Do planktonic rotifers rely on terrestrial organic matter as a food source in reservoir ecosystems

We studied the effect of input of allochthonous organic matter on rotifers in a medium-sized (9.8 km2) reservoir correlating rotifer abundance to values of δ13C in a sestonic fraction of ≥10 µm. Total density of rotifers during the study period was significantly correlated with tributary inflow during the time preceding the sampling date, with a delay of about 10–13 days. Concomitant with elevated tributary inflow, the δ13C value in the sestonic fraction of plankton samples decreased approaching a level typical of terrestrial material. Thus, the response in rotifer production might be due to the input of energy in the form of dissolved and/or particulate allochthonous organic matter that becomes available to the rotifers through the microbial food web.