a, b, Vertical distribution of Chattonella marina_cf CM2962 (a) and Prorocentrum minimum PM291 (b), both showing a split similar to that of HA452. Solid lines represent the mean of the equilibrium vertical distribution over four and three replicates respectively. Shaded regions represent ± 1 s.d. from the mean. The insets show the upward bias, r, after 300 flips (blue) and for the control, consisting of the same time in the chamber without flipping (red, mean ± s.d.). The star indicates statistical significance (two-sided t-test) between the two treatments (CM2962: t6 = 3.66, P = 0.01; PM291: t4 = 2.85, P = 0.04). c, d, Upward bias index, r (mean ± s.d.), for seven raphidophyte strains (c) and ten dinoflagellate strains (d). The error bars of the upward bias, r, are extracted from the cells’ vertical distribution. Full names of strains are provided in Extended Data Table 1. The number of cells analysed for each case is given in Extended Data Table 1. Many of these strains showed a moderate to strong response to flipping, as shown by the change in their upward bias between treatment and control.