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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
    Format: text
    DOI: 10.3354/meps12632
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Simultaneous analysis of δ13C, δ15N and δ34S ratios uncovers food web relationships and the trophic importance of epiphytes in an eelgrass, Zostera marina community (2014)
    Inter Research
    In:  Marine Ecology Progress Series, 497 . pp. 93-103.
    Details
    Publication Date: 2019-02-06
    Description: Simultaneous analysis of carbon, nitrogen and sulphur stable isotope ratios was applied in this pilot study to examine the food web of a Zostera marina L. system in the western Baltic Sea. Samples of three potential food sources: eelgrass, epiphytic algae and seston, as well as 69 consumer species were collected during the growing season of Z. marina from March to September 2011. The measured δ13C values of epiphytes (-14.1‰ ± 1.8 SD) were close to δ13C values of eelgrass (-11.6‰ ± 1.8 SD), impeding a clear distinction of those two carbon sources, whereas seston δ13C values (-20.9‰ ± 3.5 SD) were clearly different. This frequently encountered problem was solved by the additional use of δ34S, which resulted in easily distinguishable values for sediment and seawater derived sulphur. Values of primary producer δ34S ranged from 5.6‰ (± 2.3 SD) for Z. marina leaves to 14.2‰ (± 1.6 SD) for epiphytes and 11.9‰ (± 3.3 SD) for seston. The combination of δ34S and δ13C values made a separation of carbon sources possible and enabled the allocation of potential food sources to consumers and a description of their trophic relationships. The data of stable isotope ratio analysis of this eelgrass community strongly indicate a food web based on epiphyte and seston production. δ15N values show a food web consisting of large numbers of generalists and a high degree of omnivory amongst the consumer species analysed. This implies an occupation of every trophic position possible, which is supported by a continuous distribution of δ15N values. Previously described eelgrass food webs may have to be re-evaluated to include sulfur in order to provide a clear picture on primary carbon sources.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.3354/meps10569
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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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
    Format: text
    DOI: 10.3354/meps11081
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Community interactions dampen acidification effects in a coastal plankton system (2013)
    Inter Research
    In:  Marine Ecology Progress Series, 486 . pp. 37-46.
    Details
    Publication Date: 2018-06-25
    Description: Changing seawater chemistry towards reduced pH as a result of increasing atmospheric carbon dioxide (CO2) is affecting oceanic organisms, particularly calcifying species. Responses of non-calcifying consumers are highly variable and mainly mediated through indirect ocean acidification effects induced by changing the biochemical content of their prey, as shown within single species and simple 2-trophic level systems. However, it can be expected that indirect CO2 impacts observed at the single species level are compensated at the ecosystem level by species richness and complex trophic interactions. A dampening of CO2-effects can be further expected for coastal communities adapted to strong natural fluctuations in pCO2, typical for productive coastal habitats. Here we show that a plankton community of the Kiel Fjord was tolerant to CO2 partial pressure (pCO2) levels projected for the end of this century (〈1400 µatm), and only subtle differences were observed at the extremely high value of 4000 µatm. We found similar phyto- and microzooplankton biomass and copepod abundance and egg production across all CO2 treatment levels. Stoichiometric phytoplankton food quality was minimally different at the highest pCO2 treatment, but was far from being potentially limiting for copepods. These results are in contrast to studies that include only a single species, which observe strong indirect CO2 effects for herbivores and suggest limitations of biological responses at the level of organism to community. Although this coastal plankton community was highly tolerant to high fluctuations in pCO2, increase in hypoxia and CO2 uptake by the ocean can aggravate acidification and may lead to pH changes outside the range presently experienced by coastal organisms.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.3354/meps10352
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Grazing by mesozooplankton from Kiel Bight, Baltic Sea, on different sized algae and natural seston size fractions (2000)
    Inter Research
    In:  Marine Ecology Progress Series, 199 . pp. 43-53.
    Details
    Publication Date: 2018-05-09
    Description: Grazing experiments were conducted with natural mesozooplankton from Kiel Bight, Germany, using radioactive labelled phytoplankton cultures and seston size fractions. The results of experiments using phytoplankton cultures indicated that bivalve veligers performed highest clearance of particles within a size range of 4.7 to 6.3 µm, whereas optimum particle size for copepods was 15 µm. The results of experiments using labelled natural seston size fractions identified bivalve veligers and appendicularians as those responsible for the removal of particles within the smallest size class (〈2 µm). Seston size fractions larger than 5 µm were mainly cleared by copepods and nauplii. As particle size increased, the contribution of copepod clearance to total zooplankton clearance within size classes increased from 57% (〈5 µm size class) to more than 81% (30 to 100 µm size class). When the nauplii clearance rates were included, the total copepod clearance accounted for 90 to 97.6% of the total volume cleared of particles bigger than 10 µm. Despite low abundances of bivalve veligers and appendicularians in Kiel Bight at the time of the experiment, we calculated that approximately 10 and 8.5%, respectively, of the carbon ingested by total mesozooplankton was due to veliger and appendicularian grazing. The importance of bivalve veligers might be seen in their grazing on seston particles that escape predation by copepods and on the amount of energy that is therefore directed from the water column to the benthos when larvae settle.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps199043
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  • 6
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    Positive effects of mesograzers on epiphytes in an eelgrass system (2010)
    Inter Research
    In:  Marine Ecology Progress Series, 401 . pp. 77-85.
    Details
    Publication Date: 2018-06-19
    Description: Traditionally, consumer–prey interactions have been considered as purely negative, but herbivores may have positive effects on plants and their productivity. Grazing may enhance prey biomass-specific productivity by directly or indirectly reducing the competition for light, nutrients, and space. We studied the effect of 4 common mesograzers, the isopod Idotea baltica, the amphipod Gammarus oceanicus, and the gastropods Littorina littorea and Rissoa membranacea on epiphytes in an eelgrass Zostera marina L. system. Eelgrass was grown in laboratory mesocosms for a set of experiments manipulating mesograzer species identity, mesograzer density and nutrient concentration. We measured epiphyte biomass-specific productivity via incorporation of radioactive carbon. Herbivore effects on epiphyte photosynthetic capacity were strongly positive for R. membranacea, moderately positive for L. littorea and I. baltica and zero for G. oceanicus under low nutrient supply. Both gastropods increased the nitrogen content of epiphytes, especially the small R. membranacea, and enhanced epiphyte growth. The crustacean species did not increase epiphyte nutrient content, but I. baltica probably enhanced epiphyte productivity by removing the overstory of algal cells, and thus reducing competition for light, nutrients, and space. The positive effect of the 2 gastropod species disappeared under higher nutrient supply, implying the importance of nutrient limitation for this interaction. The positive effect of I. baltica remained at moderate grazer densities despite the higher nutrient concentrations.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.3354/meps08412
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Competition between benthic cyanobacteria and diatoms as influenced by different grain sizes and temperatures (1999)
    Inter Research
    In:  Marine Ecology Progress Series, 187 . pp. 77-87.
    Details
    Publication Date: 2019-09-23
    Description: An experimental laboratory set-up was used to study the influence of different grain size compositions and temperatures on the growth of benthic cyanobacteria and diatoms, and on the competition between these 2 groups. Monospecific cultures of 3 species of cyanobacteria (Merismopedia punctata, Microcoleus chthonoplastes, Oscillatoria limosa), and of 2 species of benthic diatoms (Phaeodactylum tricornutum and Nitzschia sp.) were used. The organisms were cultured in 100 ml flasks filled with medium and 3 different kinds of sediment: (1) Sand (fine sand, 63 to 200 µm), (2) Mud-I (mixed fine sand and mud 〈63 µm in the ratio 80:20 wt %), (3) Mud-II (mixed fine sand and mud in the ratio 50:50 wt %). Experimental temperatures were 10, 15 and 25°C. At 10°C and 15°C, both diatom species achieved the highest biomass on the sediments of the finest grain size (50 wt % 〈 63 µm) while cyanobacteria achieved low biomass levels. Coarsening of sediments at the same temperature levels revealed a gradually lower biomass of the diatoms. Particularly on sand, the diatoms never reached the same concentrations of chlorophyll a as on mud. The cyanobacteria, on the other hand, had the highest biomass on sand at 15°C. In the competition experiments the benthic diatom species Nitzschia sp. dominated all types of sediments at 10°C and 15°C. The experiments at 25°C were dominated by the filamentous cyanobacterium M. chthonoplastes. This indicates the importance of abiotic conditions for the distribution and abundance of benthic phototrophic micro-organisms.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps187077
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  • 8
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    Temporal variation in stable isotope composition (δ13C, δ15N and δ34S) of a temperate Zostera marina food web (2014)
    Inter Research
    In:  Marine Ecology Progress Series, 505 . pp. 95-105.
    Details
    Publication Date: 2019-04-01
    Description: Simultaneous triple stable isotope analysis of carbon, nitrogen and sulphur was employed to study the temporal variation in the food web of a subtidal eelgrass Zostera marina bed in the western Baltic Sea. Samples of 3 potential food sources (eelgrass, epiphytes and seston) and consumer species were collected biweekly from March through September 2011. Temporal variation of stable isotope compositions was observed in primary producers and consumer species. However, variation between replicates, particularly omnivores, often exceeded variation over time. The high degree of omnivory among the generalist feeders in this eelgrass community allows for generalist feeders to flexibly switch food sources, thus enhancing food-web stability. As coastal systems are subject to seasonal changes, as well as alterations related to human disturbance and climate, these food webs may retain a certain resilience due to their plentiful omnivores.
    Type: Article , PeerReviewed
    Format: text
    Format: other
    DOI: 10.3354/meps10797
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Nutrient competition experiments with periphyton from the Baltic Sea (1996)
    Inter Research
    In:  Marine Ecology Progress Series, 140 . pp. 161-167.
    Details
    Publication Date: 2018-05-08
    Description: Nutrient competition experiments were performed with periphytic microalgae from the Kiel Fjord, western Baltic Sea. Diatoms were dominant competitors at high Si:N ratios (under N-limited conditions) and high Si:P ratios (under P-limited conditions). Under low silicate supply, cyanobacteria became dominant at low N:P ratios and chlorophytes at high ones. Changes in light intensity influenced the outcome of competition at the species level but not at the level of higher taxa. The nitrogen source (ammonium or nitrate) had no impact on the outcome of competition.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps140161
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    'Co-consumption' and 'protective coating': two new proposed effects of epiphytes on their macro algal hosts in mesograzer-epiphyte-host interactions (2000)
    Inter Research
    In:  Marine Ecology Progress Series, 205 . pp. 85-93.
    Details
    Publication Date: 2018-05-08
    Description: Multiple-choice feeding experiments were performed with the isopod Idotea granulosa and the amphipod Gammarus locusta as consumers. In a first experiment, 2 different types of tissues of the brown seaweed Fucus vesiculosus and its main macroepiphytes, Ulva lactuca and Elachista fucicola, were offered. I. granulosa rejected apices of F. vesiculosus and preferred E. fucicola, while G. locusta clearly preferred F. vesiculosus tissue, especially the meristematic apices. In a second experiment, F. vesiculosus tissue with and without E. fucicola was offered together. For I. granulosa, the consumption of F. vesiculosus was enhanced by the presence of the epiphyte, while for G. locusta there was no difference in consumed F. vesiculosus mass. G. locusta, however, showed behavioural rejection of E. fucicola, and thus, the epiphyte acted as Œprotective coating¹. We conclude that host (F. vesiculosus) tissue could be Œco-consumed¹ by mesograzers (I. granulosa) that were attracted by the presence of epiphytes and that these epiphytes therefore may have a 2-fold negative effect on the host (i.e. competion for light, nutrients etc. and attraction of consumers). ŒCo-consumption¹ and Œprotective coating¹ add 2 more facets to the very variable and case-dependent interrelationships of mesograzer-epiphyte-host systems; their relevance in nature, however, remains to be demonstrated.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps205085
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