The introduction of Littorina littorea to British Columbia, Canada: potential impacts and the importance of biotic resistance by native predators
Although the establishment and spread of non-indigenous species depends upon survival in the face of novel environmental conditions and novel biological interactions, relatively little attention has been focused on the specific role of native predators in limiting invasion success. The European common periwinkle, Littorina littorea, was recently introduced to the Pacific coast of Canada and provides a case study of an introduction into an area with an important predator guild (sea stars) that is functionally minor in the invader’s native habitat. Here, we assess the likelihood of establishment, spread, and negative ecological impact of this introduced gastropod, with an emphasis on the role of native sea stars as agents of biotic resistance. Size frequency distributions and local market availability suggest that L. littorea was most likely introduced via the live seafood trade. Non-native hitchhikers (e.g., the trematode Cryptocotyle lingua) were found on/in both market and field specimens. Laboratory studies and field observations confirmed that L. littorea can survive seasonal low salinity in Vancouver, British Columbia. Periwinkles also readily consumed native Ulva, suggesting that periwinkles could impact native communities via herbivory or resource competition. Unlike native gastropods, however, L. littorea lacked behavioural avoidance responses to Northeast Pacific predatory sea stars (Pisaster ochraceus and Pycnopodia helianthoides), and sea star predation rates on L. littorea were much higher than predation rates on native turban snails (Chlorostoma funebralis) in common garden experiments. We therefore expect periwinkle establishment in British Columbia to be limited to areas with low predator density, as is seen in its field distribution to date. We caution that this conclusion may understate the importance of the L. littorea introduction if it also serves as a vector for additional non-indigenous species such as C. lingua.
KeywordsUlva Hermit Crab Native Predator Biotic Resistance Market Sample
We thank D. Reid for assisting with the identification of the snails. R. Gooding brought the L. littorea population at Acadia Beach to our attention. The students in the University of British Columbia’s Experimental Biology of Invertebrates course assisted with data collection for the herbivory trials. M. Frey kindly surveyed sites at Clover Point (Victoria) and Sidney. Additional assistance in the field was provided by B. Arney, F. Choi, C. Murray, Z. Harley, C.G. Harley, M. Harley, B. Harley, J. Nelson, and M. Picard. R. Whippo assisted with the statistical analyses. Comments by P. Kraufvelin and four anonymous referees improved the manuscript. Funding for this work was provided by a National Science and Engineering Research Council (NSERC) Discovery Grant to CH and by the Canadian Aquatic Invasive Species Network (an NSERC Strategic Network Grant).
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