Fig. 1

Rhodolith physiology was not impaired under elevated pCO₂. a Photosynthesis, measured as carbon uptake by live rhodolith, under ambient air (tanks 1A and 1B) and high CO₂ (Tanks 3A and 3B), at the end of the 40-day experiment. Rhodolith specimens (n = 3 per mesocosm) were cultured under 6 light levels (0, 25, 50, 100, 250, and 750 μmols photons m^− 2 s^− 1) for one hour each (in triplicate). Best-fit curves were calculated for each treatment and photosynthetic maximum (P_max) and photosynthetic efficiency (α) were calculated from these using Platt et al. (1975). b Proportion of live tissue in rhodolith holobionts under ambient air (tanks 1A and 1B) and high CO₂ (Tanks 3A and 3B), measured through decalcification assay, at the beginning (day 1) and ending (day 40) of the experiment. (*) denotes statistically significant difference over time