The experiment lasted 8 days, and water samples were collected from each container on days 1,3,6 and 8. At each sampling date and for each container, 18 mL of the supernatant water was removed, leaving the bottom 2 mL so as to collect only buoyant Microcystis that had just been recruited. This also allowed us to exclude posible accidental sediment mixing during sampling. The containners were then refilled with 18 mL of filtered lake water, which was added very carefully to avoid mixing the sediment when this was not appropriate.