Interactive effects of increased temperature and pCO2concentration on the growth of a brown algae ecklonia cava in the sporophyte and gametophyte stages

Abstract

To examine the effects of increased CO2concentration and seawater temperature on the photosynthesis and growth of forest forming Ecklonia cava (Laminariales, Phaeophyta), sporophytic discs and gametophytes were cultured under three pCO2 concentrations (380, 750, 1000 ppm), four temperatures (5, 10, 15, 20°C for sporophytes; 10, 15, 20, 25°C for gametophytes), and two irradiance levels (40, 80 μmol photons m−2s−1) for 5 days. Photosynthetic parameter values (ETRmax, Ek, and α) were generally higher as sporophytic discs were grown under low temperature and increased CO2concentration at 750 ppm. However, photosynthesis of Ecklonia sporophytes was severely inhibited under a combination of high temperature (20°C) and 1000 ppm CO2concentration at the two photon irradiance levels. The growth of gametophytes was maximal at the combination of 380 ppm (present seawater CO2concentration) and 25°C. Minimal growth of gametophytes Occurred at enriched pCO2concentration levels (750, 1000 ppm) and high temperature of 25°C. The present results imply that climate change which is increasing seawater temperature and pCO2concentration might diminish Ecklonia cava kelp beds because of a reduction in recruitments caused by the growth inhibition of gametophytes at high pCO2concentration. In addition, the effects of increased temperature and pCO2concentration were different between generations-revealing an enhancement in the photosynthesis of sporophytes and a reduction in the growth of gametophytes.