School of Engineering and Science - Jacobs University

DISCUSSION
transported around the world and released in environments where the new species can
have severe impacts on the original biocoenosis, and therefore indirectly or directly on
the human society (Shiganova et al., 2003, Gollasch, 2006, Gregg & Hallegraeff, 2007).
Higher temperatures broaden the basis for such species invasions. In turn, cold-adapted
species at the southernmost border of their geographic range can be suppressed by rising
temperatures (Beaugrand et al., 2003), their occurrence can be restricted to colder
seasons or they can disappear totally. As plankton forms the basis of the marine food
web the effects of climate-induced biodiversity changes in the plankton are not yet
assessable at the food web level but are possibly profound (Beaugrand & Kirby, 2010).
Continuous plankton monitoring programs can reveal changes in the plankton
community on an early stage and are therefore of utmost importance. Only in observing
the roots of change an estimation of the consequences of change is possible.
This short glimpse into potential impacts of climate change shows that assessing the
role of microzooplankton in future climate scenarios is extremely difficult and further
research is necessary to reveal the effects on microzooplankton and its implication for
food web functioning.
Outlook
It is obvious that we are just beginning to understand the food web processes in the
marine system. The results of the work presented here contribute to the elucidation of
the role of dinoflagellates and ciliates in a small part of the marine food web of the
North Sea. It is now clear that both groups are indeed fundamentally important
intermediaries in terms of grazing as well as for transporting energy to higher trophic
levels. In addition to these deeper insights, a lot of new questions have been raised from
this study. Fundamental for a better understanding of its ecological role in the North
Sea, we need to increase our knowledge on the species composition of
microzooplankton. This can only be achieved by more detailed and continuous
taxonomical observations. In combination with long-term data such as the Helgoland
time series, such observations can provide a powerful tool to reveal the biotic and
abiotic factors that drive microzooplankton abundance and composition. Having
demonstrated the important role of microzooplankton during the course of a spring
bloom, further investigations are now necessary for elucidating the role of
microzooplankters as grazers and also as prey items during other specific times of the
year. Clarifying interactive patterns between microzooplankton members has also been
neglected up to date. However, as such interactions can have considerable effects on
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