Percnon gibbesi
Information
It is found on rocky shorelines, in the crevices of rocks or on man-made structures such as ports and marinas at depths of 0.5–4 m.
Berried females have been recorded from May to September and juvenile crabs (carapace length = 1.5 cm) are present from October until March, suggesting the crab breeds during the summer months and recruitment takes place throughout the winter.
Percnon gibbesi may be distinguished from the native Mediterranean Pachygrapsus species by its deeply incised anterior shape, its colour pattern and its prominently spinose walking legs (particularly on the longest segment). Pachygrapsus marmoratus is mainly distinguished by the number of orbital teeth and its spoon-tipped claws; the colour of the species varies considerably and can be brown, purple, green or black. Pachygrapsus transversus is dark green to black in colour with a creamy ventral surface; it can be distinguished from P. marmoratus by having one tooth on each side of its carapace and 2–3 spines on the fifth walking leg.
It is native to the west and east coasts of America and the eastern Atlantic from Madeira to the Gulf of Guinea. In the Mediterranean, it was first recorded from Linosa Island, Italy, with nearly simultaneous records from the Balearic Islands, Sardinia, off the Ionian coast of Calabria, the south-eastern Tyrrhenian Sea, Sicily, Pantelleria Island and Malta. It then spread northward along the Tyrrhenian coast to the Gulf of Naples and Giglio Island. In 2005, it was recorded from Crete and Antikythira, Greece, as well as the Mediterranean coast of Turkey. Since then, it has spread along both the Ionian and the Aegean coasts. It is also known from Tunisia, Libya and Egypt. It may spread in the ballast waters of ships and on fishing nets as well as being transported in its larval stage by water currents.
The sally lightfoot crab is a strictly herbivorous crab, consuming filamentous and calcareous algae. It is unclear whether it competes with other algivorous animals in its habitat, such as sea urchins, but exclusion of native crabs may occur in some areas. Its habitat overlaps with the native crab Pachygrapsus marmoratus, an omnivorous species that also feeds on filamentous algae, and the pebble crab Eriphia verrucosa, a carnivorous species that feeds on molluscs and polychaetes.
Unknown.
Katsanevakis, S. et al. 2011.Twelve years after the first report of the crab Percnon gibbesi (H. Milne Edwards, 1853) in the Mediterranean: current distribution and invasion rates. Journal of Biological Research-Thessaloniki 16: 224 – 236.
