Many or most flagellates are tethered to particles when feeding, and it is generally accepted that attachment allows organisms to enhance their feeding flow. This view is challenged in a new paper in PNAS where it is shown that the opposite holds true, i.e., the clearance rate is highest for freely swimming organisms in comparison with their tethered counterparts.
Heterotrophic flagellates play a key role in the oceanic microbial food web as the main consumers of bacteria and cyanobacteria. The rate at which flagellates clear prey from suspension is therefore of interest. Several authors have independently suggested that tethering leads to a more efficient feeding flow. Using a simple fluid dynamical model, we demonstrate that tethering decreases rather than increases the clearance rate of interception feeding zooplankton, consistent with two recent computational fluid dynamics studies of choanoflagellates.
We presume that our qualitative conclusion is valid for a broad class of ecologically significant zooplankton, and our result suggests that organisms tether for reasons that are not fluid dynamical, e.g., to stay close to surfaces with high concentration of bacterial prey.
Read the paper here: https://doi.org/10.1073/pnas.2017441117
Andersen A, Kiørboe T (2020) The effect of tethering on the clearance rate of suspension-feeding plankton, Proceedings of the National Academy of Sciences. 202017441.
Header image: Tethered heterotrophic flagellates of the species Clathromonas butcheri (cell diameter 4 mu) attached to the exterior of a diatom. Transmission electron micrograph by courtesy of Helge A. Thomsen.