AME 48:169-174 (2007)  -  doi:10.3354/ame048169

ABSTRACT: Surfaces in running water are covered by a boundary layer. Virtually nothing is known about the importance of water currents in the microenvironment of nanofauna. Many questions have been partially answered concerning the effect of surface topography on the hydrodynamics in the vicinity of macrofauna; however, investigations of the 2 to 5 µm water layer where nanoprotists live have been neglected. In the present study, we show that the flow velocity at a distance of a few micrometres from the substrate is high enough to be very effective regarding the detachment of nanoprotists. We analysed the impact of flow velocity (detachment from substrate) on 8 nanoflagellate taxa (Entosiphon, Cercomonas, Codonosiga, Anthophysa, Bodo, Neobodo, Apusomonas, Spumella) with different abilities to crawl and attach to the surface. A Plexiglas disc was used to generate a defined flow velocity on the surface of a Petri dish microcosm. Laminar flow in the boundary layer was found between 0 and 700 µm above the substratum. The effect of 4 different flow velocities on heterotrophic flagellates was investigated (0.3, 0.6, 0.9 and 1.2 m s^–1 at 5 mm above the substratum, corresponding to flow velocities of 0.001 to 0.004 m s^–1 at 10 µm above the substratum). The colourless, gliding euglenid Entosiphon sulcatum showed the highest resistance towards high flow velocities. Another species, the crawling cercomonad Cercomonas crassicauda, had the weakest attachment. Small changes in the micro-topography of the substrate (e.g. Ancylus shells) may significantly influence spatial distribution of nanoflagellates.

KEY WORDS: Heterotrophic nanoflagellates · Boundary layer · Microcurrents · Biofilm · Flow velocity · Topography