A freshwater jellyfish, known as Craspedacusta sowerbyi, was found in the waters of the Fossu Frate di Ghirru stream, also known as Rio Pitrisconi, in the naturalistic oasis of Monte Nieddu in San Teodoro. The specimen was found last October 21 following a report from Yoris Palpella, a canyoning guide who operates in those areas.
The naturalist Marco Marrosu and the agronomist Giovanna Chessa gave a name to the unusual jellyfish who, in collaboration with a new project from the Spanish University of Zaragoza, carried out a preliminary investigation of the course of the stream. Studies have revealed that it is a species belonging to the class of Hydrozoans, already found in 1970 in the Liscia artificial basin, but whose presence had until now no longer been detected among the watercourses in Sardinia. In 2017, there were 40 reports of the presence of the freshwater jellyfish in Italy, to which today we also add this one from Fossu Frate di Ghirru, a tributary of the Rio San Teodoro.
The species has a diameter of variable length around 5 cm and is highly invasive thanks to the possible survival in a latent life stage (cyst) for up to 40 years, with resistance to complete desiccation; it survives all year round in a formal sessile form, tied to the substrate, and develops the medusoid swimming form when conditions are favourable.
The Craspedacusta sowerbyi joins the list of recent alien and invasive species that have arrived in Sardinia in recent years, including the infamous blue crab, the marbled crayfish and the Mississippi crayfish. The phase following the discovery of the freshwater jellyfish will concern the study of the climatic reasons that led to the development of this new species and above all we will try to understand how much it can influence our ecosystems. Similar studies have already been carried out worldwide on other unexpected and unwanted guests such as the Nile perch, Lates niloticus, which, after being introduced into Lake Victoria in the 1950s, profoundly changed the number of cichlid species endemic.
Another invasive alien species is the sea lamprey, Petromyzon marinus, found in the American Great Lakes. Scientific research in this area is managed by the European Strategy on Invasive Alien Species, which provides for important awareness-raising, prevention and planning of a whole series of interventions against already stabilized specimens and aims to identify new potential invaders.