Bringing the Urban Environment Into the Classroom: Learning From an Estuarine Mesocosm
Appendix F: Littorina Species Fact Sheet (to be handed out to students)
Note: For the purposes of uninterrupted reading by students, references are not placed in the body of the fact sheet. References may be found in Literature Cited.
Periwinkles
General Info and Habitat
Periwinkle refers to a group of snails belonging to the genus Littorina and includes the following species: the edible periwinkle (L. littorea, L. littoralis), the southern periwinkle (L. angulifera), the smooth periwinkle (L. obtusata), and the gulf periwinkle (L. irrorata). Periwinkles are very common inhabitants of salt marshes, estuaries, and intertidal zones. They are a marine snail and have gills that allow them to breathe underwater. They have a spiraled shell, and the larger species can grow up to 1 inch.
What They Eat
Periwinkles are herbivores, eating algae in the salt marsh. They will also eat cordgrass (Spartina species), which have a vital role in supporting the ecosystem of the marsh. They play an important role in breaking down the grasses that have died in the marsh.
What Eats Them
Periwinkles are often present in great abundance. Crabs, fish, birds, and small mammals in the salt marsh all feed upon them.
Geographical Range
Periwinkles are found along the Atlantic coast from Nova Scotia, Canada through the Gulf of Mexico. The edible periwinkle is actually endemic to Europe and was introduced to North America.
Life Cycle
Periwinkles reproduce sexually and may reproduce all throughout the year in parts of their range. Mating peaks in late spring or early summer. Fertilization occurs internally. The white, oval-shaped egg masses may contain over 250 eggs and hatch after four weeks. The larvae grow and metamorphose into sexually mature snails after two years. An interesting aspect of the life cycle of these snails is that they can change their sex!
The Urban Connection
Periwinkles play an important role in the ecosystem by breaking down dead plant material. They are sensitive to many types of contamination. Some pollutants affect the ability of the snail to reproduce, while others can change its sex organs! Because of this, scientists use them to study the affects of pollution upon salt marsh species.
Periwinkles are an important food source, not only for organisms like crabs and birds, but for people too! The edible periwinkle is so called because they can be eaten. Europeans have always made use of this commonly abundant food source, but it is not commonly eaten in North America.
Its use as a food source may be the reason why the edible periwinkle was introduced into North America. It first appeared off of the coasts of Nova Scotia and New Brunswick, Canada, in the 1850's. Since then, this very successful species has spread south through Florida and the Gulf of Mexico.
But the introduction of a new species is not always a good thing. Introduced species can disrupt the delicate balance of an ecosystem. A recent scientific study addressed what would happen if crabs, which are commercially harvested, were completely removed from Atlantic marshes. Without the crabs to eat the periwinkles, the periwinkle populations may grow out of control. Unchecked, these populations of periwinkles can devastate the cordgrass (Spartina) that forms the base of the salt marsh ecosystem. Without the cordgrass, all of the animals that rely on this highly productive plant cannot survive in the marsh either.
Look It Up!
If you didn't understand something you read above, look it up! A "Google" search is a good place to start (www.google.com). A good website to find information about the periwinkle is www.marlin.ac.uk/species/Litobt.htm. Try to find a recipe that uses periwinkles!