Fig. 4: Taxonomic composition of phytoplankton assemblages in the mesocosms under three different O2/CO2 combinations.

Proportions of different major phytoplankton groups are indicated in different colors on (a) day 0, (b) day 1, (c) day 3, (d) day 5, (e) day 6, and (f) day 10 under ambient (AO, ~213 μM) and low O2 levels (LO, ~57 μM) with ambient (AC, ~13 μM) and elevated CO2 levels (HC, ~27 μM). D0 represents the initial time of the experiment (22:00, December 27, 2018). Values represent the means of independent biological replicates (n = 3 mesocosms). Detailed information for the mesocosms experimental features are given in Supplementary Figs. 1 and 2. Blue * and red * indicate significant differences in proportions of dinoflagellates (P < 0.05, LSD test) caused by low O2 under ambient (LOAC) and elevated CO2 levels (LOHC), respectively, compared to the control treatment (AOAC).