Invasion of the North American Atlantic Coast by a Large Predatory Asian Mollusc

The large Asian gastropod mollusc Rapana venosa Valenciennes 1846 (Neogastropoda, formerly Muricidae, currently Thaididae) is reported for eastern North America in the lower Chesapeake Bay and James River, Virginia, USA. This record represents a transoceanic range expansion for this carnivorous species. This species has previously been introduced to the Black Sea, Adriatic Sea, and Aegean Sea. Ballast water transport of larval stages from the eastern Mediterranean or Black Sea is the suspected vector of introduction into the Chesapeake Bay; 650 adult specimens in the size range 68–165mm shell length (SL) have been collected from hard sand bottom in depths ranging from 5 to 20m at salinities of 18–28ppt. The absence of small individuals from local collections is probably related to bias in collection methods. Age of the specimens could not be determined. R. venosa is probably capable of reproducing in the Chesapeake Bay. Egg cases of R. venosa were collected from Hampton Roads, a section of the James River, in August 1998, and hatched over a 21-day period under laboratory conditions to release viable bilobed veliger larvae. Four lobed larvae developed 4 days post-hatching and apparent morphological metamorphic competency was observed 14–17 days post-hatching. Despite the provision of live substrates and/or metamorphic inducers no metamorphosis to a crawling form was observed for larvae cultured on the monospecific diet. In work performed during 1999 settlement was observed for larvae cultured on a diet of mixed flagellates and diatoms and subsequently exposed to local epifaunal species. Salinity tolerance tests were performed on larvae at 1–6 days post-hatching. No deleterious effects were observed at salinities as low as 10ppt with limited survival to 7ppt at 6 days post-hatch. Current distribution is considered in context with larval salinity tolerance tests and literature describing native Asian and introduced populations to assess potential for establishment and further range extension both within the Chesapeake Bay and along the Atlantic coast of North America. Establishment within the Bay mainstem to the Rappahannock River with minor incursions into the mouths of the southerly subestuaries is considered feasible. A projected breeding range on the Atlantic seaboard extending from Cape Cod to Cape Hatteras is considered as tenable. Potential impact of R. venosa on commercially valuable shellfish stocks throughout the projected range is cause for serious concern. Boring by the polychaete Polydora websteri is more prevalent in the younger whorls of the shell, and absent in shell laid down later in life. This pattern suggests that juvenile animals may prefer hard substrates and not adopt an infaunal lifestyle until a size in excess of 50mmSL, or after reaching maturity.