A first study of the algal flora of the Tiber River basin (Italy)

The floristic composition and spatial distribution of algal communities in 97 stations in the Tiber River and its tributaries were studied. A total of 128 taxa were found, belonging mainly to the Chlorophyta, Bacillariophyta and Cyanophyta. Filamentous algae (Cladophora glomerata, Vaucheria geminata, Oedogonium sp. and Spirogyra spp.) were the most common and abundant species. Melosira varians, Cocconeis pediculus, Gomphonema olivaceum, Cyclotella meneghiniana, Fragilaria crotonensis, Leptolyngbya valderiana and several species of Oscillatoria were also widely distributed but they were not important in terms of biomass. Spatial variations of species richness were found, with the middle and upstream sections showing a wider range of taxa than the downstream sections. Chamaesiphon incrustans and Lemanea fluviatilis were found only in the upstream sections of some watercourses of the basin in fast-flowing, cool, well-oxygenated waters, while Stigeoclonium tenue and Ulva flexuosa was recorded exclusively in downstream sections with slow-flowing, warm and eutrophic waters. algae / floristic composition / spatial distribution / Tiber River basin / Italy / watercourses Résumé – Première étude de la flore algale du bassin du Tibre (Italie). La composition floristique et la distribution spatiale des communautés algales ont été étudiées dans 97 stations dans le Tibre et ses affluents. Au total, 128 taxons ont été trouvés, appartenant principalement aux Chlorophyta, Bacillariophyta et Cyanophyta. Les algues filamenteuses (Cladophora glomerata, Vaucheria geminata, Oedogonium sp. et Spirogyra spp.) sont les plus fréquentes et les plus abondantes. Melosira varians, Cocconeis pediculus, Gomphonema olivaceum, Cyclotella meneghiniana, Fragilaria crotonensis, Leptolyngbya valderiana et différentes espèces d’Oscillatoria sont largement distribués mais peu importants du point de vue de la biomasse. Des variations spatiales de la richesse en espèces sont observées. Les secteurs du centre et en amont montrent une plus grande variété de taxons par rapports aux secteurs en aval. Chamaesiphon incrustans et Lemanea fluviatilis sont présents seulement dans les sections en amont de certains cours d’eau du bassin aux eaux rapides, fraîches, bien oxygénées, tandis que Stigeoclonium tenue et Ulva flexuosa sont présents uniquement dans les sections en aval aux eaux lentes, chaudes et eutrophes. algues / bassin du Tibre / Italie / composition floristique / distribution spatiale / rivières * Correspondence and reprints: ceschin@uniroma3.it Communicating editor: Pierre Compère 274 S. Ceschin, S. Ricci & S. Bisceglie

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