The significance of some methodological effects on filtration and ingestion rates of the rotiferBrachionus plicatilis
© Biologische Anstalt Helgoland 1982
Filtration rate(F) and ingestion rate(I) were measured in the rotiferBrachionus plicatilis feeding on the flagellateDunaliella spec. and on yeast cells(Saccharomyces cerevisiae). 60-min experiments in rotating bottles served as a standard for testing methodological effects on levels ofF andI. A lack of rotation reducedF values by 40 %, and a rise in temperature from 18° to 23.5 °C increased them by 42 %. Ingestion rates increased significantly up to a particle (yeast) concentration of ca. 600–800 cells · μl−1; then they remained constant, whereas filtration rates decreased beyond this threshold. Rotifer density (up to 1000 ind · ml−1) and previous starvation (up to 40 h) did not significantly influence food uptake rates. The duration of the experiment proved to have the most significant effect onF andI values: in 240-min experiments, these values were on the average more than 90 % lower than in 15-min experiments. From this finding it is concluded that ingestion rates obtained from short-term experiments (60 min or less) cannot be used in energy budgets, because they severely overestimate the actual long-term feeding capacity of the rotifers. At the lower end of the particle size spectrum (2 to 3 µm) there are not only food cells, but apparently also contaminating faecal particles. Their number increased with increasing duration of experiments and lead to an underestimation ofF andI. Elemental analyses of rotifers and their food suggest thatB. plicatilis can ingest up to 0.6 mJ or ca. 14 % of its own body carbon within 15 min. The long term average was estimated as 3.4 mJ · ind−1 · d−1 or ca. 75 % of body carbon · d−1.