Harding et al. (2009) reported significant mortality of Rapana venosa during a bloom of the dinoflagellate Alexandrium monilatum in the lower York River, Virginia (USA) in September 2007. The whelks stopped feeding as dissolved oxygen and chlorophyll concentrations increased with the development of the bloom. Harding et al. noted that whelk mortality was preceded by external signs of stress including reduced ventilation, inability to attach to hard substrates, periodic pumping of the opercular plate, and increased mucus production over a period of 24-48 hours prior to death. High concentrations of goniodimum A (a toxin produced by A. monilatum) were observed in bivalves attached to the shells of R. venosa. Mortality of R. venosa was 100%. Mortality of oysters (Crassostrea virginica) and northern quahog clams (Mercenaria mercenaria) in the same flow-through system was 0%. The symptoms displayed by the R. venosas in the 24-48 hours prior to death were indicative of paralysis and followed a timecourse similar to that documented for some other molluscs exposed to toxic A. monilatum.
Savini et al. (2002) suggested that the introduction of Rapana venosa to Chesapeake Bay (U.S.A.) offers cause for both ecological and economic concern. Adult Rapana venosa are large predatory gastropods that consume bivalves including commercially valuable species such as hard clams (Mercenaria mercenaria). Laboratory feeding experiments were used to estimate daily consumption rates of two sizes of whelks feeding on two size classes of hard clams. Large R. venosa (shell length, SL > 101 mm) are capable of consuming up to 2.7 g wet weight of clam tissue daily, equivalent to 0.8% of their body weight. Small whelks (60-100 mm SL) ingest an average of 3.6% of their body weight per day.
Very large striped hermit crabs (Clibinarius vittatus) have begun to use shells of the exotic Rapana venosa as shelters (Harding and Mann 1999).
Rapana venosa is a large predatory marine snail that is native to marine and estuarine waters of the western Pacific, from the Sea of Japan, Yellow Sea, East China Sea and Bohai Sea (Richerson 2006). It is now also established in many other parts of the world, where it is generally viewed as an invasive species with the potential to have a seriously negative impact.
In the Black Sea, Rapana venosa occurs down to 30 m in depth in areas with sandy bottoms, as well as in rocky and muddy habitats (Culha et al. 2009). Harding and Mann (1999) report that in the lower Chesapeake Bay (USA), Rapana venosa inhabits subtidal hard bottom habitats, where it can feed, mate, and move while completely burrowed. Rapana venosa is ecologically flexible, able to tolerate low salinity, low oxygen, and significantly polluted water (Gilberto et al. 2006; Culha et al. 2009). It feeds at night and is often found in locations that are hard to sample, making early detection of newly established populations difficult (Harding et al. 2007).
Working with animals from the Chesapeake Bay region (Virginia, USA), Harding et al. (2007) found significant differences in predation strategies and prey species consumed between the introduced veined Rapana venosa and the smaller, native Atlantic oyster drills (Urosalpinx cinerea). As Rapana venosa becomes more prevalent, these differences could result in considerable disruption of the trophic structure (feeding relationships among species) of Chesapeake Bay.
Culha et al. 2009: Moves between warmer deep waters in winter and coastal regions in summer.
Rapana venosa is native to marine and estuarine waters of the western Pacific, from the Sea of Japan, Yellow Sea, East China Sea and Bohai Sea (Richerson 2006). It is now also established in many other parts of the world, where it is generally viewed as an invasive species with the potential to have a seriously negative impact.
According to Culha et al. (2009) and references therein: Rapana venosa became established in the Black Sea in the 1930s and 1940s and spread over the coasts of the Caucasus, the Crimea, and the Azov Sea over a period of 10 years. It expanded its distribution toward the Turkish and Bulgarian coasts of the Black Sea and the coasts of Romania during 1959-1972. It has also been reported from the southeastern coast of South America and from the Red Sea and many localities in the Adriatic Sea since the 1980s. It was presumably introduced into these areas accidentally by ships.
The first specimen in North America was collected by members of the Virginia Institute of Marine Science Trawl Survey Group in August 1998 in Hampton Roads, Virginia (Harding and Mann 1999). Harding and Mann (2005) documented three range extensions of Rapana venosa in Chesapeake Bay, Virginia. These extensions into Tangier Sound, the mid James River estuary, and to Cape Henry at the Bay mouth extended respectively, the northern, western, and southeastern boundaries of the known occupied range in Virginia waters. Salinity and tidal circulation mediate the distribution of adults and larvae of this animal. During dry years (e.g., 2001 and 2002) adult R. venosa may move up-estuary in western tributaries like the James River, given increased salinity and available habitat and food resources. Declines in salinities (or return to normal salinities) will either kill the whelks in the upriver habitats or force a return to downstream habitats (Harding and Mann 2005). The species is now widely distributed in Chesapeake Bay, which harbors what is still the only known breeding population in North America (Harding et al. 2008).
Gilberto et al. (2006) studied a recently established population of Rapana venosa in the Rio de la Plata estuary along the southeastern coast of South America (Uruguay/Argentina).
Rapana venosa is ecologically flexible, able to tolerate low salinity, low oxygen, and significantly polluted water (Gilberto et al. 2006; Culha et al. 2009). It feeds at night and is often found in locations that are difficult to sample, making early detection of newly established populations difficult (Harding et al. 2007).
Harding et al. (2007) studied predation signatures of Rapana venosa, such as distinctive bore holes in prey shell remains (only R. venosa individuals too small to grasp and manipulate prey leave visible predation signatures). These signs could provide a powerful surveillance tool, allowing early detection of smaller, pre-reproductive animals than is possible by simply waiting for their appearance as fishing bycatch (R. venosa are likely to be caught by fishermen only once a population is well established and significant numbers of larger animals are present).
In the Black Sea, Rapana venosa occurs down to 30 m in depth in areas with sandy bottoms, as well as in rocky and muddy habitats (Culha et al. 2009).
Harding and Mann (1999) report that in the lower Chesapeake Bay (USA), Rapana venosa inhabits subtidal hard bottom habitats, where it can feed, mate, and move while completely burrowed.
12-18 years (Harding et al. 2007)
10-15 years (Harding et al. 2008)
The shell of Rapana venosa is globose (rounded) with a very short-spired shell and a large body whorl. The epidermal color varies from gray to reddish-brown, with dark brown dashes on the spiral ribs. Most specimens have distinctive black veins throughout the shell. A diagnostic feature for this species is the deep orange color found in the aperture and on the columella (Richerson 2006).
The reproductive biology of Korean Rapana venosa was investigated by Chung et al. (2002). They found that the total number of egg capsules per individual each year (based on 25 whelks in aquaria) ranged between 184 and 410. The mean number of eggs per egg caspsule was 976. Annual fecundity ranged from about 179,000 to 400,000 eggs per individual, with two to four broods during the spawning season. Eggs in egg capsules, which may be attached to various hard substrates (Culha et al. 2009), took 15 to 17 days at about 20 C to develop and hatch out veliger larvae. No significant deviation was detected from a 1:1 sex ratio.
Harding et al. (2008) investigated the reproductive biology of Rapana venosa from the Chesapeake Bay region (USA) and found even higher productivity, with the number of egg capsules per whelk per year ranging from 133-2759 divided among 3 to 29 broods. They found that egg capsule production is influenced by seasonal and absolute water temperatures as well as by seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay R. venosa begins at water temperatures of approximately 18 degrees C and continues for 11-15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150-200 egg capsules per female per week. Water temperatures above 28 degrees C caused reduced egg capsule production relative to temperatures of 20-25 degrees C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. The authors predict a latitudinal range of 30-41 degrees (north and south) as the realized reproductive range for Rapana venosa populations based on the environmental requirements for native whelks and reproductively active invasive Rapana venosa populations (Harding et al. 2008).
Working with animals from the Chesapeake Bay region (Virginia, USA), Harding et al. (2007) found significant differences in predation strategies and prey species consumed between the introduced veined Rapana venosa and the smaller, native Atlantic oyster drills (Urosalpinx cinerea). As Rapana venosa becomes more prevalent, these differences could result in considerable disruption of the trophic structure (feeding relationships among species) of Chesapeake Bay.
To date, there has been no successful eradication of any nonindigenous marine invertebrate in the United States. The potential for Rapana venosa to cause significant harm to the Chesapeake region's native shellfish and seafood industry is a serious concern (Richerson 2006).
May exceed 160 mm in length (Harding et al. 2007).
Can reach 180 mm (Richerson 2006).
Rapana venosa is a large predatory marine snail that has recently become established in a number of areas outside its native range, raising concerns about potentially serious ecological and economic impacts as it expands into new regions.
Rapana venosa is of significant economic value on the coasts of the Black Sea and is regularly collected during certain periods (Culha et al. 2009). However, this species has a negative impact on commercial shellfish species in both its native and introduced ranges (Harding et al. 2008).
Rapana venosa, common name the veined rapa whelk or Asian rapa whelk, is a species of large predatory sea snail, a marine gastropod mollusc or whelk, in the family Muricidae, the rock shells.
This large sea snail has become an invasive species in many different localities around the world.
The shell of Rapana venosa is globose (rounded) and heavy, possessing a very short spire, a large body whorl, a strong columella and a deep umbilicus. The aperture is large and roughly ovate. Ornamentation is present externally as axial ribs, smooth spiral ribs ending in blunt knobs at both the shoulder and body whorl, and internally as small elongated teeth disposed along the outer lip margin. The external color varies from gray to reddish-brown, with dark brown dashes on the spiral ribs. Some specimens may have distinctive black/dark blue vein-like coloration patterns throughout the inner portions of the shell, usually originating from each individual tooth at the outer lip. A diagnostic feature for this species is the deep orange color found in the aperture and on the columella. The height of the shell can reach up to 180 mm (about 7 in).[2][3]
This species is native to the marine and estuarine waters of the western Pacific, from the Sea of Japan, Yellow Sea, East China Sea and the Bohai Sea.[2]
Rapana venosa is included in Russia's Red Book as threatened with extinction. The original known habitat for this species was the Far East, but since 1947 it has been found in the Black Sea, and its shell became a popular souvenir in Crimea. Recently this species has been found as an exotic in the Chesapeake Bay, on the eastern coast of the United States.
According to some authors, it appears to be the case that the spreading of this species outside its natural range has been made possible by the planktonic larval stage being transported along with ballast water in the hulls of ships, or that egg masses may have been transported with products of marine farming.[4]
Rapa whelks were first found in the Black Sea in the 1940s. Within a decade this mollusk had spread along the Caucasian and Crimean coasts and moved into the Sea of Azov. From 1959 to 1972, its range extended into the northwest Black Sea, to the coastlines of Romania, Bulgaria and Turkey. These whelks have become established in the Adriatic and Aegean seas, and have also been found in the Tyrrhenian sea,[5] on the Northern Atlantic coast of France, and the southeast coast of South America, in Uruguay and the Rio de La Plata estuary (including Samborombon Bay), and in Argentina.[6][7] In the United States the first specimen discovered was in August 1998 by members of the Virginia Institute of Marine Science (VIMS) Trawl Survey Group in Hampton Roads, Virginia. The species is now widely distributed and established in Chesapeake Bay.[2]
Rapana venosa is considered among the 100 worst alien species in Europe in the DAISIE European Invasive Alien Species Gateway,[8] one of two marine gastropods on the list.[8] It is considered as about the 52nd the worst alien species in Europe.[9]
Veined rapa whelks favor compact sandy bottoms, in which they can burrow almost completely. The native habitat of this species is a region of wide annual temperature ranges, comparable to other localities. Fleeing cold waters in the winter, this species may migrate to warmer, deeper waters, thereby evading cool surface waters. This fertile sea snail is extremely versatile, tolerating low salinities, water pollution and oxygen deficient waters.[2]
Veined rapa whelks are carnivorous selective predatory gastropods whose main diet consists of a variety of other mollusk species, mainly epifaunal bivalves such as oysters (Crassostrea virginica) and mussels (Mytilus galloprovincialis, Modiolus and Geukensia), but also clams (Anadara inaequivalvis, Chamelea gallina, Tapes philippinarum, Venus verrucosa, and the northern quahog Mercenaria mercenaria). Prey are chosen by the whelk according to their species and size.[10][11][12] Most snails feed by drilling a hole into their bivalve prey, but rapa whelks usually smother their prey by wrapping around the hinged region of the shell and feed by introducing their proboscis between the opened valves. The whelk can also secrete a thick mucus that may or may not contain biotoxins to weaken the prey.[12] Shell drilling, however, is also not unknown in this species.[13]
Rapana venosa is dioecious, which means each individual organism belonging to this species is distinctly male or female.[11] In this species' native range, mating occurs for extended periods of time, mainly during the winter and spring.[3] It reproduces by internal fertilization,[14] after which it lays clusters of egg cases that resemble small mats of white to yellow shag carpet,[2][3] mainly during spring and summer.[11] One adult female can lay multiple egg cases throughout the season.[8] Each cluster contains 50-500 egg cases, and each egg case may contain 200-1000 eggs.[3] The pelagic veliger larvae (a larval form common to various marine and fresh-water gastropod and bivalve mollusks)[15] then hatch, persisting in the water column for 14 to 80 days[11] and feeding primarily on plankton.[8] They eventually settle on the ocean floor where they develop into hard-shelled snails. Growth is rapid over the first year of life, and reproduction occurs from the second year onwards. Large specimens may be over ten years old.[2]
It is known that the abundance of prey, the lack of competition from other gastropod species, as well as the absence of direct predators of R. venosa may be some of the factors that contributed to the successful establishment of new populations of this sea snail outside its native range.[3] The thick strong shell of the rapa whelk is arguably its strongest advantage over native whelks, because rapas can easily prey on local whelks, whereas local whelks are unable to successfully attack rapas. The thick shell also means that predators such as sea turtles are unable to feed on the invasive species, and can only feed on local whelk populations. It is suggested that once the rapa whelk reaches adulthood, it exists unchecked in the local population, and can consume and reproduce freely.[3] The Veined rapa whelk is also highly tolerant to wide variations in salinity and oxygen concentration,[11] a fact that may also help to explain its success as an invader of marine coastal and brackish ecosystems. In its native range Rapana venosa shows high temperature tolerance, being able to withstand temperatures varying from 4 to 27 °C (39.2 - 80.6 °F).[3]
Veined rapa whelks have caused significant changes in the ecology of bottom-dwelling organisms, and have become marine pests in the Black Sea. Although scientists are not completely aware of the impacts of the whelk, they are very concerned about its potential impact on native Bay species. Studies are currently under way to help determine the whelk's spread in Chesapeake Bay, so that scientists can develop a model that will define potential impacts to the Bay's ecosystem.[2]
The imposex phenomenon has been observed in the veined rapa whelk in Chesapeake Bay.[16] Imposex is characterized by the development of masculine sexual organs in female individuals as a consequence of exposure to organic tin compounds, such as tributyltin (TBT). Such compounds are biocide and antifouling agents, commonly mixed in paints to prevent marine encrustations on boats and ships. For this reason, it is not uncommon for high concentrations of such compounds to be present in the sea water near shipyards and docking areas, consequently exposing the nearby marine life to its possibly harmful effects.[17] This unnatural development of male reproductive organs, however, has shown no negative effects on populations of this species, and no loss of reproductive capabilities of female R. venosa as a consequence of Imposex has been observed so far.[16]
This article incorporates public domain text (a public domain work of the United States Government) from reference [2]
Rapana venosa, common name the veined rapa whelk or Asian rapa whelk, is a species of large predatory sea snail, a marine gastropod mollusc or whelk, in the family Muricidae, the rock shells.
This large sea snail has become an invasive species in many different localities around the world.
