Aquatic hyphomycetes and litter decomposition in tropical – subtropical low order streams

• Species diversity is low across (sub)tropical streams.
• Fungal activity in litter decomposition equals or is lower than in temperate zones.
• Shredders occurrence and involvement in decomposition is generally low.
• Fungal community composition is affected by the seasonal variation in rain fall.

Leaf litter decomposition is an important ecosystem function carried out by a diverse array of consumers, including aquatic hyphomycetes. Aquatic hyphomycetes are found in streams worldwide, but their diversity and abundance varies across systems. In general, species diversity is lower across tropical and subtropical systems when compared with temperate biomes. The low diversity in tropical and subtropical areas may be related to: (a) lower seasonality; (b) our inability to detect fungi by traditional techniques; (c) low turbulence of rivers where many studies were carried out; (d) low nutrient content in many studied tropical systems; (e) leaves highly defended against consumers; and (f) competition from other decomposers. In terms of function, fungal biomass, sporulation rates and litter decomposition by aquatic hyphomycetes in the tropics was reported to be equivalent to or much lower than observed in temperate zones. The feeding ecology of shredder invertebrates is strongly related to the presence of microbial decomposers in the environment. The lack of shredders reported for some tropical rivers may be related to a low microbial biomass, well defended tropical leaves and frequent hydrological events which remove leaves before they can be used by shredders. Seasonal variations in rain fall in tropical and subtropical systems are likely to affect litter fall, the identity and quality of litter, the reproduction of aquatic hyphomycetes (due to turbulence effects) and therefore the community composition of aquatic hyphomycetes throughout the year. Future research on aquatic hyphomycetes and litter decomposition in the tropics and sub-tropics should address the diversity/identity gap, altitudinal gradient changes and the contribution of aquatic hyphomycetes to the trophic ecology of shredders.