Abstract
Nutrient-rich deep-seawater has been pumped from Suruga Bay to a coastal site of Yaizu city, Shizuoka Prefecture. The deep-seawater contains high amounts of nitrate and it potentially alleviates nutrient limitation of seaweed growth. In this study, the effects of nitrate concentration, irradiance, and water temperature on nitrate uptake rate in juvenile Eisenia nipponica sporophytes were investigated. Nitrate uptake kinetics were fitted with Michaelis‒Menten’s equation. The maximum nitrate uptake rate (Vmax) and half-saturation concentrations (Ks) were 0.024 μmol cm－2 h－1 and 11.3 μmol L－1, respectively. The relationship between the nitrate uptake rate and irradiance exhibited an exponential curve, and the maximum uptake rate was 0.033 μmol cm－2 h－1, at an irradiance of 400 μmol m－2 s－1. Under dark conditions, no nitrate uptake was observed. The effect of water temperature on the nitrate uptake rate was parabolic curves showing a maximum nitrate uptake rate of around 13.5℃. Since nitrate concentrations in the Suruga Bay deep-seawater were consistently higher than 20 μmol L－1, the deep-seawater has a great potential to meet the nitrate demand of E. nipponica sporophytes.
