Introduced Species Summary Project
 Rough Periwinkle (Littorina saxatilis)

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Common Name: Rough Periwinkle

Scientific Name: Littorina saxatilis


Phylum or Division: Mollusca
Class: Gastropoda

Subclass: Prosobranchia

Order: Neotaenioglossa

Family: Littorinoide

Identification: A small (up to 18mm in height and 14mm wide), ovoviviparous, dioecious, herbivorous snail occurring either in off-white, greenish, reddish or brown colors.  The aperture of the shell is large, rounded and has a slightly everted lip. The throat of the shell is darker.  The shell is plump with 4-5 whorls and deep sutures. 

Original Distribution: Littorina saxatilis has a wide dispersal in the Atlantic Ocean occurring on both the east side and the west side.  It occurs in intertidal zones in salt marshes and subtidal hard substrates.  It is also found in crevices of bedrock, empty barnacle shells and under rocks. In salt marshes, it can be found on the base of Spartina species.  It may also be found on firm mudbanks as well as submerged in brackish water attached to Zostera, Fucus, Ruppia and Potamogeton species.There are maximum reported densities of well over 100,000 snails m-2.


Current Distribution: Littorina saxatilis is currently invasive in the San Francisco Bay area.  Littorina saxatilis also has been found at three isolated sites in the South Atlantic (Namibia and South Africa), likely representing introduced populations.

Site and Date of Introduction: San Francisco Bay, 1992

Mode(s) of Introduction: There is no certainty of mode of introduction.  However, it is the general concensus that the invasion was likely due to the association with bait or live seafood transport.  They have been associated with an Atlantic alga (Ascophyllum nodosum), which is often used as packing material for shipments of live animals.

Reason(s) Why it has Become Established:  Littorina saxatilis is successful in becoming established in a previously foreign area in that it has a capacity to feed on newly settled barnacles and can compete successfully with other like organisms for food supplies.  The study described below intends to pursue further research on successful invasion of this species.

Ecological Role: This snail is primarily herbivorous and is known to affect algal bloom dynamics and can prey upon newly-settled barnacles

Benefit(s): Unable to find any evidence on this front.

Threat(s): Observations of the behavior of Littorina saxatilis in the Atlantic have spawned predictions that it may have significant long-term impacts on Pacific nearshore ecosystems all up and down the coast as it continues to spread and increase in population density.  Studies performed on other similar, invasive, herbivorous snails have revealed that they have had serious ecological impacts on receiving ecosystems. 

Control Level Diagnosis: Some experts believe that the rough periwinkle should be easily eradicated.  For one thing, it does not possess a larval stage of development which would increase its chances of spreading via a “free floating state” to other areas. So far, its invasive range is believed to be restricted to areas within the San Francisco region that are easily accessible so that collections methods could be executed with relative ease.  If eradication begins, it should begin while the species is still confined to the San Francisco area, as its potential growth could reach from Baja California to Alaska. Previous eradication work has proven that early action may be imperative.

Control Method:
No method is yet forthcoming for the removal of this specific species.  In general, biocides, manual removal of marine invaders, and the introduction of biocontrol agents have been considered in the removal of invaders of marine systems. However, little has been done in the way of eradication and, in addition, pursuing research in this area in general.  There is concern that any research to be conducted should include the study of ways to avoid reintroduction of the species.  A study sponsored by NOAA and the Smithsonian Environmental Research Center is underway to determine if Littorina saxatilis can be eradicated from the San Francisco Bay area.  The Smithsonian Environmental Research Center is also attempting to determine population and expanse of the rough periwinkle the Bay area.   In addition, they are measuring the genetic and demographic changes associated with the recent invasion of the rough periwinkle by comparing newly colonized populations in San Francisco Bay to populations in its native range and source locality.

Debbie Graham
Last Edited:
February 18, 2003

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