Littorina saxatilis

Invasion History

First Non-native North American Tidal Record: 1993
First Non-native West Coast Tidal Record: 1993
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Littorina saxatilis has an extensive native distribution in the Atlantic, stretching from the Arctic Ocean (up to 80°N) south to the Mid-Atlantic States (New Jersey-Virginia) and the Iberian Peninsula (Reid 1996). Isolated southern populations in the Azores, Canary Islands, and the Mediterranean Sea (Tunisia) could represent remnants of Pleistocene populations, although fossil evidence is lacking. Natural transport by birds or rafting is also possible. In the Northeast Atlantic, L. saxatilis has colonized the isolated islet of Rockall, between Britain and Iceland (Johannesson 1988). Johannesson (1988) suggests that the ovoviparous life history has adapted this species to colonizing remote sites, since a single fertilized female rafted on driftwood or seaweed, or carried by a ship, can start a population. Alternatively, these southern records could represent early introductions by shipping. On the East coast of North America, the construction of stone jetties and riprap may have favored the extension of L. saxatilis’ range to the Atlantic coast of Virginia, near the mouth of Chesapeake Bay (Counts and Bashore 1991). The type population in Venice Lagoon, Italy, from which the species was first described in 1792, is probably introduced (Panova et al. 2011), as are occurrences in four estuaries on the coasts of South Africa and Namibia (Mead et al. 2011b). The most recent invasion is in San Francisco Bay, where this snail was first collected in 1993 (Carlton and Cohen 1998).

North American Invasion History:

Invasion History on the West Coast:

Littorina saxatilis has been introduced to the West Coast of North America, in San Francisco Bay, California. In 1993, this periwinkle was collected in rocky debris along the shore at Emeryville Marina, on central San Francisco Bay, by James T. Carlton (Carlton and Cohen 1998). In 1996, a second population was found at Taney Marina Beach, Coast Guard Island, on the Oakland estuary (Carlton and Cohen 1998). A research group, led by Whitman Miller of the Smithsonian Environmental Research Center, began a series of surveys in 2002 in order to evaluate the possibility of eradication. They found that L. saxatilis was already sufficiently widespread so that eradication was not feasible. Several populations were found on South San Francisco Bay, including one at the Port of Redwood City (Miller et al. 2004) and in Brisbane Lagoon (Cohen et al. 2005). The probable vector for introduction of this periwinkle was imported baitworms (Neanthes virens) wrapped in seaweed (Ascophyllum nodusum) from Maine and Maritime Canada. The seaweed packing material is usually discarded along the shore, and often contains living marine invertebrates, including L. littorea, L. saxatilis, and L. obtusata (Carlton and Cohen 1998; Miller et al. 2004).

Invasion History Elsewhere in the World:

Littorina saxatilis was first described from Venice Lagoon, Italy in 1792 (Reid 1996). This population has been considered to be one of several cryptogenic remnant populations in Pleistocene refuges (Reid 1996). However, genetic analysis of Venetian specimens shows low genetic diversity and similarity to British and Scandinavian populations, strongly supporting introduced status (Panova et al. 2011). Other isolated populations, in the Gulf of Gabés, Tunisia and in the Azores and Canary Islands, could be Pleistocene remnants, or natural colonists (Johannesson 1988; Reid 1996), but to our knowledge, have not been studied genetically.

Isolated populations of L. saxatilis occur in South Africa and Namibia. It was first reported in 1963 from Langebaan Lagoon, South Africa (Robinson et al. 2004; Robinson et al. 2005; Mead et al. 2011b). Fossils believed to date to about 40,000 years BP, and postglacial fossils, are known from the vicinity of Cape Town (Johannesson 1988; Reid 1996). However, dates have not been determined by radiological methods. As Mead et al. (2011b) have noted, if the fossil populations had survived to the present, this periwinkle would probably be much more widespread on the South African coast.

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Description

Littorina saxatilis is a medium-sized marine snail, with a turban-shaped shell, having a moderately elevated, pointed spire. The shell is dextrally coiled and adult shells have 4-5 convex whorls with well-defined sutures. The sculpture of the shell is variable, but consists of many poorly-defined, or as few as five, more definite spiral ribs. The color is highly variable, from drab-gray to yellow-brown or dark brown, and sometimes white, yellow, orange, red, brown, or black. Some individuals, especially young snails, are banded or spotted with yellow and black. Mature snails can range from 1.2 to 25.8 mm, but are more usually 6-13 mm. Development is direct, with young developing in a brood pouch and emerging as tiny snails, about 0.45 to 0.75 mm. Description from: Abbott 1974; Morris 1975; and Reid 1996.

The taxonomy of this snail is one of the most confused of any mollusk, including 28 synonymous names and 31 varieties, resulting from its high morphological variability (Reid 1996). At least two very similar species, L. arcana and L. compressa, are known from European waters, but have not been reported from North American waters (Reid 1996). The occurrence of numerous ecotypes and divergent populations probably stems from brooding reproduction and the limited dispersal ability of this snail (Reid 1996; Mäkinen et al. 2008; Doellman et al. 2011).

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Taxonomy

Ecology

General:

Littorina saxatilis occurs mostly on mid-to-upper shore rocky coasts, but is also found in lagoons and marshes, usually on hard substrates. Sexes are separate and fertilization is internal. This snail can mature at sizes as small as 1-2 mm. In a Quebec population, L. saxatilis matured at about 3.2-3.5 mm (Pardo and Johnson 2005). Larval development is ovoviviparous, with the young developing in a brood pouch and emerging at 0.4-0.75 mm, with a shell of 1.6-2.1 whorls. The number of embryos varies with size of the female, from 10 in a female with a shell length of 2 mm to 750-900 embryos in the largest shells. Breeding occurs year-round, but is reduced in late summer and winter (Reid 1996).

Littorina saxatilis inhabits a wide range of habitats. On the most exposed coasts, they are usually confined to sheltered crevices, but can also occur in the spray zone, above normal tidelines. More usually, they are found from the mid-tide to mean high-water of spring tides, but they also occur in subtidal regions of brackish lagoons and marshes, associated with solid substrate such as stones, shells, and the roots of Spartina. As with L. littorea, occurrence in the subtidal zone is limited by predation by crabs, fishes, and other predators (Reid 1996). In a Quebec population, the smaller snails tend to be concentrated in the upper intertidal, while larger specimens were more frequently found in the lower zone (Pardo and Johnson 2005). As an upper-intertidal snail, the Rough Periwinkle is tolerant to a wide range of air and water temperatures and also exposure to low salinity, especially over short durations (Reid 1996; Sokalova and Portner 2003). However, its range is probably limited by high temperatures in southern Europe, where it is largely confined to lagoonal habitats and the West Atlantic coast south of New York Harbor, where it is restricted to man-made rocky habitats (Reid 1996; Counts and Bashore 1991; Prezant et al. 2002).

Littorina saxatilis grazes unselectively on diatoms, cyanobacteria, and filamentous and leafy macroalgae (Reid 1996). Littorina saxatilis and L. littorea are potential competitors, and overlap in the intertidal zone, but L. saxatilis ranges higher up on the shore (Dexter 1945; Clay 1961). Predators include crabs, including Carcinus maenas (Green Crab), fishes, and shorebirds (Reid 1996). This snail also hosts a variety of parasites. Fourteen trematode species were found in L. saxatilis sampled at 29 East Coast sites from Newfoundland to Connecticut, but only 4 of those trematodes are known from its introduced range in San Francisco Bay (Blakeslee et al. 2012).

Food:

Macroalgae; microalgae

Consumers:

Fish; Shorebirds; land mammals

Competitors:

Littorina littorea

Trophic Status:

Herbivore

Herb

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Habitats

General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
General Habitat	Salt-brackish marsh	None
General Habitat	Canals	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Mid Intertidal	None
Tidal Range	High Intertidal	None
Vertical Habitat	Epibenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	-20	In air at low tide (Sokalova and Portner 2006)
Maximum Temperature (ºC)	35	In air at low tide, tolerates short term exposures up to 47 C (Sokalova and Portner 2006)
Minimum Salinity (‰)	5	Field observations for estuarine populations (Reid 1996) A marine White Sea population had more than 30% mortality at 14 ppt (Sokalova 2000). Snails from two Swedish Skaggerak (high-salinity) populations ceased activity at 16 ppt. Snails from an exposed coastal region, found in upper tidepools, survived longer in fresh water (17 days) than those from a sheltered region, occurring lower on the shore (Sundell 1985). Todd (1964) found that survival at low salinities varied with temperature, with lower limits of 8 PSU at 5 C, but 16 at 15 C.
Minimum Length (mm)	1.2	Minimum size of mature snail (Reid 1996)
Maximum Length (mm)	25.8	More usually 6-13 mm (Abbott 1974; Morris 1975; Reid 1996)
Broad Temperature Range	None	Polar-Warm Temperate
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

Impacts of Littorina saxatilis have not been studied in San Francisco Bay or in other invaded areas. However, since L. saxatilis is larger than native Northeast Pacific periwinkles and survives under a very wide range of environmental conditions, it is potentially capable of competing with and displacing native snails from California to Alaska. The native periwinkles L. scutulata, L. plena and L. keanae were absent in the immediate vicinity of introduced L. saxatilis populations in San Francisco Bay (Carlton and Cohen 1998), suggesting possible competition or behavioral exclusion. If L. saxatilis extends its range north of San Francisco Bay competition with the morphologically similar species, L. subrotundata and L. sitkana is possible (Carlton and Cohen 1998). Modeling based on the present range of L. saxatilis, and ocean conditions, indicates that it could potentially colonize the entire West Coast from California to the Arctic Ocean (de Rivera et al. 2011). If this snail develops large populations, then impacts from increased grazing on intertidal algal communities are possible (Carlton and Cohen 1998).

Partly because of potential impacts, but also based on this snail's limited introduced range and dispersal, an attempt was made to eradicate introduced populations in San Francisco Bay (Smithsonian Environmental Research Center 2004). However, in the 9+ years since its introduction, L. saxatilis had spread over enough area of the coastline to render eradication impractical (Ruiz et al., unpublished data).

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Regional Impacts

NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
The native periwinkles L. scutulata, L. plena and L. keenae were absent in the vicinity of introduced L. saxatilis populations in San Francisco Bay (Carlton and Cohen 1993). However, the mechanisms for this apparent exclusion have not been studied, to our knowledge.
P090	San Francisco Bay		Ecological Impact	Competition
The native periwinkles L. scutulata, L. plena and L. keenae were absent in the vicinity of introduced L. saxatilis populations in San Francisco Bay (Carlton and Cohen 1993). However, the mechanisms for this apparent exclusion have not been studied, to our knowledge.
CA	California		Ecological Impact	Competition
The native periwinkles L. scutulata, L. plena and L. keenae were absent in the vicinity of introduced L. saxatilis populations in San Francisco Bay (Carlton and Cohen 1993). However, the mechanisms for this apparent exclusion have not been studied, to our knowledge., The native periwinkles L. scutulata, L. plena and L. keenae were absent in the vicinity of introduced L. saxatilis populations in San Francisco Bay (Carlton and Cohen 1993). However, the mechanisms for this apparent exclusion have not been studied, to our knowledge.

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