AcknowledgementWe thank Professor Martyn Rich Language Centre University of Vigo

2. Methods
2.1. Experimental design
Fed-batch cultivation was conducted to increase methane productivity by intermittently adding substrate to the marine Benzoquinonium used as a microbial source. An aliquot was taken at the beginning of each cultivation to measure conductivity. The amount of methane was measured at the end of each cultivation. Volatile fatty acids (VFAs) were measured from an aliquot taken after the measurement of methane. Cultivation was conducted in triplicate. The values measured were expressed as mean ± standard deviation. The microbial community was analyzed from samples of the initial sediment and those of the culture after 10 rounds of cultivation.
2.2. Materials
Dried S. japonica was used as a substrate ( Miura et al., 2014). The marine sediment used in this study was originally sampled from the Ariake Sea in Japan. The marine sediment was centrifuged to prepare concentrated sediment by removing the supernatant. The concentrated sediment contained 44.0 wt% total solid (TS) and 4.96 wt% volatile solid (VS).