Occurrence of winter mortalities in the slipper limpet Crepidula fornicata (Linnaeus, 1758) in the Fal Estuary, Cornwall. Amber G. Thornton*, Craig Baldwin, Claire Eatock * Falmouth Marine School; email: amberthornton@hotmail.co.uk Abstract The natural climatic and geographic boundaries that have facilitated evolution in the past are being bypassed by globalised anthropogenic activities, which have enabled the uncontrolled spread of organisms. A relatively small number of these can become established, and even fewer are a potential cause for ecological or economic concern, such as Crepidula fornicata. This gastropod threatens biodiversity and commercial shellfish operations including the Ostrea edulis fishery within the Fal Estuary. Winter mortality events have been observed to affect C. fornicata, restricting its range and population size. This research aimed to find the degree to which C. fornicata is affected by winter mortalities in the Fal Estuary during the winter of 2010-11. Winter mortalities of -469.6% and -21.5% were observed at the two sites studied, indicating that C. fornicata is not significantly affected. The former shows a clear population increase, which may be due to continued recruitment of 2010 juveniles through the winter, after the initial surveys. The lack of winter mortalities may be due to a winter that did not feature many cold days, or did not exhibit particularly anomalous temperatures. Considering the predicted northern shift of species caused by climate change continued monitoring of the C. fornicata population in the Fal Estuary is recommended to facilitate the development of suitable management strategies. Key words Crepidula fornicata; temperature; oyster beds Introduction Natural boundaries, whether geographic or climatic, have separated communities for millions of years resulting in the evolution of species adapted to specific environments and integrated within communities (Monroe and Wicander 2009). In recent years globalised anthropogenic activities have enabled the uncontrolled spread of organisms (Hulme 2009). Whilst many organisms are unable to survive in alien conditions, one tenth are considered to become established (Williamson and Fitter 1996), and a small number of these are a cause for potential ecological or economic concern (Thieltges et al. 2004). One such potentially concerning organism is the American slipper limpet, Crepidula fornicata (Linnaeus, 1758), a gastropod originating from the east coast of North America (Walne 1956) which is now found across 24o latitude (Blanchard 1997). Outside of its native territory C. fornicata may change its environment by smothering it with pseudofaeces and by sheer numbers (Barnes et al. 1973; Chauvaud et al. 2000). Once the limpet has reached the adult morph a dearth of predators (Blanchard 2009) and parasites (Thieltges et al. 2004)
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