School of Engineering and Science - Jacobs University

DISCUSSION
and showed a clear seasonality with minima during winter and maxima during summer.
The heterotrophic part of both groups contributed to the planktonic biomass with carbon
concentrations ranging from 2 to 652 µg L -1 . Including also mixotrophic species yielded
maxima of 779 µg L -1 . These concentrations are in a typical range for the North Sea
(Riegman et al., 1993, Brussaard et al., 1995).
The community I observed was highly diverse, with 62 dinoflagellate taxa and 63 ciliate
taxa typical for the North Sea (Riegman et al., 1993, Brussaard et al., 1995, Hoppenrath,
2004, Stelfox-Widdicombe et al., 2004). The numerically most important heterotrophic
dinoflagellates were species of the genera Gyrodinium and Protoperidinium, while
Noctiluca scintillans contributed large proportions to the biomass. Mixotrophic
dinoflagellates of several genera partly also reached a high planktonic biomass during
blooms. The most important ciliates, in terms of abundance, were species of the genera
Strombidium and Strobilidium, the functionally phototrophic Myrionecta rubra and
tintinnids. Large Cyclotrichium spp. contributed substantially to ciliate biomass. The
data on ciliates presented in Chapter 1 are completely new for Helgoland Roads,
whereas dinoflagellates have been counted since 1962 (Wiltshire & Dürselen, 2004).
However, these records do not mirror the natural diversity (Hoppenrath, 2004). My
monitoring aimed at a higher taxonomic resolution in dinoflagellates and ciliates
compared to the Helgoland time series on plankton. This could partially be achieved
(Chapter I) (Protoperidinium spp., ciliates). The longer monitoring period compared to
other studies (Riegman et al., 1993, Brussaard et al., 1995, Stelfox-Widdicombe et al.,
2004) also revealed general patterns in the seasonality of both groups.
However, there is still a great need for further work on this topic at Helgoland Roads
and a microzooplankton monitoring aiming at a higher taxonomic resolution should be
included into the long-term observation for detailed insights into the species
composition. Due to the methodology used (Lugol fixation and light microscopy) many
cells could be identified to genus level only or were assigned to morphologically similar
groups (Johansson et al., 2004). Especially naked ciliates and dinoflagellates should
receive further attention. Elucidating the taxonomy of these groups by applying live
observation, epifluorescence (Elbrächter, 1994, Kraberg et al., 2010) and scanning
microscopy techniques (Hernandez-Becerril et al., 2010), as well as staining techniques
(Agatha & Tsai, 2008) is feasible. Applying these methods in combination with
molecular methods (Sherr & Sherr, 2002) provides further insights into the taxonomy of
dinoflagellates (Gottschling et al., 2005) and ciliates (Agatha, 2004). For gaining
fundamental knowledge on the role of microzooplankton in the food web we first have
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