Seasonal growth and retention of edible seaweeds and optimizing culture of Gracilaria corticata and Gracilaria salicornia in Madagascar

Seaweed farming offers a sustainable solution to malnutrition and economic challenges in southwestern Madagascar. This study assessed the seasonal performance of 12 edible seaweed species and optimized cultivation parameters for Gracilaria corticata and Gracilaria salicornia using long-line aquaculture. Environmental factors, including temperature, light intensity, salinity, and current speed, were monitored across warm and cool seasons. G. corticata, G. salicornia, and Hormophysa cuneiformis exhibited the highest retention rates (>50 %) and growth performance, with G. corticata demonstrating significant superior growth in both seasons. Smaller cuttings (0–50 g) achieved higher retention and specific growth rates, particularly in the first 30 days. Growth was significantly influenced by light intensity (4209.35 ± 3274.72 lux in the warm season; 3107.77 ± 3194.22 lux in the cool season) and temperature (30.20 ± 1.26 °C in the warm season; 24.83 ± 0.35 °C in the cool season), with optimal conditions occurring in the warm season. These findings highlight the potential of G. corticata and G. salicornia for sustainable aquaculture, contributing to species diversification and food security. Optimizing environmental conditions and cutting sizes is crucial for maximizing seaweed productivity in Madagascar.