Responses of Halimeda macroloba to growth and chemical concentrations when encountering elevated nutrient concentrations were experimentally tested in the subtidal zone. To determine the effect of nutrients, algae were fertilized using Osmocote® a slow-release fertilizer; the concentrations of nitrogen and phosphorus were enriched. A total of four treatments were manipulated: 1) enriched nitrogen that consisted of fertilizer (16-8-12 [N-P-K]); 2) enriched phosphorus (13-26-7 [N-P-K]); 3) enriched nitrogen and phosphorus (14-14-14 [N-K-P]); and 4) an ambient concentration. It was shown that only phosphorus had a positive effect on the growth and polyphenol concentrations of Halimeda. The dry weight and the length of thallus were increased after one week in enriched phosphorus plots but decreased at the third week. Enriched phosphorus resulted in increases in the polyphenol concentrations at the third week; this suggested that when phosphorus was added at the first week, Halimeda allocated more resources to growth than chemical concentrations, supporting predictions of the carbon/nutrient balance hypothesis (CNBH). Nitrogen had a negative effect on the growth and polyphenol concentrations of H. macroloba. For enriched both nutrients, the N+P had no effect on the dry weight, thallus length, and polyphenol concentrations. From the tissue nutrient, the C:N:P ratios indicated that the productivity of H. macroloba was phosphorus limited.
