Rising CO2 levels alter the responses of the red macroalga Pyropia yezoensis under light stress

Increased ocean uptake of CO2, due to rising atmospheric CO2 is leading to ocean acidification (OA) and alters light intensity due to increased turbidity and depth variation in seawater. Macroalgae have been found to alter their behavior in response to OA and other climate factors. In order to optimize farming strategies for economically important seaweeds, this study assesses the growth of Pyropia yezoensis at three different light intensities (HL:35%; ML:10%; LL:5%) and two CO2 concentrations (ambient CO2, 400 ppm; elevated CO2, 1000 ppm). Results show that P. yezoensis growth was significantly inhibited by decreased light intensity, due to reductions in photosynthesis, relative electron transfer rate (rETR) and carotenoid synthesis. However, under LL conditions, the relative growth rates (RGR), maximum net photosynthetic rate (P-max) and maximum relative electron transfer rate (rETR(max)) of PSI and PSII in P. yezoensis, were significantly enhanced under elevated CO2 concentrations. Phycocyanin (PC) and phycoerythrin (PE) levels in P. yezoensis were simultaneously increased under elevated CO2 concentrations. This study demonstrates that algal species may adapt to ocean acidification in the future and avoid light-induced growth inhibition.