The impact of planting distance on productivity and profit of Eucheuma cottonii seaweed cultivation in Karimunjawa Islands, Indonesia

Eucheuma cottonii seaweed cultivation has become one of the main livelihoods for the local community of Karimunjawa Islands, Indonesia. Therefore, research on seaweed cultivation is important to improve the welfare of seaweed farmers, including planting distance of seaweed. The purpose of this research was to estimate the effect of different planting distance treatments on the growth and profitability of E. cottonii farming in Kemojan Island, Karimunjawa Islands. In this study, a field experiment using simple longline was conducted with planting distance of 25 cm, 30 cm and 35 cm in 42 days culture time. The variables studied include absolute biomass growth, specific growth rate (SGR), and RC (revenue cost) ratio, as well as a statistical test on these variables. The research results showed that the planting distance of seaweed have not a significant effect on the confidence level of 95% (a = 0.05). The planting distance treatment of 25 cm gave the highest yield, both on seaweed growth and RC ratio. The planting distance treatment of 35 cm provided the lowest performance, both the growth of absolute biomass, SGR and RC ratio. With an average initial biomass of 3,532 g per line, treatment of 25 cm can produce an average final biomass of 11,318 g per line, or an average biomass growth of 7,787 g per line, with an average SGR value of 2.72% and an average RC ratio of 2.34.