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  • 1
    Electronic Resource
    Electronic Resource
    Long-term food modification by Acartia clausi: A preliminary view (1979)
    Springer
    Marine biology 52 (1979), S. 129-136 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract After acclimation, the copepod Acartia clausi was allowed to graze for 5 days in a mixed suspension of two discrete size classes (species) of the chaining diatoms Thalassiosira spp. derived from continuous culture. Total particle numbers and particle size distributions of Thalassiosira spp. were stable throughout the 5 days, indicating that the effects of algal removal and modification due to grazing were balanced by algal growth. Grazer ingestion is the predominant process affecting all size classes of the smaller diatom population (T. nordenskioldii); however, both ingestion and chain modification are observed with the larger diatom (T. gravida). Although the greatest percentage removal of algal volume occurs in the largest algal size classes for each algal species, the greatest volume removal occurs at the modal peak (T. nordenskioldii) or just to the right of the modal peak (T. gravida). Flask-to-flask replicability of experiments was tested with the single-celled T. fluviatilis, and these tests were compared to the long-term experiments with T. nordenskioldii and T. gravida. Net particle removal occurs on both the large and small algal species in mixed suspension, not just on the larger-cell-side of the T. gravida distribution. Although 80% of the particles ingested are from the T. nordenskioldii distribution, 80% of the volume ingested is from the T. gravida distribution. The apparent multi-peak selection observed in our data is discussed in reference to two separate hypotheses and in light of other recent work pertaining to selective grazing by copepods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390420
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Food selection capabilities of the estuarine copepod Acartia clausi (1979)
    Springer
    Marine biology 52 (1979), S. 137-146 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Existing viewpoints and theories of selective grazing by copepods are briefly reviewed in order to formulate explicit hypotheses to be tested experimentally. Based on these hypotheses, a series of grazing experiments was run to determine (1) the extent of the selective ingestion capabilities of Acartia clausi and (2) how these capabilities were affected by previous feeding histories. Groups of copepods were separately preconditioned on a small diatom (Thalassiosira pseudonana), a large diatom (T. fluviatilis), or a plastic sphere. The ingestive behavior was then examined on various combinations of spheres and food particles. Spheres offered alone were not ingested. In mixtures of diatoms and spheres, the copepods avoided ingesting spheres intermediate in size between the sizes of the diatoms. The copepods either ingested particles on either side of the spheres, or ignored all particles less than the size of the largest spheres. The pattern observed depended upon the size of the preconditioning food. However, if the spheres were larger than the largest food particles, the copepods still selectively ingested the food particles. The above results demonstrate that A. clausi has a complex grazing behavior consisting of (1) more efficient grazing on larger particles within its particle-size ingestion range; (2) the ability to alter “effective” setal spacing to optimize feeding behavior (i.e., the ability to increase efficiency of capture of food particles, and to avoid non-food particles); and (3) the ability for post-capture rejection of non-food particles when they interfere with the ingestion of food particles on which the copepod has been preconditioned. The behavioral patterns observed depend heavily on the food preconditioning and the presence or absence of non-food particles. These results clearly indicate that a simple “mechanistic” explanation of selective grazing is insufficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390421
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The rapid response of the marine diatom Skeletonema costatum to changes in external and internal nutrient concentration (1979)
    Springer
    Marine biology 53 (1979), S. 323-333 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A nitrogen-deficient batch culture of the marine diatom Skeletonema costatum, when resupplied with a mixture of nitrate and ammonium, showed an initial enhanced nitrate uptake rate leading to a large internal concentration (pool) of nitrate. Following this initial nitrate uptake event, nitrate uptake ceased, and nitrate assimilation was inhibited until the ammonium present was used. At this point, nitrate uptake resumed and nitrate assimilation began. No internal ammonium pool was observed during nitrate utilization, but a large nitrate pool remained throughout the utilization of external nitrate. The internal nitrate pool decreased rapidly after exhaustion of nitrate from the culture medium, but growth of cellular particulate nitrogen continued for about 24 h. A mathematical simulation model was developed from these data. The model cell consisted of a nitrate pool, ammonium pool, dissolved organic nitrogen pool, and particulate nitrogen. It was found that simple Michaelis-Menten functions for uptake and assimilation gave inadequate fit to the data. Michaelis-Menten functions were modified by inclusion of inhibitory and stimulatory feedback from the internal pools to more accurately represent the observed nutrient utilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391615
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    Paper (German National Licenses)
    Fulltext
  • 4
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    Hollow aggregations of moon jellyfish (Aurelia spp.) (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-23
    Description: The relative importance of behavior and currents in forming and maintaining jellyfish aggregations is not completely understood; the objective of this work was to determine how the physical properties of the water column were related to the formation of hollow aggregations of moon jellyfish ( Aurelia spp.). Hollow aggregations were observed near the surface by airborne lidar in shallow water (〈37 m) when the winds were light (〈4.3 m s –1 ). In this work, a hollow aggregation is defined as a region of few individuals surrounded by high densities in the two dimensions defined by depth and the direction of flight. Hydrographic profiles were available for most of the observations, and the bottom of the aggregation was correlated ( R 2 = 0.42, P = 8 x 10 –4 ) with the depth of the shallow (〈13 m) surface mixed layer despite differences in position and time between the lidar observations and the hydrographic measurements. The size and shape of these aggregations suggests that they are not simply a result of advection by local currents, but of active behaviors. A likely mechanism is that the individuals are swimming in a vertical circle, and this behavior is predicted to enhance mixing at the top of the pycnocline.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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    PAPER CURRENT
  • 5
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    Future marine zooplankton research - a perspective (2001)
    In:  EPIC3Marine ecology-progress series, 222, pp. 297-308
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
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