L. littorea is invasive in North America with a current range from Red Bay, Labrador, to Lewes, Delaware (Blakeslee et al., 2008; Brawley et al., 2009). Recent historical and molecular analyses support Great Britain and Ireland as the region from which L. littorea was introduced into Nova Scotia (NS) (Brawley et al., 2009; also see Blakeslee and Byers, 2008; Blakeslee et al., 2008). L. littorea was common at Pictou (NS) in 1840 (Dawson and Harrington, 1871), and spread southward from Halifax (NS) to Cape May, New Jersey by 1890 (Willis, 1863; Morse, 1880; Verrill, 1880; Ganong 1886, 1887; Bequaert, 1943) and northward to southern Labrador by 1882 (Bequaert, 1943). Rare subfossils of L. littorea exist in the Canadian Maritimes (see History of Invasion/Spread). This snail is the major herbivore of the intertidal zone within its invasive range in the northwestern Atlantic. Although not established, L. littorea is being periodically introduced to bays on the U.S. Pacific coast.
The name Littorina littorea was in common use among scientists by the 1830s-1840s, but the species was originally described by Linnaeus (1758) as Turbo littoreus. No shells or preserved specimens survive as types from Linnaeus’ work, and Reid (1996) established a lectotype from one of Linnaeus’ drawings along with a diagnosis of the species. Reid discusses the taxonomic history involving synonymies and earlier spellings of L. littorea (e.g., Menke (1828) used Litorina litorea). Reid (1996) remarks that a few authors, perhaps even Linneaus, included L. saxatilis within their concept of T. littoreus/L. littorea until the late 1830s, and still fewer authors included L. squalida from the Pacific within L. littorea during part of the 1800s. Lyell (1835) applied the name L. littorea to fossil specimens of L. littorea, and most subsequent authors applied this name to fossil and modern representatives of L. littorea with the same concept of the species as we use today. The common name of L. littorea in English is “the common periwinkle”.
The higher classification of the Gastropoda of Bouchet and Rocroi (2005) places Littorinain clade Littorinimorpha of the Caenogastropoda.
Reid (1996) gives the mature shell height of L. littorea as 10.6-52.8 mm. Many colour morphs are known, but most shells are dark (brown to black), although when older and eroded, the shell is lighter. The shell is an oblong-turbinate gastropod shell with a large body whorl and pointed spire; sutures and additional whorls are not very prominent except in young snails. Shell width is about two-thirds to three-quartersof the length. The species is unisexual, and, in the breeding season, males have a prominent penis (e.g., Fretter and Graham, 1962; Barroso et al., 2007). Further details and excellent illustrations are given by Fretter and Graham (1962, Chapter 2) and by Reid (1996, see p. 7, 9, 33, 100-105; reproductive details are taxonomically important: males have a penis with 10-42 mamilliform glands, and females have an oviduct that is composed of three loops, two of the albumen gland followed by a capsule gland).
Fossils of L. littorea in the eastern Atlantic are first found in England at ca. 2.4-3.2 My BP (the Red Crag formation) and are common in many European deposits thereafter (see discussion in Reid, 1996). The apparent range of L. littorina shifted with climate change to areas northward (Siberia) or southward (Morocco) of the present native range, based upon fossils in deposits dated from periods known to represent colder or warmer climates than present. L. littorea is unknown from Greenland, and it was last present in Iceland about 1.1 My BP (Leifsdóttir and Símonarson, 2002).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
As Wares and Blakeslee (2007) commented, scientists have regarded North American L. littorea as a classic puzzle over time. The puzzle has concerned which of these hypotheses is true: 1) L. littorea in North America is derived completely from invasive introduction(s) of snails from Europe (invasion hypothesis), 2) L. littorea is native to North America, but was rare until the 1800s (native species hypothesis), or 3) L. littorea is both introduced and native to North America. The invasive species hypothesis is supported strongly by recent analyses (Blakeslee and Byers, 2008; Blakeslee et al., 2008; Brawley et al., 2009), but there are still some unresolved issues (see below) that deserve additional research.
Over time, most scientists have considered L. littorea to be invasive in North America, because its chronicled spread is consistent with an invasive introduction (e.g., Ganong, 1886, 1887; Bequaert, 1943; Carlton, 1992, Reid, 1996; Chapman et al., 2007). L. littorea was observed to be common in Pictou Harbour (Nova Scotia) and the adjacent area of the Northumberland Strait by 1840 (Dawson and Harrington, 1871; Ganong, 1886, 1887). Pictou was an important port in the early 1800s, and 97.4% of ships arriving from 1773-1861 sailed from Great Britain/Ireland (Brawley et al., 2009). The advance of L. littorea was carefully monitored in the Canadian Maritimes and on the U.S. shore after Willis (1863) reported finding it at Halifax in 1957; this was the first published description of L. littorea in North America. The rapidity of its step-wise southward movement from Halifax was well chronicled in the U.S., where local molluscs were well described by the time of the invasion of L. littorea (Ganong, 1886; Bequaert, 1943; N.B. several studies of Canadian molluscs also did not describe L. littorea, see Dawson, 1872 [living and fossil treatment] and references in Ganong, 1886). Verrill (1880) and Morse (1880) provided vivid accounts of its southern migration: L. littorea was found in Maine by 1868, and in New Hampshire in 1871. It was rare at Provincetown, MA (Cape Cod) in 1872 but became abundant by 1879; it was abundant at Newport (Rhode Island) by 1880 but still rare at New Haven (Connecticut). By 1890, it had reached Cape May, New Jersey, close to its current southern boundary (Bequaert, 1943). Meanwhile, collections were made at points distant to Pictou in the Gulf of St Lawrence: Morse (1880) received samples from Bathurst on the New Brunswick shore near Quebec in 1855, and it was collected in southern Labrador in 1882 (Bequaert, 1943). Thus, from the time (~ 1840) that L. littorea was common in and near Pictou, it had spread within ~ 50 years to occupy its current range limits.
European fossils of L. littorea are common, in contrast to the rare finds of fossil L. littorina in North America (see discussion in Reid, 1996 and Chapman et al., 2007). Given how abundant this snail is in its native and invasive habitats, the rarity of fossils and subfossils in North America offers little support for the existence of a native population in North America. The nature of these sub-fossils remains unresolved, but their rarity led Brawley et al. (2009) to suggest that occasional introductions from Europe prior to the 1800s (by whatever natural or anthropogenic means) failed to produce population densities necessary for L. littorea to become invasive in North America. The present failure of L. littorea to become invasive on the Pacific coast of the U.S. may be helpful as a model for understanding these subfossils (i.e., low density introductions followed by local extinctions, Hanna, 1966; Carlton, 1969).
Molecular analyses strongly support introduction of L. littorea to North America from Europe (Blakeslee and Byers, 2008; Blakeslee et al., 2008; Brawley et al., 2009), and from Great Britain and Ireland, in particular (Brawley et al., 2009). Wares et al. (2002) paved the way for modern sequence-based studies of the invasion versus native hypotheses, and concluded that L. littorina was native; however, their sampling level turned out to be too low (Wares and Blakeslee, 2007) because of the very large genetic diversity of L. littorea in Europe, as demonstrated by Blakeslee et al. (2008). Blakeslee et al. (2008) found that North American haplotypes (i.e., sequences of a mitochondrial gene) were nested within European haplotypes, and their statistical analysis predicted that European L. littorea has 17.5 x times the diversity of North American L. littorea. Thus, they hypothesized that North American haplotypes in their study for which they found no matches in Europe (i.e., “unique” North American haplotypes) are shared with (and introduced from) Europe, but that the high genetic diversity in Europe requires even larger sampling to find them. Indeed, applying a historical analysis of shipping to sampling design for further molecular analyses, Brawley et al. (2009) found that the European rockweed Fucus serratus, also first recognized in North America in the mid-1800s at Pictou, came to Nova Scotia from Scotland and Ireland. Brawley et al. (2009) then used the same locations to study L. littorea haplotypes (Great Britain and Ireland were weakly sampled by Blakeslee et al. (2008), in comparison to Scandinavia and the rest of continental Europe). Eight of 9 cytochrome b haplotypes of L. littorea at Pictou had matches in Ireland and Scotland with the 9th haplotype being basal to a Scottish haplotype. Considering L. littorea from 5 different Nova Scotian sites, 11 of 13 haplotypes were shared with haplotypes found in Europe, and all of these 11 haplotypes were found in Great Britain and Ireland (10 matches to Ireland and Scotland). This study also found that there was a weak match between haplotypes in Scandinavia versus Pictou and Nova Scotia as a whole (Brawley et al., 2009). The match to haplotypes from Ireland and Great Britain is consistent with Brawley et als (2009) finding that 97.6% of all ships entering Pictou from 1773-1861 came from Great Britain and Ireland.
Brawley et al. (2009) used an Isolation by Migration (IMa) analysis of their L. littorea sequence data to predict that the introduction of L. littorea occurred between 192 and 11,794 y BP (low and high 95% confidence intervals, all Nova Scotian haplotypes compared to all haplotypes from Great Britain and Ireland). The more recent time (192 y BP) fits historical reports of the discovery of L. littorea near Pictou (Dawson and Hetherington, 1871). Continued sampling from British ports involved in 1800s trade with Pictou (Brawley et al., 2009) should provide more matches for North American haplotypes and lower the higher confidence level (11,794 y BP). If it does not, attention will need to be redirected to Clarke’s (1971) hypothesis that North American L. littorea could be both native and introduced.
In summary, rock-ballasted ships from Great Britain/Ireland sailed to Pictou in the late 1700s/early 1800s in order to obtain timber for Great Britain, and these ships dumped their ballast onto the shore and into the harbor (Brawley et al., 2009). Some of the ballast used by British ships came from the intertidal zone, and the molecular analyses support this route for the introduction of L. littorea,F. serratus, and no doubt other organisms, into North America (Brawley et al., 2009). The intensity of this “propagule pressure” (i.e., large numbers of arriving ships) was likely critical to overcome the constraining effects of L. littorea’s reproductive biology on invasion potential (see Reproductive Biology), by transporting a steady number of individuals to the same place in North America from Great Britain and Ireland.
L. littorea can survive a wide range of air and water temperatures, is tolerant of brackish water, can withstand brief anoxic periods, and feeds under both damp emersed and immersed conditions in the intertidal zone (see Physiology). Thus, its physiology makes it unusually capable of being transported and established outside its native range, whether in rock ballast on ships that took ~ 21-60 days to reach Pictou in the nineteenth century (Brawley et al., 2009) or, presently, as a hitchhiker as other marine species are transported for aquaculture, food, or fishing bait from the Atlantic to the Pacific.
A key limiting factor to establishment after introduction is likely to be that the species is unisexual (male or female, see Reproductive Biology). Given natural predation in an introduced habitat, obligate sexual reproduction requires that a large number of sexually mature females and males be introduced simultaneously in order for establishment of L. littorina as an invasive species to occur. The evidence is that this rarely occurs, and is why the repetitive, large-scale ballast discharge into Pictou Harbour is likely to have been critical to the invasion of North America (Brawley et al., 2009). Once abundantly established in a new location, however, L. littorea poses a strong risk for continued spread because of its planktonic larvae.
L. littorea reaches intertidal abundances of hundreds to thousands of animals/m2 on rocky shores, cobbled beaches, mudflats and Spartina marshes (e.g., Lubchenco, 1978; Bertness, 1984; Buschbaum, 2000; Carlson et al., 2006; Tyrell et al., 2008). Generally, it is most common in the lower half of the intertidal zone. L. littorea is found both on rock surfaces and macrophytes (e.g., Fucus vesiculosus, F. serratus, Saccharina latissima, Ascophyllum nodosum,S Brawley, University of Maine, USA, personal communication, 2009) in both the northeastern and northwestern Atlantic. The species is found at considerable depth (e.g., Huntsman, 1918 (36 m, Gulf of St Lawrence); Fretter and Graham, 1980 (60 m, northern Britain)), but predation limits its abundance subtidally (Pettitt, 1975; Perez et al., 2009). L. littorea typically moves into subtidal areas on cold shores (e.g., Maine) in winter, becoming uncommon in the intertidal zone until spring.
Following copulation by males and females, capsules (i.e., saucer-shaped structures containing the zygotes, see Reid, 1996, fig. 44P) are released into the sea by the female. Reproduction is seasonal, usually including part of the winter and spring, and capsules are typically spawned at night on full and new moon spring tides during the reproductive period (Fish, 1979). Water temperature controls the onset and duration of spawning (Chase and Thomas, 1995). The planktonic stages are a trochophore larva followed by a veliger larva, and the trochophore stage lasts for about a week (Fretter and Graham, 1962, see their fig. 235).
L. littorea is typically herbivorous, but it functions ecologically as an omnivore, because as it scrapes surfaces with its radula, many juvenile invertebrates (e.g., recently settled barnacle larvae) are also ingested (Lubchenco, 1978, 1983; Bertness, 1984; Hawkins et al., 1992; Vadas and Elner, 1992; Buschbaum, 2000). This snail feeds primarily on ephemeral filamentous and bladed algae and diatoms, including Acrosiphonia spp., Cladophora spp., Urospora spp., Ulothrix spp., Ulva spp. (all green algae), Ceramium spp., Palmaria spp., Polysiphonia spp., Porphyra spp. (red algae), Ectocarpus spp. (brown algae), and germlings of rockweeds (Ascophyllum nodosum, Fucus spp.) and other macrophytic sporelings/germlings (e.g., Lubchenco, 1978, 1983; Vadas and Elner, 1992). Bequaert (1943) reports the work of a contemporary scientist (WT Davis) who kept L. littorea alive from November 23, 1930, to April 1, 1932, “in a corked bottle of sea-water with a piece of Ulva lactuca on which it fed (p. 5)”; this emphasizes the ability of L. littorea to be transported long distances from a nutritional and environmental viewpoint. This snail also feeds on marsh grasses, perhaps with more effect on rhizomes than blades, as well as scraping surficial diatoms and epiphytes from blade surfaces (e.g., Spartina alterniflora) (Bertness, 1984; Tyrrell et al., 2008).
Trematode parasites of L. littorea reduce reproductive success and survival by feeding on the female and male reproductive organs and the digestive tract (Fretter and Graham, 1962) and also reduce grazing rates of the snails (Wood et al., 2007). Blakeslee and Byers (2008) found 11 trematode species associated with European L. littorea and 5 species associated with North American L. littorea (e.g., Cryptocotyle lingua [most common in North America]; Cercaria parvicaudata, Renicola roscovita, Microphallus similis). Trematode parasites of L. littorea are extensively studied throughout the snail’s native and invasive range (e.g., Fretter and Graham, 1962; Kristoffersen, 1991; Huxham et al., 1993; Blakeslee and Byers, 2008; Blakeslee et al., 2008; Byers et al., 2008). L. littorea is infected by trematodes by ingesting bird faeces as it grazes in the intertidal zone, and forms one part of the infective life history (birds-snails-fishes) of the trematodes.
The eurythermal tolerance of L. littorea is evident from its abundance across its native range from the White Sea to Portugal (Reid, 1996); however, acclimation occurs seasonally and in different parts of its range and there appear to be some genetic components to thermal tolerance, as well (i.e., adaptation versus acclimation). Clarke et al. (2000) found that Welsh L. littorea had higher mean heat-comma temperatures in seawater than English (Yorkshire) L. littorea, across three acclimation temperatures (12, 16, 20oC). Heat comma limits of Yorkshire L. littorea increased with acclimation temperature from a field-collected (unacclimated) value of 28.3oC to ~ 35oC when snails were acclimated at 20oC. A weekly, near-lethal heat coma event can be tolerated, but animals quickly succumb to repeated daily exposures to high temperature (Clarke et al., 2000), which explains current southern range limits on both sides of the Atlantic. The median upper lethal temperature for Scottish L. littorea was 35.3oC, and the median lower lethal temperature was -13.0oC; snails were tested in air at 100% humidity and collections were made from the shore in summer to test the high temperature tolerance and in winter to test low temperatures (Davenport and Davenport, 2005). L. littorea tolerates these freezing conditions on the shore at low tide because they can tolerate freezing of extracellular water (Kanwisher, 1955; Murphy, 1979). The freezing tolerance of L. littorea decreases at lower salinities (Murphy, 1979) and heat tolerance also is decreased at lower salinities (i.e., ~ 15 psu, Clarke et al., 2000). Hypoxia is tolerated by L. littorea as a consequence of regulation of metabolic rate and does not appear to have as much effect as salinity history on thermal tolerance (e.g., MacDonald and Storey, 1999; Davenport and Davenport, 2007).
The heavy shell of L. littorea protects it from many predators but numerous birds, fishes, and crabs are major predators (Pettitt, 1975). Birds that eat L. littorea include herring gulls (Larus argentatus), the knot (Calidris canutus), and oldsquaws (Clangula hymenalis); among the many fishes that eat L. littorea, flounders (e.g., Pleuronectes flesus) are prominent (Pettitt, 1975). Crabs crush shells, and it is common to see L. littorea on the shore that have repaired their shells after escaping crab predation (e.g., Vermeij, 1982). In Europe, the green crab Carcinus maenas is a major predator on L. littorea (e.g., Buschbaum et al., 2007), and this is also true of the crab’s invasive range in North America (Carlson et al., 2006; Ellis et al., 2007; Edgell and Rochette, 2008; Perez et al., 2009). ). L. obtusata is much more affected by C. maenas predation than L. littorea in the Gulf of Maine and Bay of Fundy, which Edgell and Rochette (2008) suggested was due to the prior evolution of predator-resistance by L. littorea in Europe, before its introduction to North America. The Jonah crab Cancer borealis is an important L. littorea predator and is especially important in limiting subtidal abundance of L. littorea (Perez et al., 2009). Lobsters (e.g., Homarus americanus) eat few L. littorea (Jones and Shulman, 2008). The Asian shore crab (Hemigrapsus sanguineus, now invasive on the U.S. shore) consumes few L. littorea directly, but it may eat juveniles as it consumes algae based upon the decreased abundance of L. littorea on one studied shore as H. sanguineus became more abundant (Bourdeau and O’Connor, 2003; Kraemer et al., 2007). Humans should also be considered a natural enemy based upon their use of periwinkles for food (Pettitt, 1975; Reid, 1996).
It is highly likely that L. littorina was introduced to North America from the intertidal or shallow subtidal zones of Great Britain and Ireland with rocks/cobbles used for ship ballast; ballast was dumped into the harbour and onshore in Pictou, Nova Scotia (and in other areas of Nova Scotia) in the late eighteenth and early nineteenth centuries (Brawley et al., 2009).
In the twentieth century, local introductions of L. littorea to several bays on the Pacific U.S. shore (see above) are believed to have occurred as Atlantic shellfish like oysters and clams were transported for fisheries/aquaculture (Hanna, 1966; Carlton, 1969, 1992, 2007). Underlining this likely route of introduction of L. littorea from the Atlantic to Pacific earlier in the twentieth century, Bequaert (1943) states that L. littorea’s “herbivorous habits are sometimes made use of to keep parked oysters free of algal growth (p. 5)”.
Transport of L. littorea is occurring currently in bunches of Ascophyllum nodosum, because this brown seaweed is commonly used as packing material for northwestern Altantic seafoods (e.g., lobsters) and worms (i.e., bait worms for fishermen) that are sold and shipped live to distant areas (Carlton, 2007; San Francisco Estuary Partnership, 2009). The type of A. nodosum that is being shipped with bait worms from Maine is, in fact, nicknamed “worm-weed” in Maine, and L. littorea (and L. saxatilis) occur on this seaweed in its natural shore habitat.
Steneck and Carlton (2001) suggested that the introduction(s) of L. littorea into Canada could have been deliberate, because periwinkles were commonly consumed in Britain and Ireland by poor people. There are no data to support this interesting idea (e.g., cargo manifests for the period do not reveal this, to date, S Brawley, University of Maine, USA, personal communication, 2009). Brawley et al. (2009) hypothesized that the major introductions in Nova Scotia occurred on rock ballast, because they found records of substantial discharge of ballast into Pictou Harbour by ships arriving from Great Britain and Ireland in the early 1800s, as well as documents showing that the Irish shore was dredged for ship ballast. The Northumberland Strait and western Cape Breton Island areas of Nova Scotia were particularly exposed to high intensity introduction potential due to the number of ships that sailed with ballast, discharging it to load timber before returning to Great Britain (Brawley et al., 2009).
This snail is a concern to fish aquaculture because, when abundant, it can cause more fish to be infected with trematode parasites (e.g., Kristoffersen, 1991). L. littorea should be considered as a potential threat to the establishment of sea vegetable aquaculture in Europe and North America because it consumes Porphyra spp. and Palmaria spp.
One of the most important demonstrations of the ecological effects of L. littorea in the northwestern Atlantic was the experimental demonstration of its ability to shift the composition of algae on the shore (Lubchenco, 1978). High intertidal pools are filled with Ulva intestinalis and similar species when L. littorea is absent, but become dominated by crustose algae and the tough red seaweed Mastocarpus stellatus when the snail is present (Lubchenco, 1978; I have updated species names). The rest of the intertidal shore can be grazed down to bare (or crust-covered) rock at high L. littorea densities. At moderate densities, L. littorea can facilitate macrophyte growth by removing epiphytes, including diatoms, after the macrophytes (e.g., Fucus spp., Lubchenco, 1978) have grown large enough to avoid being removed by grazing L. littorea). It is likely that shores of the northwestern Atlantic had different species compositions (quantitatively) prior to the introduction of L. littorea (e.g., Vadas and Elner, 1992), but recent studies of the interactions of L. littorea and the native L. saxatilis (Behrens Yamada and Mansour, 1987) show competition and lead to a contrasting viewpoint (Eastwood et al., 2007). Eastwood et al. (2007) suggest that the grazing niche occupied by L. saxatilis extended throughout the intertidal zone prior to introduction of L. littorea and the predatory green crab C. maenas. Of course, there were still native fishes, birds, and crabs that are littorinid predators, and L. saxatilis has a thinner shell and is more susceptible to predation than L. littorea. Thus, demonstration of the niche overlap of these two snails (e.g., Eastwood et al., 2007) may still reflect a greater effect of L. littorea introduction on L. saxatilis than a potential equivalence of the two species as herbivores in the northwestern Atlantic intertidal zone. The consequences of grazing by L. littorea are much less dramatic on European shores than in North America because of the presence of large, herbivorous limpets in Europe that are absent in North America (i.e., Patella vulgata); these limpets are such major grazers that they swamp out the effects of L. littorea, but L. littorea is still a locally important herbivore in its native range (Hawkins et al., 1992).
Littorea littorea can physically alter salt marsh habitats and cobbled beaches by affecting sediment accretion (Bertness, 1984). As L. littorea browse cobble surfaces, they remove (“bulldoze”) sediment from these surfaces. Grazing by L. littorea also reduces the amount of physically benign habitat at low tide for small organisms by removing leafy and filamentous green, red, and brown algae, which are otherwise often found in mats or turfs on the shore. There are both facilitations and inhibitions on settlement of invertebrate larvae (e.g., barnacle cyprids) associated with clearing of intertidal substratum by grazing L. littorea (e.g., Bertness, 1984; Buschbaum, 2000).
Impacts on Biodiversity
Grazing by L. littorea quantitatively reduces recruitment of many benthic intertidal organisms; larger sessile organisms (e.g., rockweeds) size-escape grazing and then benefit from being cleaned by surficial grazing of L. littorea on their surfaces (Lubchenco, 1983; Vadas and Elner, 1992). Locally, the quantity of green algae (in particular) is markedly reduced by the presence of L. littorea, but the overall biodiversity (species richness) of a shore is rarely affected because there are microhabitat refuges where such species escape grazing.
L. littorea in North America partly displaced the mud snail Ilyanassa obsoleta from mudflats, which may have had effects on the composition of infauna of mudflats (Brenchley and Carlton, 1983). As noted above, L. littorea competes with and may have displaced native North American L. saxatilis from portions of the mid and low intertidal zone (Behrens-Yamada and Mansour, 1987; Eastwood et al., 2007).
Scheibling et al. (2008), in the case of the invasive green alga Codium fragile ssp. tomentosoides, and Valentine et al. (2007), for the invasive ascidian Didemnum sp., asked the question, “Is L. littorea reducing the abundance of these organisms?”. Although L. littorea did reduce the biomass of both species in the tide pool habitats of Nova Scotia and New England where the studies were done, the results would not support application of L. littorea in biocontrol. They do show how complex the northwestern Atlantic shore is in terms of interactions between native and successive waves of invasive species. An earlier use of L. littorea to control epiphytes on oysters is mentioned above.
Economic Value and Social Benefit
A fishery for periwinkles has existed for centuries in parts of Europe (e.g., Scotland and Ireland). Landings of the L. littorina fishery in Ireland in 2006 had a value of 1,663,000 Euros (first sale value) and a tonnage of 1,066 tons (Marine Institute, Ireland, 2009). Annual landings (and value) were about two times higher during most of the 1990s than landings (and value) from 2003-2006. The primary area of L. littorina collection is in western Ireland (Sligo, Mayo Galway and Claire) and the Louth and Dublin area in eastern Ireland are the second most important area (Marine Institute, Ireland, 2009). The harvested periwinkles are exported to the United Kingdom, Belgium, France, the Netherlands, and Spain (Marine Institute, Ireland, 2009).
A periwinkle fishery developed in some areas of Canada (e.g., Nova Scotia, New Brunswick) and New England (Maine) after the species attained high abundances in the twentieth century. Recent periwinkle harvests from both Canada and Maine are taken to Boston and sold from there to markets in Asia, Europe and the United States (Daigle and Dow, 2000). In the Maritimes, the best price is for animals over 19 mm shell height; these animals are four years old (Sharp, 1998). Most periwinkles in New Brunswick are harvested in southern New Brunswick (Atlantic New Brunswick), and in Nova Scotia, the main periwinkle landings come from Digby-St. Mary’s Bay (Sharp, 1998). Thus, both in Maine and Canada, the Bay of Fundy region is a major site of L. littorina harvest. Sharp et al. (1998) reported that there were at least 150 regular harvesters and hundreds more occasional harvesters working in the New Brunswick periwinkle fishery.
Within the period of available records (1950-2008), the periwinkle harvest in Maine expanded beginning about 1981, and achieved its highest landings and value in 1989 (3,827,560 pounds valued at $1, 343,318). The lowest annual value from 1989-2008 was in 2004 ($47,860). The 2008 periwinkle fishery brought in 720,004 pounds valued at $601,410 (Department of Marine Resources, State of Maine, 2009a). Because of concern about use of suction collection devices and potential depletion of the periwinkle fishery, the State of Maine instituted regulations (Department of Marine Resources, State of Maine, 2009b) for the periwinkle fishery in 2009 (with a personal exemption for collection of up to 2 quarts/day for personal use without a license). These regulations make it unlawful to use SCUBA, snorkelling, pumps or suction-devices to harvest periwinkles, and they require that undersize periwinkles be returned to the waters where they were collected.
L. littorea is easy to spot on shipped live seafoods or potential aquaculture targets, and to prevent spread to the North American Pacific coast, this should be carried out by traders in seafoods, shellfish, and bait worms. However, there are no regulations in the State of Maine that enforce such inspections presently (Department of Marine Resources, State of Maine, personal communication to S Brawley, University of Maine, USA, December 2009), and the best strategy to change behaviour (e.g., type of packing materials) is probably for regulation to occur at the level of receiving states and countries.
In its invasive range in the Atlantic, L. littorea is most similar to L. saxatilis, but is easily distinguished when mature by its larger size and the less pronounced ridges (roughness) of the L. littorea shell compared to L. saxatilis. Also, L. saxatilis is rarely found below the high intertidal zone, and L. littorea becomes more common below the high zone (but is also found in abundance in many high intertidal zones and pools). In the Pacific, L. squalida, which is considered to be L. littorea’s sister species (Reid, 1996), has a similar shell shape, but L. littorea’s shell is a little narrower and less incised. These two species are also distinguished by differences in reproductive anatomy, and the number of zygotes/capsule that are spawned (14-15 zygotes/capsule in L. squalida; 1-3 [less commonly to 9] zygotes/capsule in L. littorea; see Reid, 1996, Table 3, p. 91). When in doubt (e.g., with immature specimens), molecular techniques will separate L. littorina from other species (Reid et al., 1996).
Once a large breeding population is established, eradication is not feasible, and the snail can be expected to extend its range substantially. Thus, control of this potentially invasive snail in the Pacific is best based upon care in avoiding accidental transport with other live organisms from the intertidal zone. The San Franscisco Bay Estuary Partnership (2009) is sponsoring local eradication efforts for L. littorea, which appear to be helpful to preventing invasion.
Maine Sea Grant and the Department of Marine Resources (State of Maine) have prepared posters showing several species that would be invasive to the U.S. West Coast if established from Atlantic shores and distributed them to fishing shops, etc. throughout the U.S. (Department of Marine Resources, State of Maine, personal communication to S Brawley, University of Maine, USA, December 2009). This is an attempt to limit shipment and introduction of invasives. The San Francisco Estuary Partnership (2009) also has a website and outreach programs designed to increase public awareness of the danger of release of L. littorea (and other hitchhiking species) to the local shore.