A light-limited growth model considering the nutrient effect for improved understanding and prevention of macroalgae bloom

A useful growth process model for Ulva prolifera with light limitation considering the nutrient effect was proposed to better understand the development of macroalgae bloom. The interrelationship between light and nutrient limitation was demonstrated to obtain the mechanism. As a case study, thresholds of light and nutrients for different stages of Ulva prolifera growth were estimated using the proposed model. Limits of light intensity, nitrate, and phosphate concentration on the initial growth were found to be 40.0 W m⁻², 6.5 μmol L⁻¹, and 0.27 μmol L⁻¹, respectively. The minimal light intensity for initial growth was found to increase monotonously with decrease in the nutrient concentration. It was also observed that the minimal light intensity for growth increases as the density of Ulva prolifera increases and the nutrient concentration decreases. Similarly, the minimal nutrient concentration for initial growth increases monotonously with decrease in the light intensity. In addition, the minimal nutrient concentration for growth increases with increase in the density of Ulva prolifera and decrease in the light intensity. It was demonstrated that the phosphate limitation on the initial growth of Ulva prolifera seedling can occur in most coastal waters of the southern Yellow Sea and a tendency of approaching the phosphate limitation on the growth of the floating thalli of Ulva prolifera exists. Evidence was provided to support the argument that the macroalgae thalli from aquaculture rafts, rather than that from seedlings or spores, can contribute to the original biomass of the floating green Ulva prolifera in the southern Yellow Sea. The model presented in this study can provide new insights into the interrelationship between the light and nutrient limitation, as well as into the growth mechanism of floating seaweeds. It can also provide a more accurate prediction of seaweed growth in light- and nutrient-limited environments.