Crayfish as Predators (Nonhosts) of the Digenetic Trematode Cercaria, Proterometra macrostoma, at North Elkhorn Creek, Kentucky, U.S.A.

The role of parasites as prey for nonhost species has received increasing attention over the last 3 decades as (1) such a reduction of infectious agents decreases disease transmission by reducing parasite numbers and (2) the importance of parasites in energy flow within aquatic food webs is acknowledged. Previous predation studies of digenetic trematode cercariae have assessed species in which large numbers of cercariae are released daily by individual snails. By contrast, the cercaria of the azygiid trematode Proterometra macrostoma averages less than 1 cercaria released per infected snail per day. The objective of this study was to evaluate the preference of crayfish (i.e., Procambarus spp. and Faxonius juvenilis) as predators of 3 different prey items of similar size and swimming ability including the comparatively large cercaria (i.e., 3–9 mm) of P. macrostoma. Four experiments were conducted, 2 with F. juvenilis and 2 with Procambarus spp. Each experiment consisted of 25 crayfish, which were individually exposed to 1 of 5 treatment levels consisting of a control (i.e., no prey), individual prey (i.e., cercariae, Daphnia magna, or Xenopus laevis tadpoles only), or a mixture of all 3 prey over a 7-hr exposure at 20°C and continuous light. In both the single-prey and mixed-prey experiments, cercariae were consumed at a similar or faster rate than tadpoles and D. magna, and these differences were most notable within the first hour postexposure. These results suggest that P. macrostoma cercariae are a legitimate component of the food web in freshwater habitats, and may play an important role in energy flow between trophic levels in such systems. [ABSTRACT FROM AUTHOR]