Abstract: Guangxi Shankou Mangrove National Ecological Nature Reserve is facing a severe invasion by Spartina alterniflora and urgently needs to be eradicated and restored. We conducted a field experiment to examine the effects of three concentrations of herbicide-spraying groups \[i.e., 50.0 (D1), 62.5 (D2), 75.0 (D3) g·L^-1 of imazapyr herbicide\] on S. alterniflora, from April 2022 to April 2023 on the intertidal flat of Yingluo Bay, Guangxi, China. During the experiment, eight samplings were taken to monitor the changes in the macrobenthos community. Multiple community indices were used to evaluate the impacts of imazapyr on the macrobenthos community. In total, 7 phyla, 8 classes, and 44 species of macrobenthos were captured, with the mollusks and arthropods species being more abundant. The species composition of community in each treatment group fluctuated greatly throughout the entire investigation period, while there was no regular trend affected by pesticide application. The density and biomass of the groups D1 and D2 increased in the early stage. The number of dominant species in the three herbicide-spraying groups remained stable or even increased in the early stage, but showed a downward trend in the middle and late stages, with Paracleistostoma depressum as the dominant population. The difference in the turnover rate of dominant species among the four treatment groups was not significant in the early stage, but significant in the middle and late stages. The species turnover index did not show significant phased changes, with substantial species gain and loss. The species migration index showed that the difference in the number of species migrating in and out was relatively small for most of the time. The macrobenthos pollution index indicated the habitat qualities in vast majority of sampling times were clean. Based on a comprehensive assessment, the ecological impact of using the imazapyr herbicide solution with a concentration of 50.0 g·L^-1 and a dosage of 60 L·hm^-2 to remove Spartina alterniflora on the macrobenthic community was acceptable.

Key words: Spartina alterniflora, imazapyr acid, intertidal macrobenthos community, Yingluo Bay of Guangxi