Estimation of the Origin of suspended fine particulate organic matter in the subtropical Amami-Oshima Island streams

Abstract

 The trophic pathways of suspended fine particulate organic matter (SFPOM) in streams in the Amami-Oshima Island are still unknown. In this study, we aimed to estimate the origin and the trophic pathways of SFPOM using carbon and nitrogen stable isotope ratios. Within the habitat of Amami Rabbit, Pentalagus furnessi, the contribution of feces to SFPOM was 39%. The density of Ryukyu Ayufish, Plecoglossus altivelis ryukyuensis, also increased in the area of high algal biomass, but the contribution of algae to SFPOM biomass was only 0.5 mg L^-1. In addition, the density of algae-derived SFPOM showed no significant correlation to the density of Plecoglossus altivelis ryukyuensis. These results suggested that Pentalagus furnessi plays a significant role in converting terrestrial plant into SFPOM in the river ecosystem, whereas that Plecoglossus altivelis ryukyuensis has a low contribution to the production of algae-derived SFPOM in the Amami-Oshima Island.