Feeding currents of particle-attached nanoflagellates - A novel mechanism for aggregation of submicron particles

Abstract

In this study we present several lines of evidence suggesting a 'non-ingestive' mechanism by which nanoflagellates attached to sinking or suspended particles can enhance aggregation and enlargement of smaller particles in marine environments. Using epifluorescence microscopy, we observed the adhesion of model particles (0.5 μm fluorescent latex beads) in the feeding current from a particle-attached flagellate, Paraphysomonas imperforata, to the aggregate colonized by the flagellate. Particle counter measurements showed a significant increase in larger aggregates occurring only in the presence of living P. imperforata. The transfer rate of model particles to larger aggregates was determined by a flow cytometric technique and was observed to be higher in the presence of the attached flagellate than in free-living ones. In nutrient-enriched coastal seawaters, the transfer of model submicron particles to large particles (5 to 20 μm) was significantly reduced with the addition of eucaryotic and respiratory inhibitors (thiuram, NaN3). Ingestion of the latex beads by nanoflagellates did not explain the observed transfer rates of beads to larger particles. Collectively, the feeding current of attached flagellates, which has been ignored before as a mechanism for particle aggregation in marine environments, accelerates the attachment of submicron particles to larger particles. This process might be important in coastal productive waters, where both attached flagellates and submicron particles are abundant.