Floating raft culture of Gracilariopsis longissima for optimum biomass yield performance on the coast of Cox’s Bazar, Bangladesh

Seaweed cultivation is an eco-friendly method and attracts growing interest which needs a multi-criteria approach for its sustainability. In our present study, an economically significant red alga, Gracilariopsis longissima was cultured using a floating raft method on the coast of Cox’s Bazar, Bangladesh for a period of 90 days from January to March 2022. The effects of different factors such as rope materials, culture type, raft shape, seeding intensity, harvesting phase and water depth on the biomass yield production of G. longissima were evaluated during a 90-day culture period. The biomass yield production and daily growth rate (DGR% day −1 ) were estimated to evaluate the possibilities of G. longissima cultures in a floating raft culture method. The range of biomass yield production (3.03–13.37 kg/m 2 ) and DGR (3.08–4.72% day −1 ) is satisfactory in the floating raft culture method. Different water quality variables, the seasonal appearance of epiphytic algae and a cost–benefit analysis of seaweed culture were also performed. A total of eight epiphytic algal species were recorded, which resulted in major challenges for the growth of Gracilariopsis . The per month income for a seaweed farmer was estimated to be US$175.17 for 20 rafts. Our research concluded that farming of G. longissima in the floating raft method could be successfully performed from January to March on the coast of Cox’s Bazar.