Non-indigenous freshwater molluscs and their distribution in Italy

Since the second half of the 19th century, there have been reports of the presence of non-indigenous freshwater molluscs in Italy, though they were not yet recognized as “alien”. Most species of molluscs were introduced into Italy more recently, in the second half of the 20th century, as the result of the development of commercial routes and the intensification of intercontinental traffic (Fig. 1). A complete list of non-indigenous freshwater mollusc species was not published until recently (Cianfanelli et al. 2007), though certain species were already considered “alien” in the “Checklist delle specie della fauna italiana” (Bodon et al. 1995, 2005a, 2005b; Castagnolo 1995; Manganelli et al. 1995, 1998) and in other articles (Lori et al. 2005). Eleven species of non-indigenous freshwater molluscs, differing in invasiveness (Fig. 2), are currently known (Table 1). Using data from the literature and unpublished records from field research, we created a data bank that enabled mapping of the distribution of non-indigenous molluscs. To show collection sites, UTM maps (10 km grid) were used (Fig. 3a–h, Fig. 4a–d).