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  • 1
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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
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    DOI: 10.1093/plankt/fbx046
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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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
  • 3
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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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  • 4
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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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  • 5
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    Phytoplankton Cell Size Reduction in Response to Warming Mediated by Nutrient Limitation (2013)
    Public Library of Science
    In:  PLoS ONE, 8 (9). e71528.
    Details
    Publication Date: 2017-06-22
    Description: Shrinking of body size has been proposed as one of the universal responses of organisms to global climate warming. Using phytoplankton as an experimental model system has supported the negative effect of warming on body-size, but it remains controversial whether the size reduction under increasing temperatures is a direct temperature effect or an indirect effect mediated over changes in size selective grazing or enhanced nutrient limitation which should favor smaller cell-sizes. Here we present an experiment with a factorial combination of temperature and nutrient stress which shows that most of the temperature effects on phytoplankton cell size are mediated via nutrient stress. This was found both for community mean cell size and for the cell sizes of most species analyzed. At the highest level of nutrient stress, community mean cell size decreased by 46% per degrees C, while it decreased only by 4.7% at the lowest level of nutrient stress. Individual species showed qualitatively the same trend, but shrinkage per degrees C was smaller. Overall, our results support the hypothesis that temperature effects on cell size are to a great extent mediated by nutrient limitation. This effect is expected to be exacerbated under field conditions, where higher temperatures of the surface waters reduce the vertical nutrient transport.
    Type: Article , PeerReviewed
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    DOI: 10.1371/journal.pone.0071528
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  • 6
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    Warming and Ocean Acidification Effects on Phytoplankton - From Species Shifts to Size Shifts within Species in a Mesocosm Experiment (2015)
    Public Library of Science
    In:  PLoS ONE, 10 (5). e0125239.
    Details
    Publication Date: 2017-04-13
    Description: While the isolated responses of marine phytoplankton to climate warming and to ocean acidification have been studied intensively, studies on the combined effect of both aspects of Global Change are still scarce. Therefore, we performed a mesocosm experiment with a factorial combination of temperature (9 and 15°C) and pCO2 (means: 439 ppm and 1040 ppm) with a natural autumn plankton community from the western Baltic Sea. Temporal trajectories of total biomass and of the biomass of the most important higher taxa followed similar patterns in all treatments. When averaging over the entire time course, phytoplankton biomass decreased with warming and increased with CO2 under warm conditions. The contribution of the two dominant higher phytoplankton taxa (diatoms and cryptophytes) and of the 4 most important species (3 diatoms, 1 cryptophyte) did not respond to the experimental treatments. Taxonomic composition of phytoplankton showed only responses at the level of subdominant and rare species. Phytoplankton cell sizes increased with CO2 addition and decreased with warming. Both effects were stronger for larger species. Warming effects were stronger than CO2 effects and tended to counteract each other. Phytoplankton communities without calcifying species and exposed to short-term variation of CO2 seem to be rather resistant to ocean acidification.
    Type: Article , PeerReviewed
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    DOI: 10.1371/journal.pone.0125239
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  • 7
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    Dominance of the planktonic diatom Thalassiosira minima in recent summers in the Bahia Blanca Estuary, Argentina (2012)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 34 (11). pp. 995-1000.
    Details
    Publication Date: 2018-06-06
    Description: The diatom Thalassiosira minima was first recorded in the Baha Blanca Estuary in 1992. In 19921993 it exhibited a broad seasonal occurrence. A recent survey (20062007) showed a seasonal appearance restricted mainly to summer together with a greater relative abundance within the phytoplankton. A close connection was found with warmer, more saline and highly turbid conditions experienced in recent summers in the estuary. Whether these changes will impact the estuary trophic dynamics remains an open question.
    Type: Article , PeerReviewed
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    DOI: 10.1093/plankt/fbs060
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  • 8
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    Phytoplankton cell size: intra- and interspecific effects of warming and grazing (2012)
    Public Library of Science
    In:  PLoS ONE, 7 (11). e49632.
    Details
    Publication Date: 2018-01-22
    Description: Decreasing body size has been suggested as the third universal biological response to global warming after latitudinal/altitudinal range shifts and shifts in phenology. Size shifts in a community can be the composite result of intraspecific size shifts and of shifts between differently sized species. Metabolic explanations for the size shifts dominate in the literature but top down effects, i.e. intensified size-selective consumption at higher temperatures, have been proposed as alternative explanation. Therefore, we performed phytoplankton experiments with a factorial combination of warming and consumer type (protist feeding mainly on small algae vs. copepods mainly feeding on large algae). Natural phytoplankton was exposed to 3 (1st experiment) or 4 (2nd experiment) temperature levels and 3 (1st experiment: nano-, microzooplankton, copepods) or 2 (2nd experiment: microzooplankton, copepods) types of consumers. Size shifts of individual phytoplankton species and community mean size were analyzed. Both, mean cell size of most of the individual species and mean community cell size decreased with temperature under all grazing regimes. Grazing by copepods caused an additional reduction in cell size. Our results reject the hypothesis, that intensified size selective consumption at higher temperature would be the dominant explanation of decreasing body size. In this case, the size reduction would have taken place only in the copepod treatments but not in the treatments with protist grazing (nano- and microzooplankton).
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1371/ journal.pone.0049632
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  • 9
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    Silicate and the functional geometry of marine phytoplankton (1998)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 20 (9). pp. 1853-1859.
    Details
    Publication Date: 2018-05-30
    Description: The impact of nutrient supply ratios on the functional geometry of phytoplankton has been studied by means of competition experiments with phytoplankton communities from the Arabian Sea. Cell length and deviation from spherical shape of dominant competitors increased with Si:N ratios.Surface:volume ratios were minimal at intermediate Si:N ratios. Grazing by the rotifer Brachionus plicatilis did not lead to a qualitative shift in the response of geometric properties to Si:N ratios; however, mean cell lengths increased while surface:volume ratios decreased.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/plankt/20.9.1853
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  • 10
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    Comparative nutrient status and competitive interactions of two Antarctic diatoms (Corethron criophilum and Thalassiosira antarctica) (1991)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 13 (1). pp. 61-75.
    Details
    Publication Date: 2018-05-30
    Description: The nutrient status of two common Antarctic diatoms (Corethron criophilum and Thalassiosira cf. antarctica) was analysed by studying the growth response in enrichment bioassays and by estimates of the cell quotas of Si, N and P after size-fractionation of net plankton samples Corethron had higher biomass-specific N-quotas; Si- and P-quotas were quite similar between both species. Corethron was Si-limited in five enrichment experiments and not nutrient limited in five experiments. Thalassiosira was not nutrient limited in six experiments, N-hmited in four experiments and Si-limited in one experiment Droop-kinetics of Si-limited growth of Corethron and of N-hmited growth of Thalassiosira were obtained by combining the growth rates in the bioassays and the cell quotas from the natural populations. The minimal Si-quota of Corethron was 0 041 mol Si/mol C, the saturating cell quota was 0.158 mol Si/mol C respectively The minimal N-quota of Thalassiosira was 0 0223 mol N/mol C, the saturating cell quota was 0.208 mol N/mol C Corethron was N-saturated at cell quotas of 〉0 106 mol N/mol C; Thalassiosira was Si-saturated at cell quotas of 〈0 132 mol Si/mol C. As the better competitor for N and the poorer one for Si, Corethron became more important with increasing Si N ratios, while Thalassiosira became more important with decreasing Si:N ratios in the water
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/plankt/13.1.61
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