Spatial and bathymetric distribution, population density, habitat preferences, fecundity, breeding season and interspecific
interactions of the alien grapsoid crab Percnon gibbesi (H. Milne-Edwards, 1853) from the Maltese Islands (Malta and Gozo)
are compared among localities in the Mediterranean where established populations have been reported since 1999. In the
Maltese Islands, habitat preferences and bathymetric distribution were similar to those in other Mediterranean localities.
Spatial distribution was found to be limited by the availability of the boulder habitat in which this crab nearly always occurs.
Fecundity was higher in the Maltese Islands than in Linosa and Lampedusa, the breeding season lasting from the end of
May until September. On Maltese shores the habitat of the alien overlapped with that of the native grapsid Pachygrapsus
marmoratus (Fabricius, 1787) (Crustacea: Brachyura: Grapsoidea) and, to a lesser extent, that of the native xanthid Eriphia
verrucosa (Forska°l, 1775). Laboratory studies to assess the possible interactions of the alien species with P. marmoratus
suggest that the latter shows a competitive advantage over P. gibbesi, since 80.8% of encounters between the two species were
initiated by P. marmoratus, and in 80% of the encounters it prevailed. This suggests that P. marmoratus is unlikely to be
excluded from its natural habitat by the alien species, and that significant spatial resource partitioning on the part of P.
marmoratus is unlikely to occur.peer-reviewe
