BACKGROUND: The main obstacle associated with methane production in anaerobic digestion processes from marine macroalgae is inhibited by the sea salts. This study aims to investigate the anaerobic digestion performance of marine macroalgae by acclimating inoculum to varying salinity, and to analyze the influence of salinity on microbial community by high-throughput gene sequencing. RESULTS: The relationship between specific methane yield and salinity followed the third-order polynomial equation: y=271.533+6.449X-0.261X(2) + 0.002X(3). The acclimating inoculum produced methane efficiently at 35 g L-1 with a specific methane yield of 220.88 mL CH4 g(-1) VS. Methanogenesis was considerably impeded at salinity greater than 55 g L-1. The bacterial phyla Bacteroidetes, Firmicutes, and Proteobacteria and the Methanobacterium, Methanosaeta, and Methanosarcina genera in archaea were predominant at different salinities. Hydrogenotrophic methanogens such as Methanobacterium can tolerate salinity up to 85 g L-1, whereas acetoclastic methanogens, Methanosaeta and Methanosarcina were severely inhibited at salinity greater than 65 g L-1. CONCLUSION: The acclimating inoculum can be used as anaerobic microbial resources for efficient methane production from marine macroalgae under seawater conditions of 35 g L-1. The hydrolytic, acidogenic, acetogenic bacteria and hydrogenotrophicmethanogens normally metabolized at different salinities, whereas acetoclastic methanogens were severely inhibited at high saline conditions. (C) 2017 Society of Chemical Industry