S. 498-505 
    Details
    ISSN: 1432-072X
    Keywords: Chromatium weissei ; Prokaryote epibiont ; Life cycle ; Dissolved organic carbon ; Microbial plate ; Anaerobic aquatic bacteria ; Meromictic lakes ; Bacterial interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In natural populations of the anaerobic phototrophic bacterium Chromatium weissei, many cells support a prokaryotic epibiont. This epibiont appears in several forms, all from the life cycle of a single species. A typical epibiont consists of one to five flattened coccoid cells stacked one above the other, perpendicular to the C. weissei surface. The cells at the proximal and distal ends of the stack are 0.6 μm in diameter and 0.8 μm in length; mid-stack cells are slightly shorter. A typical three or four cell stack is 2 μm in length. Small mesosome-like inclusions in the distal cell are involved in the development of ‘droplet’ shaped cells which are released from the end of each stack. These specialised ‘droplet’ cells probably transfer to new hosts when C. weissei cells collide, thereafter developing into new epibiont stacks. It is likely that the epibiont grows heterotrophically using the substantial production of dissolved organic carbon within the dense plates of photosynthesising C. weissei which develop naturally. Thus the epibiont uses its unusual method of growth and dispersion to maintain position in the microbial plate upon which it depends.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00249026
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  • 2
    Electronic Resource
    Electronic Resource
    Continental-scale patterns of nutrient and fish effects on shallow lakes: introduction to a pan-European mesocosm experiment (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Shallow lake ecosystems are normally dominated by submerged and emergent plants. Biological stabilising mechanisms help preserve this dominance. The systems may switch to dominance by phytoplankton, however, with loss of submerged plants. This process usually takes place against a background of increasing nutrient loadings but also requires additional switch mechanisms, which damage the plants or interfere with their stabilising mechanisms.2. The extent to which the details or even major features of this general model may change with geographical location are not clear. Manipulation of the fish community (biomanipulation) has often been used to clear the water of algae and restore the aquatic plants in northerly locations, but it is again not clear whether this is equally appropriate at lower latitudes.3. Eleven parallel experiments (collectively the International Mesocosm Experiment, IME) were carried out in six lakes in Finland, Sweden, England, the Netherlands and Spain in 1998 and 1999 to investigate the between-year and large-scale spatial variation in relationships between nutrient loading and zooplanktivorous fish on submerged plant and plankton communities in shallow lakes.4. Comparability of experiments in different locations was achieved to a high degree. Cross-laboratory comparisons of chemical analyses revealed some systematic differences between laboratories. These are unlikely to lead to major misinterpretations.5. Nutrient addition, overall, had its greatest effect on water chemistry then substantial effects on phytoplankton and zooplankton. Fish addition had its major effect on zooplankton and did not systematically change the water chemistry. There was no trend in the relative importance of fish effects with latitude, but nutrient addition affected more variables with decreasing latitude.6. The relative importance of top-down and bottom-up influences on the plankton differed in different locations and between years at the same location. The outcome of the experiments in different years was more predictable with decreasing latitude and this was attributed to more variable weather at higher latitudes that created more variable starting conditions for the experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2004.01302.x
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  • 3
    Electronic Resource
    Electronic Resource
    Continental-scale patterns of nutrient and fish effects on shallow lakes: synthesis of a pan-European mesocosm experiment (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Results are analysed from 11 experiments in which effects of fish addition and nutrient loading on shallow lakes were studied in mesocosms. The experiments, five in 1998, six in 1999, were carried out in six lakes, distributed from Finland to southern Spain, according to a standard protocol.2. Effects of the treatments on 29 standard chemical, phytoplankton and zooplankton variables are examined to assess the relative importance of bottom-up (nutrient enrichment) and top-down (fish predation) effects. For each year, the experiments in different locations are treated as replicates in a meta-analysis. Results of individual experiments are then compared in terms of the patterns of significant influences of nutrient addition and fish predation with these overall results (the baseline), and between years in the same location.3. The overall meta-analysis gave consistent results across the 2 years, with nutrient loading influencing all of the chemical variables, and on average 31% of primary producer and 39% of zooplankton variables. In contrast, fish influenced none of the chemical variables, 11% of the primary producer and 44% of the zooplankton variables. Nutrient effects on the system were thus about three times greater than fish effects, although fish effects were not inconsiderable.4. The relative importance of nutrients and fish in individual experiments often differed between years at the same location and effects deviated to varying degrees from the baseline. These deviations were treated as measures of consistency (predictability) of conclusions in repeat experiments. Consistency increased southwards and this is interpreted as a consequence of more variable annual weather northwards.5. The influence of nutrient loading was greater southwards and this was probably manifested through naturally greater annual macrophyte abundance in warmer locations in consequence of the longer plant growing-season. There was no trend in the relative importance of fish effects with latitude but this may partly be an artefact of the simple fish community used. These findings suggest that nutrient control should be a greater priority than biomanipulation in the restoration of eutrophicated shallow lakes in warm temperate regions.6. Starting conditions affected the outcome of experiments. High initial concentrations of total phosphorus and planktonic chlorophyll a concentration (created by local conditions prior to the experiment) led to de-emphasis of the importance of nutrient loading in the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2004.01304.x
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  • 4
    Electronic Resource
    Electronic Resource
    Responses of phytoplankton to fish predation and nutrient loading in shallow lakes: a pan-European mesocosm experiment (2004)
    Oxford, UK : Blackwell Publishing
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The impacts of nutrients (phosphorus and nitrogen) and planktivorous fish on phytoplankton composition and biomass were studied in six shallow, macrophyte-dominated lakes across Europe using mesocosm experiments.2. Phytoplankton biomass was more influenced by nutrients than by densities of planktivorous fish. Nutrient addition resulted in increased algal biomass at all locations. In some experiments, a decrease was noted at the highest nutrient loadings, corresponding to added concentrations of 1 mg L−1 P and 10 mg L−1 N.3. Chlorophyll a was a more precise parameter to quantify phytoplankton biomass than algal biovolume, with lower within-treatment variability.4. Higher densities of planktivorous fish shifted phytoplankton composition toward smaller algae (GALD 〈 50 μm). High nutrient loadings selected in favour of chlorophytes and cyanobacteria, while biovolumes of diatoms and dinophytes decreased. High temperatures also may increase the contribution of cyanobacteria to total phytoplankton biovolume in shallow lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2004.01307.x
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  • 5
    Electronic Resource
    Electronic Resource
    A perspective on aging in rotifers (1980)
    Springer
    Hydrobiologia 73 (1980), S. 13-19 
    Details
    ISSN: 1573-5117
    Keywords: aging ; senescence ; rotifers ; life histories ; population dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Most research on aging in rotifers has been performed with populations, not with individuals. As a consequence, the dependent variable in these studies is usually either mean lifespan or rate of survivorship. After a brief consideration of the literature published since the last major review (King, 1969), the results of a series of experiments are presented. Males and females of three genetically distinct clones of Brachionus plicatilis were used for a factorial life table analysis at three different temperatures. The results of these experiments indicate several potential problems in using populations to study the aging process of individuals. These problems derive from the fact that lifespan is only one component of fitness, and its relative duration may not reflect the evolutionary success of the clone. That is, lifespan is free to vary in response to both stochastic and deterministic events without significantly reducing fitness. Under these conditions, neither mean lifespan nor pattern of survivorship will provide meaningful data on the determinants of individual senescence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00019416
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  • 6
    Electronic Resource
    Electronic Resource
    Summer phytoplankton assemblages across trophic gradients in hard-water reservoirs (1998)
    Springer
    Hydrobiologia 369-370 (1998), S. 27-43 
    Details
    ISSN: 1573-5117
    Keywords: phytoplankton ; trophic level ; reservoirs ; hypertrophic ecosystems ; nutrients ; diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Summer phytoplankton assemblages are described and characterised according to their prevalence in a series of hard-water reservoirs of eastern Spain that had been classified in trophic categories on OECD criteria. Distribution patterns of phytoplankton species were ordinated statistically by principal components analysis (PCA). The first component was strongly related to trophic gradient and it particularly discriminated the eutrophic and hypertrophic reservoirs. The second component segregated life-forms, so that (1), on the oligo-mesotrophic side, large dinoflagellates were separated from small centric diatoms, unicellular chrysophytes and filamentous ullotrichales and, on the eu-hypertrophic side (2), colonial greens and large desmids were separated from unicellular volvocales and small centric diatoms. The large differences between eutrophic and hypertrophic reservoirs were also clearly identified in a second PCA, in which physical and chemical factors were used with the principal components solved from the phytoplankton data. From these results, a new trophic category was discerned, for which we propose the name ‘holotrophic’. This category applies to water bodies having the following main features: (1) concentrations of chorophyll, total P and total N in the range of the hypertrophic systems, but with much higher concentrations of dissolved phosphorus and ammonia and (2) phytoplankton predominantly composed by unicellular green flagellates (Pteromonas, Chlamydomonas) and chlorococcales (Scenedesmus), without cyanobacterial blooms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017051322293
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  • 7
    Electronic Resource
    Electronic Resource
    Population dynamics and ecology of subdominant phytoplankton species in a shallow hypertrophic lake (Albufera of Valencia, Spain) (1994)
    Springer
    Hydrobiologia 273 (1994), S. 37-56 
    Details
    ISSN: 1573-5117
    Keywords: ricefields area ; phytoplankton ; subdominant species ; long-term study ; population dynamics ; ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Long-term population dynamics and ecology of the abundant but non-dominant phytoplankton species of the shallow hypertrophic lake the Albufera of Valencia (Spain) are described for the period 1980–1988. The lake is used as a reservoir for the surrounding ricefield cultivation. It is continuously dominated by three filamentous blue-green algae, Planktothrix agardhii, Pseudanabaena galeata and Geitlerinema sp. Horizontal differences of the phytoplankton were less important than annual and seasonal variations. An annual increasing trend was observed for Planktolyngbya subtilis, Planktolyngbya contorta, Cylindrospermopsis raciborskii, Microcystis incerta, Nitzschia palea var. tenuirostris and Rhodomonas lacustris var. nannoplanctica, whereas Anabaenopsis elenkinii, Scenedesmus acuminatus, Scenedesmus quadricauda and Cyclotella meneghiniana showed an opposite trend. This pattern seems related to the increase of nitrogen and phosphorus loading in the lake and certain hydrological changes occurred in the latter years of the study. Seasonal pattern of the subdominant species showed the presence of Cyclotella meneghiniana, Scenedesmus species and Chlamydomonas spp. in spring, during moderate water renovation rates and phosphate availability. Periodicity shifted to blue-green algae and Nitzschia species in summer and early autumn, during reduced phosphate levels and initial low but later high water renewal. Autumn and winter species, such as Monoraphidium contortum, Nitzschia gracilis, Rhodomonas lacustris var. nannoplanctica and Cryptomonas erosa, were mainly related to light intensity and temperature. Although the lake has a typical hypertrophic phytoplankton assemblage, the general seasonal variation of the species is similar to that often described in temperate lakes. Diatom species composition differs to that cited in other shallow hypertrophic lakes of Europe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00126767
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  • 8
    Electronic Resource
    Electronic Resource
    Biometric analysis of Brachionus plicatilis ecotypes from Spanish lagoons (1983)
    Springer
    Hydrobiologia 104 (1983), S. 279-291 
    Details
    ISSN: 1573-5117
    Keywords: rotifers ; Brachionus plicatilis ; biometry ; ecotypes ; cyclomorphosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Univariate comparisons and several multivariate statistical analyses have been performed to study the morphometric variability of B. plicatilis. Both laboratory clones kept under constant conditions and natural populations from different Spanish lagoons and different times of the year have been compared. The results show that not only size, but also allometric coefficients are influenced by environmental factors. However, an important genetic component in the variation of shape and size has been visualized. A clear North-South ordination of the populations of the different lagoons and an important dispersion between their summer populations as well as great differences due to seasonal variation became apparent by the multivariate statistical analysis used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00045979
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  • 9
    Electronic Resource
    Electronic Resource
    Size distribution of Daphnia longispina in the vertical profile (1997)
    Springer
    Hydrobiologia 360 (1997), S. 187-196 
    Details
    ISSN: 1573-5117
    Keywords: Daphnia longispina ; toothed morph ; size distribution ; vertical migration ; predation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract D. longispina of the meromictic lake El Tobar is a round-headed form. It never has a helmet, but in summer a small proportion of immature individuals (0.9–1.2 mm females and males) have one or two neck teeth. The size structure of this Daphnia population, as well as the vertical distribution and migration of different size-classes, were studied in September and November of 1991 and April of 1992. The large variation in mean size and size at first reproduction, as well as the occurrence of different patterns of vertical migration are interpreted as responses to different predator situations. At the end of April, when Daphnia mortality by visually hunting predators is dominating, a typical nocturnal migration is adopted and size distribution is biased to smaller size classes. In November, when mortality is mainly attributed to the nocturnally migrating Chaoborus, Daphnia shows a reversed migration pattern. In September, when the population of Daphnia is responding to both visual (fish) and non-visual predators (Chaoborus), it adopts a pattern of twilight migration. The presence of neck teeth in vulnerable size classes in September might be an additional adaptative response to Chaoborus predation. In September, the size structure of the Daphnia population is shifted to larger classes and the vertical distribution of size classes shows a pronounced segregation between juveniles and adults. Juveniles are found closer to the surface, while adults dwell predominantly in the rich, deep waters near the oxicline. This suggests that an additional advantage of the ascent of the adult Daphnia exploiting those deep resources is the release of young in more oxygenated and warmer waters. The Daphnia population of lake El Tobar is known to be clonally diverse, and the changing frequency of genotypes could play an important part in the observed seasonal differences in behaviour and size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003173504463
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  • 10
    Electronic Resource
    Electronic Resource
    Rotifer vertical distributions in a meromictic basin of Lake Banyoles (Spain) (1993)
    Springer
    Hydrobiologia 255-256 (1993), S. 371-380 
    Details
    ISSN: 1573-5117
    Keywords: rotifers ; vertical distribution ; succession ; Filinia species distribution ; oxycline ; meromictic lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The vertical distribution of rotifer populations has been analyzed in a meromictic basin (III) of the karstic Lake Banyoles. This basin had, at the time of the study, an anaerobic monimolimnion from around 17 m in summer or 21 in winter to 25 m, its maximum depth. However, below this layer a warmer microaerophilic zone with suspended marls is found in a chimney to a depth of 130 m. The rotifer distributions of several years are compared. The presence of large populations of rotifers at the oxic-anoxic interface is constant through the years, but highly variable regarding the total abundance and relative proportions of the species, depending on the importance of the vertical mixing in winter and the posterior segregation of water layers as a function of production and decomposition processes. Filinia hofmanni, Filinia longiseta longiseta are species with a restricted occurrence at the oxycline and are not present in the other non meromictic basins of the lake. Filinia terminalis, more broadly distributed, also has dense populations in summer at the oxycline in basin III, but disappears from the plankton during this season in the other basins. Other species, such as Polyarthra dolichoptera, Anuraeopsis fissa, Keratella cochlearis and Kellicottia longispina, also showed maxima at the oxycline in summer, as well as other maxima in the metalimnion. Populations at the oxycline are probably different ecotypes adapted to low oxygen conditions, but having the advantage of high food availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025862
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