The aim of our study is the preparation of a risk assessment protocol for managing R. venosa distribution, population structure, and ecology in Italian waters. Since 2001, our research group is conducting baseline investigations in order to understand R. venosa a dangerous alien species for which study efforts should be prioritised (ICES 2004). So far, no similar threats to the ecosystem were reported in the other localities of introduction, but the international scientific community agrees in considering R. This large (up to 160 mm shell length) predatory gastropod is considered a pest it has been causing the depletion of large stocks of commercial bivalves (oysters, mussels, and clams) in the Black Sea since the 1950s (Drapkin 1963 Ciuhcin 1984 Zolotarev 1996). Ballast water transport was claimed as the main vector of introduction for the species (ICES 2004), although trade of bivalve stocks and spat could represent an additional important dissemination route (Goulletquer 2002). Few live specimens were reported also for the Tyrrhenian Sea (Terreni 1980 Paolini 1987) and the Northern Atlantic coasts of France/Quiberon Bay (Goulletquer 2000).
The whelk has been spreading very fast in the last century when it colonised the Black Sea since 1947 (Drapkin 1953), the Adriatic Sea since 1973 (Ghisotti 1974), the Aegean Sea since 1990 (Koutsoubas and Voultsiadou-Koukoura 1991), the American Atlantic Sea/ Chesapeake Bay since 1998 (Harding and Mann 1999), and the South Atlantic/Bahia Samborombon, Uruguay and Argentina since 1999 (Pastorino et al. Its native distribution includes the Sea of Japan, Yellow Sea, Bohai Sea and the East China Sea to Taiwan (Lai and Pan 1980 Tsi et al.
Moreover, throughout spring and summer this dioecious species produces a large number of planktonic veliger larvae which persist in the water column for a minimum of 14 to a maximum of 80 days prior settlement on the sea bottom (ICES 2004), thus granting high dispersal opportunity (Savini and Occhipinti Ambrogi 2004). This gastropod is a successful invader of marine coastal/brackish ecosystems, being tolerant to wide variations in temperature, salinity and oxygen concentration (Zolotarev 1996 Mann and Harding 2003). The Asian whelk Rapana venosa (Valenciennes 1846) was unintentionally introduced along the Northern Adriatic littoral in the 1970s (Ghisotti 1974). venosa in the Mediterranean Sea, thus worthy of consideration in order to understand the bioinvasion ecology of this species and to control its likely further dispersal. The large availability of food resource and the habitat characteristics of the Emilia-Romagna littoral makes this area an important breeding ground for R. On the other hand, selective predation might probably alter local community structure, influencing competition amongst filter feeder/suspension feeder bivalve species and causing long-term ecological impact. These results might reduce the concern about the economical impact on the local bivalve fishery due to the presence of the predatory gastropod. inaequivalvis consumption of the two commercial species was lower.
Predation was species and size selective towards small specimens of A. Results showed an average consumption of about 1 bivalve prey per day (or 1.2 g wet weight per day). The prey items chosen were the Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819), the introduced carpet clam Tapes philippinarum (Adams and Reeve 1850), both supporting the local fisheries, and the Indo-Pacific invasive clam Anadara (Scapharca) inaequivalvis (Bruguière 1789). A caging experiment in natural environment was performed during the summer of 2002 in Cesenatico (Emilia-Romagna, Italy) in order to estimate consumption rates and prey preference of R. Recently, this predator of bivalves has been spreading all around the world oceans, probably helped by ship traffic and aquaculture trade. The alien Asian gastropod Rapana venosa (Valenciennes 1846) was first recorded in 1973 along the Italian coast of the Northern Adriatic Sea.
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