School of Engineering and Science - Jacobs University

RESEARCH AIMS
RESEARCH AIMS
The general aim of this study was to elucidate the role of heterotrophic dinoflagellates
and ciliates at the base of the North Sea food web at Helgoland Roads. The North Sea
around the island of Helgoland has long been recognized as a reference area for the
whole German Bight and thus marine research has a long tradition on Helgoland.
Continuous work-daily measurements of several abiotic parameters and phytoplankton
counts are carried out since 1962 and result in one of the richest temporal marine data
sets available - the Helgoland Roads time series (Wiltshire et al., 2010). The
combination of its representative location and the availability of the long-term data set
provide an excellent potential for marine research on Helgoland, especially in the field
of food web interactions between planktonic organisms. This potential has been
extensively utilised during this study. The detailed research aims during this thesis are
given in the next paragraphs.
1. Before detailed studies of food web interactions were feasible baseline data on the
actual species composition and seasonality of heterotrophic dinoflagellates and ciliates
at Helgoland Roads were vital. Therefore, the first step was the set up of a continuous
monitoring study, which enumerated both groups on a regular basis. This was
fundamental to determine important “key” model species for establishing cultures
which served for detailed laboratory investigations. Furthermore, the monitoring was
aimed at revealing times in the year at which heterotrophic dinoflagellates and ciliates
potentially play a key role as grazers and at which experiments on their grazing impact
should best be conducted.
2. The second aim was to ascertain the most appropriate method to investigate the
grazing impact of microzooplankton with focus on the determination of the in situ
grazing rate of microzooplankton. Furthermore, this method was tested, weak points in
methodology addressed and if necessary improvements were considered and evaluated
experimentally.
3. These first two crucial steps were then followed by experimental studies to determine
the importance of the in situ grazing impact of the microzooplankton in comparison to
the impact of mesozooplankters, i.e. copepods, especially during phytoplankton blooms.
According to the monitoring data, the timing of the grazing experiments was planned
considering times during which microzooplankton grazers potentially play a key role.
13