School of Engineering and Science - Jacobs University

DISCUSSION
Figure 1: A rather simplified food web of the North Sea (after Sommer, 2005).
A microzooplankton diet transfers not only energy but also minerals, vitamins, amino
acids, fatty acids and sterols from lower trophic levels, thus balancing any nutritional
shortfalls of herbivory by “trophic upgrading” (Klein Breteler et al., 1999, Tang & Taal,
2005). Such shortfalls occur frequently during nutrient-limiting conditions for
phytoplankton in an ongoing bloom (Malzahn et al., 2010). These facts support my
finding that during the course of the phytoplankton bloom microzooplankton became
even more dominant in the diet of the copepods than phytoplankton, although
autotrophic prey was available in much higher concentrations. The reproductive success
in copepods can be directly enhanced by the availability of nutritionally “better”
microzooplankton prey (Tang & Taal, 2005). Copepods in turn are themselves an
important diet of fish larvae and the availability of this food source is crucial for their
survival (Castonguay et al., 2008). The availability of microzooplankton prey can thus
potentially influence fish abundances. More recent studies suggest that
microzooplankton is also important prey for fish larvae, thereby directly influencing
fish abundance (Montagnes et al., 2010).
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