INTRODUCTION
The possibility of introduction of marine organisms outside their original distribution range by shipping has been long recognized (Catta, Reference Catta1876; Chilton, Reference Chilton1910). This phenomenon has increased dramatically worldwide in recent decades due to the increase of maritime traffic, speed of vessels and the practice of loading/discharge of ballast waters (Minchin & Gollasch, Reference Minchin, Gollasch, Leppakoski, Gollasch and Olenin2002).
Some swimming-crabs of the Indo-Pacific genus Charybdis De Haan, 1833 have proved highly invasive, spreading outside their original range of distribution transported by shipping.
Two species, Charybdis hellerii (A. Milne-Edwards, 1867) and Charybdis longicollis (Leene, Reference Leene1938), have reached the eastern Mediterranean, via the Suez Canal (Holthuis & Gottlieb, Reference Holthuis and Gottlieb1958), and are common throughout the Levant Basin (Galil et al., Reference Galil, Froglia, Noël and Briand2002). Charybdis hellerii has also reached, most probably with ballast waters, the Caribbean Sea (Campos & Türkay, Reference Campos and Türkay1989) and the US Atlantic coast (Lemaitre, Reference Lemaitre1995), and has subsequently spread to southern Brazil (Mantellato & Biagi Garcia, Reference Mantelatto and Biagi Garcia2001).
Single adult specimens of two other species were recently collected in the Mediterranean Sea: Charybdis feriata (Linnaeus, 1758) and Charybdis lucifera (Fabricius, 1798) near the harbour of Barcelona, Spain (Abelló & Hispano, Reference Abelló and Hispano2006) and off Venice (Mizzan & Vianello, Reference Mizzan and Vianello2009), respectively.
The unintentional introduction in New Zealand of Charybdis japonica (A. Milne-Edwards, Reference Milne-Edwards1861) was also mediated by vessels (Smith et al., Reference Smith, Webber, McVeagh, Inglis and Gust2003) and today the species is common in the Auckland Bay (Gust & Inglis, Reference Gust and Inglis2006). The capture of C. japonica on the Adriatic coast of Italy, Mediterranean Sea, is herein discussed.
MATERIALS AND METHODS
A large swimming crab was caught with gill-net near the entrance of the harbour of Ancona (43°37′31″N 13°29′35″E), Italy, Adriatic Sea, on 10 December 2006 by the fisherman Claudio Bernardini. He noticed it was different from the other swimming crabs, usually found entangled in his nets and brought it to me.
The specimen has been identified as an adult male of Charybdis japonica, following Sakai (Reference Sakai1976) and Wee & Ng (Reference Wee and Ng1995). It is now preserved in ethanol in the author's collection (D-1998) and will be deposited in the Museo civico di Storia naturale, Verona, Italy.
SYSTEMATICS
Fig. 1. Charybdis japonica (A. Milne Edwards, Reference Milne-Edwards1861): male (carapace length 70 mm, carapace width 103 mm) collected at the entrance of Ancona harbour, Adriatic Sea.
Charybdis japonica is easily distinguished from the autochthonous Mediterranean portunid crabs in bearing 6 antero-lateral teeth and 6 frontal teeth on its carapace. It may be separated from the other alien species of the genus Charybdis previously recorded in the Mediterranean Sea on the following combination of characters: frontal teeth acute, versus rounded in C. hellerii and C. feriata; outer margin of cheliped merus unarmed versus with distal spine, and lower surface of chela smooth, versus covered with squamiform granules in C. longicollis; propodus of fifth pereopod with posterior margin smooth, versus posterior margin serrated in C. lucifera and C. hellerii.
In the present specimen, the inner margin of merus has 4 spines + 2 tubercles; and 3 spines + 4 tubercles, respectively on right and left cheliped. The dorsal surface of carapace and chelipeds is glabrous, like the larger male examined by Leene (Reference Leene1938), and not pilose as described by Wee & Ng (Reference Wee and Ng1995). Colour in life as in Figure 1, from a photograph taken a few hours after capture.
Morphometric measures taken on the crab, with a quadrant calliper, are as follows: carapace length 70.0 mm, carapace width (between tip of posterior antero-lateral teeth) 102.7 mm; right cheliped (cutter): dactylus length 44.2 mm, palm length 34.4 mm; left cheliped (crasher): dactylus length 42.3 mm, palm length 40.0 mm; merus of 5th pereopod: length 20.5 mm, height 11.1 mm; sixth abdominal segment length 12.2 mm, height 9.2 mm.
DISCUSSION
Charybdis japonica is distributed from Korea and Japan to Indonesia (Sakai, Reference Sakai1976). It is unknown in the western Indian Ocean (Crosnier, Reference Crosnier1962; Apel & Spiridonov, Reference Apel and Spiridonov1998), whereas it was recorded once in the Red Sea (Leene, Reference Leene1938), on two specimens present in the dry collection of the National Natuurhistorisch Museum Leiden, possibly collected by Rüppell in his 1822–1827 voyage to the Red Sea (Fransen et al., Reference Fransen, Holthuis and Adema1997).
Leene's (Reference Leene1938) record is puzzling because the large size of C. japonica and its habitat (shallow soft level substrates) make unlikely its presence could go undetected by all the authors who subsequently studied the Red Sea and western Indian Ocean decapods. Leene's record may be a consequence of a mixing of labels that occurred in the past, or it may result from an early accidental introduction of the species outside its native range, not followed by the establishment of a self-maintained population. Unfortunately both hypotheses are not testable.
The known species distribution lets us surmise that shipping is the most likely vector of its introduction in the Adriatic Sea.
Checking the register of arrivals kept in the Ancona port office (Capitaneria di porto) it was found that in the years 2004–2006, container-ships connecting harbours of the Far East (China, Singapore, Indonesia, etc.) arrived monthly to Ancona and other Adriatic harbours, and bulk carriers from Indonesia (Bontang and Balikpapan) loaded with coal, and from China (Shanxi) loaded with chalk were registered as well. As these vessels arrived in Ancona fully loaded from their Asiatic ports of call, the discharge of ballast water, with consequent release of crab larvae, before entering the harbour is unlikely. But in such large ships the area of the sea-chests can harbour biologically significant accumulations of macrofouling biota, including portunid crabs (see: Coutts et al., Reference Coutts, Moore and Hewitt2003, p. 1511), and the crab may have reached the Ancona harbour waters in a juvenile stage passing trough the meshes of the grid that protects the sea-chest.
No other specimen of this species has been obtained from the environs of Ancona, despite repeated samplings and examination of the catches and discards of the local fishers working with set nets, bottom trawls and hydraulic dredges for clams.
Charybdis japonica proved to be invasive in New Zealand (Gust & Iglis, Reference Gust and Inglis2006), whereas a specimen was captured in South Australia (Port River, Adelaide) and it appears the species is not established there (Ahyong & Wilkens, Reference Ahyong, Wilkens, Galil, Clark and Carlton2011). Therefore we may speculate that one or few specimens arrived to the Ancona harbour, possibly hidden in the sea-chests of a ship, and the ‘propagule pressure' (Lockwood et al., Reference Lockwood, Cassey and Blackburn2005) has been too low to establish a population, even if the local environmental conditions (shallow soft level substrates with annual temperature range 8–24°C and salinities between 30 and 36 psu) are suitable for its settlement. As C. japonica proved able to arrive in the Adriatic Sea, we may expect to see it in the future in this or in other Mediterranean sectors.
ACKNOWLEDGEMENTS
I am greatly indebted to the fisherman Mr Claudio Bernardini, who spotted the unusual crab in his nets and kindly made it available to me. I am also grateful to the Officers of the Capitaneria di Porto of Ancona for making available the register of ships' arrivals.
