The crab Percnon gibbesi and the mollusc Aplysia dactylomela are recorded for the first time from the Taranto Gulf (Italy, Ionian Sea). Both alien species have been widely reported in the Mediterranean and have established populations in Greece and Sicily. The presence of a few specimens induces us to think that only lately these two species expanded their distributional range and that new stable populations will probably soon settle in the whole area.

Percnon gibbesi is an opportunistic feeder, feeding primarily on algae, of the shallow infra-littoral rocky shores. It was first observed in 1999 in the Mediterranean Sea and has rapidly spread since then. The range expansion of the species in the Aegean and Ionian Seas was recorded and evidence of its further establishment in Greek waters was provided. Established populations were observed in areas where it had not been previously reported: the Saronikos Gulf (central Aegean Sea), Chios Island (central Aegean Sea), Milos Island (central Aegean Sea), Zakynthos Island (central Ionian Sea) and Syvota (north-eastern coast of the Ionian Sea). The species was also observed in new sites in the Messiniakos Gulf, Crete and Rhodes Island, where it had been previously reported. The species keeps spreading in the Mediterranean Sea with a high rate of expansion.

Since its first record in Spanish waters in 2000, Percnon gibbesi has expanded its distribution southwards. In the summer of 2009 it was observed in the south-east Mediterranean Sea including inside a marine reserve. Its widespread presence during the last year in many coastal sites of the Murcia Region indicates its fast colonization ability and the potential risk of competition and displacement of native crab species, which should be studied carefully.

A grapsid crab, Percnon gibbesi, is the most invasive decapod species to enter the Mediterranean. The vessel-transported crab spread within a few years from the Balearic Islands to the Tyrrhenian and Ionian coasts of Italy. In the summer of 2005 it was recorded for the first time from Greece. Its presence in the little frequented island of Antikythira possibly points to the role of recreational vessels as vectors of marine alien species.