Study on the Growth Effects of Gracilariopsis lemaneiformis Under Different Cultivation Methods and Densities

Abstract

This study comprehensively analyzed the effects of different cultivation methods (CMs) and densities on the growth of Gracilariopsis lemaneiformis in indoor settings and two representative sea areas, Ailun Bay and Nanri Island, located in the northern and southern parts of China. The findings indicate that horizontal hanging cultivation significantly enhanced macroalgal growth and biomass production in both sites. In contrast, vertical hanging cultivation resulted in significantly lower yields, primarily due to inadequate illumination below certain water depths and epibiont infestation. Moreover, integrated multitrophic aquaculture (IMTA) systems co-cultivated with scallops demonstrated biomass and specific growth rates (SGR) similar to those of horizontal hanging cultivation, and nutrient concentrations in the IMTA areas were lower than those in the scallop monoculture areas. These observations suggest a potential role for G. lemaneiformis in nutrient mitigation. Regarding cultivation density (CD), lower densities were beneficial for higher SGR in both regions, with limited impact on final biomass, suggesting that moderately reducing CD could promote growth and reduce seedling use. Within optimal ranges, light intensity positively correlated with SGR; however, excessive light appeared to induce light-related stress or photoacclimation, as well as pigment reduction, in horizontal hanging cultivation, suggesting adverse effects under high-light conditions. In vertical hanging cultivation, reduced light increased pigment content, likely as an adaptive response to insufficient light, while increased density led to decreased SGR indoors, suggesting that resource competition under high-density conditions may limit SGR. Our research indicates that horizontal hanging cultivation at a lower density (0.15 kg/m) can enhance SGR and reduce seedling use without compromising final biomass, suggesting a potential strategy for improving cultivation efficiency. However, the practical adoption of this strategy should also consider site-specific factors such as seed costs, labor availability, and seasonal risks. This study provides useful information for optimizing seaweed cultivation practices and highlights the importance of adopting ecological and sustainable methods in aquaculture.