Parasites and host energetics: Effects of a parasitic castrator on the consumption and metabolism in an aquatic snail host

Background/Question/Methods   Parasites are widespread and ubiquitous organisms, contributing a substantial amount of biomass to both aquatic and terrestrial ecosystems. Since biomass and energetics are related, we conjecture that parasites would have a considerable impact on the flow of energy through a system. In order to study how parasitism influences energy available to other trophic levels, the consumption and metabolism of the freshwater snail red-rim melania (Melanoides tuberculatus), host to the Oriental avian eye fluke (Philophthalmus gralli), was determined. Methodology was developed to quantify snail consumption and, in a separate experiment, the effect of infection on snail consumption was studied. Dried samples of algae were added to 60 cups, 30 cups containing snails and 30 cups containing no snails. Algal consumption was measured over a period of 7, 10, or 14 days. Using the developed methodology, the effect of snail size and infection status on consumption was tested over a period of 14 days.

Results/Conclusions   Data showed snail treatment resulted in a significant reduction of algae at 7, 10, and 14 days (p = 0.0112, 0.00019, < 0.0001, respectively) when compared to control treatment. Results showed snail size affected consumption (p < 0.001), but that snail infection status had no significant effect on consumption (p = 0.841). Future studies will address differences in the metabolism of infected and uninfected snails using a respirometer. The results of the experiments will be discussed in relation to potential effects of parasites on host energetics.