Sporophytic photosynthesis and gametophytic growth of the kelp Ecklonia stolonifera affected by ocean acidification and warming

Juvenile sporophytes and gametophytes of Ecklonia stolonifera were incubated in combinations of three pCO2 levels (360, 720 and 980 ppmv) and two temperatures (10 and 15°C for sporophytes; 15 and 20°C for gametophytes) to examine potential effects of climate change on photosynthesis and growth. Sporophytes had significantly higher maximum quantum yields (Fv/Fm) and maximum relative electron transport rates (rETRmax) at 720 ppmv than 360 and 980 ppmv. Also, these parameters were significantly lower at higher temperature of 15°C than at 10°C. Growth of female gametophytes was maximal at 360 ppmv rather than enriched pCO2 levels. Female gametophytes had significantly lower growth at higher temperature of 20°C than at 15°C. These results indicate effects of elevated pCO2 varied between generations: stimulating sporophytic photosynthesis and inhibiting gametophytic growth. Ocean acidification and warming would constitute a grave threat to seedling cultivation of E. stolonifera caused by growth inhibition of gametophytes at high pCO2 levels and temperatures.