Common Periwinkle

• Introduced accidentally into North America in the nineteenth century, it completely transformed the rocky shores of New England by cutting back the intertidal algae and leaving the rock bare.
• It is one of the keystone species of the intertidal: how hard it grazes determines which algae dominate the rock.
• It is the largest periwinkle on British shores, with a shell of up to 52 mm.
• It reached North America from Europe in the mid-nineteenth century, probably in ships' stone ballast. It arrived in Canada around 1840, Maine in 1870 and Cape May, New Jersey, in 1888.
• There it has reordered the New England shore: by grazing on young algae it competes with native periwinkles and reduces algal cover, changing the whole community.
• Its development of intersex features is used as a biomarker of tributyltin pollution, the compound used in ships' antifouling paints.
• Its shells hold a climate archive: analysis of those from Orkney middens has shown that in the Middle Ages they were gathered mainly in early spring, probably as a famine food.

Skeleton type

Invertebrate - external calcareous shell (mollusc)

Habitat and environment

Rocks, breakwaters and hard bottoms in the intertidal of the North Atlantic

Sources consulted: https://es.wikipedia.org/wiki/Littorina_littorea; ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid; anatomia de Gastropoda