Macroscopic cyanobacteria of the genus Nostoc: a neglected and endangered constituent of European inland aquatic biodiversity

Nostoc caeruleum, N. commune, N. microscopicum, N. parmelioides, N. prunifo rme, N. verrucosum and N, zetterstedtii are air cyanobacteria forming macro scopically visible colonies. They were selected for a nature conservation c ase study. Their specific identity is easily determined, and reliable histo rical records are available. Life conditions for these species in Europe in the 'virgin' postglacial biosphere, historical reports and the present-day situation are surveyed. Data concerning type materials, supplements to the protologues, and morphology are presented. The classic descriptions and di agnoses based only on herbarium material are supplemented by ontogenetic de tails. Global/regional changes in the biosphere (climate, regulation of rak e levers and river flows, import of plant nutrients, water pollution, acidi fication, etc.) and their consequences for aquatic biocoenoses are reviewed . The analysis of man-made impacts on the environment enables us to evaluat e the present state of habitats where these algae occur today or where they are now extinct. Documented changes in environmental conditions in the pas t serve as a basis for assessing the likely future developments of the biot opes and of the whole landscape where these cyanobacteria form part of the biocoenoses. However, there are few recent detailed ecological studies on b enthic and terrestrial cyanobacteria. It is not yet clear which of the diff erent components covered by the comprehensive term 'eutrophication' is the decisive factor for the changes in aquatic biocoenoses and the decline of c yanobacterial biodiversity.