Optimizing Depth and Strain of Kappaphycus spp. to Enhance Carbon Sequestration in Tropical Aquaculture: A Case Study from Bantaeng, Indonesia

The cultivation of seaweed, particularly the red macroalga Kappaphycus spp., has gained traction as an effective nature-based solution to mitigate climate change through its role in sequestering atmospheric carbon dioxide. This study explores how the interaction between strain type and cultivation depth can be optimized to enhance the specific growth rate (SGR), biomass yield, and carbon uptake efficiency of Kappaphycus spp., thereby supporting the advancement of sustainable aquaculture and blue carbon strategies. Fieldwork was conducted in the coastal waters of Bantaeng, South Sulawesi, Indonesia, using a factorial experimental design involving two strains (green and brown), grown at three depths (20, 70, and 120cm). Over a 45-day period, SGR, biomass accumulation, and the production-to-biomass (P/B) ratio were systematically evaluated. The study also incorporated environmental assessments and qualitative insights from local seaweed farmers. Although not all differences were statistically significant, discernible biological trends emerged. The brown strain at 20cm and the green strain at 70cm demonstrated the highest growth rates, revealing the influence of depth–strain compatibility. The green strain cultivated at 120cm exhibited the greatest biomass yield, indicating that deeper environments may buffer thermal and photic stress. Notably, the green strain at 70cm achieved the highest P/B ratio, suggesting that this depth offers optimal conditions for productive efficiency. These findings highlight the critical role of matching strain characteristics with suitable depth conditions to maximize seaweed cultivation outcomes. By combining ecological knowledge, physiological insights, and local practices, this research offers valuable guidance for implementing climate-resilient aquaculture systems in tropical coastal regions.