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  • 1.
    Hylander, Samuel
    et al.
    Lund University.
    Jephson, Therese
    Lund University.
    Lebret, Karen
    Lund University.
    von Einem, Jessica
    Lund University.
    Fagerberg, Tony
    Lund University.
    Balseiro, Esteban
    National University of Comahue, Argentina.
    Modenutti, Beatriz
    National University of Comahue, Argentina.
    Sol Souza, Maria
    National University of Comahue, Argentina.
    Laspoumaderes, Cecilia
    National University of Comahue, Argentina.
    Joensson, Mikael
    Lund University.
    Ljungberg, Peter
    Lund University.
    Nicolle, Alice
    Lund University.
    Nilsson, Per Anders
    Lund University.
    Ranaker, Lynn
    Lund University.
    Hansson, Lars-Anders
    Lund University.
    Climate-induced input of turbid glacial meltwater affects vertical distribution and community composition of phyto- and zooplankton2011In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 33, no 8, p. 1239-1248Article in journal (Refereed)
    Abstract [en]

    Receding glaciers are among the most obvious changes caused by global warming, and glacial meltwater entering lakes generally forms plumes of particles. By taking vertical samples along a horizontal gradient from such a particle source, we found that photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) attenuated 20-25% faster close to the inflow of suspended particles compared with the more transparent part of the gradient. All sampled stations had a deep chlorophyll a (Chl a) maximum at 15-20 m which was more distinct in the transparent part of the horizontal gradient. Picocyanobacteria increased in abundance in more transparent water and their numbers were tightly correlated with the intensity of the deep Chl a maxima. Motile species of phytoplankton had a deeper depth distribution in transparent versus less transparent water. Yet other species, like Chrysochromulina parva, that can withstand high PAR intensities and low nutrient concentrations, increased in abundance as the water became more transparent. Also copepods increased in abundance, indicating that they are more successful in transparent water. We conclude that sediment input into lakes creates horizontal gradients in PAR and UVR attenuation which strongly affect both distribution and behavior of phyto-and zooplankton. The input of glacial flour creates a sub-habitat that can function as a refuge for species that are sensitive to high PAR and UVR exposure. When the glacier has vanished, this habitat may disappear. During the melting period, with heavy sediment input, we predict that competitive species in transparent waters, like Chrysocromulina, picocyanobacteria and copepods, will become less common. The deep Chl a maxima is also likely to become less developed. Hence, glacier melting will probably have profound effects on both species composition and behavior of several planktonic taxa with potential effects on the food web.

  • 2.
    Johansson, Karin S. L.
    et al.
    Swedish University of Agricultural Sciences.
    Vrede, Tobias
    Swedish University of Agricultural Sciences.
    Lebret, Karen
    Lund University.
    Johnson, Richard K.
    Swedish University of Agricultural Sciences.
    Zooplankton Feeding on the Nuisance Flagellate Gonyostomum semen2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 5, p. e62557-Article in journal (Refereed)
    Abstract [en]

    The large bloom-forming flagellate Gonyostomum semen has been hypothesized to be inedible to naturally occurring zooplankton due to its large cell size and ejection of long slimy threads (trichocysts) induced by physical stimulation. In a grazing experiment using radiolabelled algae and zooplankton collected from lakes with recurring blooms of G. semen and lakes that rarely experience blooms, we found that Eudiaptomus gracilis and Holopedium gibberum fed on G. semen at high rates, whereas Daphnia cristata and Ceriodaphnia spp. did not. Grazing rates of E. gracilis were similar between bloom-lakes and lakes with low biomass of G. semen, indicating that the ability to feed on G. semen was not a result of local adaptation. The high grazing rates of two of the taxa in our experiment imply that some of the nutrients and energy taken up by G. semen can be transferred directly to higher trophic levels, although the predominance of small cladocerans during blooms may limit the importance of G. semen as a food resource. Based on grazing rates and previous observations on abundances of E. gracilis and H. gibberum, we conclude that there is a potential for grazer control of G. semen and discuss why blooms of G. semen still occur.

  • 3.
    Jonsson, Mikael
    et al.
    Lunds universitet.
    Ranaker, Lynn
    Lunds universitet.
    Nicolle, Alice
    Lunds universitet.
    Ljungberg, Peter
    Lunds universitet.
    Fagerberg, Tony
    Lunds universitet.
    Hylander, Samuel
    Lunds universitet.
    Jephson, Therese
    Lunds universitet.
    Lebret, Karen
    Lunds universitet.
    von Einem, Jessica
    Lunds universitet.
    Hansson, Lars-Anders
    Lunds universitet.
    Nilsson, P. Anders
    Lunds universitet.
    Balseiro, Esteban
    CONICET Univ Nacl Comahue, INIBIOMA, Lab Limnol, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina.
    Modenutti, Beatriz
    CONICET Univ Nacl Comahue, INIBIOMA, Lab Limnol, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina.
    Glacial clay affects foraging performance in a Patagonian fish and cladoceran2011In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 663, no 1, p. 101-108Article in journal (Refereed)
    Abstract [en]

    Climate change is altering temperatures and precipitation patterns all over the world. In Patagonia, Argentina, predicted increase in precipitation together with rapidly melting glaciers increase the surface runoff, and thereby the transport of suspended solids to recipient lakes. Suspended solids affect the visual conditions in the water which in turn restricts visual foraging. The native fish Aplochiton zebra Jenyns, and its filter-feeding cladoceran prey, Daphnia commutata Ekman, were subjected to foraging experiments at three turbidity levels. A. zebra foraging rate was substantially reduced at naturally occurring turbidity levels and the filtering rate of D. commutata was reduced at the highest turbidity level. This indicates that Daphnia may be partly released from predation from A. zebra at the same time as it can maintain relatively high feeding rates as turbidity increases. Lower foraging rates at the same time as the metabolic demand increases, through increased temperatures, may result in larger effects on A. zebra than could be expected from increases in turbidity or temperature alone. Turbidity may, as an indirect effect of climate change, decrease planktivore foraging rates and thereby alter the interaction strength between trophic levels.

  • 4.
    Leblond, Jeffrey D.
    et al.
    Middle Tennessee State University, USA.
    Dahmen, Aaron S.
    Middle Tennessee State University, USA.
    Lebret, Karen
    Lund University.
    Rengefors, Karin
    Lund University.
    Sterols of the Green-Pigmented, Freshwater Raphidophyte, Gonyostomum semen, from Scandinavian Lakes2013In: Journal of Eukaryotic Microbiology, ISSN 1066-5234, E-ISSN 1550-7408, Vol. 60, no 4, p. 399-405Article in journal (Refereed)
    Abstract [en]

    Sterols are a class of membrane-reinforcing, ringed lipids which have a long history of examination in algae as a means of deriving chemotaxonomic relationships and as potential lipidic biomarkers. The Raphidophyceae represent a class of harmful, bloom-forming, marine and freshwater algae. To date, there have been four published examinations of their sterol composition, focusing primarily on brown-pigmented, marine species within the genera, Chattonella, Fibrocapsa, and Heterosigma. Lacking in these examinations has been the species Gonyostomum semen Ehrenb., which is a green-pigmented, freshwater raphidophyte with a worldwide distribution. The goal of this study was to examine the sterol composition of this nuisance alga, determine the potential of using its sterol profile as a biomarker, and finally to determine if there is any intraspecific variability between isolates. We have examined 21 isolates of G. semen from a number of Scandinavian lakes, and all were found to produce two major sterols, 24-ethylcholesta-5,22E-dien-3-ol and 24-ethylcholest-5-en-3-ol, and 24-methylcholest-5-en-3-ol as a minor sterol; the presence of 24-ethylcholesta-5,22E-dien-3-ol differentiates G. semen from brown-pigmented, marine raphidophytes which generally lack it. The results of this study indicate that isolates of G. semen from geographically separate lakes across Finland and Scandinavia have the same sterol biosynthetic pathway, and that there is no evolutionary divergence between the isolates with regard to sterol composition. The sterols of G. semen are not considered to be useful biomarkers for this particular organism because they are commonly found in other algae and plants.

  • 5.
    Lebret, Karen
    et al.
    Lund University.
    Fernandez, Maria Fernandez
    Hagman, Camilla H. C.
    Rengefors, Karin
    Hansson, Lars-Anders
    Grazing resistance allows bloom formation and may explain invasion success of Gonyostomum semen2012In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 3, p. 727-734Article in journal (Refereed)
    Abstract [en]

    The nuisance alga Gonyostomum semen (Raphidophyceae) has expanded in the Nordic countries during the last decades and can dominate lake phytoplankton communities almost completely. A possible explanation to its dominance could be limited grazing by zooplankton. We investigated the potential grazing pressure on G. semen using an experimental approach supported by field data. We determined the grazing rate by cladocerans, calanoid copepods, and Chaoborus larvae to determine which were able to feed on G. semen. Only the large cladoceran Daphnia magna was able to feed successfully on G. semen. The large cell size of G. semen was likely a limiting factor for the filtering apparatus of smaller cladocerans. The copepod Eudiaptomus gracilis did not graze on G. semen, although the mechanism behind this selective feeding is still unknown. In addition to the experimental study, we quantified the zooplankton and phytoplankton communities in 40 lakes to determine the composition and abundance of the zooplankton communities co-occurring with G. semen, suggesting that large cladoceran species were not present in lakes where G. semen occurred. Hence, the growth of G. semen is not significantly controlled by grazing in natural systems, which likely facilitates bloom formation and invasion success of G. semen.

  • 6.
    Lebret, Karen
    et al.
    Lund University.
    Kritzberg, Emma S.
    Figueroa, Rosa
    Rengefors, Karin
    Genetic diversity within and genetic differentiation between blooms of a microalgal species2012In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 14, no 9, p. 2395-2404Article in journal (Refereed)
    Abstract [en]

    The field of genetic diversity in protists, particularly phytoplankton, is under expansion. However, little is known regarding variation in genetic diversity within populations over time. The aim of our study was to investigate intrapopulation genetic diversity and genetic differentiation in the freshwater bloom-forming microalga Gonyostomum semen (Raphidophyceae). The study covered a 2-year period including all phases of the bloom. Amplified fragment length polymorphism (AFLP) was used to determine the genetic structure and diversity of the population. Our results showed a significant differentiation between samples collected during the two blooms from consecutive years. Also, an increase of gene diversity and a loss of differentiation among sampling dates were observed over time within a single bloom. The latter observations may reflect the continuous germination of cysts from the sediment. The life cycle characteristics of G. semen, particularly reproduction and recruitment, most likely explain a high proportion of the observed variation. This study highlights the importance of the life cycle for the intraspecific genetic diversity of microbial species, which alternates between sexual and asexual reproduction.

  • 7.
    Lebret, Karen
    et al.
    Lund University.
    Kritzberg, Emma S.
    Lund University.
    Rengefors, Karin
    Lund University.
    Population Genetic Structure of a Microalgal Species under Expansion2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 12, p. e82510-Article in journal (Refereed)
    Abstract [en]

    Biological invasions often cause major perturbations in the environment and are well studied among macroorganisms. Less is known about invasion by free-living microbes. Gonyostomum semen (Raphidophyceae) is a freshwater phytoplankton species that has increased in abundance in Northern Europe since the 1980's and has expanded its habitat range. In this study, we aimed to determine the genetic population structure of G. semen in Northern Europe and to what extent it reflects the species' recent expansion. We sampled lakes from 12 locations (11 lakes) in Norway, Sweden and Finland. Multiple strains from each location were genotyped using Amplified Fragment Length Polymorphism (AFLP). We found low differentiation between locations, and low gene diversity within each location. Moreover, there was an absence of genetic isolation with distance (Mantel test, p = 0.50). According to a Bayesian clustering method all the isolates belonged to the same genetic population. Together our data suggest the presence of one metapopulation and an overall low diversity, which is coherent with a recent expansion of G. semen.

  • 8.
    Lebret, Karen
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Uppsala University.
    Langenheder, Silke
    Uppsala University.
    Colinas, Noemi
    Uppsala University.
    Östman, Örjan
    Swedish University of Agricultural Sciences.
    Lindström, Eva S.
    Uppsala University.
    Increased water colour affects freshwater plankton communities in a mesocosm study2018In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 81, no 1, p. 1-17Article in journal (Refereed)
    Abstract [en]

    Increases in water colour (brownification) have been observed in aquatic systems in the Northern Hemisphere, partly caused by increased loading of organic carbon from terrestrial origins. We investigated the effect of increase in water colour on the composition, structure and function of lake plankton communities (bacteria, phytoplankton and zooplankton) conducting a mesocosm experiment in 3 medium-coloured lakes (average absorbance at 420 nm: 0.034 cm(-1)), with different nutrient concentrations and phytoplankton community composition. To simulate an increase in water colour, we added humic substances (HuminFeed) at 3 different concentrations. The additions significantly affected the water colour of the mesocosms, but had no measurable effect on total organic carbon concentration, thus change in light conditions was the main effect of our treatment on the plankton communities. The increase in water colour did not significantly affect the measured functions (productivity, respiration) and biomass of the plankton communities (bacteria, phytoplankton and zooplankton), but led to changes in the relative abundance of some phytoplankton taxa and, to a lesser extent, the bacterial community (differences in relative abundance). The treatments had no significant effect on zooplankton biomass or composition. Our study suggests that increases in water colour favour low-light-adapted phytoplankton species, which in turn also can affect bacterial composition, whereas the change in light climate had no clear impact on the functioning of plankton communities in weakly humic lakes.

  • 9.
    Lebret, Karen
    et al.
    Lund University.
    Tesson, Sylvie V. M.
    Lund University.
    Kritzberg, Emma S.
    Lund University.
    Tomas, Carmelo
    University of North Carolina at Wilmington, USA.
    Rengefors, Karin
    Lund University.
    Phylogeography of the freshwater raphidophyte Gonyostomum semen confirms a recent expansion in northern Europe by a single haplotype2015In: Journal of Phycology, ISSN 0022-3646, E-ISSN 1529-8817, Vol. 51, no 4, p. 768-781Article in journal (Refereed)
    Abstract [en]

    Gonyostmum semen is a freshwater raphidophyte that has increased in occurrence and abundance in several countries in northern Europe since the 1980s. More recently, the species has expanded rapidly also in north-eastern Europe, and it is frequently referred to as invasive. To better understand the species history, we have explored the phylogeography of G. semen using strains from northern Europe, United States, and Japan. Three regions of the ribosomal RNA gene (small subunit [SSU], internal transcribed spacer [ITS] and large subunit [LSU]) and one mitochondrial DNA marker (cox1) were analyzed. The SSU and partial LSU sequences were identical in all strains, confirming that they belong to the same species. The ITS region differentiated the American from the other strains, but showed high intra-strain variability. In contrast, the mitochondrial marker cox1 showed distinct differences between the European, American, and Japanese strains. Interestingly, only one cox1 haplotype was detected in European strains. The overall low diversity and weak geographic structure within northern European strains supported the hypothesis of a recent invasion of new lakes by G. semen. Our data also show that the invasive northern European lineage is genetically distinct from the lineages from the other continents. Finally, we concluded that the mitochondrial cox1 was the most useful marker in determining large-scale biogeographic patterns in this species.

  • 10.
    Lebret, Karen
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Uppsala University.
    Östman, Örjan
    Swedish University of Agricultural Sciences.
    Langenheder, Silke
    Uppsala University.
    Drakare, Stina
    Swedish University of Agricultural Sciences.
    Guillemette, Francois
    Univ Quebec Trois Rivieres, Canada.
    Lindström, Eva S.
    Uppsala University.
    High abundances of the nuisance raphidophyte Gonyostomum semen in brown water lakes are associated with high concentrations of iron2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 13463Article in journal (Refereed)
    Abstract [en]

    Algal blooms occur frequently in lakes and oceans and the causes and consequences of those are often studied. In this study, we focus on a less well known type of algal bloom by the freshwater raphidophyte Gonyostomum semen. This species' abundance and occurrence is increasing, especially in brown water lakes, the most abundant lake type in the boreal zone. The aim of the study was to investigate which environmental factors are associated with G. semen by statistical evaluation of field data of 95 Swedish lakes over five years. Although we found G. semen to be associated with dark waters it was, contrary to our expectations, mainly high concentrations of iron, and only to a lesser extent high TOC (total organic carbon) concentrations, that were associated with blooms of G. semen. In addition, high phosphorus concentrations and low pH also appear to facilitate G. semen blooms. We suggest that browning of lakes caused by increased iron concentrations may decrease net heterotrophy by fostering heavy algal blooms, i.e. the opposite to commonly assumed effects of increased DOM (dissolved organic matter).

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