Distribution and abundance of motile seawater bacteria over time around two diatoms and a fecal pellet collected from coastal seawater. The diatoms were Chaetoceros sp. and Rhizosolenia sp., respectively. In all cases, clusters were already formed at the start of movie capture and either dissipated over ∼30 min (for both diatoms) or remained accumulated for >60 min (for the fecal pellet). (Left) Contours of cell concentration, quantified as the number of swimming bacteria in an area of 300 μm2 (color bar). Each frame was obtained from a 2-s-long video (cell concentration was averaged over the 2 s) and videos were captured at 1-min intervals. (Upper Right) Total number of motile bacteria in 5-μm-wide concentric annuli, as a function of the distance from the surface of the diatom or fecal pellet. Progressively darker brown lines indicate later time points, for the same total duration shown in the video on the left. (Lower Right) Total number of swimming bacteria in each movie as a function of time. The dashed line indicates the current time point in the video on the left.