**2.4.1 Fungal diversity in streams**

Upland stream habitats are characterised by a pool and riffle structure with relatively swift flow and high levels of dissolved oxygen. These streams are narrow and tend to be lined by overhanging riparian vegetation. These characteristics create an ideal habitat for aquatic hyphomycetes. Nikolcheva & Bärlocher (2004) have investigated the structure of fungal

Aquatic Fungi 237

Considering filamentous and higher fungi, the pelagic zone only supports a few specialised fungal species, but seems to be mainly used as a medium for propagules dispersal (Wurzbacher et al., 2010). Fungi from the littoral zone, in turn, are saprobes, parasites, predators, endosymbionts or occasionally lichens. These organisms colonise substrates ranging from submerged plants and litter to the carapaces of dead micro-crustaceans

In the pelagic zone, fungi consist mainly of species that live parasitically on phytoplankton, zooplankton and fish. Taxonomically, the fungal community consists of *Ascomycete* and *Basidiomycete* yeasts and "zoosporic fungi" (*Chytridiomycota* and *Oomycetes*; Rankovic 2005; Lefevre et al., 2007). It has been suggested that "zoosporic fungi" and their propagules are important for pelagic food web dynamics since they are important parasites of freshwater algae and thus may be important in controlling phytoplankton blooms associated with

The profundal zone and lake sediments, however, mainly serve as a propagule bank, where resting spores are stored. Therefore, both aquatic and terrestrial species are frequently isolated from deep lake sediments. Moreover, it has been suggested that yeasts in lake sediments are derived from terrestrial plant litter (Kurtzman & Fell, 2004), and fungal CFU associated with the *Mucoromycotina* (*Mucor* and *Rhizopus* sp.) isolated from various Serbian reservoirs may be also of terrestrial origin (Rankovic, 2005). However, there are a few species of yeasts, *Chytridiomycetes* and *Oomycetes* that are able to grow vegetatively in lake

Fungi may also be found in aquatic habitats with harsh environmental conditions, such as sulfidic springs (Luo et al., 2005), acidic peat bogs and lakes (Thormann, 2006; Voronin, 2010) and volcanic lakes (Sabetta, et al., 2000). When studying fungal diversity in sediments of an estuary, Mohamed & Martiny (2011) found that community composition (at division level) did not differ substantially between fresh, brackish and seawater. However, the proportion of *Chytridiomycetes* and unknown species from basal lineages increased with salinity, and species diversity was at a maximum in the brackish zone. Although several studies have examined the fungi that can be isolated from saline lakes (Butinars et al., 2005; Zalar et al., 2005; Takishita et al., 2007) and mangroves (Suryanarayanand & Kumaresan, 2000; Kumaresan & Suryanarayanan, 2001; Ananda & Sridhar, 2002), fungal biodiversity in

Actual fungal biodiversity suggests that the most species-rich regions of the globe are situated in temperate rather than in tropical regions. Given that many fungal species are host or substrate specific, and that biodiversity of plants and animals is highest in tropical regions, this notion is counter-intuitive. It is very likely that sampling efforts for fungal biodiversity have been largely restricted to temperate regions, where most fungal taxonomists are situated (Shearer et al., 2007). Alternatively, seasons, cooler temperatures and moist conditions may be more amenable to fungal evolution and niche differentiation. From the above mentioned discrepancies and gaps of knowledge in diversity of aquatic fungi, it appears timely to commence co-ordinated world-wide

diatoms (Kagami et al., 2004) and cyanobacteria (*Microcystis* spp.; Chen et al., 2010).

(Czeczuga et al., 2002; 2004; 2007).

sediments (e.g. Ali & Abdel–Raheem, 2003).

these systems requires further investigation.

**3. Hidden biodiversity of aquatic fungi** 

**2.4.4 Other aquatic habitats** 

communities on leaves submerged in an upland stream by using molecular methods. The authors were able to resolve the diversity within the *Ascomycota, Basidiomycota, Chytridiomycota, Zygomycetes* and *Oomycetes* and found, that the leaf decomposer community was dominated by *Ascomycota*, whereas *Basidiomycota* comprised a small but consistent fraction of aquatic fungi. *Chytridiomycota* represented a substantial proportion of the fungal community in winter, while *Oomycetes* were only present in summer. *Glomeromycota*, however, were of minor importance in the stream environment. Species common in an Australian upland stream included *Tetrachaetum elegans*, *Lunulospora cymbiformis*, *Flagellospora penicillioides* and *Alatospora acuminata* (Thomas et al., 1992). These species of aquatic hyphomycetes have not yet been associated with a teleomorph, but are likely affiliated with the *Ascomycota* since they lack morhpological features characteristic of the *Basidiomycota* (Nawawi 1985).

In lowland rivers, flow remains substantial but water quality and the source of primary production are substantially different from those in upland streams. Wider channels lead to a proportional reduction in litter from riparian plants, and production from phytoplankton is of increased significance (Vannote et al., 1980). Nutrient concentrations and dissolved organic carbon may also be higher, leading to lower or fluctuating concentrations of dissolved oxygen. Thus, while aquatic hyphomycetes still dominate submerged litter in these streams (Baldy et al., 2002), fungal community composition differs from upland streams (Shearer & Webster, 1985) and biomass accumulation may be limited by competition with other microorganisms, substrate burial and lower oxygen availability (Bärlocher, 1992; Medeiros et al., 2009).

### **2.4.2 Fungal diversity in shallow lakes and wetlands**

The dominant fungi colonising submerged plant litter in shallow, stagnant habitats common in wetlands and shallow lakes are the aero-aquatic hyphomycetes (Glen-Bott, 1951; Shearer et al., 2007). On occasion, aero-aquatic hyphomycetes may be found in streams and aquatic hyphomycetes in wetlands (Bärlocher & Kendrick, 1974; Fisher et al., 1983; Bärlocher, 1992), but aero-aquatic hyphomycetes are capable of out-competing aquatic hyphomycetes when colonising substrates in water with lower oxygen or higher nutrient concentrations (Voronin, 1997). *Oomycetes* and terrestrial fungi can also be found in wetlands (Bärlocher, 1992).

Fungal genera commonly found in wetlands include *Alternaria, Cylindrocarpon, Cladosporium, Penicillium, Fusarium, Trichoderma* and aquatic hyphomycetes (*Alatospora, Tetracladium, Helicodendron, Helicoon*; Kaushik & Hynes, 1971; Kjoller & Struwe, 1980; Ford, 1993). Aquatic lichens (a symbiotic partnership between a fungus and an alga) are potentially present in the littoral zone of wetlands, lakes and streams (McCarthy & Johnson, 1997), in particular in temperate or boreal regions (Hawksworth, 2000). There are ca. 200 species of lichenised fungi known from freshwater systems (Hawksworth, 2000). The main orders of *Oomycetes* found in aquatic environments are the *Leptomitales*, *Saprolegniales* and *Peronosporales*. Their requirement for dissolved oxygen varies widely among species, and many are intolerant of high salinity (Dick & Newby, 1961; Dick 1962; 1963; 1969; 1972).

### **2.4.3 Fungal diversity in deep lakes and reservoirs**

In deep lakes and reservoirs, the abundance (as colony forming units; CFU) and diversity of aquatic fungi is greatest in both the littoral and profundal zone (Rankovic, 2005).

communities on leaves submerged in an upland stream by using molecular methods. The authors were able to resolve the diversity within the *Ascomycota, Basidiomycota, Chytridiomycota, Zygomycetes* and *Oomycetes* and found, that the leaf decomposer community was dominated by *Ascomycota*, whereas *Basidiomycota* comprised a small but consistent fraction of aquatic fungi. *Chytridiomycota* represented a substantial proportion of the fungal community in winter, while *Oomycetes* were only present in summer. *Glomeromycota*, however, were of minor importance in the stream environment. Species common in an Australian upland stream included *Tetrachaetum elegans*, *Lunulospora cymbiformis*, *Flagellospora penicillioides* and *Alatospora acuminata* (Thomas et al., 1992). These species of aquatic hyphomycetes have not yet been associated with a teleomorph, but are likely affiliated with the *Ascomycota* since they lack morhpological features characteristic of the

In lowland rivers, flow remains substantial but water quality and the source of primary production are substantially different from those in upland streams. Wider channels lead to a proportional reduction in litter from riparian plants, and production from phytoplankton is of increased significance (Vannote et al., 1980). Nutrient concentrations and dissolved organic carbon may also be higher, leading to lower or fluctuating concentrations of dissolved oxygen. Thus, while aquatic hyphomycetes still dominate submerged litter in these streams (Baldy et al., 2002), fungal community composition differs from upland streams (Shearer & Webster, 1985) and biomass accumulation may be limited by competition with other microorganisms, substrate burial and lower oxygen availability

The dominant fungi colonising submerged plant litter in shallow, stagnant habitats common in wetlands and shallow lakes are the aero-aquatic hyphomycetes (Glen-Bott, 1951; Shearer et al., 2007). On occasion, aero-aquatic hyphomycetes may be found in streams and aquatic hyphomycetes in wetlands (Bärlocher & Kendrick, 1974; Fisher et al., 1983; Bärlocher, 1992), but aero-aquatic hyphomycetes are capable of out-competing aquatic hyphomycetes when colonising substrates in water with lower oxygen or higher nutrient concentrations (Voronin, 1997). *Oomycetes* and terrestrial fungi can also be found

Fungal genera commonly found in wetlands include *Alternaria, Cylindrocarpon, Cladosporium, Penicillium, Fusarium, Trichoderma* and aquatic hyphomycetes (*Alatospora, Tetracladium, Helicodendron, Helicoon*; Kaushik & Hynes, 1971; Kjoller & Struwe, 1980; Ford, 1993). Aquatic lichens (a symbiotic partnership between a fungus and an alga) are potentially present in the littoral zone of wetlands, lakes and streams (McCarthy & Johnson, 1997), in particular in temperate or boreal regions (Hawksworth, 2000). There are ca. 200 species of lichenised fungi known from freshwater systems (Hawksworth, 2000). The main orders of *Oomycetes* found in aquatic environments are the *Leptomitales*, *Saprolegniales* and *Peronosporales*. Their requirement for dissolved oxygen varies widely among species, and many are intolerant of

In deep lakes and reservoirs, the abundance (as colony forming units; CFU) and diversity of aquatic fungi is greatest in both the littoral and profundal zone (Rankovic, 2005).

*Basidiomycota* (Nawawi 1985).

(Bärlocher, 1992; Medeiros et al., 2009).

in wetlands (Bärlocher, 1992).

**2.4.2 Fungal diversity in shallow lakes and wetlands** 

high salinity (Dick & Newby, 1961; Dick 1962; 1963; 1969; 1972).

**2.4.3 Fungal diversity in deep lakes and reservoirs** 

Considering filamentous and higher fungi, the pelagic zone only supports a few specialised fungal species, but seems to be mainly used as a medium for propagules dispersal (Wurzbacher et al., 2010). Fungi from the littoral zone, in turn, are saprobes, parasites, predators, endosymbionts or occasionally lichens. These organisms colonise substrates ranging from submerged plants and litter to the carapaces of dead micro-crustaceans (Czeczuga et al., 2002; 2004; 2007).

In the pelagic zone, fungi consist mainly of species that live parasitically on phytoplankton, zooplankton and fish. Taxonomically, the fungal community consists of *Ascomycete* and *Basidiomycete* yeasts and "zoosporic fungi" (*Chytridiomycota* and *Oomycetes*; Rankovic 2005; Lefevre et al., 2007). It has been suggested that "zoosporic fungi" and their propagules are important for pelagic food web dynamics since they are important parasites of freshwater algae and thus may be important in controlling phytoplankton blooms associated with diatoms (Kagami et al., 2004) and cyanobacteria (*Microcystis* spp.; Chen et al., 2010).

The profundal zone and lake sediments, however, mainly serve as a propagule bank, where resting spores are stored. Therefore, both aquatic and terrestrial species are frequently isolated from deep lake sediments. Moreover, it has been suggested that yeasts in lake sediments are derived from terrestrial plant litter (Kurtzman & Fell, 2004), and fungal CFU associated with the *Mucoromycotina* (*Mucor* and *Rhizopus* sp.) isolated from various Serbian reservoirs may be also of terrestrial origin (Rankovic, 2005). However, there are a few species of yeasts, *Chytridiomycetes* and *Oomycetes* that are able to grow vegetatively in lake sediments (e.g. Ali & Abdel–Raheem, 2003).
