First Record of Alien Species Craspedacusta sowerbii Lankester 1880 in a Stream of Sardinia (Italy)

In recent decades, the number of invasive alien species introduced outside of their natural distribution range has increased. These species can rapidly spread from the place of introduction, acting as agents of change, threatening ecosystems, habitats, and indigenous species. Craspedacusta sowerbii Lankester, 1880 has invaded freshwater systems all over the world. This article reports the first occurrence of this freshwater jellyfish in a stream on the island of Sardinia, Italy. There is no previous data useful to understand the development of this species in the river systems of the island where streams are usually seasonal, with a strong water reduction, and native animal species are concentrated in a few pools during critical seasons. In our study, we carried out an observation of the phenomenon in order to provide preliminary information about this new population, its characteristics, and environmental features. Endangered and extremely rare endemic species, such as Discoglossus sardus and Euproctus platycephalus, live in Sardinian streams, so this is one more reason to focus on the biological invasion processes of this organism in order to understand its role in this ecosystem’s ecological functioning.