DETERMINING THE ECOLOGICAL ROLE OF EUSPIRA LEWISII: PART I: FEEDING ECOLOGY

The predatory naticid snail Euspira Lewisii, Lewis' moon snail, native to the west coast of North America, is stated to be an economic threat to the shellfish aquaculture industry in British Columbia (BC). This species is being manually removed from the intertidal ecosystem, yet little is known about the ecology of this species. Enclosures and beach shell assemblages were used to determine the prey preference, feeding rates, and community impacts of E. lewisii. In the enclosures. Protothaca staminea, the native little neck clam, was found to be the preferred prey, whereas the commercially valuable Manila clam, Venerupis philippinarum, was avoided when E. lewisii was offered other clam prey choices. Drilled shells collected from the intertidal revealed similar feeding preferences. The feeding rate averaged for a variety of clam species was found to be 0.09 clams/day or 1 clam every 14 days. The feeding rate was dependent on prey species, and was highest for the preferred species and significantly lower on avoided species. The overall impact of E. lewisii to the bivalve community was found to be low. Based on these results, E. lewisii consumed only approximately 3% of the clam population over 1 y, assuming maximal feeding rates and typical population densities found on the west coast of BC. E. lewisii has minimal impacts to the Manila clam industry in BC and control measures are not necessary for this species. Baseline ecological field studies are important for gaining an understanding of poorly understood species, especially those considered threats to industry.