The short-term effects of elevated CO2 and ammonium concentrations on physiological responses in Gracilariopsis lemaneiformis (Rhodophyta)

Abstract Ocean acidification (OA) and coastal eutrophication affect coastal marine organisms. We studied the physiological responses of Gracilariopsis lemaneiformis (Gracilariales, Rhodophyta) to increased concentrations of CO2 and NH4 +. Incubation treatments were applied at two different pH units (low, 7.5; high (control), 7.9) and three different NH4 + concentrations (low, 10; medium, 50; high, 100 μM). Growth, rates of photosynthetic oxygen evolution, and NH4 + uptake rates were affected by both elevated CO2 and NH4 + conditions. The changes in the pH of culture media were influenced by elevated CO2 or NH4 + treatments. However, chlorophyll fluorescence was affected only by the level of NH4 +. These results indicate that the physiological responses of G. lemaneiformis might be enhanced when the concentrations of CO2 and NH4 + rise. Therefore, cultures of this alga could provide a good mitigation solution against ongoing problems with OA and coastal eutrophication.