Abstract

Exposure of the toxigenic dinoflagellate Alexandrium catenella to variations in pCO2/pH, comparable to current and near-future levels observed in Southern Chilean fjords, revealed potential functional adaptation mechanisms. Under calculated conditions for pH(total scale) and pCO2 ranging from 7.73–8.66 to 69.7–721.3 latm, respectively, the Chilean strain Q09 presented an optimum growth rate and dissolved inor- ganic carbon (DIC) uptake at near-equilibrium pCO2/pH conditions (????8.1). DistaLM analysis between physiological relevant carbonate system parameters (CO2, HCO????3 , and Hþ) and cellular rates (growth rate and DIC uptake) identified HCO????3 as the unique variable explaining a signifi- cant portion of the physiological response. Estimations of equivalent spherical diameter (ESD) and chain-formation index (CI) revealed reduced cell size and enhanced chain formation at high pH/low pCO2 conditions. Light intensity as co-factor during experiments (50 vs. 100 lmol photons m????2 s????1) produced no effect on ESD and CI. Cells exposed to low light; however, had reduced cell growth and DIC uptake especially at high pH/low pCO2. We suggest that A. catenella Chilean strains are highly adapted to spatio-temporal pCO2/pH fluctuations in Chilean fjords, becoming a resilient winner from expected climate change effects.