Rough Periwinkle (Littorina saxatilis)
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Name: Rough Periwinkle
Scientific Name: Littorina saxatilis
or Division: Mollusca
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
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.
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.
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.
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
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.
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
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.
Author: Debbie Graham
Last Edited: February 18, 2003
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