Italian scientists report that most of them were introduced in the 1980s and 1990s, whereas in the last few years the number of new records has decreased. The highest number of alien species has been observed in the northern Adriatic Sea, particularly in the Lagoon of Venice, which is the main hotspot of introduction.

The majority of marine and brackish water alien established species in Italy (up to 42% of algae and 38% of fishes) are native to the western Indian Ocean and Red Sea: in several cases these species have entered the Mediterranean through the Suez Canal (Lessepsian introductions). However, invasive species are also entering through the Straits of Gibraltar. Species that have autonomously entered through the Strait of Gibraltar from the eastern Atlantic, where they are considered alien, are classified as cases of secondary dispersal of alien species.

There is of course some natural movement of species. Such as species that have autonomously entered through the Strait of Gibraltar, and are not considered alien in the eastern Atlantic, in the absence of reliable proof of their human-mediated introduction, have to be regarded as cases of natural range expansion.

With a total number of 165 marine and brackish aliens recorded along the 7,375 km of the Italian coasts, it means that, on average, Italy has received at least 2.2 alien species for every 100 km of its coastline since 1945. The set of alien species includes; 33 Macrophyta, 1 Porifera, 2 Ctenophora, 15 Cnidaria, 33 Annelida Polychaeta, 31 Mollusca, 26 Crustacea, 2 Picnogonida, 7 Bryozoa, 4 Tunicata and 11 Osteichthyes. Out of these, 55 species are indicated as first records for the whole Mediterranean, mainly represented by cnidarians (9 species), macrophytes (11 species) and crustaceans (16 species). Amongst the most recent records mentioned: was a single adult specimen of the red king crab (Paralithoides camtschaticus), collected in 2008 in the Ionian Sea.

This study was undertaken by Italian scientists, who have undertaken this task on a voluntary basis, being part of the ‘‘Allochtonous Species Group’’ (ASG) within the Italian Society of Marine Biology (SIBM), have aimed at presenting an updated status of introduced specific and intraspecific taxa (hereafter referred to as ‘‘species’’ for convenience) in the coastal water bodies of the Italian Peninsula. The report is deriving from a plethora of different research programs and published records in Italy.