The growth performance and quality of red seaweed, Betaphycus gelatinus (Esper), cultured on a frame net at different water depths

Abstract

The red seaweed Betaphycus gelatinus contains many bioactive compounds believed to inhibit tumor cell growth and viral infections by promoting the human immune system. This species is listed in the Red Book as rare due to its over-exploitation. This study evaluated environmental conditions and their effects on the growth, biochemical composition, and carrageenan quality of the red seaweed Betaphycus gelatinus cultured on a net frame at different water depths for 2.5 months. Results indicated no significant monthly variation in temperature, with maximum values ranging from 23.0 to 26.5oC (p > 0.05), which were generally suitable for seaweed growth. However, afternoon temperatures slightly exceeded optimal levels reported in previous studies. pH remained stable (7.85–7.99), DIN ranged from 0.34 to 0.38 mg/L, and DO (6.6–6.8 mg/L) and salinity showed minimal variation, reflecting stable and favorable farming conditions. In addition, culture depth significantly influenced seaweed growth rate, with the lowest growth at 0.5 m and the highest at 3 m (p < 0.05). Carrageenan content increased with depth, reaching the highest levels in seaweed cultured near the bottom. Similarly, carrageenan quality, evaluated through gel strength and viscosity, improved at greater depths, with significantly higher values at 3 m and near-bottom treatments. In contrast, chlorophyll-a content decreased with increasing depth, showing the highest values at 0.5 m and the lowest near the bottom. Overall, deeper-water cultivation enhanced growth performance and carrageenan yield and quality in B. gelatinus, highlighting culture depth as a critical factor for optimizing seaweed farming productivity.