Intraspecific variation in multiple trait responses of Alexandrium ostenfeldii towards elevated pCO 2

Dissolved oceanic CO concentrations are rising as result of increasing atmospheric partial pressure of CO (pCO ), which has large consequences for phytoplankton. To test how higher CO availability affects different traits of the toxic dinoflagellate Alexandrium ostenfeldii, we exposed three strains of the same population to 400 and 1,000 µatm CO , and measured traits including growth rate, cell volume, elemental composition, C fractionation, toxin content, and volatile organic compounds (VOCs). Strains largely increased their growth rates and particulate organic carbon and nitrogen production with higher pCO and showed significant changes in their VOC profile. One strain showed a significant decrease in both PSP and cyclic imine content and thereby in cellular toxicity. Fractionation against C increased in response to elevated pCO , which may point towards enhanced CO acquisition and/or a downscaling of the carbon concentrating mechanisms. Besides consistent responses in some traits, other traits showed large variation in both direction and strength of responses towards elevated pCO . The observed intraspecific variation in phenotypic plasticity of important functional traits within the same population may help A. ostenfeldii to negate the effects of immediate environmental fluctuations and allow populations to adapt more quickly to changing environments.