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  • 1
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    Baltic Sea diazotrophic cyanobacterium is negatively affected by acidification and warming (2018)
    Inter Research
    In:  Marine Ecology Progress Series, 598 . pp. 49-60.
    Details
    Publication Date: 2021-02-08
    Description: Nitrogen fixation is a key source of nitrogen in the Baltic Sea which counteracts nitrogen loss processes in the deep anoxic basins. Laboratory and field studies have indicated that single-strain nitrogen-fixing (diazotrophic) cyanobacteria from the Baltic Sea are sensitive to ocean acidification and warming, two drivers of marked future change in the marine environment. Here, we enclosed a natural plankton community in twelve indoor mesocosms (volume ~1400 L) and manipulated pCO2 to yield six CO2 treatments with two different temperature treatments (16.6°C and 22.4°C, pCO2 range = 360 – 2030 μatm). We followed the filamentous, heterocystous diazotrophic cyanobacteria community (Nostocales, primarily Nodularia spumigena) over four weeks. Our results indicate that heterocystous diazotrophic cyanobacteria may become less competitive in natural plankton communities under ocean acidification. Elevated CO2 had a negative impact on Nodularia sp. biomass, which was exacerbated by warming. Our results imply that Nodularia sp. may contribute less to new nitrogen inputs in the Baltic Sea in future.
    Type: Article , PeerReviewed
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    DOI: 10.3354/meps12632
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Overwintering effects on the spring bloom dynamics of phytoplankton (2017)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 39 (5). pp. 772-780.
    Details
    Publication Date: 2020-02-06
    Description: The influence of winter on the selection of dominant taxa for the phytoplankton spring bloom was studied in batch culture experiments. Different natural phytoplankton assemblages from different phases of the temperate zone winter were exposed to varying periods of darkness (0, 6/7, 13 and 19 weeks) followed by a re-exposure to saturating light intensity for 14 days to experimentally simulate the onset of spring. The results showed that dark incubation has a strong effect on shaping the phytoplankton community composition. Many taxa disappeared in the absolute darkness. Dark survival ability might be an important contributing factor for the success of diatoms in spring. Different phytoplankton starting assemblages were dominated by the same bloom-forming diatoms, Skeletonema marinoi and Thalassosira spp., after dark incubation for only 6 weeks, irrespective of the high dissimilarities between phytoplankton communities. The growth capacity of surviving phytoplankton is almost unimpaired by darkness. Similar growth rates as that before darkness could be resumed for the surviving taxa with a potential lag time of 1–7 days dependent on taxon and the duration of darkness.
    Type: Article , PeerReviewed
    Format: text
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    DOI: 10.1093/plankt/fbx046
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Quantifying top-down control and ecological traits of the scyphozoan Aurelia aurita through a dynamic plankton model (2018)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 40 (6). pp. 678-692.
    Details
    Publication Date: 2021-02-08
    Description: Aurelia aurita (Linneaus, 1758) is a cosmopolitan scyphozoan, probably the most investigated jellyfish in temperate and highly productive coastal ecosystems. Despite a prominent top-down control in plankton food webs, a mechanistic understanding of A. aurita population dynamics and trophic interactions has been barely addressed. Here we develop a food web dynamic model to assess A. aurita role in the seasonal plankton dynamics of the Kiel Fjord, southwestern Baltic Sea. The model couples low trophic level dynamics, based on a classical Nutrient Phytoplankton Zooplankton Detritus (NPZD) model, to a stage-resolved copepod model (referencing Pseudocalanus sp.) and a jellyfish model (A. aurita ephyra and medusa) as consumers and predators, respectively. Simulations showed the relevance of high abundances of A. aurita, which appear related with warm winter temperatures, promoting a shift from a copepod-dominated food web to a ciliate and medusa dominated one. The model captured the intraspecific competition triggered by the medusae abundance and characterized by a negative relationship between population density and individual size/weight. Our results provide a mechanistic understanding of an emergent trait such as size shaping the food web functioning, driving predation rates and population dynamics of A. aurita, driving its sexual reproductive strategy at the end of the pelagic phase.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    DOI: 10.1093/plankt/fby041
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Light effects on phytoplankton morphometric traits influence nutrient utilization ability (2018)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 40 (5). pp. 568-579.
    Details
    Publication Date: 2021-02-08
    Description: Light and nutrients are essential resources for phytoplankton growth and considered to shape the size structure and other morphometric traits (surface:volume ratio, deviation from spherical shape) of phytoplankton communities. If morphometric traits influence the growth and resource use, shifts by one of the two factors should influence the capability to utilize the other factor. We performed a two-step experiment, where a natural phytoplankton community was first exposed to three different light levels (supposed to be limiting, saturating and slightly inhibiting for the majority of species) and grown until stationary phase. Then, the pre-conditioned communities were split into two nutrient treatments (control and saturating nutrient pulse) and again grown until stationary phase under the medium light intensity. During the experimental light phase, community mean cell-size increased with light, but surface:volume ratio and deviation from spherical shape decreased. Moreover, in response to the following nutrient pulse, the low light pre-conditioned communities showed the highest initial growth rates in response to the nutrient pulse. The high light pre-conditioned communities showed the highest conversion of the nutrient pulse into biomass during the stationary phase. These results demonstrate how the imprint of one environmental factor on trait distribution influences the ability to cope with another.
    Type: Article , PeerReviewed
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    DOI: 10.1093/plankt/fby037
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  • 5
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    Effects of high CO2 and warming on a Baltic Sea microzooplankton community (2016)
    Oxford Univ. Press
    In:  ICES Journal of Marine Science, 73 (3). pp. 772-782.
    Details
    Publication Date: 2019-02-01
    Description: Global warming and ocean acidification are among the most important stressors for aquatic ecosystems in the future. To investigate their direct and indirect effects on a near-natural plankton community, a multiple-stressor approach is needed. Hence, we set up mesocosms in a full-factorial design to study the effects of both warming and high CO2 on a Baltic Sea autumn plankton community, concentrating on the impacts on microzooplankton (MZP). MZP abundance, biomass, and species composition were analysed over the course of the experiment. We observed that warming led to a reduced time-lag between the phytoplankton bloom and an MZP biomass maximum. MZP showed a significantly higher growth rate and an earlier biomass peak in the warm treatments while the biomass maximum was not affected. Increased pCO2 did not result in any significant effects on MZP biomass, growth rate, or species composition irrespective of the temperature, nor did we observe any significant interactions between CO2 and temperature. We attribute this to the high tolerance of this estuarine plankton community to fluctuations in pCO2, often resulting in CO2 concentrations higher than the predicted end-of-century concentration for open oceans. In contrast, warming can be expected to directly affect MZP and strengthen its coupling with phytoplankton by enhancing its grazing pressure.
    Type: Article , PeerReviewed
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    DOI: 10.1093/icesjms/fsv198
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Some like it hot: the protozooplankton–copepod link in a warming ocean (2015)
    Inter Research
    In:  Marine Ecology Progress Series, 519 . pp. 103-113.
    Details
    Publication Date: 2020-01-21
    Description: The combined effects of warming and overwintering copepod densities on the spring succession of Baltic Sea plankton were investigated using indoor mesocosms. Three zooplankton (1.5, 4 and 10 copepods L-1) and two temperature levels called ∆0°C and ∆6°C (0°C and 6°C above the present day temperature scenario for Kiel Bight) were chosen. Both, the timing and the duration of the protozooplankton (PZP) bloom were significantly affected by temperature, but not by copepod density. In contrast, the bloom intensity of PZP was highly affected by the factors temperature and copepod density and its interaction. This suggests that at elevated temperature conditions PZP grows faster but, at the same time, are subject to higher top-down control by copepods. At low temperatures and low copepod densities, PZP in turn fully escaped from copepod predation. Further changes in the overwintering copepod densities resulted in a strong ciliate suppression of which small-sized ciliates (〈30 µm) were especially vulnerable to copepod predation while other PZP size classes remained unaffected. In conclusion, the results presented point at a pivotal regulating role of overwintering copepods under future warming condition. Further, warming was shown to cause a distinct match between phytoplankton and PZP thus strengthening trophic pathways through PZP. Our findings are discussed in the context of the ‘trophic link-sink’ debate by considering potential alterations in the flux of matter and energy up the food web.
    Type: Article , PeerReviewed
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    DOI: 10.3354/meps11081
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Benefits, costs and taxonomic distribution of marine phytoplankton body size (2017)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 39 (3). pp. 494-508.
    Details
    Publication Date: 2020-02-06
    Description: Phytoplankton cell or colony sizes range from 〈1 µm to several cm, i.e. 4–5 orders of magnitude in linear dimensions, which is roughly equivalent to the log-size span within terrestrial vegetation. It is commonplace to assume that smaller phytoplankton have an advantage in growth related traits while larger ones are more resistant to losses. However, the current state of literature calls for a more differentiated view. It is still controversial, whether smaller phytoplankton have higher maximal growth rates (µmax) or if there is a peak of µmax at intermediate size (102 µm3 cell volume). Smaller phytoplankton have an advantage in nutrient acquisition at low concentrations while larger phytoplankton have an advantage in utilizing nutrient pulses and exploiting vertical gradients. At equal density, larger phytoplankton experience bigger sinking losses. Small phytoplankton (〈5–10 µm) are more affected mostly from grazing by protists and tunicates, while larger phytoplankton are more affected by copepod and krill grazing. Size spectra within the most important higher taxa show some conspicuous differences between marine and lake phytoplankton, e.g. the absence of very large diatoms (〉105 µm3) in lake phytoplankton and the absence of large (〉103 µm3) green algae in marine plankton. Overall, size is one of the most important traits for the performance of phytoplankton, but it is overly simplistic to equate small size with metabolic advantages
    Type: Article , PeerReviewed
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    DOI: 10.1093/plankt/fbw071
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Warming, but not enhanced CO2 concentration, quantitatively and qualitatively affects phytoplankton biomass (2015)
    Inter Research
    In:  Marine Ecology Progress Series, 528 . pp. 39-51.
    Details
    Publication Date: 2017-04-12
    Description: We investigated the impacts of predicted ocean acidification and future warming on the quantity and nutritional quality of a natural phytoplankton autumn bloom in a mesocosm experiment. Since the effects of CO2-enrichment and temperature have usually been studied independently, we were also interested in the interactive effects of both aspects of climate change. Therefore, we used a factorial design with 2 temperature and 2 acidification levels in a mesocosm experiment with a Baltic Sea phytoplankton community. Our results show a significant time-dependent influence of warming on phytoplankton carbon, chlorophyll a, and particulate organic carbon. Phytoplankton carbon, for instance, decreased by more than half with increasing temperature at bloom time. Additionally, elemental carbon to phosphorus ratios (C:P) increased significantly, by approximately 5 to 8%, due to warming. Impacts of CO2 or synergetic effects of warming and acidification could not be detected. We suggest that stronger grazing pressure induced by temperature was responsible for the significant decline in phytoplankton biomass. Our results suggest that the biological effects of warming on Baltic Sea phytoplankton are considerable and will likely have fundamental consequences for trophic transfer in the pelagic food web
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps11264
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    The importance of phytoplankton trait variability in spring bloom formation (2015)
    Oxford Univ. Press
    In:  ICES Journal of Marine Science, 72 (6). pp. 1908-1915.
    Details
    Publication Date: 2017-12-19
    Description: About 60 years ago, the critical depth hypothesis was proposed to describe the occurrence of spring phytoplankton blooms and emphasized the role of stratification for the timing of onset. Since then, several alternative hypotheses appeared focusing on the role of grazing and mixing processes such as turbulent convection or wind activity. Surprisingly, the role of community composition—and thus the distribution of phytoplankton traits—for bloom formation has not been addressed. Here, we discuss how trait variability between competing species might influence phytoplankton growth during the onset of the spring bloom. We hypothesize that the bloom will only occur if there are species with a combination of traits fitting to the environmental conditions at the respective location and time. The basic traits for formation of the typical spring bloom are high growth rates and photoadaptation to low light conditions, but other traits such as nutrient kinetics and grazing resistance might also be important. We present concise ideas on how to test our theoretical considerations experimentally. Furthermore, we suggest that future models of phytoplankton blooms should include both water column dynamics and variability of phytoplankton traits to make realistic projections instead of treating the phytoplankton bloom as an aggregate community phenomenon.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/icesjms/fsv059
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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