大雨及び出水が宍道湖の底生生物群集に及ぼす影響

抄録

A macrobenthic community is sensitive to changes in the environment such as heavy rainfall and flooding. Lake Shinji is the largest fishing ground for the brackish water clam Corbicula japonica in Japan. The macrobenthic community of this lake has been surveyed for approximately 40 years since the 1980s, and it was surveyed in 2021. However, the amount of precipitation from June to September in 2021 was higher than ordinary years. The purpose of this study was to clarify the effects of the heavy rainfall and flooding on the macrobenthic community in Lake Shinji. Macrobenthic communities were compared between the heavy rainfall and flooding years (1997 and 2021) and ordinary year (1992). The amount of precipitation from June to September in 2021 was about 1279 mm (the average precipitation from 1981 to 2021 was 764.0 mm), which was the second highest value since the 1980s. In this study, we collected 21 macrobenthos species. Dominant macrobenthic species were Prinospio (Minuspio) japonica, Corbicula japonica, Iravadia elegantula, and Tanypus sp.. P. japonica and C. japonica were collected from the central area and the shoreline of the lake, indicating the effects of the heavy rainfall and flooding. Arcuatula senhousia was rarely collected, possibly due to low salinity. Results of cluster analysis showed that the ratios of brackish water polychaeta in the macrobenthic community were lower for the heavy rainfall and flooding years (1997 and 2021) than the ordinary year (1992). It is assumed that community structure and spatial distribution of macrobenthos in this lake was modified in the year 2021 due to heavy rainfall and flooding.