Laboratory and in situ grazing rates of freshwater rotifers and their contribution to community grazing rates
Gosselain, V.; Joaquim-Justo, C.; Viroux, L.; Mena, M.; Metens, A.; Descy, J.-P.; Thome, J.-P.
Laboratory experiments on filtration and ingestion rates of the rotifer Brachionus calyciflorus were carried out using the 14C-labelled green alga Dictyosphaerium ehrenbergianum as food. Values for ingestion and filtration (with maxima ranging between 10 and 15 µ ind-1 h-1) were expressed as a function of algal biomass; relationships were curvilinear for ingestion. Between 15 and 25 °C, maximal ingestion rates ranged between 3 and 9 ng C ind-1 h-1 and temperature dependence had a Q10 of 2.8. In situ zooplankton grazing was studied in 1994, using a Haney chamber with 14C-labelled D. ehrenbergianum, at one location on the River Meuse during the growing season, and on the rivers Moselle and Sarre on one occasion in summer. Community and individual grazing rates were measured and the contribution of rotifer sub-communities to the total community grazing rate was evaluated. Individual filtering rates ranged from 2.84 to 4.15 µ ind-1 h-1 for B. calyciflorus and from 1.83 to 4.58 for Keratella cochlearis. Community grazing rates ranged from 8 to 32% day-1. Laboratory and in situ results were compared to assess the impact of rotifers on large river phytoplankton.