Oxychilus cellarius in Carmel, California
I have just returned from a month in California, mostly spending time with family and friends, very much taking a break from PhD work. I couldn’t resist making some mental notes about the river mouth and brackish lagoon at the beach in Carmel, however, nor picking up the shell above when I saw it in the garden of the house we were staying in. It is an Oxychilus cellarius, interesting to me because it is a European species, familiar to me from my PhD and commercial work, and now well-established in various parts of the United States. It has previously been reported in landscaped areas of San Francisco, along with a number of other European species (Roth 1986). Invasive snails are an ecological problem in the United States, where European and African taxa, including giant African land snails, have made themselves at home to the detriment of native fauna.
In contrast, few American snails have been introduced to the UK. While working on some wood recording at the offices of the Newport Ship project, I noticed a small population of the American freshwater snail Physella acuta living in the water tanks. These are now well established in Britain. Probably the most famous ecologically troublesome introduction from America is the grey squirrel Sciurus carolinensis, which has almost entirely displaced the native red squirrel Sciurus vulgaris. A number of American marine molluscs, such as the Atlantic oyster drill Urosalpnix cinerea and especially the slipper limpet Crepidula fornicata, were accidentally introduced to Britain in the late 19th Century along with the oyster Crassostrea virginica. This was deliberately introduced at a time when oysters were exceptionally popular and stocks of the native oyster Ostrea edulis were declining. The accidental introductions have caused further difficulties for native oysters.
Part of my PhD research is to look at when new species of snail or marine mollusc arrive in the Outer Hebrides. Building a database of well-dated archaeological contexts in which a known non-native arrival is present or absent allows that species to be used for relative dating of nearby sites, the same way pottery sherds or lithic technologies might be used to give a rough date for a context.
Roth, B., 1986. Notes on three European land mollusks introduced to California. Bulletin of the Southern California Academy of Sciences, 85 (1). pp. 22-28. Available online here