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  • 1
    Electronic Resource
    Electronic Resource
    Species-specific sedimentation and sinking velocities of diatoms (1991)
    Springer
    Marine biology 108 (1991), S. 449-455 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sedimentation rates were determined for various diatom species, and both average and maximum sinking velocities of sedimenting diatoms were calculated during a spring bloom investigation in the central Baltic Sea in 1986. Up to 25 and 50% of theChaetoceros spp. andThalassiosira levanderi populations, respectively, sedimented daily. Daily sedimentation rates of other diatoms, dinoflagellates andMesodinium rubrum, however, were less than 1% of their respective standing stocks. TheT. levanderi population was divided into two subpopulations: while one was sinking, the second was actively dividing (recognizable by paired-cell stages) with a specific growth rate of 〉0.2 to 0.3 d−1. These paired cells were never found in sediment trap samples. The average sinking velocity ofChaetoceros spp. was 15 to 30 m d−1; that ofT. levanderi was higher. The maximum sinking velocity of cells was at least 70 m d−1. According to these observations, the formation of aggregates (which enhances sinking velocity), and their sedimentation, represent a highly selective process. This indicates that diatom aggregates do not act as roving filters, sweeping the water clear while sinking.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313655
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Vertical migration ofGonyaulax catenata andMesodinium rubrum (1991)
    Springer
    Marine biology 110 (1991), S. 455-463 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Diel migration patterns ofGonyaulax catenata andMesodinium rubrum in the central Baltic during spring 1986 are presented. The depth at which maximum cell concentration of these species occurred was dependent during daytime to a great degree on light intensity; it is hypothesized that the organisms migrated upwards toward higher light intensities until a certain threshold irradiance was reached, after which migration was directed downwards to avoid light intensities higher than the threshold. This threshold level probably depended on nutrient conditions and on the daily average of total irradiance of the foregoing days (light history). Furthermore, it is hypothesized that migration is an important mechanism for adapting to daily irradiance fluctuations. The dependence of migration on irradiance was more obvious forG. catenata than forM. rubrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01344364
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    Paper (German National Licenses)
    Fulltext
  • 3
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    Distribution of calcifying and silicifying phytoplankton in relation to environmental and biogeochemical parameters during the late stages of the 2005 North East Atlantic Spring Bloom (2009)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 6 (10). pp. 2155-2179.
    Details
    Publication Date: 2018-03-09
    Description: The late stage of the North East Atlantic (NEA) spring bloom was investigated during June 2005 along a transect section from 45 to 66° N between 15 and 20° W in order to characterize the contribution of siliceous and calcareous phytoplankton groups and describe their distribution in relation to environmental factors. We measured several biogeochemical parameters such as nutrients, surface trace metals, algal pigments, biogenic silica (BSi), particulate inorganic carbon (PIC) or calcium carbonate, particulate organic carbon, nitrogen and phosphorus (POC, PON and POP, respectively), as well as transparent exopolymer particles (TEP). Results were compared with other studies undertaken in this area since the JGOFS NABE program. Characteristics of the spring bloom generally agreed well with the accepted scenario for the development of the autotrophic community. The NEA seasonal diatom bloom was in the late stages when we sampled the area and diatoms were constrained to the northern part of our transect, over the Icelandic Basin (IB) and Icelandic Shelf (IS). Coccolithophores dominated the phytoplankton community, with a large distribution over the Rockall-Hatton Plateau (RHP) and IB. The Porcupine Abyssal Plain (PAP) region at the southern end of our transect was the region with the lowest biomass, as demonstrated by very low Chla concentrations and a community dominated by picophytoplankton. Early depletion of dissolved silicic acid (DSi) and increased stratification of the surface layer most likely triggered the end of the diatom bloom, leading to coccolithophore dominance. The chronic Si deficiency observed in the NEA could be linked to moderate Fe limitation, which increases the efficiency of the Si pump. TEP closely mirrored the distribution of both biogenic silica at depth and prymnesiophytes in the surface layer suggesting the sedimentation of the diatom bloom in the form of aggregates, but the relative contribution of diatoms and coccolithophores to carbon export in this area still needs to be resolved.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-6-2155-2009
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Microbial dynamics in autotrophic and heterotrophic seawater mesocosms. I. Effect of phytoplankton on the microbial loop (2007)
    Inter Research
    In:  Aquatic Microbial Ecology, 49 . pp. 109-121.
    Details
    Publication Date: 2016-05-26
    Description: The effect of phytoplankton on the other compartments of a simple microbial loop consisting of dissolved matter, bacteria and nanoflagellates was investigated in three 1000 l mesocosms. These mesocosms were inoculated with a natural bacterial community and (1) no other additions (No Addition tank), (2) Phaeocystis globosa (Phaeocystis tank), or (3) 2 diatom species (Diatom tank). During the 20 d experiment, autotrophic activity was negligible in the No Addition tank. In contrast a small P. globosa bloom developed in the Phaeocystis tank and a large diatom bloom dominated the Diatom tank. In this paper we describe the experiment, the changes in chlorophyll a and heterotrophic nanoflagellate concentrations, as well as the cycling of nitrogen, phosphorus, and silica. Then we provide a synthesis of the structure and functioning of the microbial loops in these 3 systems using cluster analysis, a statistical pattern recognition tool. The goal was to test the hypothesis that differences in the resident phytoplankton populations would be reflected in (1) the composition and concentration of dissolved organic matter, (2) the composition of the bacterial community, (3) the food web, and (4) the cycling of elements and organic matter. In all 3 mesocosms, nitrate and silicic acid remained abundant. Orthophosphate was preferred by diatoms, whereas Phaeocystis appeared to prefer dissolved organic phosphorus. The hypothesis that phytoplankton composition shapes the structure and functioning of the microbial loop was partially supported: 6 d after inoculation each mesocosm exhibited a distinct organic matter signature. After 10 to 12 d, concentrations of heterotrophic nanoflagellates were high enough to exert significant grazing pressure in all 3 mesocosms. A parallel shift in bacterial community composition was visible in all mesocosms at this time, possibly reflecting grazing pressure. The food-web structure developed divergently in the 3 mesocosms during the second half of the experiment. Differences in biochemical cycling between mesocosms were predominantly driven by the large quantitative differences in autotrophs.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/ame01138
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Overview of a mesocosm experiment investigating the impact of phytoplankton on the microbial loop (2007)
    In:  [Talk] In: ASLO 2007 Aquatic Sciences Meeting: Water Rocks, 04.-09.02.2007, Santa Fe, USA .
    Details
    Publication Date: 2019-08-09
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 6
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    The effect of different CO2 concentrations on bacterial abundance and activity in the course of a diatom bloom (2004)
    In:  [Talk] In: Abstract VAM, 2004, Braunschweig, Germany .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 7
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    The role of aggregation for the dissolution of diatom frustules (2002)
    In:  [Talk] In: 8. Symposium on Aquatic Microbial Ecology (SAME-8), 25.-29.10.2002, Taormina, Sicily, Italy .
    Details
    Publication Date: 2019-08-09
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 8
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    The Role of Transparent Exopolymer Particles (TEP) in determining C:N ratios of particulate matter (2001)
    In:  [Talk] In: ASLO Aquatic Sciences Meeting 2001, 12.-15.02.2001, Albuquerque, USA .
    Details
    Publication Date: 2019-08-09
    Description: Particulate organic matter which displays a fairly constant C:N ratio (Redfield ratio) consists of different particle types, including organisms, detritus and transparent exopolymer particles (TEP). Whereas the C:N-ratio of cells frequently lies below Redfield, the C:N ratio of TEP, which are formed abiotically from exuded polysaccharides is higher. The mean molar C:N ratios of TEP derived from cultures and natural diatom populations grown under different conditions exhibited a mean value of 26. This is considered a low estimate, as the nitrogen fraction can be explained through adsorption of amino acids onto TEP. The TEP-derived carbon concentration was calculated in 6 marine environments, based on the derived relationship between carbon and TEP. The contribution of TEP-carbon to the total carbon pool was large, in some cases as high as the POC contribution. TEP are also an essential component of marine snow and contribute appreciably to carbon flux. Because TEP are enriched in carbon over nitrogen, an increase in the formation rate of TEP due to global warming would provide a pathway for the sequestration of excess carbon to the deeper water column.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 9
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    Testing the effect of CO2 concentration on dynamics of marine heterotrophic bacterioplankton (2006)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 51 (1). pp. 1-11.
    Details
    Publication Date: 2019-09-23
    Description: To date no study exists that directly addresses changes in dynamics of heterotrophic bacteria in surface waters in relation to partial pressure of CO2 (pCO2). Therefore, we studied the effect of changes in pCO2 on bacterial abundance and activities by using mesocosms with different pCO2 levels (~190, ~370, and ~700 ppmV, representing past, present-day, and future atmospheric pCO2, respectively). Abundance of total bacteria did not differ with increasing pCO2 throughout the whole study period, whereas bacterial protein production (BPP) was highest at highest pCO2. This effect was even more pronounced for cell-specific production rates, especially those of attached bacteria, which were up to 25 times higher than those of free bacteria. During the breakdown of the bloom, however, the abundance of both free and attached bacteria was significantly increased with pCO2. Differences in bacterial growth rate (µ) were smaller than those of BPP, but both µ and BPP of attached bacteria were elevated under high pCO2. Averages of total protease as well as α- and α -glucosidase activities were highest at elevated pCO2 levels, but a statistically significant dependence on pCO2 was only evident for protease activity. There is a measurable but indirect effect of changes in pCO2 on bacterial activities that are mainly linked to phytoplankton and presumably particle dynamics
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2006.51.1.0001
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Contribution of Transparent Exopolymer Particles (TEP) to the marine carbon cycle (2000)
    In:  [Poster] In: International JGOFS Workshop Biogeochemical Cycles: German contributions to the International Joint Global Ocean Flux Study, 18.-21.09.2000, Bremen, Germany .
    Details
    Publication Date: 2019-08-09
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
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