Taxonomic name: Rapana venosa (Valenciennes, 1846)
Synonyms: Rapana pontica (Nordsieck, 1969), Rapana thomasiana (Crosse, 1861)
Common names: Asian rapa whelk, rapa whelk, veined rapa whelk, veined whelk
Organism type: mollusc
Rapana venosa is a predatory marine snail which may impact both natural and cultivated populations of oysters, mussels and other molluscs. In areas where it has been introduced it has caused significant changes to the ecosystem. It has a high ecological fitness as evidenced by its high fertility, fast growth rate and tolerance to low salinity, high and low temperatures, water pollution and oxygen deficiency. Long distance dispersal is facilitated by ship ballast water, in which the larvae of the snail is found in its plankton phase.
Rapana venosa is a member of the Muricidae, a family of predatory marine snails (Kerckhof et al. 2006). It has a large and heavy shell with a short spire. A very distinctive feature is the deep orange colour of the inside of the shell. The outer colour is variable from dull grey to red brown, with more or less conspicuous dark brown dashes on the spiral ribs, which tend to make an interrupted vein-like pattern throughout the entire shell.
It has a large inflated body whorl and a deep umbilicus. The aperture is large and ovate, and the columella broad and smooth. The edge of the outer lip has small, elongate teeth. Smooth spiral ribs develop regular blunt knobs at the shoulder and the periphery of the body whorl. Fine spiral ridges are crossed by low vertical riblets. Spiral, vein-like colouration, varying from black to dark blue, occasionally occurs internally, originating at the individual teeth at the outer lip of the aperture (Mann and Harding 2000).
Rapana bezoar, Rapana rapiformis
coastland, estuarine habitats, marine habitats
Rapana venosa is a prolific, extremely versatile species tolerating low salinities, water pollution and oxygen deficient waters. All larval stages exhibit 48-h tolerance to salinities as low as 15 ppt with minimal mortality. Below this salinity, survival grades to lower values. Percentage survival of R. venosa larvae is significantly less at 7 ppt than at any other salinity. There were no differences in percentage survival at salinities greater than 16 ppt (Mann and Harding 2003). In its native Korean range R. venosa demonstrates large annual temperature tolerances (from 4°C to 27°C) (Chung et al. 1993, in Mann and Harding 2000). It may migrate to warmer, deeper waters in winter thereby evading cool surface waters (USGS-NAS Undated).
It favours sandy bottoms where the snails can burrow, thus, the seafloor of the southern North Sea is a very suitable habitat (Kerckhof et al. 2006), however, the species colonises hard substrates too.
Due to its predatory impact Rapana venosa is considered as one of the most unwelcome invaders worldwide. R. venosa is an active predator of epifaunal bivalves, and its proliferation is a serious limitation cultivated and natural populations of oysters and mussels (CEISM 2000). R. venosa are very voracious predators and Rapana is blamed in the Black Sea for the decline of the native, edible bivalve fauna (Zolotarev 1996, in Harding 2003). They have caused significant changes in the ecology of bottom-dwelling organisms and have resulted in the near extinction of the Gudaut oyster (Chukhchin 1984, in Harding 2003). (USGS-NAS Undated). Although scientists are still studying the impacts of R. venosa, they are very concerned about its potential damage to native species.
In Chesapeake Bay (Mid-Atlantic, USA) studies are currently under way to help determine R. venosa spread to develop a model to define potential impacts to the ecosystem. For example, vulnerable prey include infaunal shellfish such as Mya arenaria, Ensis directus and Cyrtopleura costata). In this region predation has also been demonstrated on a range of commercially valuable shellfish species. Another ecological change precipitated by the viened whelk is that the presence of large empty R. venosa shells in the area appears to increase population numbers of the local hermit crab Clibanarius vittatus (Harding and Mann 1999). It is already known that in this region the veined whelk is less susceptible to predation by seasonally migrating large predators (turtles) due to their thick broad shells when compared to large native gastropods such as Busycon and Busycotypus (Harding and Mann 1999). Once this predator refuge size is attained, it is suggested that Rapana venosa may remain as an unchallenged predator for up to a decade (ICES 2004).
CIESM (2000) states that, "In Japan, R. venosa has been sold as seafood on Japanese markets, and could be equivalent to other muricids consumed in countries of Mediterranean culture."
Liang et al. (2004) state that, "R. venosa manifested the most bioaccumulation capacity of Cd (Cadmium). R. venosa and the short necked clam Ruditapes philippinarum were hopeful bioindicators for monitoring Cd and Ni (Nickle) pollution in waters, ..."
Native range: Rapana venosa is native to the Sea of Japan, the Yellow Sea, the Bohai Sea, the East China Sea to Taiwan in the south, and Peter the Great Bay off Vladivostok in the north (Mann and Harding, 2003)
Known introduced range: R. venosa was introduced into the Black Sea in the 1940s and within a decade spread along the Caucasian and Crimean coasts and to the Sea of Azov. Its range extended into the northwest Black Sea to the coastlines of Romania, Bulgaria and Turkey from 1959 to 1972. Subsequent introductions have been reported in the northern Adriatic and Aegean seas (Mann and Harding, 2000).
Recent transoceanic invasions by R. venosa, have resulted in occurrence of the species in the Chesapeake Bay on the Mid-Atlantic coast of the United States (Harding and Mann, 1999; (Mann and Harding, 2000), on the Brittany coast of France (Dr. Philippe Goulletquer, IFREMER, pers. comm., 1999), and in the Rio del Plata between Uruguay and Argentina (in Mann and Harding, 2003).
Introduction pathways to new locations
Aquaculture: Accidental introductions of veined whelk egg cases with acquaculture products is very likely (Kerckhof et al. 2006).
Seafreight (container/bulk): USGS-NAS (UNDATED) reports that, "Egg masses may have been transported with products of marine farming."
Ship ballast water: USGS-NAS (UNDATED) reports that, "Possible pathways of introduction of Rapana venosa in the Chesapeake Bay area include planktonic larvae in ballast water tanks of ships."
Ship/boat hull fouling: Accidental introductions of veined whelk egg cases in hull fouling is very plausible (Kerckhof et al. 2006).
Local dispersal methods
Natural dispersal (local): CIESM (2000) states that, "Rapana venosa reproduces by laying clusters of egg capsules that resemble small mats of yellow shag carpet, which produce pelagic larvae that eventually settle on the bottom where they develop into hard-shelled snails."
As with many introductions, the probability of observing the initial introduction event is minimal. The cryptic nature of the veined whelk contributes to the improbability of observing individuals until they are large and imposing members of the benthic community (ICES 2004). Attempts to target the species for control or eradication must choose the most susceptible lifecycle stage. Unfortunately egg case mats, although visible and concentrated, may be spread over vast areas represent considerable propagule pressure even in small numbers. Larval forms are too dispersed to be considered tractable target and while large epifaunal individuals are identified with comparative ease, their selective collection represents an enormous investment of diver time (ICES 2004).
Preventing the spread of marine invasives such as the veined whelk that are transported by ballast water could involve the sampling and treating of ballast water systems. International compliance with the Ballast Water Management Convention (prepared by the International Maritime Organization) is necessary. The GEF/UNDP/IMO Global Ballast Water Management Programme (GloBallast) is assisting developing countries to reduce the transfer of harmful aquatic organisms and pathogens in ships' ballast water, implement the IMO ballast water Guidelines and prepare for the new IMO ballast water Convention.
Knowing the potential spread of a marine invasive may highlight areas at risk of invasion and indicate appropriate areas to prioritise in terms of preventing its introduction into new locations. A study by Savini and collegues (2004) on the population structure of the veined whelk in Cesenatico, Northern Adriatic Sea (Emilia-Romagna coast), indicated that breakwaters could represent preferential sites for the maintenance of R. venosa as they are utilised as spawning and feeding grounds. In the USA an evaluation of the potential spread of the whelk indicates that the invader could colonise the higher salinity regions of most East Coast estuaries and survive on exposed shorelines from Cape Cod, MA to Charleston, SC (Mann and Harding 2000).
The probable habitat overlap between juvenile blue crabs and R. venosa in Chesapeake Bay and the predation by blue crabs on epifaunal R. venosa is a form of natural biological control which may be occurring in Chesapeake Bay, USA (Harding and Mann 2003). Blue crabs, mud crabs, and spider crabs (Libinia emarginata) also consume R. venosa. Howeve,r this is not an incentive to distribute crabs into estuarine habitats infested with the veined whelk as no host range testing has been conducted. In addition, this form of control is only likely to be effective for the first three to four years following settlement, as following this period crabs reach a large enough size to escape predation.
Rapana venosa are carnivorous gastropods whose main diet consists of a variety of molluscs including native oysters (USGS-NAS Undated). Adult R. venosa are voracious predators of commercially valuable shellfish including oysters and hard clams (Harding and Mann 2002). Most marine predatory snails feed by drilling a hole into their prey, but R. venosa smothers its prey by wrapping around the hinged region of the shell and feeding between the opened valve. However R. venosa may also drill (Roger Mann, Pers. Comm. 2005).
Rapana venosa is dioecious with separate sexes (ICES, 2004).
Rapana venosa lays mats of eggs with 50–500 egg cases per mat (ICES 2004). Each case may contain 200–1,000 eggs (Ware et al., 2001). Egg capsules resemble small mats of yellow shag carpet; between 14 and 21 days later (depending on temperature and salinity) pelagic larvae hatch that eventually settle on the bottom where they develop into hard-shelled snails (ICES 2004; CIESM 2000). Pelagic larvae have a long planktonic phase which may last to a maximum of 80 days (Kerckhof et al 2006). Veligers larvae settle successfully on a wide range of attached macrofauna including bryozoans and barnacles. They grow quickly on mixed algal diets, reaching shell lengths in excess of 0.5mm at 21 days (Harding and Mann In Prep.).
Reviewed by: Roger L. Mann Professor of Marine Science & Juliana M. Harding, Ph.D. Virginia Institute of Marine Science Department of Fisheries Science College of William & Mary USA
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Thursday, 13 July 2006