Invasive Control of Spartina alterniflora in Coastal Wetlands: Suitability Assessment of Mangrove Planting in Quanzhou Bay Based on Macrobenthic Communities and Environmental Responses

To evaluate the early-stage effects of different mangrove species on macrobenthic communities along the southern coast of Quanzhou Bay, this study examined restoration sites dominated by K. obovata (Q), A. corniculatum (T), and A. marina (B), together with an adjacent unvegetated mudflat (Y). Sediment physicochemical properties, species composition, density, biomass, diversity indices, abundance-biomass comparison (ABC) curves, and cluster/NMDS results were compared before mangrove planting and during the spring and autumn after planting. The results showed that sediment backgrounds were relatively similar among sites before planting. After planting, total carbon (TC) and total nitrogen (TN) increased in autumn, and the number of macrobenthic species increased from 13 before planting to 24 after planting. Species number, density, and diversity were generally higher in autumn than in spring. Redundancy analysis (RDA) further showed that the relationships between sediment environmental variables and macrobenthic community metrics varied across restoration stages. Before planting, the three original sites showed relatively weak separation along the environmental gradients. After planting, the ordination pattern became more structured. In spring, biomass was mainly associated with the A. marina site, whereas TC and TN were more closely related to the K. obovata site. In autumn, TN and biomass were more closely associated with the A. corniculatum and A. marina sites, while TC, TP, and salinity were more strongly related to the K. obovata site. These results indicate that sediment carbon and nitrogen dynamics, together with salinity and pH gradients, jointly shaped macrobenthic community recovery during the early restoration stage. The A. corniculatum site had the highest density and biomass in autumn and showed relatively high abundance-biomass comparison (ABC)-based community stability, as indicated by positive W values and biomass curves generally lying above abundance curves. The A. marina site had relatively high species richness and diversity, whereas the recovery performance of the K. obovata site was comparatively weaker. Overall, A. corniculatum and A. marina are more suitable as the main species for mangrove restoration along the southern coast of Quanzhou Bay, while K. obovata can be used as an auxiliary species in mixed planting.