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(Pipitone et al., 2001; Abelló et al., 2003). A third possible vector that may not be
excluded is aquarium trade, as for other Mediterranean aliens (Jousson et al., 1998;
Padilla & Williams, 2004). Abelló et al. (2003) suggested larvae of Percnon gibbesi
have entered the Mediterranean with the Atlantic currents. These currents sweep
east wards along the southern Mediterranean coast. Similarly, Pipitone et al. (2001)
proposed that the mechanism for the introduction and spread of Percnon gibbesi in
the Mediterranean are larval transport by surface currents.

Figure 17. Distribution of Percnon gibbesi in Mediterranean Sea (CIESM, 2014).

Only three crabs (Callinectes sapidus, Dyspanopeus sayi and Rhithropanopeus
harrisii) are definitely established in the Adriatic Sea and all three originate from the
Atlantic coast of USA. The spreading of the two panopeid crabs in the Adriatic Sea in
recent years (Froglia and Speranza, 1993; Mizzan and Zanella, 1996; Onofri et al.,
2008) has been facilitated by the development of mussel aquaculture both in
lagoons and open sea, with transfer of mussels’ seed and half grown mussels among
aquaculture plants.

Dyspanopeus sayi
Dyspanopeus sayi (Smith, 1869) is a species of mud crab that is native to the Atlantic
coast of North America (Fig. 18). It has become established in the Mediterranean Sea
since the 1970s (Fig. 19). It can reach a carapace width of 20 mm, and has black tips
to its unequal claws. It feeds on bivalves and barnacles, and is in turn eaten by
predators including the Atlantic blue crab, Callinectes sapidus. Dyspanopeus sayi
lives predominantly on muddy bottoms, where it is a predator of bivalve molluscs
(Williams, 1965). It is very abundant in the Venice lagoon, locally may outnumber the
autochthonous crabs Carcinus aestuarii and Pilumnus spp (CIESM, 2014).