Effect of stocking density and water depth on the growth and production of red seaweed, Gracilaria tenuistipitata in the Kuakata coast of Bangladesh

Seaweed aquaculture, the quickly growing global food production segment, provides plenty of options for mitigating and adapting to developed-world conditions. In Bangladesh, the rise of seaweed cultivation gives hope for increasing incomes in fishing villages. The effect of stocking density (1, 2, 3, and 4 Kg/m2) and water depth (surface, 0.5 m, and 1.0 m) on cultivating red seaweed, Gracilaria tenuistipitata, using the square raft (1 m × 1 m) method was evaluated on the Kuakata coast of Bangladesh from December 2021 to March 2022. The raft was made of bamboo, rope, and plastic containers. Hydrological parameters and other growth indicators were monitored fortnightly. Temperature (27.3–29.5 °C), transparency (53.8–57.3 cm), salinity (18.6–21.4), pH (7.4–7.9), and dissolved oxygen (5.7–6.2 mg/L) were all found to be adequate for seaweed farming, however, salinity was somewhat lower than the ideal range. The initial stocking density of 2 Kg/m2 with a culture period of 60 days was found to be the most suitable for G. tenuistipitata than other stocking densities in terms of daily growth rate (DGR). The maximum biomass yield (13.52 ± 2.04 Kg/m2) was observed at a stocking density of 4 Kg/m2, but no significant difference (p < 0.05) was detected among stocking densities of 2, 3, and 4 Kg/m2. Furthermore, as compared to the surface and 1.0 m water depth, the daily growth rate was significantly higher at a depth of 0.5 m. However, at a water depth of 0.5 m, there was a rising trend in biomass yield, after which it declined significantly (p < 0.05). Based on the findings, the current study suggests that cultivating G. tenuistipitata at a stocking density of 2 Kg/m2 at a water depth of 0.5 m can produce greater DGR and biomass production, which might provide monetary benefits to small farmers in Bangladesh's Kuakata coast, Bay of Bengal.