Twelve years after the first report of the crab Percnon gibbesi (H. Milne Edwards, 1853) in the Mediterranean: current distribution and invasion rates.

The distribution of the alien crab Percnon gibbesi in the Mediterranean Sea was assessed, based on new data from four independent surveys in Albania-Montenegro, Tunisia, Libya, and Crete (Greece), personal observations of the authors and a thorough compilation of existing information. The species is reported herein for the first time from Albania, Algeria, Cyprus, Israel, and Lebanon. Percnon gibbesi rapidly increased its spatial distribution in the Mediterranean Sea after its first report in 1999. At present, twelve years after its introduction, P. gibbesi is established in most Mediterranean coasts, especially in middle latitudes. It is absent from the Adriatic Sea (except from its southern limit in the Albanian part of Otranto Strait), the Ligurian Sea, the Corsica Island, and the northern Aegean Sea, possibly because of the low winter temperatures prevailing in these areas. In the North African coasts, P. gibbesi has not yet been observed in Morocco. After its initial introduction, its further spreading in the Mediterranean basin seems to be governed primarily by natural dispersal via larval transport by currents. The invasion rate of P. gibbesi was assessed in the Kas - Kekova Marine Protected Area in southern Turkey, based on a time series of monitoring data from 2002 to 2010. The species was first observed in 2006 in two sites and rapidly increased its occupancy and abundance the following years. Its occupancy (probability of presence in 500 m length of coastline) reached 23% within four years from its first sighting. Its abundance increased exponentially with an intrinsic rate of increase r = 0.79, corresponding to more than doubling of the population per year.