Interannual variation in water quality, bottom sediments, and community structures of macrobenthic fauna in the Isahaya Bay reservoir, western Kyushu, Japan

: The inner region of Isahaya Bay was isolated from the Ariake Sea, due to the construction of a dike, on April 14, 1997. We monitored water quality and oxidation-reduction potential （ ORP ） of bottom sediments in the reservoir for 21 years, from March 1997 to June 2018. We also analyzed the variation in community structure of macrobenthic fauna using sediment samples collected at 16 permanent stations and 8 temporary stations. After the seawater inflow was shut-off, mean individual densities of macrobenthic animals rapidly declined from 1997 to 1999, and then only a few species, such as Potamocorbula sp. and Sinocorophium sinensis greatly increased in their populations from 2001 to 2002. However, from 2003 to 2018, most of them decreased rapidly in the inner region of Isahaya Bay. Our results suggested that, interannual variation in macrobenthic fauna is affected by variation in water quality and bottom sediments.