| Summary: | 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.
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