Clement K.M. Tsui

Role of fungi in freshwater ecosystems

There are more than 600 species of freshwater fungi with a greater number known from temperate, as compared to tropical, regions. Three main groups can be considered which include Ingoldian fungi, aquatic ascomycetes and non-Ingoldian hyphomycetes, chytrids and, oomycetes. The fungi occurring in lentic habitats mostly differ from those occurring in lotic habitats. Although there is no comprehensive work dealing with the biogeography of all groups of freshwater fungi, their distribution probably follows that of Ingoldian fungi, which are either cosmopolitan, restricted to pantemperate or pantropical regions, or in a few cases, have a restricted distribution. Freshwater fungi are thought to have evolved from terrestrial ancestors. Many species are clearly adapted to life in freshwater as their propagules have specialised aquatic dispersal abilities. Freshwater fungi are involved in the decay of wood and leafy material and also cause diseases of plants and animals. These areas are briefly reviewed. Gaps in our knowledge of freshwater fungi are discussed and areas in need of research are suggested.

Longitudinal and temporal distribution of freshwater ascomycetes and dematiaceous hyphomycetes on submerged wood in the Lam Tsuen River, Hong Kong

Longitudinal and temporal distribution patterns of freshwater ascomycetes and dematiaceous hyphomycetes on submerged wood were investigated at 3 sites along the Lam Tsuen River in Hong Kong. Two-hundred-and-six species were recorded. Ascomycete genera were dominated by Annulatascaceae, Halosphaeriaceae, Lasiosphaeriaceae, Lophiostomataceae, and Magnaporthaceae; the most common taxa were Aniptodera chesapeakensis, Aquaticola ellipsoidea, Helicosporium griseum, Massarina purpurascens, M. thalassioidea, Ophioceras commune, and Sporoschisma uniseptatum. There were no significant differences (ANOVA, p > 0.05) in total number of species among the sites. However, the number of species of Halosphaeriaceae (p < 0.01) and Lasiosphaeriaceae (p < 0.05) was significantly higher at Site 3, and Annulatascaceae was dominant at Sites 1 and 2 (p < 0.05). Downstream changes in species composition were strongly correlated with elevated concentrations of NO3-N (r2 = 0.66), NH3-N (r2 = 0.66), and PO4-P (r2 = 0.73) resulting from human disturbance. The variation in species composition was also weakly correlated with other physico-chemical variables such as conductivity (r2 = 0.16) and aluminum (r2 = 0.11). Species diversity fluctuated temporally but did not change (ANOVA, p > 0.05) between dry and wet seasons. Species composition shifted and the frequency of occurrence of certain dominant taxa declined after heavy rainfall associated with El Niño, possibly because increased discharge washed away well-colonized woody substrata.

The genera Aniptodera, Halosarpheia, Nais and Phaeonectriella from freshwater habitats

The generic concepts inAniptodera, Halosarpheia, Nais andPhaeonectriella are discussed and those species occurring in freshwater are described, some with illustrations. Five new species:Aniptodera lignicola, A. mauritaniensis, A. megalospora, A. palmicola, Phaeonectriella appendiculata are also described. A key to the freshwater species in the above genera and a synoptic diagram of their ascospores are provided.

Colonization patterns of wood-inhabiting fungi on baits in Hong kong rivers, with reference to the effects of organic pollution

The diversity of wood-inhabiting fungi was investigated by submerging woody baits at upstream and downstream sites of the Lam Tsuen and Tai Po Rivers in Hong Kong. The diversity of fungi in the Lam Tsuen River was also compared with that on natural woody substrates found in a previous study. There were differences in the species composition between the upstream and downstream sites, possibly reflecting natural variations along the river. The Tai Po River downstream was organically polluted, which appeared to have little effect on species diversity since more species were recorded. Organic pollution may, however, cause a shift in species composition. The fungal communities on baits and natural substrates in the Lam Tsuen River were similar, although a lower diversity was observed on baits. This may be related to the period of submergence and the fact that a single wood type was used. Cercophora spp. occurred frequently downstream in the Tai Po River, while the common species in the Lam Tsuen River were Aquaticola rhomboidea and Pseudoproboscispora aquatica. Further interpretation on the effects of organic pollution was limited because of single collection data but appropriate experimental designs – putting baits in unimpacted sites for assessing human impacts in streams – are suggested.

Brunneosporella aquatica gen. et sp. nov., Aqualignicola hyalina gen. et sp. nov., Jobellisia viridifusca sp. nov. and Porosphaerellopsis bipolaris sp. nov. (ascomycetes) from submerged wood in freshwater habitats

Brunneosporella aquatica gen. et sp. nov., Aqualignicola hyalina gen. et sp. nov., Jobellisia viridifusca sp. nov. and Porosphaerellopsis bipolaris sp. nov. are described and illustrated from wood submerged in freshwater collected in Hong Kong. Both Brunneosporella and Aqualignicola have characteristic features of the Annulatascaceae and their placement within this family is discussed. Jobellisia viridifusca sp. nov. differs from all described species in having an ascomatal wall with a bright orange middle wall layer and fusiform, greenish-brown ascospores. Porosphaerellopsis bipolaris sp. nov. is unique in producing multiseptate ascospores with bipolar mucilagilous pads.

Fungi on submerged wood in the Koito River, Japan

Abstract Woody substrates were collected from the Koito River in Japan, and the biodiversity of fungi on these substrates was investigated. Twenty-eight species were identified, comprising 12 ascomycete and 16 anamorphic taxa. The common fungi included Chaetosphaeria sp., Ophioceras commune, Pseudohalonectria lignicola, and Savoryella lignicola. The occurrence of fungi on submerged wood is discussed, and three interesting taxa – Pseudohalonectria lignicola, Bactrodesmium arnaudii, and B. pallidum – are described and illustrated.

Three new species of Annulatascus (Ascomycetes) from Hong Kong freshwater habitats

Abstract Annulatascus joannae, A. lactus, and A. tropicalis are described and illustrated from decaying woody substrata in freshwater habitats in Hong Kong. Annulatascus joannae is distinguished by ellipsoidal and thick-walled ascospores whereas A. lacteus has milky ascomata and A. tropicalis has relatively large, fusiform, 1–3-septate ascospores. Annulatascus biatriisporus is reported as a new record in Hong Kong. A key to and a synoptic table of Annulatascus species are provided.

Torrentispora fibrosa gen. sp. nov. (Annulatascaceae) from freshwater habitats

Torrentispora fibrosa gen. sp. nov. (Ascomycota, Annulatascaceae) is described based on specimens from submerged wood collected from streams in Tai Po Kau Forest Reserve, Hong Kong. T. fibrosa is characterized by immersed to superficial ascomata with a peridium of black cells arranged in irregular rows, wide septate paraphyses, long cylindrical asci with a relatively massive refractive apical ring, and unicellular ascospores with a fibrillar sheath. Illustrations from light and scanning electron microscopy are provided. It is compared with species in the genus Annulatascus, from which it differs in ascoma peridium and ascospore sheath morphology, and with other aquatic ascomycetes possessing ascospores with a similar fibrillar sheath structure.

Three new Ophioceras species (Ascomycetes) from the tropics

Ophioceras guttulatum sp. nov.,O. hongkongense sp. nov. andO. palmae sp. nov. are described and illustrated from decaying terrestrial palms and woody substrates in freshwater habitats. They all have black perithecia with long necks, cylindrical asci with refractive apical rings and filiform ascospores.

Reflections on the genus Vanakripa, and a description of V. ellipsoidea sp. nov.

The genus Vanakripa (hyphomycetes) is reviewed based on the examination of type specimens, and V. ellipsoidea sp. nov. is described on submerged wood from Hong Kong. Vanakripa is characterized by punctiform sporodochial colonies, micronematous conidiogenous cells and pigmented conidia with vermiform separating cells. Vanakripa is compared with similar genera, and a synopsis of its morphological characters is provided.