Veined rapana whelk

Type Description

"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)."

Habitat

"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."

Reproductive Information

"Rapana venosa is dioecious with separate sexes (ICES, 2004).
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Lifecycle

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.).

Nutrition Information

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).

General Impact Information

"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)."

General Management Information

General Pathway Information

Accidental introductions of veined whelk egg cases with acquaculture products is very likely (Kerckhof et al. 2006).Accidental introductions of veined whelk egg cases in hull fouling is very plausible (Kerckhof et al. 2006).

Notes

References