MEPS 682:111-122 (2022)  -  DOI: https://doi.org/10.3354/meps13933

ABSTRACT: The availability of nitrogen (N) and phosphorus (P) is crucial for maintaining coral-dinoflagellate symbiosis, whereas excess nutrients and skewed N:P ratios are often associated with coral reef decline. It is thus essential to understand the general patterns of species-specific as well as dose-dependent responses of corals to elevated nutrient concentrations and skewed N:P ratios. Here, we found that the impacts of nutrient enrichment on the corals Acropora millepora and Platygyra crosslandi from Weizhou Island, South China Sea, were highly dependent on nutrient dose, N:P ratios, and coral species. Moderate nutrient enrichment (N: 19-140 µmol l^-1 and P: 0.5-1.5 µmol l^-1) did not lead to bleaching of either coral species, but their metabolic processes (calcification, nutrient uptake, and dinitrogen fixation) were affected. More depleted δ¹³C and lower dinitrogen fixation rates of A. millepora than of P. crosslandi indicated that A. millepora was more vulnerable to the disturbance of nutrient enrichment. However, N:P ratios (±SD) as high as 106 ± 10 decreased the photosynthetic efficiency and nutrient uptake rates of P. crosslandi, indicating that this species may be vulnerable to high N:P ratios, although it was one of the dominant coral assemblages at Weizhou Island. The results provide an important basis for understanding coral reef degradation triggered by nutrients and a suggestion that coastal management should focus not only on the concentrations but also on the ratios of nutrients.

KEY WORDS: Coral · Nutrient enrichment · N:P ratio · Physiology · Metabolism rates