**4. Importance of fungi for aquatic food webs**

The importance of fungi as secondary producers of biomass has been well described for headwater streams with leaf litter (Suberkropp, 1992) and for reed stands in littoral zones of lakes and in marshlands. The foregut content of 109 different aquatic insects collected on submerged wood showed that in 66% of all studied insect species fungi were part of their diet (Pereira et al., 1982) and many conidia of aquatic fungi were found in faeces of fish (Sridhar & Sudheep, 2011). Furthermore, it has been shown that food web manipulations greatly alter the fungal biomass in lakes (Mancinelli et al., 2002). This suggests that saprophytic fungi transfer organic matter directly to the higher trophic levels of aquatic food webs. It is therefore likely that environmental change can have severe consequences for overall food web topology, and hence nutrient and energy cycling.

In addition, fungi can be important parasites of primary producers, e.g. phytoplankton, which fuel the aquatic food web with organic matter and energy. Lysis of aquatic organisms by fungal and protozoan parasites increases organic matter and energy cycling. These processes are often solely attributed to *Bacteria* and *Archaea*, however, aquatic fungi actively contribute as mineralisers and parasites.
