School of Engineering and Science - Jacobs University

OUTLINE OF THE THESIS
OUTLINE OF THE THESIS
Species composition of ciliates and dinoflagellates at Helgoland Roads
As a first approach a 2.5 year monitoring for species composition and succession of
naturally occurring heterotrophic dinoflagellates and ciliates was established on a
weekly basis at Helgoland Roads. This monitoring program served as a background to
determine the seasonal distributions of dinoflagellate and ciliate species at Helgoland
Roads and their relative importance to other organisms throughout the year. Results of
this monitoring are reported in Manuscript I.
Improvement of the methodology of microzooplankton grazing experiments
There is a lot of debate on the loss of fragile microzooplankton species during
manipulation of microzooplankton communities when setting up seawater dilution
experiments and other grazing experiments. As this fragility could lead to a bias in
microzooplankton composition, problematic for biodiversity considerations and in situ
grazing studies, I investigated a potential improvement of the method for manipulating
water samples containing microzooplankton communities. The resulting alternative
“filling” technique is evaluated in comparison to a standard technique in Manuscript II.
The role of microzooplankton and copepod grazers during the spring bloom
The role of ciliates, heterotrophic dinoflagellates and copepods in structuring spring
plankton communities was investigated during the course of a spring bloom.
Experiments on microzooplankton and copepod grazing as well as on food selectivity
were carried out on four occasions during different phases of the phytoplankton spring
bloom. Furthermore, detailed species succession of microzooplankton as well as
phytoplankton was monitored during this bloom. General patterns of grazing and
selectivity in dinoflagellates and ciliates in comparison to copepods, and the role of the
selective grazing of microzooplankton in shaping the phytoplankton bloom assemblage
are discussed in Manuscript III.
Interactions within microzooplankton grazers
Several experiments were designed to investigate specific interactions between two
different microzooplankton grazers. A model system consisting of a large ciliate
predator, a small dinoflagellate predator and a phototrophic dinoflagellate prey
organism co-occurring at Helgoland Roads was used. Hypothetical interactions between
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