The Common Periwinkle is a small species of sea snail (16-38mm) that originates in the North Atlantic (the coast of northern Spain north to Scandinavia and Russia) but was introduced to North America in 1840 in the Gulf of St. Lawrence (probably with rock ballast) and is now invasive (Benson 2011). It is now found along both the east and west coasts, where it occurs in "intertidal areas, rocky waters to estuarine brackish water and mud flats to 60 m" (Benson 2011). In British Columbia, it has been found in several locations, including Stanley Park and at Acadia Beach and Tower Beach near UBC (Harley 2011).
Read about the discovery of the Common Periwinkle in BC.
Benson (2011) provides the following description for this species: "broadly ovate, thick, sharply pointed except when eroded; color grayish to gray-brown, often with dark spiral bands; inside of shell is whitish".
Ecology and Biology
There are 5 species of Littorina winkles in British Columbia, one of which, Littorina littorea, has been introduced within the past few years likely via imports for the shellfish trade. Except for this one, which is large in size and easy to distinguish, the other 4 indigenous species are difficult to separate out. However, if you are keen to learn the different species you can check out IDENTIFICATION OF LITTORINES in A Snail's Odyssey website. All indigenous species are relatively small in size, live in the high reaches of the intertidal zone, and feed on various seaweeds, including diatoms. "Winkle-picking" connoisseurs from the Atlantic coast of North America or Europe and disappointed at the small sizes of our local species may be gratified to learn that their big, tasty favourites have been located on several Vancouver beaches. Thus far these introductions are restricted in numbers but, judging from the success of L. littorea in colonizing most of the east coast and lately the west coast (from California north to Washington, and now present in B.C.), chances are they are here to stay. The 5 species differ in their reproductive modes, with L. scutulata, L. plena, and L. littorea producing several small eggs in capsules that are spawned into the ocean. The eggs hatch into swimming larvae that feed for several weeks on phytoplankton and then settle out onto rocky shorelines. The other species L. sitkana and L. subrotundata also encapsulate their eggs, but do so singly and deposit them directly onto the substratum. The embryos of these 2 species feed on yolk and emerge from their capsules as crawl-away juveniles. You can learn more about life cycles and reproductive behaviour at PATTERNS OF DEVELOPMENT in the Odyssey website. For protection from predatory birds, fishes, and crabs, these small snails mostly have only their shells to rely on. However, for protection from drying they have an unusual strategy. If you look carefully on pilings around the shore on a dry day you may see L. scutulata or L. sitkana attached on its shell edge by a blob of mucous glue. The operculum is similarly glued shut, and the animal can survive like this for many days until once again wetted by spring tides or waves. Within a few moments of wetting, the snail pops out and crawls off to find food.
Learn more about feeding and growth of Littorines and their relatives on A Snail's Oddysey.
Ecology and Biology Note Author: Tom Carefoot, Department of Zoology, University of British Columbia