Contribution to the knowledge of Percnon gibbesi (Decapoda, Grapsidae), an exotic species spreading rapidly in Sicilian waters

Percnon gibbesi, a subtropical crab recently recorded for the first time in the Mediterranean, has now been found in Pantelleria (Strait of Sicily) and in mainland Sicily. The main morphological traits of the collected specimens are presented. It seems that P. gibbesi is forming stable populations in Sicilian waters, where juveniles as well as ovigerous females have been found. A few hypotheses are suggested to explain the spread of this species into the western Mediterranean: (i) wide capability of adaptation, (ii) larval strategy, (iii) favourable environmental conditions, probably linked to recent climate change, and (iv) absence of competitors