Effects of Enriching Nitrogen and Phosphorus on the Growth of Sargassum Podacanthum Cultured in Potassium-Fortified Inland Saline Water

Potassium-fortified inland saline water (K⁺ISW) has shown potential for growing marine species, including seaweed species. The response of a brown seaweed species, Sargassum podacanthum, to nitrogen and phosphorus enrichments were evaluated by culturing the species for 84 days in K⁺ISW and comparing it with Ocean Water (OW). The culture media were enriched weekly with ammonium chloride and sodium dihydrogen phosphate, with ammonium and phosphate ratios of 10:1 at five different concentrations 80:8, 120:12, 160:16, 200:20 and 240:24 µM. The culture medium with no enrichment was used as a control. The water quality and biomass of S. podacanthum were measured fortnightly. The S. podacanthum biomass increase significantly with different concentrations of the nutrient supplementations. The standing biomass and Specific Growth Rate (SGR) of S. podacanthum were similar in OW and K⁺ISW in the absence of any nutrient supplementation and at the supplement concentration of ammonium and phosphate 160:16 µM. However, from day 42 onwards, at the ratios of 80:8, 120:12, 200:20 and 240:24, S. podacanthum cultured in OW grew significantly faster than in K⁺ISW. In K⁺ISW, optimal growth of S. podacanthum was observed at the 160:16 and the increase in biomass was significantly higher than the initial biomass until day 70, whereas at the other four nutrient supplement concentrations, the S. podacanthum biomass remained unchanged during the entire culture period. The nitrite, total Kjeldahl nitrogen and phosphate concentrations in water were found to be significantly (p<0.05) and negatively correlated (p<0.05) with S. podacanthum biomass. Therefore, the results showed that the enrichment of 160 µM ammonium and 16 µM phosphate is required in the K⁺ISW for S. podacanthum to achieve optimal growth.