School of Engineering and Science - Jacobs University

INTRODUCTION
within the microzooplankton, have rarely been investigated. In addition, experiments on
microzooplankton are hampered by the fragility of certain groups (Gifford, 1985). The
methodological approaches for the investigation of these species have to be improved as
the conservation of fragile species for and also in experiments is fundamental to the
ability to answer questions about their ecology.
These examples, proxies for a whole list of unanswered questions, show that there is
still a great need for further research on microzooplankton and its role in the marine
food web. In the following paragraphs I will focus on the current knowledge on
dinoflagellates and ciliates to give a brief insight into their ecology.
The most important microzooplankton groups: Dinoflagellates and ciliates
Dinoflagellates and ciliates are cosmopolitan groups in marine, freshwater, benthic and
planktonic habitats. In the oceans they occur in such contrasting ecosystems as the
eutrophic, turbid and shallow Wadden Sea, the oligotrophic tropical Pacific, the
Mediterranean and the Polar Regions. Many species of both groups are known to be
mixotrophic and their nutrition ranges from phototrophic with the ability to ingest
organic particles, to phagotrophic with the additional ability to retain chloroplasts of
their prey organisms (so-called ‘kleptochloroplasts’) and to use these for
photosynthesis. Examples of mixotrophy among phototrophic species are the ciliate
Myrionecta rubra (Johnson & Stoecker, 2005) and a variety of phototrophic
dinoflagellates (Du Yoo et al., 2009); phagotrophs with the ability to retain chloroplasts
are, e.g., the ciliate Laboea strobila (Stoecker et al., 1988) and the dinoflagellate genus
Dinophysis (Carvalho et al., 2008). However, many species in both groups display a
purely heterotrophic nutrition.
Dinoflagellates
Dinoflagellates span a large size range from 2 µm (Gymnodinium simplex) to 2 mm
(Noctiluca scintillans) (Taylor, 1987), but the size of the majority lies within 20 to 200
µm thus belonging to the microzooplankton (Sieburth et al., 1978).
Today approximately 2500 living species of various morphologically highly variable
genera of dinoflagellates have been described, of which roughly 40 – 60% are
photosynthetic. However, among those dinoflagellates regarded as photosynthetic a
growing number is found to be capable of taking up organic carbon (mixotrophy) and of
active feeding (Du Yoo et al., 2009) (in this thesis the terms “dinoflagellates” and
“heterotrophic dinoflagellates” refer to the same: Species capable of active feeding).
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