Benthic animal contribution to cellulose breakdown in sediments of mangrove estuaries in the southwestern islands of Japan

Abstract

To determine the process of cellulose degradation in mangrove estuaries of the South-Western Islands, Japan, the cellulase activity of sediments was examined at a total of 9 sites on Okinawa Main Island (the River Gesashi and Manko), Ishigaki Island (Nagura Gulf and River Miyara), and Iriomote Island (rivers Urauchi, Mare, Hinai, Shira and Maira). Zymographic analysis was used to record cellulase activity in all sediment samples and in the meiobenthos. A 27-kDa cellulase activity band was expressed by several animal groups examined in the meiobenthos, including Gammaridea, Turbellaria, Ostracoda, Oligochaeta, Nematoda, and Polychaeta. However, the mangrove whelk, Terebralia palustris, which is a widely distributed member of the macrobenthos in these areas except Okinawa Main Island, expressed cellulase activities at 29, 31, 49, and 56 kDa. Interestingly, 31-kDa cellulase activity levels were recorded both in sediments and in the feces of T. palustris. The results of this study indicate that various benthic animals contribute to cellulose degradation in mangrove sediments of estuaries in the Southwestern Japanese Islands.