Two centuries for an almost complete community turnover from native to non-native species in a riverine ecosystem.

Non-native species introductions affect freshwater communities by changing community compositions, functional roles, trait occurrences and ecological niche spaces. Reconstructing such changes over long periods is difficult due to limited data availability. We collected information spanning 215 years on fish and selected macroinvertebrate groups (Mollusca and Crustacea) in the inner-Florentine stretch of the Arno River (Italy) and associated water grid, to investigate temporal changes. We identified an almost complete turnover from native to non-native fish (1800: 92% native; 2015: 94% non-native species) and macroinvertebrate species (1800: 100% native; 2015: 70% non-native species). Non-native fish species were observed ~50 years earlier compared to macroinvertebrate species, indicating phased invasion processes. In contrast, α-diversity of both communities increased significantly following a linear pattern. Separate analyses of changes in α-diversities for native and non-native species of both fish and macroinvertebrates were nonlinear. Functional richness and divergence of fish and macroinvertebrate communities decreased non-significantly, as the loss of native species was compensated by non-native species. Introductions of non-native fish and macroinvertebrate species occurred outside the niche space of native species. Native and non-native fish species exhibited greater overlap in niche space over time (62%-68%) and non-native species eventually replaced native species. Native and non-native macroinvertebrate niches overlapped to a lesser extent (15%-30%), with non-natives occupying mostly unoccupied niche space. These temporal changes in niche spaces of both biotic groups are a direct response to the observed changes in α-diversity and species turnover. These changes are potentially driven by deteriorations in hydromorphology as indicated by alterations in trait modalities. Additionally, we identified that angling played a considerable role for fish introductions. Our results support previous findings that the community turnover from native to non-native species can be facilitated by, for example, deteriorating environmental conditions and that variations in communities are multifaceted requiring more indicators than single metrics.

Diversity and taxonomy of the genus Unio Philipsson in Italy, with the designation of a neotype for Unio elongatulus C. Pfeiffer (Mollusca, Bivalvia, Unionidae).

Novel Unio spp. populations from Slovenia, the Italian peninsula, Sardinia and Sicily were genetically analysed in order to define the distribution and diversity of the genus Unio in Italy and neighbouring areas. The presence of two primarily allopatric autochtonous species, Unio elongatulus Pfeiffer, and Unio mancus Lamarck, is confirmed for the Italian peninsula, Corsica, Sardinia, and Sicily.Autochthonous populations of Unio elongatulus are present in the peri-Adriatic drainages of the Italian and Balkan peninsulas, south as far as the Ofanto River (Apulia, Italy) and Lake Skadar (Albania), while its presence in the Tyrrhenian rivers of Tuscany is likely due to anthropogenic introduction events. Conversely, Unio mancus turtonii Payraudeau, an endangered peri-Tyrrhenian taxon, was found with autochthonous populations in the Apennine-Tyrrhenian drainages of peninsular Italy, eastern Mediterranean France, Corsica, Sardinia and Sicily, while the actual autochthony of the single population found in the Ionian basin of the Italian peninsula (Bradano River, Basilicata) deserves further investigation. The Italian population of U. mancus requienii Michaud, reported from Lake Montepulciano is to be considered allochthonous.The binomen U. elongatulus, although widely used in the recent scientific literature, was, to date, assigned to a doubtful species, because its type locality includes a large area inhabited by different Unio taxa, which are not clearly distinguishable by their shell alone; furthermore, no type material is present in historical collections. To retain the recently-used name, a new restricted type locality is established, where only U. elongatulus lives, and a neotype is designated. The validity of the subspecies of Unio mancus is also discussed and confirmed.Finally, hypotheses on the origin of Italian mussels, and considerations on their conservation status are discussed.