1. Vertical transport of nutrients in sedimenting faecal material is greatly reduced by coprophageous organisms. Unfortunately, nearly all work on faecal production, sedimentation and coprophagy has dealt with copepods in marine ecosystems. Here, we report the first evidence of coprophagy in freshwater zooplankton from oligotrophic and eutrophic lakes. We used 14C-labelled algae and faecal material to estimate the rates of algal clearance and coprophagy.
2. Measured feeding rates per individual on faecal material were similar (Daphnia pulex, D. rosea, Leptodiaptomus tyrelli) or even higher (D. lumholtzi) than filtering rates on phytoplankton. This finding does not necessarily implicate active selection of faeces over algae because: (i) we did not use the same food concentrations for faeces and algae, and (ii) grazers of slightly different sizes were used in each test.
3. Weight-specific clearance rates of L. tyrelli and Holopedium gibberum on faecal matter (0.084–0.089 mL μg−1 h−1) were higher than in the daphniids (0.026 mL μg−1 h−1).
4. The data indicate that coprophagy in freshwater ecosystems is an important mechanism of nutrient recycling, and this process should be taken into account when studying nutrient fluxes within lakes and reservoirs.