Physiological and Biochemical Responses of the Green Tide-Forming Algae, <i>Ulva</i> Species, under Different Nutrient Conditions on Jeju Island, Korea
Kyeonglim Moon | Sun Kyeong Choi | Seong Bin Ham | Young Baek Son | Yun Hee Kang | Sang Rul Park
In this study, we investigated the physiological and biochemical responses of <i>Ulva</i> species to variation in nutrient availability. Sampling was conducted at two sites on Jeju Island, Korea, namely, Handong, which is close to seven intensive land-based fish farms, and Hado, which has no apparent nearby nutrient sources. We examined the water column nutrient concentrations, nitrate reductase (NR) activity, nitrate uptake efficiency, tissue C, N, and P content, and stable isotope ratios of <i>Ulva</i> species. Water column NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>−</sup> + NO<sub>2</sub><sup>−</sup>, and PO<sub>4</sub><sup>3−</sup> concentrations were significantly higher at Handong than at Hado. NR activity and tissue N content of <i>Ulva</i> species were significantly higher at Handong than at Hado. Notably, nitrate uptake efficiency was inversely proportional to NR activity and tissue N content. The physiological and biochemical responses of <i>Ulva</i> species were closely related to dissolved inorganic nitrogen, which stimulates <i>Ulva</i> species to regulate growth. Additionally, the δ<sup>15</sup>N values of <i>Ulva</i> tissues at both sites were within the previously reported range for fresh groundwater. Therefore, the main nitrogen source for <i>Ulva</i> growth may be submerged groundwater with high nutrient concentrations. Our results provide invaluable information for estimating dissolved inorganic nitrogen levels in water, which may facilitate development of management policies.
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