A novel method to assess the cercariae emission intensity of littorinid populations

Abstract

The ecological implications of parasitism of Littorina littorea (L.) (Gastropoda: Prosobranchia) and other gastropods by larval digenean trematodes has attracted considerable research interest (e.g. Lambert & Farley, 1968; Williams & Ellis, 1975; Lauckner, 1987; Sokolova, 1995). Such implications hinge on an accurate quantification of parasite loading within an infected population. There are several techniques available for determining parasite load or an index of it. Dissection, usually of the digestive gland, is the most commonly used destructive technique (e.g. Williams & Brailsford, 1990; Granovitch, 1992; Siddal et al., 1993), which can give an accurate estimate of parasite load in terms of the number of cercariae present. The subjective ‘foot colour’ technique correlates the intensity of orange colour of the foot of L. littorea to the degree of infection by Cryptocotyle lingua (Creplin) (Digenea: Heterophyidae), (e.g. Willey & Gross, 1957; Huxham et al., 1993), however, dissection should be employed to investigate the presence of other trematode cercariae.