Interannual changes in the oligochaete communities in the reservoir pond of Isahaya Bay in the Ariake Sea, Kyushu, since shut of the floodgate

Species composition of aquatic oligochaetes was studied almost annually in the reservoir pond of Isahaya Bay in the Ariake Sea, Kyushu, Japan, starting after the closing of the floodgate in 1997 until 2018. Ten species all belonging to the family Naididae were recorded in the reservoir pond during the study period. Short after the closing of the floodgate, oligochaete species composition changed drastically from an epibenthos-dominated to a burrowing-dominated community. The change could be partly caused by eutrophication and mud sedimentation in the bottom. The present oligochaete community in the pond is composed of a small number of freshwater thermophile species with salinity and low-oxygen resistance, with Limnodrilus hoffmeisteri surpassing the others. A brackish limnodriloidine Doliodrilus tener, which became abundant soon after opening the floodgate in 2002, is newly recorded in Japan and re-described based on the specimens from the reservoir pond.