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Figure 15. Matuta victor (Galil and Mendelson, 2013).

Percnon gibbesi
In the Western Mediterranean Sea the only crab species markedly invasive is
Percnon gibbesi (Fig. 16), which shows a rapid expansion of its geographical
distribution range, e.g. in the east Spanish coast (Deudero et al., 2005): first recorded
from the Balearic Archipelago in 1999 (Garcia and Reviriego, 2000), it established
populations since 2002 in Barcelona, 2003 in Alicante and Murcia, 2006 in Almeria.
This crab species is also well established in the Central Mediterranean Sea (e.g. Relini
et al., 2002; Sciberras and Schembri, 2008; Pipitone et al., 2001; Elkrwe et al., 2008)
and in the eastern part of the Mediterranean also, like in Greece, Turkey, Syria,
Cyprus, Israel, Egypt (Cannicci et al., 2006; Katsanevakis et al., 2011; Konstantinou
and Kapiris, 2012 in Thessalou-Legaki et al., 2012) (Fig. 17). It lives under boulders, or
in narrow crevices, where it seeks shelter when threatened in depths down to 30 m.
It is active during daytime with feeding peaks at sunset. It is strictly herbivorous,
using its small claws to pick off the fine film of algal growth.

Figure 16. Percnon gibbesi. Male specimen, collected near Al Haniyah, 29 July 2007. Photograph by H.
M. Elkrwe. (Elkrwe et al., 2008).

Two vectors of introduction of P. gibbesi have been speculated, either through
shipping (Mori and Vacchi, 2002; Galil et al., 2002) or by larval drift by the Atlantic
surface current that enters the Mediterranean Sea through the strait of Gibraltar