Kinetics of dissolved inorganic carbon acquisition by red seaweeds (Rhodophyta) with and without carbon-dioxide concentrating mechanisms

Seaweed responses to ocean acidification (OA) may depend on whether they possess a carbon dioxide (CO 2 ) concentrating mechanism (CCM). Using photosynthesis versus dissolved inorganic carbon (DIC) experiments, we determined the photosynthetic affinity ( K 0.5 (CO 2 )) for CO 2 for the red algae Pollexfenia lobata (CCM), and Callophyllis rangiferina , Delisea pulchra and Plocamium cirrhosum (non-CCM). K 0.5 (CO 2 ) was statistically similar for CCM and non-CCM species, but P. lobata had values lower than those published for isolated red algal Rubiscos. Maximum photosynthetic rates ( P max ) were 2.5 times higher for Pl . cirrhosum and D. pulchra . Non-CCM species may benefit from future OA because photosynthesis would be less limited by DIC.