Grazing affects periphytic algal biomass in the periphyton-macrophyte relationship independently of the substrate type and nutrient status

The macrophyte–algae relationship has primary importance in affecting the functioning of shallow lake ecosystems. However, how substratum type, grazing, and nutrient status affect the relationship, is still largely unknown. Here, we studied algal assemblages covering either the submerged macrophyte, Ceratophyllum demersum, or artificial plastic plants with similar morphological complexity to answer these questions. Nutrient status was assessed as eu- and hypertrophic conditions in two separate lakes. In contrast to previous studies, the algal community on artificial substrates resembled to those observed on C. demersum. Independently of nutrient status (lakes), algae colonised artificial substrates intensively, but the highest algal biomass was observed in the hypertrophic lake. The community of periphytic algae was represented by diatoms, chlorophytes, and cyanobacteria. In the eutrophic lake, rather diatoms were present with high relative abundance, whereas, in the hypertrophic lake, rather cyanobacteria prevailed. Grazing pressure was high in both lakes and in the case of both substrate types, affecting the biomass of periphytic algae significantly. Our results indicate that macroinvertebrate grazing plays a crucial role in affecting periphytic algal biomass, independently of nutrient status and substratum type in shallow lakes.

Diatom biodiversity in the lake littoral of Rara Lake, a high altitude lake in the Himalaya of western Nepal

Diatoms were investigated in the littoral of Rara Lake, Nepal, to investigate the impact of land use, substratum type and season. Species composition and diversity differed between areas, seasons and between stones, sediment and macrophytes. Both communities on stones and on sediment differed between the settlement and forested areas, but communities on stones showed the greatest differentiation between land use types.

Revision of the Verrucaria elaeomelaena species complex and morphologically similar freshwater lichens (Verrucariaceae, Ascomycota)

The freshwater lichens Verrucaria elaeomelaena, V. alpicola, and V. funckii (Verrucariaceae/Ascomycota) have long been confused with V. margacea and V. placida and conclusions on the substratum preference and distribution have been obscured due to misidentifications. Independent phylogenetic analyses of a multigene dataset (RPB1, mtSSU, nuLSU) and an ITS-dataset combined with morphological and ecological characters confirm that the Verrucaria elaeomelaena agg. consists of several cryptic taxa. It includes V. elaeomelaena s.str. with mostly grey to mid-brown thalli and transparent exciple base which cannot be distinguished morphologically from several other unnamed clades from low elevations, the semi-cryptic V. humida spec. nov., which is characterised by smaller perithecia, shorter and more elongated spores compared to other species in this group and V. alpicola with specimens mostly from high elevations, dark brown to black thalli, a brown exciple base and large ascospores. While Verrucaria funckii is confirmed to be restricted to siliceous substrata, limestone and siliceous substrata are both colonised by V. elaeomelaena s.str. as well as by representatives of various other clades. The substratum type cannot be seen as a diagnostic character for taxa within this species group. The taxa included in Verrucaria elaeomelaena agg. are closely related to V. submersella and together with V. funckii they form a sister clade to the “Endocarpon-group” in the Verrucariaceae. Verrucaria margacea is superficially similar to some specimens of V. elaeomelaena agg. It is nested within an unresolved larger clade with Dermatocarpon, the subclades of the Endocarpon- and the V. elaeomelaena-group. Verrucaria margacea can be distinguished from most of the specimens in the V. elaeomelaena group by its generally non subgelatinous thallus, often with distinct cracks, narrowly ellipsoidal ascospores and the general absence of a black basal layer or dark pigments in the exciple base. The form and size of the ascospores distinguish V. placida from most specimens in the V. elaeomelaena complex, but there is overlap with some forms of V. alpicola. Epitypes are proposed for V. elaeomelaena, V. alpicola and V. margacea and a European key to the species of subgelatinous freshwater Verrucaria with spreading involucrellum and large ascospores is provided.