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  • ASLO (Association for the Sciences of Limnology and Oceanography)  (20)
  • Nature Research  (9)
Publikationsart
Erscheinungszeitraum
  • 1
    Publikationsdatum: 2021-02-08
    Beschreibung: Ocean acidification—the decrease in seawater pH due to rising CO2 concentrations—has been shown to lower survival in early life stages of fish and, as a consequence, the recruitment of populations including commercially important species. To date, ocean-acidification studies with fish larvae have focused on the direct physiological impacts of elevated CO2, but largely ignored the potential effects of ocean acidification on food web interactions. In an in situ mesocosm study on Atlantic herring (Clupea harengus) larvae as top predators in a pelagic food web, we account for indirect CO2 effects on larval survival mediated by changes in food availability. The community was exposed to projected end-of-the-century CO2 conditions (~760 µatm pCO2) over a period of 113 days. In contrast with laboratory studies that reported a decrease in fish survival, the survival of the herring larvae in situ was significantly enhanced by 19 ± 2%. Analysis of the plankton community dynamics suggested that the herring larvae benefitted from a CO2-stimulated increase in primary production. Such indirect effects may counteract the possible direct negative effects of ocean acidification on the survival of fish early life stages. These findings emphasize the need to assess the food web effects of ocean acidification on fish larvae before we can predict even the sign of change in fish recruitment in a high-CO2 ocean.
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  • 2
    Publikationsdatum: 2020-02-06
    Beschreibung: Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity.
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  • 3
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    Nature Research
    In:  Nature Ecology & Evolution, 2 . pp. 611-613.
    Publikationsdatum: 2021-02-08
    Beschreibung: Climate change challenges plankton communities, but evolutionary adaptation could mitigate the potential impacts. Here, we tested with the phytoplankton species Emiliania huxleyi whether adaptation to a stressor under laboratory conditions leads to equivalent fitness gains in a more natural environment. We found that fitness advantages that had evolved under laboratory conditions were masked by pleiotropic effects in natural plankton communities. Moreover, new genotypes with highly variable competitive abilities evolved on timescales significantly shorter than climate change.
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  • 4
    Publikationsdatum: 2021-04-23
    Beschreibung: Ocean acidification, the change in seawater carbonate chemistry due to the uptake of anthropogenic CO2, affects the physiology of marine organisms in multiple ways1. Diverse competitive and trophic interactions transform the metabolic responses to changes in community composition, seasonal succession and potentially geographical distribution of species. The health of ocean ecosystems depends on whether basic biotic functions are maintained, ecosystem engineers and keystone species are retained, and the spread of nuisance species is avoided2. Here, we show in a field experiment that the toxic microalga Vicicitus globosus has a selective advantage under ocean acidification, increasing its abundance in natural plankton communities at CO2 levels higher than 600 µatm and developing blooms above 800 µatm CO2. The mass development of V. globosus has had a dramatic impact on the plankton community, preventing the development of the micro- and mesozooplankton communities, thereby disrupting trophic transfer of primary produced organic matter. This has prolonged the residence of particulate matter in the water column and caused a strong decline in export flux. Considering its wide geographical distribution and confirmed role in fish kills3, the proliferation of V. globosus under the IPCC4 CO2 emission representative concentration pathway (RCP4.5 to RCP8.5) scenarios may pose an emergent threat to coastal communities, aquaculture and fisheries.
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  • 5
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    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 60 (6). pp. 2145-2157.
    Publikationsdatum: 2018-10-01
    Beschreibung: Global change leads to a multitude of simultaneous modifications in the marine realm among which shoaling of the upper mixed layer, leading to enhanced surface layer light intensities, as well as increased carbon dioxide (CO2) concentration are some of the most critical environmental alterations for phytoplankton. In this study, we investigated the responses of growth, photosynthetic carbon fixation and calcification of the coccolithophore Gephyrocapsa oceanica to elevated inline image (51 Pa, 105 Pa, and 152 Pa) (1 Pa ≈ 10 μatm) at a variety of light intensities (50–800 μmol photons m−2 s−1). By fitting the light response curve, our results showed that rising inline image reduced the maximum rates for growth, photosynthetic carbon fixation and calcification. Increasing light intensity enhanced the sensitivity of these rate responses to inline image, and shifted the inline image optima toward lower levels. Combining the results of this and a previous study (Sett et al. 2014) on the same strain indicates that both limiting low inline image and inhibiting high inline image levels (this study) induce similar responses, reducing growth, carbon fixation and calcification rates of G. oceanica. At limiting low light intensities the inline image optima for maximum growth, carbon fixation and calcification are shifted toward higher levels. Interacting effects of simultaneously occurring environmental changes, such as increasing light intensity and ocean acidification, need to be considered when trying to assess metabolic rates of marine phytoplankton under future ocean scenarios.
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  • 6
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    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 59 (5). pp. 1570-1580.
    Publikationsdatum: 2017-09-02
    Beschreibung: Thermal reaction norms for growth rates of six Emiliania huxleyi isolates originating from the central Atlantic (Azores, Portugal) and five isolates from the coastal North Atlantic (Bergen, Norway) were assessed. We used the template mode of variation model to decompose variations in growth rates into modes of biological interest: vertical shift, horizontal shift, and generalist–specialist variation. In line with the actual habitat conditions, isolates from Bergen (Bergen population) grew well at lower temperatures, and isolates from the Azores (Azores population) performed better at higher temperatures. The optimum growth temperature of the Azores population was significantly higher than that of the Bergen population. Neutral genetic differentiation was found between populations by microsatellite analysis. These findings indicate that E. huxleyi populations are adapted to local temperature regimes. Next to between-population variation, we also found variation within populations. Genotype-by-environment interactions resulted in the most pronounced phenotypic differences when isolates were exposed to temperatures outside the range they naturally encounter. Variation in thermal reaction norms between and within populations emphasizes the importance of using more than one isolate when studying the consequences of global change on marine phytoplankton. Phenotypic plasticity and standing genetic variation will be important in determining the potential of natural E. huxleyi populations to cope with global climate change.
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  • 7
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    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 56 (6). pp. 2040-2050.
    Publikationsdatum: 2020-10-16
    Beschreibung: The coccolithophore Emiliania huxleyi was cultured under a broad range of carbonate chemistry conditions to distinguish the effects of individual carbonate system parameters on growth, primary production, and calcification. In the first experiment, alkalinity was kept constant and the fugacity of CO2 (fCO2) varied from 2 to 600 Pa (1 Pa ≈ 10 µatm). In the second experiment, pH was kept constant (pHfree = 8) with fCO2 varying from 4 to 370 Pa. Results of the constant-alkalinity approach revealed physiological optima for growth, calcification, and organic carbon production at fCO2 values of ∼ 20 Pa, ∼ 40 Pa, and ∼ 80 Pa, respectively. Comparing this with the constant-pH approach showed that growth and organic carbon production increased similarly from low to intermediate CO2 levels but started to diverge towards higher CO2 levels. In the high CO2 range, growth rates and organic carbon production decreased steadily with declining pH at constant alkalinity while remaining consistently higher at constant pH. This suggests that growth and organic carbon production rates are directly related to CO2 at low (sub-saturating) concentrations, whereas towards higher CO2 levels they are adversely affected by the associated decrease in pH. A pH dependence at high fCO2 is also indicated for calcification rates, while the key carbonate system parameter determining calcification at low fCO2 remains unclear. These results imply that key metabolic processes in coccolithophores have their optima at different carbonate chemistry conditions and are influenced by different parameters of the carbonate system at both sides of the optimum.
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  • 8
    Publikationsdatum: 2019-02-01
    Beschreibung: Ocean acidification (OA), a process of increasing seawater acidity caused by the uptake of anthropogenic carbon dioxide (CO 2) by the ocean, is expected to change surface ocean pH to levels unprecedented for millions of years, affecting marine food web structures and trophic interactions. Using an in situ mesocosm approach we investigated effects of OA on community composition and trophic transfer of essential fatty acids (FA) in a natural plankton assemblage. Elevated pCO 2 favored the smallest phytoplankton size class in terms of biomass, primarily picoeukaryotes, at the expense of chlorophyta and haptophyta in the nano-plankton size range. This shift in community composition and size structure was accompanied by a decline in the proportion of polyunsaturated FA (PUFA) to total FA content in the nano- and picophytoplankton size fractions. This decline was mirrored in a continuing reduction in the relative PUFA content of the dominant copepod, Calanus finmarchicus, which primarily fed on the nano-size class. Our results demonstrate that a shift in phytoplankton community composition and biochemical composition in response to rising CO 2 can affect the transfer of essential compounds to higher trophic levels, which rely on their prey as a source for essential macromolecules.
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  • 9
    Publikationsdatum: 2020-06-18
    Beschreibung: Coccolithophores—single-celled calcifying phytoplankton—are an important group of marine primary producers and the dominant builders of calcium carbonate globally. Coccolithophores form extensive blooms and increase the density and sinking speed of organic matter via calcium carbonate ballasting. Thereby, they play a key role in the marine carbon cycle. Coccolithophore physiological responses to experimental ocean acidification have ranged from moderate stimulation to substantial decline in growth and calcification rates, combined with enhanced malformation of their calcite platelets. Here we report on a mesocosm experiment conducted in a Norwegian fjord in which we exposed a natural plankton community to a wide range of CO2-induced ocean acidification, to test whether these physiological responses affect the ecological success of coccolithophore populations. Under high-CO2 treatments, Emiliania huxleyi, the most abundant and productive coccolithophore species, declined in population size during the pre-bloom period and lost the ability to form blooms. As a result, particle sinking velocities declined by up to 30% and sedimented organic matter was reduced by up to 25% relative to controls. There were also strong reductions in seawater concentrations of the climate-active compound dimethylsulfide in CO2-enriched mesocosms. We conclude that ocean acidification can lower calcifying phytoplankton productivity, potentially creating a positive feedback to the climate system.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 10
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    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 48 . pp. 55-67.
    Publikationsdatum: 2014-01-30
    Beschreibung: Carbon acquisition in relation to CO2 supply was investigated in three marine bloom-forming microalgae, the diatom Skeletonema costatum, the flagellate Phaeocystis globosa, and the coccolithophorid Emiliania huxleyi. In vivo activities of extracellular (eCA) and intracellular (iCA) carbonic anhydrase activity, photosynthetic O2 evolution, CO2 and HCO uptake rates were measured by membrane inlet mass spectrometry in cells acclimated to pCO2 levels of 36, 180, 360, and 1,800 ppmv. Large differences were obtained between species both with regard to the efficiency and regulation of carbon acquisition. While eCA activity increased with decreasing CO2 concentration in S. costatum and P. globosa, consistently low values were obtained for E. huxleyi. No clear trends with pCO2 were observed in iCA activity for any of the species tested. Half saturation concentrations (K1/2) for photosynthetic O2 evolution, which were highest for E. huxleyi and lowest for S. costatum, generally decreased with decreasing CO2 concentration. In contrast, K1/2 values for P. globosa remained unaffected by pCO2 of the incubation. CO2 and HCO3- were taken up simultaneously by all species. The relative contribution of HCO3- to total carbon uptake generally increased with decreasing CO2, yet strongly differed between species. Whereas K1/2 for CO2 and HCO3- uptake was lowest at the lowest pCO2 for S. costatum and E. huxleyi, it did not change as a function of pCO2 in P. globosa. The observed taxon-specific differences in CO2 sensitivity, if representative for the natural environment, suggest that changes in CO2 availability may influence phytoplankton species succession and distribution. By modifying the relative contribution of different functional groups, e.g., diatomaceous versus calcareous phytoplankton, to the overall primary production this could potentially affect marine biogeochemical cycling and air-sea gas exchange.
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