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  • PANGAEA  (28)
  • Oxford Univ. Press  (6)
  • Mare
  • 2015-2019  (34)
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  • 1
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    Oxford Univ. Press
    In:  Journal of Plankton Research, 39 (5). pp. 772-780.
    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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  • 2
    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
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  • 3
    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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  • 4
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    Oxford Univ. Press
    In:  Journal of Plankton Research, 39 (3). pp. 494-508.
    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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  • 5
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    Oxford Univ. Press
    In:  Journal of Plankton Research, 40 (5). pp. 568-579.
    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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  • 6
    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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  • 7
    Publication Date: 2023-02-24
    Keywords: BIOACID; Biological Impacts of Ocean Acidification; Cell, diameter; Cell biovolume; Cell size; Taxon/taxa
    Type: Dataset
    Format: text/tab-separated-values, 620 data points
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  • 8
    Publication Date: 2023-04-25
    Keywords: DATE/TIME; Experimental treatment; Identification; Nitrate; Phosphate; Silicate; Treatment: light intensity; Treatment: nutrients
    Type: Dataset
    Format: text/tab-separated-values, 1008 data points
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  • 9
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    PANGAEA
    In:  Supplement to: Garzke, Jessica; Hansen, Thomas; Ismar, Stefanie M; Sommer, Ulrich; Ross, Pauline M (2016): Combined Effects of Ocean Warming and Acidification on Copepod Abundance, Body Size and Fatty Acid Content. PLoS ONE, 11(5), e0155952, https://doi.org/10.1371/journal.pone.0155952
    Publication Date: 2023-04-24
    Description: Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1-5) and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA) and arachidonic acid (ARA) to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts
    Keywords: BIOACID; Biological Impacts of Ocean Acidification
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 10
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    PANGAEA
    In:  Supplement to: Ismar, Stefanie M; Kottmann, Johanna S; Sommer, Ulrich (2018): First genetic quantification of sex- and stage-specific feeding in the ubiquitous copepod Acartia tonsa. Marine Biology, 165(2), https://doi.org/10.1007/s00227-017-3281-z
    Publication Date: 2023-01-13
    Description: Marine copepods provide the major food-web link between primary producers and higher trophic levels, and their feeding ecology is of acute interest in light of global change impacts on food-web functioning. Recently, quantitative polymerase chain reaction (qPCR) protocols have been developed, which can complement classic diet quantification methods, such as stable isotope or fatty acid analyses tools. Here, we present first results of feeding experiments assessing sex- and stage-specific food intake by the ubiquitous calanoid copepod Acartia tonsa by 18S targeted qPCR and microscopic grazing assessment. In triplicated mixed-diet feeding treatments, three suitable A. tonsa diets, the cryptophyte Rhodomonas balthica, the haptophyte Isochrysis galbana, and the diatom Thalassiosira weissflogii, were offered in equal biomass proportions under constant conditions. Prey uptake substantially varied between different algal species, as did the extent of sex- and stage-specificity of prey uptake. Male adult copepods had higher R. balthica gut contents than females, and nauplii contained more of this prey source than copepodites or adult copepods in mixed treatments. A trend towards higher amounts of ingested T. weissflogii in adult females than in males and in nauplii than in other stages was detected. Genetic gut content quantifications indicated low feeding on I. galbana, and no consistent sex- or stage-specific differences of I. galbana content in A. tonsa. Our results highlight diet-specific feeding differences between Acartia life stages and sexes, which can have implications on food-web dynamics and specific nutrient transfer to higher trophic levels in copepod populations of varying age composition under changing environmental parameters, such as rising temperatures and increasing ocean acidification.
    Type: Dataset
    Format: application/zip, 2 datasets
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