Range expansion and biometric features of Pinctada imbricata radiata (Bivalvia: Pteriidae) around Linosa Island, Central Mediterranean Sea (Italy)

In the summer of 2011, the infralittoral fringe of Linosa Island (Sicilian Channel, Italy) was surveyed through visual census, by both scuba diving and snorkelling, with the aim of collecting updated data on marine alien species distribution and abundance on the island. Surveys revealed the presence of Pinctada imbricata radiata, an invasive alien bivalve of Indo-Pacific origin, first recorded in the Mediterranean Sea at the end of the 19th century in Egyptian waters. Since then, the species has successfully spread throughout the Mediterranean, systematically colonizing new habitats of the eastern basin and becoming very abundant in the Levantine Sea. Conversely, occurrences in the western basin have been reported only sporadically. Many studies have been carried out on P. imbricata radiata in its native range (Indian Ocean and Red Sea) while the Mediterranean populations have been investigated only in Tunisia. The finding of P. imbricata radiata around Linosa Island (Sicilian Channel, Italy) is discussed analysing the biometric features of the species and taking into consideration its ecological characteristics and possible pathways of introduction in the Marine Protected Area of Linosa Island.